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Swordfish - North Atlantic
Marine Resource  Fact Sheet
Stock status report 2013
Swordfish - North Atlantic
Fact Sheet Citation  
Northern Atlantic swordfish
Owned byInternational Commission for the Conservation of Atlantic Tunas (ICCAT) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Swordfish, fr - Espadon, es - Pez espada, ru - Меч-рыба
Geographic extent of Swordfish - North Atlantic
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Management unit: Yes        Reference year: 2011
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateF2011/FMSY = 0.82 range (0.73-0.91)Moderate fishing mortalityGreen
Abundance levelB2011/BMSY = 1.14 range (1.05-1.24)Intermediate abundance
History
 

The status of the North Atlantic swordfish stocks was assessed in September 2013, by means of applying statistical modelling to the available data up to 2011. Complete information on the assessment can be found in the Report of the 2013 ICCAT Swordfish Stock Assessment Meeting (SCRS/2013/019). Other information relevant to Atlantic swordfish is presented in the Report of the Sub-Committee on Statistics, included as Appendix 7 to this SCRS Report, and recommendations pertinent to Atlantic swordfish are presented in Item 17.


Habitat and Biology
Climatic zone: Temperate.   Horizontal distribution: Oceanic.   Vertical distribution: Pelagic.  


Swordfish (Xiphias gladius) are members of the family Xiphiidae and are in the suborder Scombroidei. They can reach a maximum weight in excess of 500 kg. They are distributed widely in the Atlantic Ocean and Mediterranean Sea. In the ICCAT Convention area, the management units of swordfish for assessment purposes are a separate Mediterranean group, and North and South Atlantic groups separated at 5°N. This stock separation is supported by recent genetic analyses. However, the precise boundaries between stocks are uncertain. Swordfish feed on a wide variety of prey including groundfish, pelagic fish, deep-water fish, and invertebrates. They are believed to feed throughout the water column, and from recent electronic tagging studies, undertake extensive diel vertical migrations.

Swordfish mostly spawn in the western warm tropical and subtropical waters throughout the year, although seasonality has been reported in some of these areas. They are found in the colder temperate waters during summer and fall months. Young swordfish grow very rapidly, reaching about 140 cm LJFL (lower-jaw fork length) by age three, but grow slowly thereafter. Females grow faster than males and reach a larger maximum size. Tagging studies have shown that some swordfish can live up to 15 years. Swordfish are difficult to age, but about 50% of females were considered to be mature by age five, at a length of about 180cm. However, the most recent information indicates a smaller length and age at maturity.

New length-weight relationships were proposed for the North Atlantic, but these will be considered interim solutions until further analysis is conducted with new and more recent data..

The Committee reviewed document SCRS/2013/151 which presented the horizontal tracking of 21 swordfish tagged with pop-up satellite tags in the central and eastern North Atlantic. The analysis of the horizontal movements evidenced seasonal patterns with fish generally moving south by winter and returning to the temperate foraging grounds in spring. Broader areas of mixing between some eastern and western areas were also suggested. These new results obtained by pop-up satellite tags fully confirm the previous knowledge that was available from fishery data: deep longline catch swordfish during the day time as a by-catch, while shallow longliners target swordfish at night in very shallow waters.

The Committee also reviewed document SCRS/2013/161 that demonstrated a significant relation between temperate fishery CPUE residuals and the size of the Atlantic Warm Pool (AWP), which was shown to be highly correlated with the Atlantic Multidecadal Oscillation (AMO). This supported the information provided in Sunby et al. (2013), that described the occurrence of swordfish (1.5 to 2.65 m) off the Norwegian coast (58 to 70ºN latitude) from 1967 to 2011. The effect of AWP was thought to be responsible for conflicting signals in the CPUEs from the northern temperate and tropical regions. Further analysis and hypothesis testing was recommended to determine if this relationship was due to a swordfish temperature preference, a change in prey distribution, or perhaps both.


