Fisheries and Resources Monitoring System

EspañolFrançais
EPO Tunas and billfishes fishery
Fishery  Fact Sheet
Fishery report 2018
EPO Tunas and billfishes fishery
Fact Sheet Citation  
Tunas and billfishes in the Eastern Pacific Ocean
Owned byInter-American Tropical Tuna Commission (IATTC) – more>>

more>>
<<less
Overview: The eastern Pacific Ocean (EPO) fishery for tunas and tuna-like species is a fully developed international industrial fishery that has been managed by the IATTC since 1950. Until about 1960, fishing for tunas in the EPO was dominated by pole-and-line vessels operating in coastal regions and in the vicinity of offshore islands and banks. By 2012, fewer than five of these vessels remained in the fishery. By 1961 the EPO fishery was dominated by purse seine vessels, which by 2012 numbered more than 200. Longline fisheries expanded from the western Pacific into the EPO during the 1950s, and by about 1965 operated throughout the EPO. The IATTC has adopted a vessel registry and has in place restrictions on catch and on vessels and fishing capacity operating in the EPO. Catch of the tropical tunas, bigeye, skipjack, and yellowfin, in the EPO has ranged from about 500,000 to 830,000 t since 2000, averaging about 560,000 t per year since 2007.

Location of EPO Tunas and billfishes fishery
 

Geographic reference:  EPO
Spatial Scale: Regional
Reference year: 2017
Approach: Fishery Management Unit

Jurisdictional framework
Management Body/Authority(ies): Inter-American Tropical Tuna Commission (IATTC)
Mandate: Scientific Advice; Management
Area of Competence: IATTC area of competence
Maritime Area: High seas
Maritime Area: National waters

Harvested Resource
Target Species: Yellowfin tuna; Skipjack tuna; Bigeye tuna …  
more>>

Associated Species: Pacific bluefin tuna; Striped marlin; Swordfish
Fishery Area: East Pacific Ocean

Fishery Indicators
Catch
Effort

Harvested Resource
Type of production system: Industrial   

Fishery Area
Climatic zone: Polar; Temperate; Tropical.   Horizontal distribution: Oceanic.   Vertical distribution: Pelagic.  

Geo References

This document summarizes the fisheries for species covered by the IATTC Convention (“tunas and tuna-like species and other species of fish taken by vessels fishing for tunas and tuna-like species”) in the eastern Pacific Ocean (EPO). The most important of these are the scombrids (Family Scombridae), which include tunas, bonitos, seerfishes, and mackerels. The principal species of tunas caught are yellowfin, skipjack, bigeye, and albacore, with lesser catches of Pacific bluefin, black skipjack, and frigate and bullet tunas; other scombrids, such as bonitos and wahoo, are also caughht.

This document also covers other species caught by tuna-fishing vessels in the EPO: billfishes (swordfish, marlins, shortbill spearfish, and sailfish) carangids (yellowtail, rainbow runner, and jack mackerel), dorado, elasmobranchs (sharks, rays, and skates), and other fishes.

Most of the catches are made by the purse-seine and longline fleets; the pole-and-line fleet and various artisanal and recreational fisheries account for a small percentage of the total catches.

Detailed data are available for the purse-seine and pole-and-line fisheries; the data for the longline, artisanal, and recreational fisheries are incomplete.

The IATTC Regional Vessel Register contains details of vessels authorized to fish for tunas in the EPO. The IATTC has detailed records of most of the purse-seine and pole-and-line vessels that fish for yellowfin, skipjack, bigeye, and/or Pacific bluefin tuna in the EPO. The Register is incomplete for small vessels. It contains records for most large (overall length >24 m) longline vessels that fish in the EPO and in other areas.

The data in this report are derived from various sources, including vessel logbooks, observer data, unloading records provided by canners and other processors, export and import records, reports from governments and other entities, and estimates derived from the species and size composition sampling program.

All weights of catches and discards are in metric tons (t). In the tables, 0 means no effort, or a catch of less than 0.5 t; - means no data collected; * means data missing or not available.
Resources Exploited
The principal species of tunas caught are:
Albacore - Northern Pacific
Bigeye tuna - Eastern Pacific (EPO)
Skipjack tuna - Eastern Pacific
Yellowfin tuna - Eastern Pacific
The principal species of tunas caught are yellowfin, skipjack, bigeye, and albacore, with lesser catches of Pacific bluefin, black skipjack, and frigate and bullet tunas; other scombrids, such as bonitos and wahoo, are also caught. This report also covers other species caught by tuna-fishing vessels in the EPO: billfishes (swordfish, marlins, shortbill spearfish, and sailfish) carangids (yellowtail, rainbow runner, and jack mackerel), dorado, elasmobranchs (sharks, rays, and skates), and other fishes.
Fleet segment

THE FLEETS

The purse-seine and pole-and-line fleets
The IATTC staff maintains detailed records of gear, flag, and fish-carrying capacity for most of the vessels that fish with purse-seine or pole-and-line gear for yellowfin, skipjack, bigeye, and/or Pacific bluefin tuna in the EPO. However, since 2016 there have been no pole-and-line vessels fishing for tuna in the EPO. Only purse-seine vessels that fished for any of these four species during all or part of the year are included in the following paragraphs describing the purse seine fleet.

The IATTC uses well volume, in cubic meters (m3), to measure the carrying capacity of vessels. Until 2000, the owner's or builder's estimates of the carrying capacity of individual vessels, in tons of fish, were used, but since the density of fish in a well can vary, measuring carrying capacity in weight is subjective. Using volume as a measure of capacity eliminates this problem.

The IATTC staff began collecting capacity data by volume in 1999, but has not yet obtained this information for all vessels. For vessels for which reliable information on well volume is not available, the estimated capacity in metric tons was converted to cubic meters.

Until about 1960, fishing for tunas in the EPO was dominated by pole-and-line vessels operating in coastal regions and in the vicinity of offshore islands and banks. During the late 1950s and early 1960s most of the larger pole-and-line vessels were converted to purse seiners, which by 1961 dominated the EPO fishery. Since then the number of pole-and-line vessels has decreased from 93, with a total well volume of about 11 thousand m3, to zero, and the number of purse-seine vessels has increased from 125 to 254, and their total well volume from about 32 thousand to about 263 thousand m3, an average of about 1,035 m3 per vessel. An earlier peak in numbers and total well volume of purse seiners occurred from the mid-1970s to the early 1980s, when the number of vessels reached 282 and the total well volume about 195 thousand m3, an average of about 700 m3 per vessel (Table A-10); (Figure 2).
Figure 2:  Carrying capacity, in cubic meters of well volume, of the purse-seine and pole-and-line fleets in the EPO, 1961-2017

The catch rates in the EPO were low during 1978-1981, due to concentration of fishing effort on small fish, and the situation was exacerbated by a major El Niño event, which began in mid-1982 and persisted until late 1983 and made the fish less vulnerable to capture. The total well volume of purse-seine and pole-and-line vessels then declined as vessels were deactivated or left the EPO to fish in other areas, primarily the western Pacific Ocean, and in 1984 it reached its lowest level since 1971, about 119 thousand m3. In early 1990 the U.S. tuna-canning industry adopted a policy of not purchasing tunas caught during trips during which sets on tunas associated with dolphins were made. This caused many U.S.-flag vessels to leave the EPO, with a consequent reduction in the fleet to about 117 thousand m3 in 1992. With increases in participation of vessels of other nations in the fishery, the total well volume has increased steadily since 1992, and in 2017 was 263 thousand m3.

The 2016 and preliminary 2017 data for numbers and total well volumes of purse-seine vessels that fished for tunas in the EPO are shown in (Table A-11a) and (Table A-11b). During 2017, the fleet was dominated by vessels operating under the Ecuadorian and Mexican flags, with about 35% and 23%, respectively, of the total well volume; they were followed by the United States (12%), Panama (8%), Venezuela (7%), Colombia (6%), Nicaragua (4%), El Salvador (2%), Peru (2%) and the European Union (Spain) (1%). The sum of the percentages may not add up to 100% due to rounding.

The cumulative capacity at sea during 2017 is compared to those of the previous five years in Figure 3.
Figure 3:  Cumulative capacity of the purse-seine and pole-and-line fleet at sea, by month, 2010-2015

The monthly average, minimum, and maximum total well Volumes At Sea (VAS), in thousands of cubic meters, of purse-seine and pole-and-line vessels that fished for tunas in the EPO during 2007-2016, and the 2017 values, are shown in (Table A-12). The monthly values are averages of the VAS estimated at weekly intervals by the IATTC staff. Since 2000 the fishery has been regulated during some or all of the last four months of the year, so the VAS values for September-December 2017 are not comparable to the average VAS values for those months of 2000-2017. The average VAS values for 2007-2016 and 2017 were a little over 138 thousand m3 (61% of total capacity) and about 160 thousand m3 (61% of total capacity), respectively.

Other fleets of the EPO

Information on other types of vessels that are authorized to fish or that fish for tunas in the EPO is available in the IATTC’s Regional Vessel Register, on the IATTC website. The Register is incomplete for small vessels. In some cases, particularly for large longline vessels, the Register contains information for vessels authorized to fish not only in the EPO, but also in other oceans, and which may not have fished in the EPO during 2017, or ever.
Catch
Estimating the total catch of a species of fish is difficult, for various reasons. Some fish are discarded at sea, and the data for some gear types are incomplete. Data for fish discarded at sea by purse-seine vessels with carrying capacities greater than 363 metric tons (t) have been collected by observers since 1993, which allows for better estimation of the total amounts of fish caught by the purse-seine fleet. Estimates of the total amount of the catch that is landed (hereafter referred to as the “retained catch”) are based principally on data from unloadings. Beginning with Fishery Status Report 3, which reports on the fishery in 2004, the unloading data for purse-seine and pole-and-line vessels have been adjusted, based on the species composition estimates for yellowfin, skipjack, and bigeye tunas. The current species composition sampling program, described in “Purse-seine, pole-and-line, and recreational fisheries” section, began in 2000, so the catch data for 2000-2017 are adjusted, based on estimates by flag for each year. The catch data for the previous years were adjusted by applying the average ratio by species from the 2000-2004 estimates, by flag, and summing over all flags. This has tended to increase the estimated catches of bigeye and decrease those of yellowfin and/or skipjack. These adjustments are all preliminary, and may be improved in the future. All the purse-seine and pole-and-line data for 2016 and 2017 are preliminary.

Data on the retained catches of most of the larger longline vessels are obtained from the governments of the nations that fish for tunas in the EPO. Longline vessels, particularly the larger ones, direct their effort primarily at bigeye, yellowfin, albacore, or swordfish. Data from smaller longliners, artisanal vessels, and other vessels that fish for tunas, billfishes, dorado, and sharks in the EPO were gathered either directly from the governments, from logbooks, or from reports published by the governments. Data for the western and central Pacific Ocean (WCPO) were provided by the Ocean Fisheries Programme of the Secretariat of the Pacific Community (SPC). All data for catches in the EPO by longlines and other gears for 2015, 2016 and 2017 are preliminary.

The data from all the above sources are compiled in a database by the IATTC staff and summarized in this report. In recent years, the IATTC staff has increased its effort toward compiling data on the catches of tunas, billfishes, and other species by other gear types, such as trolls, harpoons, gillnets, and recreational gears. The estimated total catches of yellowfin, skipjack, and bigeye in the entire Pacific Ocean from all sources mentioned above are shown in (Table A-1), and are discussed further in the sections below.

Estimates of the annual retained and discarded catches of tunas and other species taken by tuna-fishing vessels in the EPO during 1988-2017are shown in (Table A-2a), (Table A-2b) and (Table A-2c). The catches of yellowfin, skipjack, and bigeye tunas by flag, during 1988-2017, are shown in (Table A-3a), (Table A-3b), (Table A-3c), (Table A-3d), (Table A-3e), and the purse-seine and pole-and-line catches and landings of tunas and bonitos during 2016-2017 are summarized by flag in (Table A-4a), ( Table A-4b). The data for yellowfin, skipjack, and bigeye tunas in Table A-4b have not been adjusted to the species composition estimates, and are preliminary.

There were no restrictions on fishing for tunas in the EPO during 1988-1997, but the catches of most species have been affected by restrictions on fishing during some or all of the last six months of 1998-2017. Furthermore, regulations placed on purse-seine vessels directing their effort at tunas associated with dolphins have affected the way these vessels operate, especially since the late 1980s, as discussed in “The Fleets” section.

The catches have also been affected by climate perturbations, such as the major El Niño events that occurred during 1982-1983 and 1997-1998. These events made the fish less vulnerable to capture by purse seiners due to the greater depth of the thermocline, but had no apparent effect on the longline catches. Yellowfin recruitment tends to be greater after an El Niño event.

Catches by species

Yellowfin tuna

The annual catches of yellowfin during 1986-2017 are shown in (Table A-1). The EPO totals for 1993-2017 include discards from purse-seine vessels with carrying capacities greater than 363 t. The El Niño event of 1982-1983 led to a reduction in the catches in those years, whereas the catches in the WCPO were apparently not affected. Although the El Niño episode of 1997-1998 was greater in scope, it did not have the same effect on the yellowfin catches in the EPO. In the EPO, catches increased steadily to a high of 443 thousand t in 2002; they decreased substantially in 2004, reaching their lowest level during 2006-2008, at only 44% of the highest catches of the 2001-2003 period. The 2017 catch of 212 thousand t is less than the average for the previous 5-year period (239 thousand t). In the WCPO, the catches of yellowfin reached a new high of 642 thousand t in 2017, surpassing the previous record of 607 thousand t in 2012.

The annual retained catches of yellowfin in the EPO by purse-seine and pole-and-line vessels during 1988-2017 are shown in (Table A-2a). The average annual retained catch during 2002-2016 was 247 thousand t (range: 167 to 413 thousand t). The preliminary estimate of the retained catch in 2017, 210 thousand t, was 13% less than that of 2016, and 15% less than the average for 2002-2016. The average amount of yellowfin discarded at sea during 2002-2016 was about 0.7% of the total purse-seine catch (retained catch plus discards) of yellowfin (range: 0.1 to 1.5%) (Table A-2a).

The annual retained catches of yellowfin in the EPO by longliners during 1988-2017 are shown in Table A-2a. During 1990-2003 catches averaged about 23 thousand t (range: 12 to 35 thousand t), or about 8% of the total retained catches of yellowfin. Longline catches declined sharply beginning in 2005, averaging 10 thousand t per year (range: 8 to 13 thousand t), or about 4% of the total retained catches, through 2016. Yellowfin are also caught by recreational vessels, as incidental catch in gillnets, and by artisanal fisheries. Estimates of these catches are shown in Table A-2a, under “Other gears” (OTR); during 2002-2016 they averaged about 2 thousand t.

Skipjack tuna

The annual catches of skipjack during 1988-2017 are shown in (Table A-1). Most of the skipjack catch in the Pacific Ocean is taken in the WCPO. Prior to 1998, WCPO skipjack catches averaged about 900 thousand t. Beginning in 1998, catches increased steadily, from 1.2 million t to an all-time high of 2 million t in 2014. In the EPO, the greatest yearly catches occurred between 2003 and 2017, ranging from 153 to 343 thousand t, the record catch in 2016.

The annual retained catches of skipjack in the EPO by purse-seine and pole-and-line vessels during 1988-2017 are shown in (Table A-2a). During 2000-2014 the annual retained catch averaged 234 thousand t (range 144 to 297 thousand t). The preliminary estimate of the retained catch in 2015, 329 thousand t, is 41% greater than the average for 2000-2014, and 11% higher than the record-high retained catch of 2008. Discards of skipjack at sea decreased each year during the period, from 11% in 2000 to a low of less than 1% in 2014. During the period about 4% of the total catch of the species was discarded at sea (Table A-2a).

Small amounts of EPO skipjack are caught with longlines and other gears (Table A-2a).

Bigeye tuna

The annual catches of bigeye during 1988-2017 are shown in (Table A-1). Overall, the catches in both the EPO and WCPO have increased, but with considerable fluctuations. In the EPO, the average catch for the period was 104 thousand t, with a low of 73 thousand t in 1989 and a high of 149 thousand t in 2000. In the WCPO the catches of bigeye increased to more than 77 thousand t during the late 1970s, decreased during the early 1980s, and then increased steadily to 113 thousand t in 1996. In 1997 the total jumped to 158 thousand t, and reached a high of 180 thousand t in 2004. Since 2004 the catch has fluctuated between 132 and 158 thousand t.

The annual retained catches of bigeye in the EPO by purse-seine and pole-and-line vessels during 1988-2017 are shown in Table A-2a. The number of fish-aggregating devices (FADs), placed in the water by fishermen to attract tunas, increased from 550 in 1992 to over 2,700 by 1995. This led to a sudden and dramatic increase in the purse-seine catches. Prior to the increase in number of FADs, the annual retained purse-seine catch of bigeye in the EPO was about 5 thousand t, by 1994 it was 35 thousand t, and in 1996 was over 60 thousand t. Since then, it has fluctuated between 44 and 95 thousand t. The preliminary estimate of the retained catch in the EPO in 2017 is 66 thousand t (Table A-2a). During 2000-2016 the percentage of the purse-seine catch of bigeye discarded at sea has steadily decreased, from 5% in 2000 to less than 1% in 2014, for an average discard rate of about 1.9%. No bigeye catch has been reported by pole-and-line vessels in recent years.

From 1985 to 1993, before the expansion of the FAD fishery, longliners caught an average of 95% of the bigeye in the EPO (average 86 thousand t; range; 66 to 104 thousand t). During 2002-2016 this average dropped to 38%, with a low of 25% in 2008 (average: 39 thousand t; range: 26 to 74 thousand t) (Table A-2a). The preliminary estimate of the longline catch in the EPO in 2017 is 31 thousand t (Table A-2a).

Small amounts of bigeye are caught by other gears, as shown in Table A-2a.

Bluefin tuna

The catches of Pacific bluefin in the EPO during 1988-2017, by gear, are shown in (Table A-2a). Purse-seine and pole-and-line vessels accounted for over 94% of the total EPO retained catch during 2002-2016. During this period the annual retained catch of bluefin in the EPO by purse-seine vessels averaged 4.8 thousand t (range 1.8 to 9.9 thousand t); the preliminary estimate for 2017 is 4.1 thousand t (Table A-2a).

The catches of Pacific Bluefin in the entire Pacific Ocean, by flag and gear, are shown in (Table A-5a). The data, which were obtained from the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), are reported by fishing nation or entity.

Catches of Pacific bluefin by recreational gear in the EPO are reported in numbers of individual fish caught, whereas all other gears report catches in weight. These numbers are then converted to metric tons for inclusion in the EPO catch totals for all gears. The original catch data for 1988-2017, in numbers of fish, are presented in (Table A-5b).

Albacore tuna

The catches of albacore in the entire Pacific Ocean, by gear and area (north and south of the equator) are shown in (Table A-6). The catches of albacore in the EPO, by gear, are shown in (Table A-2a). A portion of the albacore catch is taken by troll vessels, included under “Other gears” (OTR) in Table A-2a

Other tunas and tuna-like species

While yellowfin, skipjack, and bigeye tunas comprise the most significant portion of the retained catches of the purse-seine and pole-and-line fleets in the EPO, other tunas and tuna-like species, such as black skipjack, bonito, wahoo, and frigate and bullet tunas, contribute to the overall harvest in this area. The estimated annual retained and discarded catches of these species during 1988-2017 are presented in (Table A-2a). The catches reported in the “unidentified tunas” category (TUN) in Table A-2a contain some catches reported by species (frigate or bullet tunas) along with the unidentified tunas. The total retained catch of these other species by the purse-seine fishery in 2017 was 8.6 thousand t, which is greater than the 2002-2016 average retained catch of 7.6 thousand t (range: 500 to 19 thousand t).

Black skipjack are also caught by other gears in the EPO, mostly by coastal artisanal fisheries. Bonitos are also caught by artisanal fisheries, and have been reported as catch by longline vessels in some years.

Billfishes

Catch data for billfishes (swordfish, blue marlin, black marlin, striped marlin, shortbill spearfish, and sailfish) are shown in (Table A-2b).

Swordfish are caught in the EPO with large-scale and artisanal longlines, gillnets, harpoons, and occasionally with recreational gear. During 1999-2008 the longline catch of swordfish averaged 12 thousand t, but during 2014-2016 this almost doubled, to over 23 thousand t. More research is needed to determine whether this is due to increased abundance of swordfish, increased effort directed toward that species, increased reporting, or a combination of all of these.

Other billfishes are caught with large-scale and artisanal longlines and recreational gear. The average annual longline catches of blue marlin and striped marlin during 2002-2016 were about 3.2 thousand and 1.9 thousand t, respectively. Smaller amounts of other billfishes are taken by longline.

Unfortunately, little information is available on the recreational catches of billfishes, but they are believed to be substantially less than the commercial catches for all species.

Prior to 2011, all billfishes caught in the purse-seine fishery were classified as discarded dead; however, the growing rate of retention of bycatches of billfishes made it important to reflect this in the data, and since 2011 retained catch and discards are reported separately in Table A-2b. During 2002-2016 purse seiners accounted about 1% of the total catch of billfishes in the EPO; some are retained, and others are considered to be discarded, although some may be landed but not reported.

Other species

Data on the catches and discards of carangids (yellowtail, rainbow runner, and jack mackerel), dorado, elasmobranchs (sharks, rays, and skates), and other fishes caught in the EPO are shown in (Table A-2c).

Since 2011, bycatches in the purse-seine fishery are reported in Table A-2c as either retained or discarded.

Dorado are unloaded mainly in ports in Central and South America. The reported catches of dorado have declined, from a high of 71 thousand t in 2009 to 14 thousand t in 2016.

Distributions of the catches of tunas

Purse-seine catches

The average annual distributions of the purse-seine catches of yellowfin, skipjack, and bigeye, by set type, in the EPO during 2010-2014, are shown in Figures A-1a, A-2a, and A-3a,
Figure A-1a: Average annual distributions of the purse-seine catches of yellowfin, by set type, 2012-2016. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.