Geographical Distribution
Jurisdictional distribution: Highly migratory


Swordfish are distributed widely in the Atlantic Ocean and Mediterranean Sea, in coastal and offshore areas, mostly ranging from 45ºN to 45ºS,and range from Canada to Argentina on the western side, and from Norway to South Africa on the eastern side (Figure 1).
Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: Yes


A Workshop on swordfish stock structure took place in Crete in early 2006, in response to Resolution by ICCAT on the clarification of the stock structure and boundaries between the swordfish stocks in the Atlantic [Res. 99-03], at which 13 scientific documents on swordfish biology were presented. The results of the research presented gave general support to the stock structure currently assumed for Atlantic Swordfish (Mediterranean and North and South Atlantic stocks). The Workshop agreed that the precise delimitation between these three stocks cannot be improved upon without intensified collaborative and multi-disciplinary research. Similarly, the classification of swordfish caught near the boundaries to their stock of origin is subject to uncertainty and cannot be made accurately without intensified collaborative and multi-disciplinary research taking into account fine-scale (e.g., 1º squares) and quarterly sampling strata. The Workshop also noted that while there was some mixing between Atlantic and Mediterranean stocks near the Straits of Gibraltar, there was strong evidence that the Mediterranean is genetically distinct from the Atlantic, Pacific and Indian Ocean stocks.

In the ICCAT convention area, the management units of swordfish for assessment purposes are a separate Mediterranean group, and North and South Atlantic groups separated at 5°N. However, the precise boundaries between stocks are uncertain, and mixing is expected to be highest at the boundary in the tropical zone.
Figure 1 Geographic distribution of swordfish cumulative catch (t) by gear, in the Convention area, shown on a decadal scale. The maps (a-f) are scaled to the maximum catch observed during 1950-2009. Map g is scaled to the maximum catch observed from 2010-2011.
Exploitation
 

Description of fisheries

Due to the broad geographical distribution of Atlantic swordfish (Figure 1) in coastal and off-shore areas (mostly ranging from 50ºN to 45ºS), this species is available to a large number of fishing countries (Figure 2). Directed longline fisheries from Canada, EC-Spain, and the United States have operated since the late 1950s or early 1960s, and harpoon fisheries have existed at least since the late 1800s. Other directed swordfish fisheries include fleets from Brazil, Morocco, Namibia, EC-Portugal, South Africa, Uruguay, and Venezuela. The primary by-catch or opportunistic fisheries that take swordfish are tuna fleets from Chinese Taipei, Japan, Korea and EC-France. The tuna longline fishery started in 1956 and has operated throughout the Atlantic since then, with substantial catches of swordfish that are produced as a by-catch of tuna fisheries. The largest proportion of the Atlantic catches is made using surface-drifting longline. However, many additional gears are used, including traditional gillnets off the coast of western Africa.

For the past decade, the North Atlantic estimated catch (landings plus dead discards) has averaged about 11,500 t per year (Table 1 and Figure 2). The catch in 2012 (13,972 t) represents a 31 % decrease since the 1987 peak in North Atlantic landings (20,236 t). These reduced landings have been attributed to ICCAT regulatory recommendations and shifts in fleet distributions, including the movement of some vessels in certain years to the South Atlantic or out of the Atlantic. In addition, some fleets, including at least the United States, EU-Spain, EU-Portugal and Canada, have changed operating procedures to opportunistically target tuna and/or sharks, taking advantage of market conditions and higher relative catch rates of these species previously considered as by-catch in some fleets. Recently, socio-economic factors may have also contributed to the decline in catch.

Available catch per unit effort (CPUE) series were evaluated by the Committee and certain indices were identified as suitable for use in assessment models (Japan, Portugal, Morocco, Canada, Spain and USA). Trends in standardized CPUE series by fleets contributing to the production model are shown in Figure 3. Most of the series have an increasing trend since the late 1990s, but the U.S. catch rates remained relatively flat. There have been some recent changes in United States regulations that may have impacted catch rates, but these effects remain unknown.

Many of the indices of abundance were affected by changes in gear technology and management that could not be accounted for in the CPUE standardization, and therefore had to be split. Splitting the indices reduces the abundance signal and, to the degree possible continuity of the indices can be maintained, it will increase the reliability of the assessment results.

The most frequently occurring ages in the catch include ages 2 and 3.

The trends in mean fish weight taken in the North and South Atlantic fisheries is shown in Figure 4.

Discards

Since 1991, several fleets have reported dead discards (see Table 1). The volume of Atlantic-wide reported discards since then has ranged from 215 t to 1,139 t per year. Reported annual dead discards (in tonnes) have been declining in recent years.


Figure 2. North Atlantic swordfish catches and TAC (t).
Figure 3. Standardized CPUEs series provided by CPCs for the North Atlantic swordfish and the combined index of the base production model. The CPUE series were scaled to their mean for the overlapping years.
Figure 4. Trends in mean weight (kg) for the entire North and South Atlantic swordfish stocks. The information for 2010 is being reviewed and should be considered preliminary.
Assessment
 
Assessment Model
North Atlantic
Results

Two stock assessment platforms were used to provide estimates of stock status for the North Atlantic swordfish stock, non-equilibrium surplus production model (ASPIC) and Bayesian Surplus Production Model (BSP2).