Figure A-2a: Average annual distributions of the purse-seine catches of skipjack, by set type, 2012-2016. The sizes of the circles are proportional to the amounts of skipjack caught in those 5° by 5° areas.


Figure A-3a: Average annual distributions of the purse-seine catches of bigeye, by set type, 2012-2016. The sizes of the circles are proportional to the amounts of bigeye caught in those 5° by 5° areas.

respectively, and preliminary estimates for 2017 are shown in Figures A-1b, A-2b, and A-3b.
Figure A-1b: Annual distributions of the purse-seine catches of yellowfin, by set type, 2017. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.


Figure A-2b: Annual distributions of the purse-seine catches of skipjack, by set type, 2017. The sizes of the circles are proportional to the amounts of skipjack caught in those 5° by 5° areas.


Figure A-3b: Annual distributions of the purse-seine catches of bigeye, by set type, 2017. The sizes of the circles are proportional to the amounts of bigeye caught in those 5° by 5° areas.

Most of the yellowfin catches in 2017 were taken in sets associated with dolphins, in three main areas: from 10°N to the coast of Mexico between about 105°W and 120°W, east of 95°W and north of 5°S, and from about 110°W to 130°W between the equator and 5°S. Lesser amounts of yellowfin were taken in unassociated sets along the coast of South America, and in floating-object sets south of 10°N throughout the EPO (Figure A-1b).
Figure A-1b: Annual distributions of the purse-seine catches of yellowfin, by set type, 2017. The sizes of the circles are proportional to the amounts of yellowfin caught in those 5° by 5° areas.



The distribution of skipjack catches in the EPO in 2017 closely matched the previous 5-year average, in both total catches and types of set. Most of the catch was taken in sets associated with floating objects throughout the EPO, with lesser amounts taken in unassociated sets east of the Galapagos Islands and near the coast of Peru (Figure A-2b).
Figure A-2b: Annual distributions of the purse-seine catches of skipjack, by set type, 2017. The sizes of the circles are proportional to the amounts of skipjack caught in those 5° by 5° areas.



Bigeye are not often caught north of about 7°N in the EPO. With the development of the fishery for tunas associated with FADs, the relative importance of the inshore areas has decreased, while that of the offshore areas has increased. As in most years, most of the 2017 bigeye catches were taken in sets on FADs between 5°N and 5°S, with above-average catches near 150°W (Figure A-3b).
Figure A-3b: Annual distributions of the purse-seine catches of bigeye, by set type, 2017. The sizes of the circles are proportional to the amounts of bigeye caught in those 5° by 5° areas.

Longline catches

The IATTC holds data on the spatial and temporal distributions of EPO longline catches dating back to 1952. Since 2009 the IATTC has received catch and effort data from Belize, China, France (French Polynesia), Japan, the Republic of Korea, Spain, Chinese Taipei, the United States, and Vanuatu. Albacore, bigeye and yellowfin tunas make up the majority of the catches by most of these vessels. The distributions of the catches of bigeye and yellowfin in the Pacific Ocean by Chinese, Japanese, Korean, and Chinese Taipei longline vessels during 2012-2016 are shown in Figure A-4.
Figure A-4: Distributions of the average annual catches of bigeye and yellowfin tunas in the Pacific Ocean, in metric tons, by Chinese, Japanese, Korean, and Chinese Taipei longline vessels, 2012-2016. The sizes of the circles are proportional to the amounts of bigeye and yellowfin caught in those 5° by 5° areas.

Size compositions of the catches of tunas

Purse-seine, pole-and-line, and recreational fisheries

Length-frequency samples are the basic source of data used for estimating the size and age compositions of the various species of fish in the landings. This information is necessary to obtain age-structured estimates of the populations for various purposes, including the integrated modeling that the staff uses to assess the status of the stocks. The results of such studies have been described in several IATTC Bulletins, in its Annual Reports for 1954-2002, and in its Stock Assessment Reports.

Length-frequency samples of yellowfin, skipjack, bigeye, Pacific bluefin, and, occasionally, black skipjack are collected from the catches of purse-seine vessels in the EPO by IATTC personnel at ports of landing in Ecuador, Mexico, Panama, the United States, and Venezuela. Data on catches of yellowfin and skipjack have been collected since 1954, bluefin since 1973, and bigeye since 1975.

The methods for sampling the catches of tunas are described in the IATTC Annual Report for 2000 and in IATTC Stock Assessment Reports 2 and 4. Briefly, the fish in a well of a purse-seine vessel are selected for sampling only if all the fish in the well were caught during the same calendar month, in the same type of set (floating-object, unassociated, or dolphin), and in the same sampling area. These data are then categorized by fishery (Figure A-5),
Figure A-5: The fisheries defined by the IATTC staff for stock assessment of yellowfin, skipjack, and bigeye in the EPO. The thin lines indicate the boundaries of the 13 length-frequency sampling areas, and the bold lines the boundaries of the fisheries.

Data for fish caught during the 2012-2017 period are presented in this report. Two sets of length-frequency histograms are presented for each species, except bluefin and black skipjack; the first shows the data by stratum (gear type, set type, and area) for 2017, and the second shows the combined data for each year of the 2012-2017 period. For bluefin, the histograms show the 2007-2012 catches by commercial and recreational gear combined. For black skipjack, the histograms show the 2012-2017 catches by commercial gear. Only a small amount of catch was taken by pole-and-line vessels during 2013-2017, and no samples were obtained from these vessels.

For stock assessments of yellowfin, nine purse-seine fisheries (four associated with floating objects, three associated with dolphins, and two unassociated) and one pole-and-line fishery are defined in Figure A-5. The last fishery includes all 13 sampling areas. Of the 968 wells sampled during 2017, 740 contained yellowfin. The estimated size compositions of the fish caught are shown in Figure A-6a.
Figure A-6a: Estimated size compositions of the yellowfin caught in the EPO during 2017 for each fishery designated in Figure A-5. The value at the top of each panel is the average weight of the fish in the samples.

Most of the yellowfin catch was taken in sets associated with dolphins in the Northern and Southern dolphin fisheries throughout the year, and in the Inshore dolphin fishery, primarily in the first quarter. These fisheries also produced most of the larger (>90 cm) yellowfin. Smaller yellowfin were caught primarily in the floating-object fisheries throughout the year.

The estimated size compositions of the yellowfin caught by all fisheries combined during 2012-2017 are shown in Figure A-6b.
Figure A-6b: Estimated size compositions of the yellowfin caught by purse-seine and pole-and-line vessels in the EPO during 2012-2017. The value at the top of each panel is the average weight of the fish in the samples.

The average weight of the yellowfin in 2017, 7.2 kg, was higher than 2016 (6.3 kg), but lower than any of the other annual averages for the six-year period (range: 6.3-13.3 kg). Additionally, the overall size distribution was more uniform than other years during the period.

For stock assessments of skipjack, seven purse-seine fisheries (four associated with floating objects, two unassociated, one associated with dolphins) and one pole-and-line fishery are defined (Figure A-5). The last two fisheries include all 13 sampling areas. Of the 968 wells sampled, 738 contained skipjack. The estimated size compositions of the fish caught during 2017 are shown in Figure A-7a.
Figure A-7a: Estimated size compositions of the skipjack caught in the EPO during 2017 for each fishery designated in Figure A-5. The value at the top of each panel is the average weight of the fish in the samples.

Most of the 2017 skipjack catch was taken in the Northern and Southern floating-object fisheries throughout the year, and in the Equatorial and Inshore floating-object fisheries, and the Southern unassociated fishery, in the first and second quarters. The smallest skipjack, less than 45 cm, were caught in the Northern and Southern floating-object fisheries in the third and fourth quarters.

The estimated size compositions of the skipjack caught by all fisheries combined during 2012-2017 are shown in Figure A-7b.
Figure A-7b: Estimated size compositions of the skipjack caught by purse-seine and pole-and-line vessels in the EPO during 2012-2017. The value at the top of each panel is the average weight of the fish in the samples.

The average weight of skipjack in 2017 (2.2 kg) was higher than in 2016 (1.8 kg), and consistent with the other average annual weights for the 6-year period (1.9-2.5 kg).

For stock assessments of bigeye, six purse-seine fisheries (four associated with floating objects, one unassociated, one associated with dolphins) and one pole-and-line fishery are defined (Figure A-5). The last three fisheries include all 13 sampling areas. Of the 968 wells sampled, 276 contained bigeye. The estimated size compositions of the fish caught during 2017 are shown in Figure A-8a.
Figure A-8a: Estimated size compositions of the bigeye caught in the EPO during 2017 for each fishery designated in Figure A-5. The value at the top of each panel is the average weight.

Most of the 2017 catch of bigeye was taken in the Northern and Southern floating-object fisheries throughout the year. Lesser amounts were caught in the Equatorial floating-object fishery, and the majority were 100 cm or larger.

The estimated size compositions of bigeye caught by all fisheries combined during 2012-2017 are shown in Figure A-8b.
Figure A-8b: Estimated size compositions of the bigeye caught by purse-seine vessels in the EPO during 2012-2017. The average weights of the fish in the samples are given at the tops of the panels.

The average weight of bigeye in 2017 (4.7 kg) was consistent with the previous two years.

Pacific bluefin are caught by purse-seine and recreational gear off California and Baja California from about 23°N to 35°N, with most of the catch being taken during May through October. During 2012 bluefin were caught between 28°N and 32°N from June through August. Most of the catches of bluefin by both commercial and recreational vessels were taken during July and August. Prior to 2004, the sizes of the fish in the commercial and recreational catches have been reported separately. During 2004-2012, however, small sample sizes made it infeasible to estimate the size compositions separately. Therefore, the sizes of the fish in the commercial and recreational catches of bluefin were combined for each year of the 2004-2012 period. The average weight of the fish caught during 2012 (14.2 kg) was less than that of 2011 (15.4 kg), but very close to the average weights in 2009 and 2010. The estimated size compositions are shown in Figure A-9.
Figure A-9: Estimated catches of Pacific bluefin by purse-seine and recreational gear in the EPO during 2007-2012. The value at the top of each panel is the average weight.

Prior to 2013, IATTC staff collected length-frequency samples from recreational vessels with landings in San Diego and from purse seiners. Beginning in 2013, sampling of recreational vessels was taken over by the U.S. National Marine Fisheries Service (NMFS). Very few samples were collected from commercial purse-seiners during 2013-2017. The size composition estimates for bluefin will be updated after development of a methodology that will incorporate the changes in sampling.

Black skipjack are caught incidentally by fishermen who direct their effort toward yellowfin, skipjack, and bigeye tuna. The demand for this species is low, so most of the catches are discarded at sea, but small amounts, mixed with the more desirable species, are sometimes retained. The estimated size compositions for each year of the 2012-2017 period are shown in Figure A-10.
Figure A-10: Preliminary size compositions of the catches of black skipjack by purse-seine vessels in the EPO during 2012-2017. The value at the top of each panel is the average weight.

Longline fishery

The size compositions of yellowfin and bigeye caught by the Japanese longline fleet (commercial and training vessels) in the EPO during 2012-2015 are shown in Figures A-11
Figure A-11: Estimated size compositions of the catches of yellowfin by the Japanese longline fleet in the EPO, 2012-2015. The value at the top of each panel is the average weight.

and Figure A-12.
Figure A-12: Estimated size compositions of the catches of bigeye by the Japanese longline fleet in the EPO, 2012-2015. The value at the top of each panel is the average weight.

The average annual weight during that period ranged from 49.4 to 60.5 kg for yellowfin, and from 57.3 kg to 63.5 kg for bigeye. The data for 2016 are incomplete, and available for training vessels only, found in document SAC-07-03d. Information on the size compositions of fish caught by the Japanese longline fishery in the EPO during 1958-2008 is available in IATTC Bulletins describing that fishery.

Catches of tunas and bonitos, by flag and gear

The annual retained catches of tunas and bonitos in the EPO during 1988-2017 by flag and gear, are shown in (Table A-3a), (Table A-3b), (Table A-3c), (Table A-3d), (Table A-3e). These tables include all the known catches of tunas and bonitos compiled from various sources, including vessel logbooks, observer data, unloading records provided by canners and other processors, export and import records, reports from governments and other entities, and estimates derived from the species- and size-composition sampling program. Similar information on tunas and bonitos prior to 2001, and historical data for tunas, billfishes, sharks, carangids, dorado, and miscellaneous fishes are available on the IATTC website. The purse-seine catches of tunas and bonitos in 2016 and 2017, by flag, are summarized in (Table A-4). Of the nearly 615 thousand t of tunas and bonitos caught in 2017, 47% were caught by Ecuadorian vessels, and 18% by Mexican vessels. Other countries with significant catches of tunas and bonitos in the EPO included Panama (11%), Colombia (6%), United States (6%) and Venezuela (4%). The purse-seine landings of tunas and bonitos in 2016 and 2017, by flag, are summarized in (Table A-4b). Of the more than 657 thousand t of tunas and bonitos landed in the EPO in 2017 (which include some catches from 2016), 61% were landed in Ecuadorian ports, and 21% in Mexican ports. Other countries with landings of tunas and bonitos in the EPO included Peru (3%) and Colombia (2%).


Effort
Purse-seine
Estimates of the numbers of purse-seine sets of each type (associated with dolphins, associated with floating objects, and unassociated) in the EPO during the 2002-2017 period, and the retained catches of these sets, are shown in (Table A-7) and in Figure 1.
Figure 1: Purse-seine catches of tunas, by species and set type, 2000-2015

The estimates for vessels ≤363 t carrying capacity were calculated from logbook data in the IATTC statistical data base, and those for vessels >363 t carrying capacity were calculated from the observer data bases of the IATTC, Colombia, Ecuador, the European Union, Mexico, Nicaragua, Panama, the United States, and Venezuela.

There are two types of floating objects, flotsam and fish-aggregating devices (FADs). The occurrence of the former is unplanned from the point of view of the fishermen, whereas the latter are constructed by fishermen specifically for the purpose of attracting fish. The use of FADs increased sharply in the mid-1990s, and they now account for 98% of all floating-object sets by vessels of >363 t carrying capacity (Table A-8).

Longline
The reported nominal fishing effort (in thousands of hooks) by longline vessels in the EPO, and their catches of the predominant tuna species, are shown in (Table A-9).
Ecosystem Assessment
 
INTRODUCTION

The 1995 FAO Code of Conduct for Responsible Fisheries stipulates that States and users of living aquatic resources should conserve aquatic ecosystems and it provides that management of fisheries should ensure the conservation not only of target species, but also of species belonging to the same ecosystem or associated with or dependent upon the target species (The Code also provides that management measures should ensure that biodiversity of aquatic habitats and ecosystems is conserved and endangered species are protected and that States should assess the impacts of environmental factors on target stocks and species belonging to the same ecosystem or associated with or dependent upon the target stocks, and assess the relationship among the populations in the ecosystem). In 2001, the Reykjavik Declaration on Responsible Fisheries in the Marine Ecosystem elaborated these principles with a commitment to incorporate an ecosystem approach into fisheries management.

Consistent with these instruments, one of the functions of the IATTC under the 2003 Antigua Convention is to “adopt, as necessary, conservation and management measures and recommendations for species belonging to the same ecosystem and that are affected by fishing for, or dependent on or associated with, the fish stocks covered by this Convention, with a view to maintaining or restoring populations of such species above levels at which their reproduction may become seriously threatened”.

Consequently, the IATTC has taken account of ecosystem issues in many of its decisions, and this report on the offshore pelagic ecosystem of the tropical and subtropical Pacific Ocean, which is the habitat of tunas and billfishes, has been available since 2003 to assist in making its management decisions. This section provides a coherent view, summarizing what is known about the direct impact of the fisheries upon various species and species groups of the ecosystem, and reviews what is known about the environment and about other species that are not directly impacted by the fisheries but may be indirectly impacted by means of predator-prey interactions in the food web.

This report does not suggest objectives for the incorporation of ecosystem considerations into the management of fisheries for tunas or billfishes, nor any new management measures. Rather, its main purpose is to demonstrate that the Commission considers the ecological sustainability of the fisheries which it manages.

It is important to remember that the view that we have of the ecosystem is based on the recent past; we have almost no information about the ecosystem before exploitation began. Also, the environment is subject to change on a variety of time scales, including the well-known El Niño fluctuations and more recently recognized longer-term changes, such as the Pacific Decadal Oscillation and other climate changes.

However, the view that we have of the ecosystem is based on the recent past; there is almost no information available about the ecosystem before exploitation began. Also, the environment is subject to change on a variety of time scales, including the well-known El Niño fluctuations and more recently recognized longer-term changes, such as the Pacific Decadal Oscillation (PDO) and other climate-related changes

In addition to reporting the catches of the principal species of tunas and billfishes, the staff estimates catches (retained and discarded) of non-target species. In this report, data on those species are presented in the context of the effect of the fishery on the ecosystem. While relatively good information is available for catches of tunas and billfishes across the entire fishery, this is not the case for bycatch species. The information is comprehensive for large (carrying capacity greater than 363 metric tons) purse-seine vessels that carry observers under the Agreement on the International Dolphin Conservation Program (AIDCP), and some information on retained catches is also reported for other purse-seine vessels, and much of the longline fleet can be found in SAC-08-07b document. There is little information available on bycatches and discards by fishing vessels that use other gear types like gillnet, harpoon, and recreational gear in the document SAC-07-INF-C(d).

Detailed information on past ecosystem studies can be found in documents for previous meetings of the Scientific Advisory Committee like SAC-08-07a, and current and planned ecosystem-related work by the IATTC staff is summarized in the Strategic Science Plan (SAC-09-01) and the Staff Activities and Research report (SAC-09-02).

IMPACT OF CATCHES

Single-species assessments

This report presents current information on the effects of the tuna fisheries on the stocks of individual species in the EPO. An ecosystem perspective requires a focus on how the fishery may have altered various components of the ecosystem. The tunas section and the billfishes section of this report refer to information on the current biomass of each stock. The influences of predator and prey abundances are not explicitly described. The marine mammals, sea turtles, sharks and rays and other large fishes section, include estimates of catch data by vessels of the large purse-seine and large-scale longline (herein ‘longline fisheries’) fisheries reported to the IATTC.

Observer data were used to provide estimates of total catches (retained catches and discards) during sets by large purse-seine vessels in the EPO on floating objects (OBJ), unassociated schools (NOA), and dolphins (DEL).

Complete data are not available for small purse-seine, longline, and other types of vessels. There is considerable variability in reporting formats of longline data by individual CPCs through time, thereby limiting application of catch and effort data as shown in SAC-08-07b, SAC-08-07d, SAC-08-07e documents. Some catches of non-target species by the tuna longline fisheries in the EPO are reported to the IATTC, but often in a highly summarized form (e.g. monthly aggregation of catch by broad taxonomic group (e.g. “Elasmobranchii”)), often without verification of whether the reported catch has been raised to total catch in SAC-08-07b document. Because of data limitations, catch data for longline fisheries were obtained using IATTC’s 5°x5° catch tables following methods described in SAC-08-07b and SAC-08-07d. Such estimates must be regarded as minimum estimates only. However, due to the paucity of catch data in the IATTC longline database, a report on establishing minimum data standards and reporting requirements for longline observer programs was discussed at the Eighth Meeting of the SAC in SAC-08-07e document. As data reporting improves, better estimations of catches by longline vessels will be available.

Tunas

Information on the effects of EPO fisheries on bigeye, yellowfin, and skipjack tunas is found in Documents SAC-09-05, 06, and 07, respectively. A report of the Bluefin Working Group of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) and outcomes of the Joint Tuna RFMO meeting of Pacific bluefin tuna were presented at the Ninth Meeting of the SAC. The ISC Northern Albacore Working Group completed its stock assessment in 2017, and an update on management strategy evaluation (MSE) work on north Pacific albacore tuna was also presented at SAC-09.

Preliminary estimates of the catches of tunas and bonitos in the EPO during 2017 are found in Table A-2a of Document SAC-09-03.

Billfishes

Information on the effects of the tuna fisheries on swordfish, blue marlin, striped marlin, and sailfish is presented in Sections G-J of IATTC Fishery Status Report 15. Stock assessments and/or stock structure analyses for swordfish (2007, structure), eastern Pacific striped marlin (2010, assessment and structure), northeast Pacific striped marlin (2011, assessment), southeast Pacific swordfish (2012, assessment), and eastern Pacific sailfish (2013, assessment) were completed by the IATTC staff. Stock assessments of striped marlin (2015), Pacific blue marlin (2016), and north Pacific swordfish (2017) were completed by the ISC Billfish Working Group.


Black marlin (Makaira indica), sailfish (Istiophorus platypterus), and shortbill spearfish (Tetrapterus angustirostris)

No recent stock assessments have been made for these species, although there are some data published jointly by scientists of the National Research Institute of Far Seas Fisheries (NRIFSF) of Japan and the IATTC in the IATTC Bulletin series that show trends in catches, effort, and catches per unit of effort (CPUEs).

Preliminary estimates of the catches of billfishes in the EPO during 2017 are found in Table A-2b of Document SAC-09-03.



Marine mammals

Marine mammals, especially spotted dolphins (Stenella attenuata), spinner dolphins (S. longirostris), and common dolphins (Delphinus delphis), are frequently found associated with yellowfin tuna in the EPO. Purse-seine fishermen commonly set their nets around herds of dolphins and the associated schools of yellowfin tuna, and then release the dolphins while retaining the tunas. Whilst the incidental mortality of dolphins in the fishery was high during the 1960s and 1970s, it decreased precipitously since the 1980s. Preliminary estimates of the incidental mortality of marine mammals in the fishery in 2017 are shown in (Table 1

), and estimates during 1993-2017 are shown in Figure L-1.
Figure L-1: Incidental dolphin mortalities, in numbers of animals, reported by observers on large purse-seine vessels, 1993-2017, by set type (dolphin (DEL), unassociated (NOA), floating object (OBJ). Data for 2017 are preliminary.