Results from the North Atlantic base case ASPIC model are shown in Figure 5. The estimated relative biomass trend shows a consistent increase since 1997. The bias corrected deterministic outcome indicates that the stock is at or above BMSY (Figure 6). The relative trend in fishing mortality shows that the level of fishing peaks in 1995, followed by a decrease until 2001, followed by small increase in the 2002-2005 period and downward trend since then (Figure 5). Fishing mortality has been below FMSY since 2000. The estimate of stock status in 2011 is relatively similar to the estimated status in the 2009 assessment, and suggests that there is greater than 90% probability that the stock is at or above BMSY. However, it is important to note that for the first time since 2002 the reported catches in 2012 (13,972 t) exceeded the TAC of 13,700 t. The most recent estimate of stock productivity is very consistent with previous estimates. The absolute biomass trajectory showed a consistent upturn from the estimated 1997 value, and the biomass values for the most recent years are near the level estimated in the mid-1980s (Figure 7). The high value in 1963 is not well fit as in prior evaluations. Trends in both fishing mortality and biomass are consistent with those produced by the BSP2 model, with the latter model estimating larger stock biomass and lower fishing mortality across the entire time series (Figure 7). Estimates of stock status from the BSP2 model are consistent with ASPIC results (Figure 8).

The stock is considered rebuilt, consistent with the 2009 evaluation. Compared with the 2009 ASPIC base case model, the trajectory of biomass and F ratios are similar until the late 1990s, thereafter the current model predicted slightly lower fishing mortality rates and higher relative biomass, but certainly within the estimated 80% confidence bounds (Figure 9).


Figure 5: Results from the North Atlantic base case ASPIC model: trends in swordfish relative biomass (top) and fishing mortality (bottom) point estimates.
Figure 6: North Atlantic swordfish stock status trajectory (solid line) for the period 1950-2011, from the base ASPIC model (solid circle is the estimated median point). The pie chart represents the probabilities of stock being in the different color quadrates.
Figure 7: Trends in North Atlantic swordfish absolute biomass and fishing mortality estimates from the ASPIC and BSP2 base case models.
Figure 8: Plots of the ratios of i) stock biomass to BMSY and ii) fishing mortality rate to FMSY from the base case BSP for North Atlantic swordfish.
Figure 9: Comparison of the relative biomass (left) and fishing mortality (right) estimated by the North Atlantic ASPIC base case models in 2009 and 2013 assessments. Thin lines indicate the 80% confidence bounds for the 2013 estimates.
Overall Assessment Results
Projection

Outlook

North Atlantic

Based on the currently available information to the Committee, the ASPIC base model was projected to the year 2021 under constant TAC scenarios of 8 to 20 thousand tones. Projections used reported catch as of September 5, 2013 for 2012. For those CPCs whose reported catch was not yet available, their catch was assumed to be the average of the last three years (2009-2011), giving a total catch of 14,038 t. Median trajectories for biomass and fishing mortality rate for all of the future TAC scenarios are plotted in Figure 10. Results from the 2013 assessment indicated that there is greater than 90% probability that the northern swordfish stock has rebuilt to or above BMSY (Figure 6), therefore the Commission’s rebuilding plan goal has been achieved.

Future TACs above 15,000 t are projected to result in 50% or lower probabilities of the stock biomass remaining above BMSY over the next decade (Figure 11) as the resulting probability of F exceeding FMSY for these scenarios would trend above 50% within four years. A TAC of 13,700 t would have an 83% probability of maintaining the stock and fishing mortality at a level consistent with the Convention objective over the next decade. Projections with BSP also used similar specifications for 2012 and 2013 yields and projected over the same time frame. Both models provide very consistent advice that TAC levels of 13,700 t would maintain the stock at a level consistent with the Convention Objectives over the next decade.


Figure 10: Median trends of the relative biomass (B/BMSY) and fishing mortality (F/FMSY) for the projected North Atlantic swordfish stock based on the ASPIC SP model base under different constant catch scenarios (thousand tons). The lines show the median value of bootstrap runs and the dashed lines are 80% confidence intervals around projection at 13,700 t in the projection time period and the observed catch in the historical time period. The TAC in 2012 is 13,700 t.
Figure 11: North Atlantic swordfish, probability contours of B>BMSY and F <FMSY for the constant catch scenarios indicated over time. Red areas represent probabilities less than 50%, yellow from 50-75%, and green above 75%. The 90th, 75th, 60th, and 50th probability contours are also depicted.
Management
Management unit: Yes


Effects of current regulations

In 2006, the Committee provided information on the effectiveness of existing minimum size regulations. New catch regulations were implemented on the basis of Rec. 06-02, which entered into effect in 2007 (Rec. 08-02 extended the provisions of Rec. 06-02 to include 2009). Rec. 09-02 came into effect in 2010 and extended most of the provisions of Rec. 06-02 for one year only. Rec. 10-02 came into effect in 2011, and again extended those provisions for one year only, but with a slight reduction in total allowable catch (TAC).

Catch limits
The total allowable catch in the North Atlantic during the 2007 to 2009 period was 14,000 t per year. The reported catch during that period averaged 11,969 t and did not exceed the TAC in any year. In 2010, the TAC was reduced to 13,700 t, compared with 2012 catches of 13,972 t. Reports for 2012 are considered provisional and subject to change.

Minimum size limits
There are two minimum size options that are applied to the entire Atlantic: 125 cm LJFL with a 15% tolerance, or 119 cm LJFL with zero tolerance and evaluation of the discards.

There are two minimum size options that are applied to the entire Atlantic: 125 cm LJFL with a 15% tolerance, or 119 cm LJFL with zero tolerance and evaluation of the discards.

For the 2006-2008 period, the estimate of the percentage of swordfish reported landed (throughout the Atlantic) less than 125 cm LJFL was about 24% (in number) overall for all nations fishing in the Atlantic (28% in the northern stock and 20% in southern stock). If this calculation is made using reported landings plus estimated dead discards, then the percentage less than 125 cm LJFL would be of the same order given the relatively small amount of discards reported. These estimates are based on the overall catch at size, which have high levels of substitutions for a significant portion of the total catch.

Other implications
The Committee is concerned that in some cases national regulations have resulted in the unreported discarding of swordfish caught in the North stock and, to a certain extent, could have influenced similar behavior of the fleet that fishes the South Atlantic swordfish stock. The Committee considers that these regulations may have had a detrimental effect on the availability and consistency of scientific data on catches, sizes and CPUE indices of some of the Atlantic fleets. The Committee expressed its serious concern over this limitation on data for future assessments.


Management Advice



North Atlantic

For continuity of advice relative to previous assessments, ASPIC results are provided in SWO-ATL-Table 2, which shows the ranges of total catch limits and associated probabilities associated with stock status by year. The current TAC of 13,700 t has an 83% probability of maintaining the North Atlantic swordfish stock in a rebuilt condition by 2021 almost maintaining the level of biomass. This TAC would be in accordance with [Rec. 11-13], adopted by the Commission that indicates that ‘For stocks that are not overfished and not subject to overfishing (i.e., stocks in the green quadrant of the Kobe plot), management measures shall be designed to result in a high probability of maintaining the stock within this quadrant’. However, the Committee acknowledges that without better direction from the Commission with regard to what constitutes a ‘high probability’, it cannot provide more specific advice. TACs up to 14,300 t would still have a higher than 50% probability of maintaining the stock in a rebuilt condition by 2021 but would be expected to lead to greater biomass declines.



NORTH ATLANTIC SWORDFISH SUMMARY

 

 

 

 

Maximum Sustainable Yield 1

 

13,660 t (13,250-14,080)3

 

Current (2012) TAC

 

13,700 t

 

Current (2012) Yield2

 

13,972 t

 

Yield in last year of assessment (2011)

 

12,834 t4

 

BMSY

 

65,060 t (54,450-76,700)

 

FMSY

 

0.21 (0.17-0.26)

 

Relative Biomass (B2011/SSBMSY1 )

 

1.14 (1.05-1.24)

 

Relative Fishing Mortality (F2011/FMSY1)

 

0.82 (0.73-0.91)

 

Stock Status

 

Overfished: NO

 

 

 

Overfishing: NO

 

Management measures in effect:

 

Country-specific TACs [Rec. 11-02]
125/119cm LJFL minimum size:

 

1 Base Case production model (Logistic) results based on catch data 1950-2011.
2 Provisional and subject to revision.
3 Point estimate, 80% bias corrected confidence intervals are shown.
4 As of 5 September 2013.
Source of information
 
Report of the Standing Committee on research and Statistics (SCRS) . “Atlantic Swordfish, executive summaries.” Madrid, Spain September 30 to October 4, 2013. Click to openhttp://www.iccat.int/Documents/BienRep/REP_EN_12-13_II_2.pdf
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