Dolphin mortality rarely occurred in sets on unassociated tuna schools and on floating objects. Decreasing mortalities were observed for northeastern spotted dolphins, whitebelly spinner dolphins, western-southern spotted dolphins, central common dolphins, and other delphinidae. Numbers of mortalities were variable for northern common dolphins and eastern spinner dolphins, and those of southern common dolphins were generally less than 40 individuals, with the exception of peaks to 220 in 2004 and about 120 in 2008.

Sea turtles

Sea turtles are caught on longlines when they take the bait on hooks, are snagged accidentally by hooks, or are entangled in the lines. Estimates of incidental mortality of turtles due to longline and gillnet fishing are few. The mortality rates in the EPO industrial longline fishery are likely to be lowest in “deep” sets (around 200-300 m) targeting bigeye tuna, and highest in “shallow” sets (<150 m) for albacore and swordfish. In addition, there is a sizeable fleet of artisanal longline vessels that also impact sea turtles shown in the “Actions by the IATTC and the AIDCP addressing ecosystem” section of this report.

Sea turtles are occasionally caught in purse seines in the EPO tuna fishery, generally when the turtles associate with floating objects, and are captured when the object is encircled. Also, sets on unassociated tunas or tunas associated with dolphins may capture sea turtles that happen to be at those locations. Sea turtles sometimes become entangled in the webbing under fish-aggregating devices (FADs) and drown. In some cases, they are entangled by the fishing gear and may be injured or killed.

The olive Ridley turtle (Lepidochelys olivacea) is, by far, the species of sea turtle taken most often by purse seiners. It is followed by green sea turtles (Chelonia mydas) and, very occasionally, by loggerhead (Caretta caretta) and hawksbill (Eretmochelys imbricata) turtles (Figure L-2).
Figure L-2: Sea turtle interactions and mortalities, in numbers of animals, reported by observers on large purse-seine vessels, 1993-2017, by set type (dolphin (DEL), unassociated (NOA), floating object (OBJ). Data for 2017 are preliminary.

Since 1990, when IATTC observers began recording this information, only three mortalities of leatherback (Dermochelys coriacea) turtles have been recorded. Some of the turtles are unidentified because they were too far from the vessel or it was too dark for the observer to identify them.

Preliminary estimates of the mortalities and interactions (in numbers) of turtles in sets by large purse-seine vessels on floating objects (OBJ), unassociated tunas (NOA), and dolphins (DEL) during 2017, based on IATTC observer data, are shown in (

Table 2), and for 1993-2017 in Figure L-2.

Data on sea turtle interactions or mortality were deficient for the longline fisheries is shown in SAC-08-07b.

The mortalities of sea turtles due to purse seining for tunas are probably less than those due to other human activities, which include exploitation of eggs and adults, beach development, pollution, entanglement in and ingestion of marine debris, and impacts of other fisheries.

Sharks and rays

Sharks are caught as bycatch or targeted catch in EPO tuna longline and purse-seine fisheries as well as multi-species and multi-gear fisheries of the coastal nations.

Stock assessments or stock status indicators (SSIs) are available for only five shark species in the EPO: silky (Carcharhinus falciformis) (IATTC: SAC-05 INF-F, SAC-08-08a(i), SAC-09-13), blue (Prionace glauca) (ISC Shark Working Group), shortfin mako (Isurus oxyrinchus) (ISC Shark Working Group), common thresher (Alopias vulpinus) (NMFS), and bigeye thresher (Alopias superciliosus) (FAO Common Oceans Tuna Project). A Pacific-wide assessment of the porbeagle shark (Lamna nasus) in the southern hemisphere was completed in late 2017 as part of the FAO Common Oceans Tuna Project. Whale shark interactions with the tuna purse-seine fishery in the EPO are summarized in Document BYC-08 INF-A. The impacts of tuna fisheries on the stocks of other shark species in the EPO are unknown.

Preliminary estimates of the catches of sharks and rays reported by observers on large purse-seine vessels in the EPO during 2017 and minimum estimates of catches by longline vessels in 2016 are shown in (

Table 3). Catches of sharks and rays in the purse-seine and longline fisheries during 1993-2017 are shown in Figure L-3.
Figure L-3: Retained and discarded catches, in tons, of sharks and rays reported by observers on large purse-seine vessels, 1993-2017, by set type (dolphin (DEL), unassociated (NOA), floating-object (OBJ)) (left y-axis). Longline data (right y-axis) are considered minimum catch estimates, using available IATTC 5°x5° data, due to incomplete reporting, see section “Impact of catches” and SAC-08-07b for limitations associated with longline data). Purse-seine data for 2017 are preliminary; longline data for 2017 not available.

Silky sharks are the most commonly-caught species of shark in the purse-seine fishery. Shark catches were generally greatest in sets on floating objects (mainly silky, oceanic whitetip (C. longimanus), hammerhead (Sphyrna spp.) and mako (Isurus spp.) sharks), followed by unassociated sets and, at a much lower level, dolphin sets as seen in Figure L-3. Until about 2007, thresher sharks (Alopias spp.) occurred mostly in unassociated sets (Figure L-3). Historically, oceanic whitetip sharks were commonly caught in sets on floating objects, but they became much less common after 2005. In general, the bycatch rates of manta rays (Mobulidae) and stingrays (Dasyatidae) are greatest in unassociated sets, followed by dolphin sets, and lowest in floating-object sets, although catches by set type can be variable as shown in Figure L-3. The numbers of purse-seine sets of each type in the EPO during 2002-2017 are shown in Table A-7 of Document SAC-09-03.

The reported longline catches of sharks increased sharply after 2008 with catches of silky, oceanic whitetip, and hammerhead sharks declining thereafter. Catches of thresher, mako, and blue sharks increased through 2016. These data should be interpreted with caution due to limitations in data-reporting requirements for non-target species caught in the longline fishery resulting from Resolutions C-03-05 and C-11-08 and documented in SAC-08-07b.

The small-scale artisanal longline fisheries of the coastal CPCs target sharks, tunas, billfishes and dorado (Coryphaena hippurus), and some of these vessels operate in areas beyond coastal waters and national jurisdictions, as described by Martínez-Ortiz, J., Aires-da-Silva, A.M., Lennert-Cody, C.E., Maunder, M.N. in “The Ecuadorian artisanal fishery for large pelagics: species composition and spatio-temporal dynamics”. However, essential shark data from longline fisheries is lacking, and therefore conventional stock assessments and/or stock status indicators cannot be produced (see data challenges outlined in SAC-07-06b(iii)). A project is underway to improve data collection on sharks, particularly for Central America, for the artisanal longline fleet through funding from the Food and Agriculture Organization of the United Nations (FAO) and the Global Environmental Facility (GEF) under the framework of the ABNJ Common Oceans program (SAC-07-06b(ii), SAC-07-06b(iii)). Data obtained from this project may be included in future iterations of the Ecosystem Considerations report to provide better estimates of sharks caught by the various longline fleets.

Other large fishes

Preliminary estimates of the catches of dorado (Coryphaena spp.) and other large fishes in the EPO by large purse-seine vessels during 2017 are shown in (Table 4), along with minimum estimates from longline data in 2016. Catch trends for the most important species during 1993-2017, by set type and fishery, are shown in Figure L-4.
Figure L-4:  Catches, in tons, of commonly-caught fishes by large purse-seine vessels, 1993-2017, by set type (dolphin (DEL), unassociated (NOA), floating object (OBJ)) (left y-axis). Longline data (right y-axis) are considered minimum catch estimates using available IATTC 5°x5° data, due to incomplete reporting (see “Single-species assessment” section and SAC-08-07b for limitations associated with longline data). Purse-seine data for 2017 are preliminary; longline data for 2017 not available.

Dorado is the most commonly reported fish species caught incidentally in the EPO purse-seine tuna fishery. It is also one of the most important species caught in the artisanal fisheries of the coastal nations of the EPO, leading to an exploratory stock assessment (SAC-07-06a(i)) and management strategy evaluation (MSE) in the south EPO (SAC-07-06a(ii)).

Around 2006 sharp increases were observed in longline catches of dorado, wahoo, pomfrets and opahs, although this may be related to changes in data reporting. Purse-seine catches of dorado, wahoo, rainbow runner, and yellowtail were variable, and occurred primarily in sets on floating objects



OTHER FAUNA

Seabirds

There are approximately 100 species of seabirds in the tropical EPO. Some of them associate with epipelagic predators, such as fishes (especially tunas) and marine mammals, near the ocean surface. Feeding opportunities for some seabird species are dependent on the presence of tuna schools feeding near the surface. Most species of seabirds take prey, mainly squid (primarily Ommastrephidae), within half a meter of the surface, or in the air (flyingfishes, Exocoetidae). Subsurface predators, such as tunas, often drive prey to the surface to trap it against the air-water interface, where it becomes available to the birds, which also feed on injured or disoriented prey, and on scraps of large prey.

Some seabirds, especially albatrosses (waved (Phoebastria irrorata), black-footed (P. nigripes), Laysan (P. immutabilis), and black-browed (Thalassarche melanophrys)) and petrels, are susceptible to being caught on baited hooks in pelagic longline fisheries. There is particular concern for the waved albatross, because it is endemic to the EPO and nests only in the Galapagos Islands. Observer data from artisanal vessels show no interactions with waved albatross during those vessels’ fishing operations. Data from the US pelagic longline fishery in the north EPO indicate that bycatches of black-footed and Laysan albatrosses occur.

The IATTC has adopted two measures on seabirds as shown at “Considerations” section for seabirds; also, the Agreement on the Conservation of Albatrosses and Petrels (ACAP) and BirdLife International have updated their maps of seabird distribution in the EPO, and have recommended guidelines for seabird identification, reporting, handling, and mitigation measures (SAC-05 INF-E, SAC-07-INF-C(d), SAC-08-INF-D(a), SAC-08-INF-D(b), SAC-08-INF-D(d) ). Additionally, ACAP has reported on the conservation status for albatrosses and large petrels (SAC-08-INF-D(c)).

Data pertaining to interactions with seabirds is deficient in the IATTC longline database(SAC-08-07b).

Forage

A large number of taxa occupying the middle trophic levels in the EPO ecosystem—generically referred to as “forage” species—play a key role in providing a trophic link between primary producers at the base of the food web and the upper-trophic-level predators, such as tunas and billfishes. Cephalopods, especially squids, play a central role in many marine pelagic food webs by linking the massive biomasses of micronekton, particularly myctophid fishes, to many oceanic predators. For example, the Humboldt squid (Dosidicus gigas) is a common prey for yellowfin and bigeye tunas and other predatory fishes, but is also a voracious predator of small fishes and cephalopods. Recent changes in the abundance and geographic range of Humboldt squid could affect the foraging behavior of the tunas and other predators, perhaps affecting their vulnerability to capture and the trophic structure of pelagic ecosystems. Given the high trophic flux passing through the squid community, concerted research on squids is important for understanding their role as key prey and predators.

Some small forage fishes are incidentally caught in the EPO by purse-seine vessels on the high seas, mostly in sets on floating objects, and by coastal artisanal fisheries, but are generally discarded at sea. Frigate and bullet tunas (Auxis spp.), for example, are a common prey of many high trophic level predators, and can comprise 10% or more of their diet biomass. Preliminary estimates of the catches of small fishes by large purse-seine vessels in the EPO during 2017 are shown in (
  Set type Total
  OBJ NOA DEL  
Triggerfishes (Balistidae) and filefishes (Monacanthidae) 86 <1 - 87
Other small fishes 12 <1 - 12
Frigate and bullet tunas (Auxis spp.) 153 103 - 256





), and catches during 1993-2017 are shown in Figure L-5.


Figure L-5:  Catches, in tons, of commonly-caught fishes by large purse-seine vessels, 1993-2017, by set type (dolphin (DEL), unassociated (NOA), floating object (OBJ)) (left y-axis). Longline data (right y-axis) are considered minimum catch estimates using available IATTC 5°x5° data, due to incomplete reporting (see “Single-species assessment” section and SAC-08-07b for limitations associated with longline data). Purse-seine data for 2017 are preliminary; longline data for 2017 not available.

Declines in catches of small teleost fishes over the 25-year period were observed.

Larval fishes and plankton

Larval fishes have been collected in surface net tows in the EPO for many years by personnel of the Southwest Fisheries Science Center of the US National Marine Fisheries Service (NMFS). Of the 314 taxonomic categories identified, 17 were found to be most likely to show the effects of environmental change; however, the occurrence, abundance, and distribution of these key taxa revealed no consistent temporal trends. Research* has shown a longitudinal gradient in community structure of the ichthyoplankton assemblages in the eastern Pacific warm pool, with abundance, species richness, and species diversity high in the east (where the thermocline is shallow and primary productivity is high) and low but variable in the west (where the thermocline is deep and primary productivity is low).

The phytoplankton and zooplankton populations in the tropical EPO are variable. For example, chlorophyll concentrations on the sea surface (an indicator of phytoplankton blooms) and the abundance of copepods were markedly reduced during the El Niño event of 1982-1983, especially west of 120°W. Similarly, surface concentrations of chlorophyll decreased during the 1986-1987 El Niño episode and increased during the 1988 La Niña event due to changes in nutrient availability.

The species and size composition of zooplankton is often more variable than the zooplankton biomass. When the water temperatures increase, warm-water species often replace cold-water species at particular locations. The relative abundance of small copepods off northern Chile, for example, increased during the 1997-1998 El Niño event, while the zooplankton biomass did not change.

* Vilchis, L.I., L.T. Ballance, and W. Watson. 2009. Temporal variability of neustonic ichthyoplankton assemblages of the eastern Pacific warm pool: Can community structure

TROPHIC INTERACTIONS

The following is a brief summary of current knowledge of trophic interactions. Proposed studies on trophic interactions are outlined in the IATTC’s Strategic Science Plan (SAC-09-01) and the staff activities and research work plan (SAC-09-02).

Tunas and billfishes are wide-ranging, generalist predators with high energy requirements, and, as such, are key components of pelagic ecosystems. The ecological relationships among large pelagic predators, and between them and animals at lower trophic levels, are not well understood, but are required to develop models to assess fishery and climate impacts on the ecosystem. Knowledge of the trophic ecology of predatory fishes in the EPO has been derived from stomach contents analysis, and more recently from chemical indicators. Each species of tuna appears to have a generalized feeding strategy (high prey diversity and low abundance of individual prey types) that varies spatially and ontogenetically.

Stable isotope analysis can complement dietary data for delineating the trophic flows of marine food webs. While stomach contents represent a sample of the most-recent feeding events, stable carbon and nitrogen isotopes integrate all components of the entire diet into the animal’s tissues, providing a history of recent trophic interactions. Finer-resolution information is provided by compound-specific isotope analysis of amino acids (AA-CSIA). For example, the trophic position of a predator in the food web can be determined from its tissues by relating “source” amino acids (e.g. phenylalanine) to “trophic” amino acids (e.g. glutamic acid), which describe the isotopic values for primary producers and the predator, respectively.

Trophic studies have revealed many of the key trophic connections in the tropical pelagic EPO, and have formed the basis for representing food-web interactions in an ecosystem model (IATTC Bulletin, Vol. 22, No. 3) to explore the ecological impacts of fishing and climate change. The staff aim to continue and improve trophic data collection for many components of the EPO ecosystem, such as small and large mesopelagic fishes, which will allow the ecosystem dynamics to be better understood, but also enable the development of an improved ecosystem model that represents the entire EPO.



PHYSICAL ENVIRONMENT*

Environmental conditions affect marine ecosystems, the dynamics and catchability of tunas and billfishes, and the activities of fishermen. Tunas and billfishes are pelagic during all stages of their lives, and the physical factors that affect the tropical and sub-tropical Pacific Ocean can have important effects on their distribution and abundance.

The ocean environment varies on a variety of time scales, from seasonal to inter-annual, decadal, and longer (e.g. climate phases or regimes). The dominant source of variability in the upper layers of the EPO is known as the El Niño-Southern Oscillation (ENSO), an irregular fluctuation involving the entire tropical Pacific Ocean and global atmosphere. El Niño events occur at 2- to 7-year intervals, and are characterized by weaker trade winds, deeper thermoclines, and abnormally high sea-surface temperatures (SSTs) in the equatorial EPO. El Niño’s opposite phase, commonly called La Niña, is characterized by stronger trade winds, shallower thermoclines, and lower SSTs. The changes in the physical and chemical environment due to ENSO have a subsequent impact on the biological productivity, feeding, and reproduction of fishes, birds, and marine mammals.

With respect to commercially important tunas and billfishes, ENSO is thought to cause considerable variability in their recruitment and availability for capture. For example, a shallow thermocline in the EPO during La Niña events can contribute to increased success of purse-seine fishing for tunas, by compressing the preferred thermal habitat of small tunas near the sea surface. In contrast, during an El Niño event, when the thermocline is deep, tunas are apparently less vulnerable to capture, and catch rates can decline. Furthermore, warmer- or cooler-than-average SSTs can also cause these mobile fishes to move to more favorable habitats.

Climate-induced variability on a decadal scale (i.e. 10 to 30 years) also affects the EPO and has often been described in terms of “regimes” characterized by relatively stable means and patterns in the physical and biological variables. Decadal fluctuations in upwelling and water transport coincide with higher-frequency ENSO patterns, and have basin-wide effects on the SSTs and thermocline slope that are similar to those caused by ENSO, but on longer time scales. For example, analyses by the IATTC staff have indicated that yellowfin in the EPO have experienced regimes of lower (1975-1982) and higher (1983-2001) recruitment, thought to be due to a shift in the primary productivity regime in the Pacific Ocean.

Indices of variability in oceanographic conditions—from shorter-term, inter-annual ENSO events assessed in different regions of the EPO, to the longer-term interdecadal PDO index—are used to describe SST anomalies in the Pacific Ocean. Oceanographic indices can be used to explore the influence of environmental drivers on the vulnerability of non-target species impacted by fisheries as shown in SAC-08-08a(i) document. Some of these indices include the Oceanic Niño Index (ONI), the Índice Costero El Niño (ICEN) and the PDO. The ONI is used by the US National Oceanic and Atmospheric Administration (NOAA), and is the primary indicator of warm El Niño (ONI ≥+0.5) and cool La Niña (ONI ≤-0.5) conditions within the Niño 3.4 region in the east-central tropical Pacific Ocean between 120° and 170°W**.

The ICEN index is used by the Comité Multisectorial para el Estudio del Fenómeno El Niño (ENFEN) to monitor the occurrence and magnitude of El Niño in the Niño 1+2 region (the smallest of the El Niño regions, from 0° to 10°S between 90° and 80°W), corresponding to the highly dynamic region along the coast of Peru. The PDO—a long-lived El Niño-like pattern of Pacific climate variability—tracks large-scale interdecadal patterns of environmental and biotic changes, primarily in the North Pacific Ocean***, with secondary signatures in the tropical Pacific****. Monthly ONI*****, ICEN****** and PDO******* data from 1993-2017 are shown in Figure L-6 to provide a general overview of variability in these indices over the past two decades.
Figure L-6:  Oceanographic indices used to characterize SST anomalies and El Niño-Southern Oscillation (ENSO) events in the Pacific Ocean, 1993-2017. ICEN: Índice Costero El Niño; ONI: Oceanic Niño Index; PDO: Pacific Decadal Oscillation.

ICEN values have been categorized from “strong cold” events (values <-1.4) to “extraordinary warm” events (values >3)********. ICEN values were >3 during the 1997-1998 El Niño; values peaked to a high of 2.23 in October 2015, indicating a “very strong” event. Similarly, ONI values were >2 during the 1997-1998 and 2015-2016 El Niño events, representing “very strong” events*********. PDO values peaked at 2.79 in August 1997, and at 2.62 in April 2016.

Maps of mean SSTs across the EPO for each year during 1993-2017 were created using NOAA_OI_SST_V2 data********** provided by the NOAA/OAR.ESRL PSD, Boulder, Colorado, USA. Figure L-7a and Figure L-7b shows the expansion of warmer waters during the extreme El Niño events of 1997-1998 and 2015-2016.
Figure L-7a:  Mean annual SSTs in the EPO, 1993-2004.
Figure L-7a:  Mean annual SSTs in the EPO, 1993-2004.

*Some of the information in this section is from Fiedler, P.C. 2002. Environmental change in the eastern tropical Pacific Ocean: review of ENSO and decadal variability. Mar. Ecol. Prog. Ser. 244: 265-283

**Dahlman, L. 2016. Climate Variability: Oceanic Niño Index. National Oceanic and Atmospheric Administration. https://www.climate.gov/news-features/understanding-climate/climate-variability-oceanic-ni%C3%B1o-index.

*** Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis. 1997. A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin of the American Meteorological Society 78: 1069-1079.

**** Hare, S.R., and N.J. Mantua. 2000. Empirical evidence for North Pacific regime shifts in 1977 and 1989. Progress in Oceanography 47: 103-145.

*****http://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

******http://www.met.igp.gob.pe/variabclim/indices.html

*******http://research.jisao.washington.edu/pdo/

********http://www.imarpe.pe/imarpe/archivos/informes/imarpe_comenf_not_tecni_enfen_09abr12.pdf

*********http://ggweather.com/enso/oni.htm

**********https://www.esrl.noaa.gov/psd/data/gridded/data.noaa.oisst.v2.html

ECOLOGICAL INDICATORS

Over the past two decades, many fisheries worldwide have broadened the scope of management to consider fishery impacts on non-target species and the ecosystem more generally. This ecosystem approach to fisheries management is important for maintaining the integrity and productivity of ecosystems while maximizing the utilization of commercially important assets. However, demonstrating the ecological sustainability of EPO fisheries is a significant challenge, given the wide range of species with differing life histories with which those fisheries interact. While biological reference points have been used for single-species management of target species, alternative performance measures and reference points are required for the many non-target species for which reliable catch and/or biological data are lacking; for example, incidental mortality limits for dolphins have been set in the EPO purse-seine fishery under the AIDCP.

Another important aspect of assessing ecological sustainability is to ensure that the structure and function of the ecosystem is not negatively impacted by fishing activities. Several ecosystem metrics or indicators have been proposed to address this issue, such as community size structure, diversity indices, species richness and evenness, overlap indices, trophic spectra of catches, relative abundance of an indicator species or group, and numerous environmental indicators.

Given the complexity of marine ecosystems, no single indicator can completely represent their structure and internal dynamics. In order to monitor changes in these multidimensional systems and detect the potential impacts of fishing and the environment, a variety of indicators is required. Therefore, a range of indicators that can be calculated with the ecosystem modelling software Ecopath with Ecosim (EwE) are used in this report to describe the long-term changes in the EPO ecosystem. The analysis covers the 1970-2014 period, and the indicators included are: mean trophic level of the catch (MTLc), the Marine Trophic Index (MTI), the Fishing in Balance index (FIB), Kempton’s Q diversity index, and three indicators that describe the mean trophic level of three components, or ‘communities’ (TL 2.0-3.5, 3.5-4.0, and >4.0), after fisheries have extracted biomass as catches. These indicators, and the results derived from the ecosystem model of the pelagic Eastern Tropical Pacific Ocean (ETP)*, are summarized below.

In exploited pelagic ecosystems, fisheries that target large piscivorous fishes act as the system’s apex predators. Over time, fishing can cause the overall size composition of the catch to decrease, and, in general, the TLs of smaller organisms are lower than those of larger organisms. The mean trophic level of the catch (MTLc) by fisheries can be a useful metric of ecosystem change and sustainability, because it integrates an array of biological information about the components of the system. MTLc is also an indicator of whether fisheries are changing their fishing or targeting practices in response to changes in the abundance or catchability of traditional target species. For example, declines in the abundance of large predatory fish by overfishing has resulted in fisheries progressively targeting species at lower trophic levels in order to remain profitable. Studies that have documented this phenomenon, referred to as ‘fishing down the food web’, have shown that the MTLc decreased by around 0.1 of a trophic level per decade.

The Marine Trophic Index (MTI) is essentially the same as MTLc, but it includes only high trophic level species—generally TL>4.0—that are the first indicator of ‘fishing down the food web’. Some ecosystems, however, have changed in the other direction, from lower to higher TL communities, sometimes as a result of improved technologies to allow exploitation of larger species—referred to as ‘fishing up the food web’—but it can also result from improved catch reporting, as previously unreported catches of discarded predatory species, such as sharks, are recorded.

The Fishing in Balance (FIB) index indicates whether fisheries are balanced in ecological terms and not disrupting the functionality of the ecosystem (FIB = 0). A negative FIB indicates overexploitation, when catches do not increase as expected given the available productivity in the system, or if the effects of fishing are sufficient to compromise the functionality of the ecosystem, while a positive FIB indicates expansion of a fishery, either spatially, or through increased species richness of the catch.

Kempton’s Q index measures the diversity and evenness in the ecosystem of species or functional groups with a trophic level greater than 3. Because the number of functional groups defined by an ecosystem model is fixed, a decrease in the index indicates that the relative contribution of each group to the overall biomass has changed relative to a reference year.

In contrast to MTLc, the mean trophic level of the community essentially describes what the expected trophic level of components of the ecosystem is after fishing has extracted biomass as catches. There are three components—referred to as “communities”—that aggregate the biomass of functional groups in the model by trophic level: 2.0-3.5 (MTL2.0), 3.5-4.0 (MTL3.5), and >4.0 (MTL4.0). These indicators can be used in unison to detect trophic cascades, whereby a decline in biomass of MTL4.0 due to fishing would reduce predation pressure on MTL3.5 and thus increase its biomass, which would in turn increase predation pressure on MTL2.0 and reduce its biomass.

Monitoring the EPO ecosystem using ecological indicators. Given the potential utility of combining ecological indicators for describing the various structures and internal dynamics of the EPO ecosystem, annual indicator values were estimated from a 1970-2014 time series of annual catches and discards, by species, for three purse-seine fishing modes, the pole-and-line fishery, and the longline fishery in the EPO. The estimates were made by assigning the annual catch of each species from the IATTC tuna, bycatch, and discard databases to a relevant functional group defined in the ETP ecosystem model, and refitting the Ecosim model to the time series of catches to estimate MTLc and the other aforementioned ecological indicators.

Values for MTLc and MTI increased from 4.63 in 1970 to 4.66 in 1993, the year for which the ecosystem model was characterised, and coincidentally the year when the purse-seine fishing effort on FADs increased significantly (Figure L-9). After 1993, MTLc continued to increase, to a peak of 4.72 in 1997, due to the expansion of the FAD fishery, which increased bycatches of other high trophic level species that also aggregate around floating objects (e.g. sharks, billfishes, wahoo and dorado). This expansion is seen in the positive FIB index during the same period, and also a change in the composition of the community indicated by Kempton’s Q index. After 1997, MTLc, MTI, FIB and Kempton’s Q index all show a gradual decline (Figure L-9). Since its peak in 1997, MTLc declined by 0.08 of a trophic level in the subsequent 18 years, or 0.044 trophic levels per decade.

The above indicators generally describe the change in the exploited components of the ecosystem, whereas community biomass indicators describe changes in the structure of the ecosystem once biomass has been removed due to fishing. The biomass of the MTL4.0 community peaked at 4.444 in 1993, but has continued to decline, to 4.439 in 2014 (Figure L-9).
Figure L-9:  Annual values for seven ecological indicators of changes in different components of the tropical EPO ecosystem, 1970-2014 (see Section 6 of text for details), and an index of longline (LL) and purse-seine (PS) fishing effort, by set type (dolphin (DEL), unassociated (NOA), floating object (OBJ)), relative to the model start year of 1993 (vertical dashed line), when the expansion of the purse-seine fishery on FADs began.

As a result of changes in predation pressure on lower trophic levels, between 1993 and 2014 the biomass of the MTL3.0 community increased from 3.799 to 3.800, while that of the MTL2.0 community decreased from 3.306 to 3.305.

Together, these indicators show that the ecosystem structure has likely changed over the 44-year analysis period. However, these changes, even if they are a direct result of fishing, are not considered ecologically detrimental, but the patterns of changes, particularly in the mean trophic level of the communities, certainly warrant the continuation, and possible expansion, of monitoring programs for fisheries in the EPO.

Trophic structure of the EPO ecosystem. Ecologically-based approaches to fisheries management require accurate depictions of trophic links and biomass flows through the food web. Trophic levels (TLs) are used in food-web ecology to characterize the functional role of organisms and to estimate energy flows through communities. A simplified food-web diagram, with approximate TLs, from the ETP model is shown in Figure L-8.
Figure L-8:  Simplified food-web diagram of the pelagic ecosystem in the tropical EPO. The numbers inside the boxes indicate the approximate trophic level of each group.



Toothed whales (Odontoceti, average TL 5.2), large squid predators (large bigeye tuna and swordfish, average TL 5.2), and sharks (average TL 5.0) are top-level predators. Other tunas, large piscivores, dolphins (average TL 4.8), and seabirds (average TL 4.5) occupy slightly lower TLs. Smaller epipelagic fishes (e.g. Auxis spp. and flyingfishes, average TL 3.2), cephalopods (average TL 4.4), and mesopelagic fishes (average TL 3.4) are the principal forage of many of the upper-level predators in the ecosystem. Small fishes and crustaceans prey on two zooplankton groups, and the herbivorous micro-zooplankton (TL 2) feed on the producers, phytoplankton and bacteria (TL 1).



ECOLOGICAL RISK ASSESSMENT

The primary goal of ecosystem-based fisheries management is to ensure the long-term sustainability of all species impacted—directly or indirectly—by fishing. However, this is a significant challenge for fisheries that interact with many non-target species with diverse life histories, for which sufficiently reliable catch and biological data for single-species assessments are lacking. An alternative approach for such data-limited situations is Ecological Risk Assessment (ERA), a tool for prioritizing management action or further data collection and research for potentially vulnerable species.

‘Vulnerability’ is defined here as the potential for the productivity of a stock to be diminished by direct and indirect fishing pressure. The IATTC staff has applied an ERA approach called ‘productivity-susceptibility analysis’ (PSA) to estimate the vulnerability of data-poor, non-target species caught in the EPO purse-seine fishery by large (Class-6) vessels in 2010 and in the longline fishery in 2017. PSA considers a stock’s vulnerability as a combination of its susceptibility to being captured by, and incur mortality from, a fishery and its capacity to recover, given its biological productivity.

Purse-seine fishery. A preliminary evaluation of three purse-seine “fisheries” in the EPO was made in 2014, using 32 species (3 target tunas, 4 billfishes, 3 dolphins, 7 large fishes, 3 rays, 9 sharks, 2 small fishes and 1 turtle) that comprised the majority of the biomass removed by the purse-seine fleet during 2005-2013 (Table L-1). The overall productivity (p) and susceptibility (s) values that contributed to the overall vulnerability score (v) are shown in Table L-1. Vulnerability was highest for the shortfin mako shark (Isurus oxyrinchus), bigeye thresher shark (Alopias superciliosus), pelagic thresher shark (A. pelagicus), giant manta ray (Manta birostris), hammerhead sharks (Sphyrna mokarran, S. lewini, and S. zygaena), and silky shark (Carcharhinus falciformis). Billfishes, dolphins, rays, and turtles were all moderately vulnerable, while small fishes, most large fishes, and two of the three target tuna species had the lowest vulnerability scores as shown in Table L-1 and Figure L-10a.
Figure L-10a:  Productivity and susceptibility x-y plot for target and bycatch species caught by the purse-seine fishery (a) and the longline fishery (b) in the EPO during 2005-2013 and 2017, respectively. See Tables L-1 and L-2 for species codes for each fishery.

Large-scale tuna longline fishery. A preliminary assessment of the longline fishery in the EPO was undertaken for 2016 for 68 species that had some level of interaction (captured, discarded, or impacted) with the fishery. There were 12, 38, and 18 species classified as having low, moderate, and high vulnerability, respectively as shown in (Table L-2), and Figure L-10b.
Figure L-10b:  Productivity and susceptibility x-y plot for target and bycatch species caught by the purse-seine fishery (a) and the longline fishery (b) in the EPO during 2005-2013 and 2017, respectively. See Tables L-1 and L-2 for species codes for each fishery.

Of the 18 highly vulnerable species, 13 were elasmobranchs—with the bigeye thresher, tiger, porbeagle and blue sharks identified as most vulnerable— and 5 were commercially important tunas and billfishes (albacore, Pacific bluefin, and yellowfin tunas, swordfish, and striped marlin). Other tuna-like and mesopelagic species were classified as either having moderate or low vulnerability in the fishery, although four species—wahoo, snake mackerel, and the two species of dorado—had v scores close to 2.0, in close vicinity to being highly vulnerable as shown in Figure L-10b and Table L-2.

In response to requests by participants at SAC-07 in 2016 to expand the ERA to other fisheries operating in the EPO, the IATTC staff produced three documents for SAC-08, covering (1) methodological improvements to PSA by resolving redundancy in productivity attributes (SAC-08-07c), (2) a metadata review for the large-scale longline fishery in the EPO (SAC-08-07b) to establish a list of impacted species and susceptibility parameters required for PSAs, and (3) a preliminary PSA for the large-scale longline fishery in the EPO (SAC-08-07d). Responding to requests for more quantitative cumulative ecological assessments for the EPO has been a priority for IATTC staff, and has led to the development of a new flexible spatially-explicit approach that quantifies the cumulative impacts of multiple fisheries on data-poor species (SAC-09-12). A demonstration of a preliminary form of the method was presented at SAC-09.

ECOSYSTEM MODELING

Although ERA approaches can be useful for assessing the ecological impacts of fishing, they generally do not consider changes in the structure and internal dynamics of an ecosystem. As data collection programs improve and ecological studies (e.g. on diet) are conducted on components of the ecosystem, more data-rich ecosystem models can be employed that quantitatively represent ecological interactions among species or ecological ‘functional groups’. These models are most useful as descriptive devices for exploring the potential impacts of fishing and/or environmental perturbations on components of the system, or the ecosystem structure as a whole.

The IATTC staff has developed a model of the pelagic ecosystem in the tropical EPO (IATTC Bulletin, Vol. 22, No. 3) to explore how fishing and climate variation might affect the animals at middle and upper trophic levels. The ecosystem model has 38 components, including the principal exploited species (e.g. tunas), functional groups (e.g. sharks and flyingfishes), and species of conservation importance (e.g. sea turtles). Fisheries landings and discards are included as five fishing “gears”: pole-and-line, longline, and purse-seine sets on tunas associated with dolphins, with floating objects, and in unassociated schools. The model focuses on the pelagic regions; localized, coastal ecosystems are not included.

The model has been calibrated to time series of biomass and catch data for a number of target and non-target species for 1961-1998. There have been significant improvements in data collection programs in the EPO since 1998, and these new data may allow the model to be calibrated to the most recent data.

One shortcoming of the model is that it describes only the tropical component of the EPO ecosystem, and results cannot be reliably extrapolated to other regions of the EPO. Therefore, future work may aim to update the model to a spatially-explicit model that covers the entire EPO. This is a significant undertaking, but it would allow for an improved representation of the ecosystem and the potential fishery and climate impact scenarios that may be modelled to guide ecosystem-based fisheries management.


Management
Management unit: Yes

Jurisdictional framework
Management Body/Authority(ies): Inter-American Tropical Tuna Commission (IATTC)
Mandate: Scientific Advice; Management.  
Area of Competence: IATTC area of competence
Maritime Area: High seas; National waters.  
Status of Management
ACTIONS BY THE IATTC AND THE AIDCP ADDRESSING ECOSYSTEM CONSIDERATIONS

Both the IATTC’s Antigua Convention and the AIDCP have objectives that involve the incorporation of ecosystem considerations into the management of the tuna fisheries in the EPO. Actions taken in the past include:

Dolphins

a. For many years, the impact of the fishery on the dolphin populations has been assessed, and programs to reduce or eliminate that impact have met with considerable success.

b. The incidental mortalities of all stocks of dolphins have been limited to levels that are insignificant relative to stock sizes.

Sea turtles

a. A database on all sea turtle sightings, captures, and mortalities reported by observers has been compiled.

b. Resolution C-04-07 on a three-year program to mitigate the impact of tuna fishing on sea turtles was adopted by the IATTC in June 2004; it includes requirements for data collection, mitigation measures, industry education, capacity building, and reporting.

c. Resolution C-04-05 REV 2, adopted by the IATTC in June 2006, contains provisions on releasing and handling of sea turtles captured in purse seines. The resolution also prohibits vessels from disposing of plastic containers and other debris at sea, and instructs the Director to study and formulate recommendations regarding the design of FADs, particularly the use of netting attached underwater to FADs.

d. Resolution C-07-03, adopted by the IATTC in June 2007, contains provisions on implementing observer programs for fisheries under the purview of the Commission that may have impacts on sea turtles and are not currently being observed. The resolution requires fishermen to foster recovery and resuscitation of comatose or inactive hard-shell sea turtles before returning them to the water. CPCs with purse-seine and longline vessels fishing for species covered by the IATTC Convention in the EPO are directed to avoid encounters with sea turtles, to reduce mortalities using a variety of techniques, and to conduct research on modifications of FAD designs and longline gear and fishing practices.

Seabirds

a. Recommendation C-10-02, adopted by the IATTC in October 2010, reaffirmed the importance that IATTC Parties and cooperating non-Parties, fishing entities, and regional economic integration organizations implement, if appropriate, the FAO International Plan of Action for Reducing the Incidental Catch of Seabirds in Longline Fisheries (“IPOA-Seabirds”).

b. Resolution C-11-02, adopted by the IATTC in July 2011, reaffirmed the importance of implementing the IPOA-Seabirds (see 9.3.a) and provides that Members and Cooperating non-Members (CPCs) shall require their longline vessels of more than 20 meters length overall and that fish for species covered by the IATTC in the EPO to use at least two of the specified mitigation measures, and establishes minimum technical standards for the measures.

Other species

a. Resolution C-00-08, adopted in June 2000, establishes guidelines on live release of sharks, rays, billfishes, dorado, wahoo, and other non-target species.

b. Resolution C-04-05, adopted in June 2006, instructs the Director to seek funds for reduction of incidental mortality of juvenile tunas, for developing techniques and equipment to facilitate release of billfishes, sharks, and rays from the deck or the net, and to carry out experiments to estimate the survival rates of released billfishes, sharks, and rays.

c. Resolution C-11-10, adopted in July 2011, prohibits retaining onboard, transshipping, landing, storing, selling, or offering for sale any part or whole carcass of oceanic whitetip sharks in the fisheries covered by the Antigua Convention, and to promptly release unharmed, to the extent practicable, oceanic whitetip sharks when brought alongside the vessel.

d. Resolution C-15-04, adopted in July 2015, prohibits retaining onboard, transshipping, landing, storing, selling, or offering for sale any part or whole carcass of manta rays (Mobulidae) (which includes Manta birostris and Mobula spp.) and requires vessels to release all mobulid rays alive wherever possible.

e. Resolution C-16-05, adopted in July 2016, states that the IATTC scientific staff shall develop a workplan for completing full stock assessments for the silky shark (Carcharhinus falciformis) and hammerhead sharks (i.e., Sphyrna lewini, S. zygaena and S. mokarran). CPCs shall require their fishers to collect and submit catch data for silky and hammerhead sharks, and shall submit the data to the IATTC in accordance with IATTC data reporting requirements.

f. Resolution C-16-06, adopted in July 2016, prohibits retaining on board, transshipping, landing, or storing, in part or whole, carcasses of silky sharks caught by purse-seine vessels in the IATTC Convention Area.



Fish-aggregating devices (FADs)

a. Resolution C-16-01, adopted in July 2016, amends and replaces Resolution C-15-03, adopted by the IATTC in July 2015. It requires all purse-seine vessels, when fishing on FADs in the IATTC Convention Area, to collect and report FAD information including an inventory of the FADs present on the vessel, specifying, for each FAD, identification, type, and design characteristics. To reduce entanglement of sharks, sea turtles, or any other species, principles for the design and deployment of FADs are specified. Setting a purse seine on tuna associated with a live whale shark is prohibited, if the animal is sighted prior to the set. A working group on FADs is established and its objectives are to collect and compile information on FADs, review data collection requirements, compile information regarding developments in other tuna-RFMOs on FADs, compile information regarding developments on the latest scientific information on FADs, including information on non-entangling FADs, prepare annual reports for the SAC, and identify and review possible management measures.

b. Resolution C-17-02, adopted in July 2017, specifies measures for the fishery on FADs, including the number of allowable active FADs.



All species

a. Data on the bycatches of large purse-seine vessels are being collected, and governments are urged to provide bycatch information for other vessels.

b. Data on the spatial distributions of the bycatches and the bycatch/catch ratios have been collected for analyses of policy options to reduce bycatches.

c. Information to evaluate measures to reduce the bycatches, such as closures, effort limits, etc., has been collected.

d. Assessments of habitat preferences and the effect of environmental changes have been made.

e. Requirements have been adopted for the CPCs to ensure that, from 1 January 2013, at least 5% of the fishing effort made by its longline vessels greater than 20 m length overall carry a scientific observer.
Management Advice
FUTURE DEVELOPMENTS

It is unlikely, in the near future at least, that there will be stock assessments for most of the bycatch species. The IATTC staff’s experience with dolphins suggests that the task is not trivial if relatively high precision is required. In lieu of formal assessments, it may be possible to develop indices to assess trends in the populations of these species, which is currently undertaken for silky sharks.

An ecosystem-based approach to fisheries management may be best facilitated through a multi-faceted approach involving the development and monitoring of biologically and ecologically meaningful indicators for key indicator species and ecosystem integrity. Ecological indicators may be aggregate indices describing the structure of the entire ecosystem (e.g. diversity), or specific components (e.g. trophic level of the catch). Biological indicators may generally relate to single species—perhaps those of key ecological importance or ‘keystone’ species—and be in the form of commonly-used fishery reference points (e.g. F(MSY)), CPUE, or other simple measures such as changes in size spectra. However, the indicator(s) used depend heavily on the reliability of the information available at the species to ecosystem level.

The distributions of the fisheries for tunas and billfishes in the EPO are such that several regions with different ecological characteristics may be included. Within them, water masses, oceanographic or topographic features, influences from the continent, etc., may generate heterogeneity that affects the distributions of the different species and their relative abundances in the catches. It would be desirable to increase our understanding of these ecological strata so that they can be used in the analyses.

It is important to continue studies of the ecosystems in the EPO. The power to resolve issues related to fisheries and the ecosystem will increase with the number of habitat variables, taxa, and trophic levels studied and with longer time series of data.

Future ecosystem work is described in the IATTC Strategic Science Plan (SAC-09-01) and staff activities report (SAC-09-02). Briefly, this work will include improving ERAs, developing and maintaining databases of key biological and ecological parameters (e.g. growth parameters), developing research proposals for biological sampling, ecosystem monitoring and field-based research on consumption and evacuation experiments, development of a spatially-explicit ecosystem model of the EPO and ecological indicators, and continued reporting of bycatch estimates.
Source of Information
 
Inter-American Tropical Tuna Commission (IATTC)  “Fishery Status Report 14. Tunas and Billfishes in the Eastern Pacific Ocean in 2015. ” 2018 Click to openhttps://www.iattc.org/PDFFiles/FisheryStatusReports/_English/No-16-2018_Tunas%20billfishes%20and%20other%20pelagic%20species%20in%20the%20eastern%20Pacific%20Ocean%20in%202017.pdf
powered by FIGIS  © FAO, 2019
Powered by FIGIS
crawl