|Pelagic armourhead - South East Atlantic|
|Marine Resource Fact Sheet|
|Pelagic armourhead - South East Atlantic|
|Considered a single stock: No Spatial Scale: Regional|
Management unit: Yes Reference year: 2013
Biological State and Trend
The only fishery for Pelagic armourhead (southern boarfish) in recent years has been the Korean trawl fishery for southern boarfish that started in 2010. In the period 2010-2013 two fishing vessels participated, F/V Adventure and F/V Dongsan Ho, and there was no fishery this year as of September 2014. The fishery is described as a midwater trawl fishery, but the observer records submitted to SEAFO include a high proportion of hauls recorded as “Demersal” (94% of the observed tows). Whether or not these trawls were bottom trawls remains uncertain, and this is an issue that needs further attention and clarification.
Habitat and Biology
Climatic zone: Temperate. Bottom type: Unspecified. Depth zone: Slope - Upperslope (200 m - 500 m). Horizontal distribution: Oceanic. Vertical distribution: Demersal/Benthic. Geo Form: Seamounts.
The Pentacerotid Pseudopentaceros richardsoni
(Smith 1844) is a southern circumglobal, benthopelagic species inhabiting outer shelf and upper continental shelves as well as seamounts and underwater ridges (100-1000 m) between 0 and 1 000 m depth (Heemstra, 1986). The species inhabits such habitats at e.g. Tristan de Cunha, on the Walvis Ridge and seamounts off South Africa (Southeast Atlantic); south of Madagascar (Western Indian Ocean) as well as in southern Australia, New Zealand and the Southeast Pacific. The potential distribution area in the SEAFO CA and adjacent waters is shown in Figure 1. It is unlikely that the species is abundant south of about 40O
S, i.e. in Sub-Area D.
It is known from adjacent areas that adults inhabit the steep and flat hard bottoms down to 800 m on the seamounts and underwater ridges in the open ocean. Eggs, larvae and juveniles are pelagic. Pelagic armourhead recruit to the summit of the seamounts after approximately 4 years of pelagic life and thereafter aggregates.
Jurisdictional distribution: High Seas Purely
During the period from 2010 to 2013 Korean trawler vessels (Dongsan Ho and/or Adventure) conducted a targeted fishery for Pelagic armourhead in the southern and northern parts of the Valdivia Bank, in Division B1 of the SEAFO CA. In 2013, a single haul was also conducted at North Walvis Ridge in Division B1 (Table 1, Fig. 2, lower).
|Figure 2 Spatial distribution of fishing positions and reported catches of Pelagic armourhead (P. richardsoni) aggregated to 10km diameter hexagonal cells, 2010-2013. Lower map shows the single fishing position in the NE seamount of B1 (NE Walvis Ridge) reported in 2013. Data from observer reports submitted to SEAFO until Sept. 2014. |
Number of trawl hauls by year and location (ref. Fig. 5).
|Year ||Valdivia Bank ||North Walvis Ridge |
|2010 ||63 || |
|2011 ||88 || |
|2012 ||117 || |
|2013 ||9 ||1 |
|2014 ||N/F ||N/F |
Considered a single stock: No
Starting in 1976, Table 2 presents the historical records of annual catches and bycatches of Pelagic armourhead by country, fishing gear and the SEAFO CA sub-divisions. The main fishing countries were:
Russia that operated with bottom trawlers in the late 1970s and 1993;
Ukraine (bottom trawl) fishing in the mid-1990s.
Namibia and South Africa ( bottom trawlers) in the mid-1990s;
South Korea primarily operating with mid-water trawl in in the period 2010-2013.
The higher annual catches were recorded by Russia with 1,273 and 1,000 t in 1977 and 1993, respectively, and by Korea with 688 t in 2010. Spain and Cyprus landed small catches in 2 and 1 years, respectively. Table 2
Reported catches (tonnes) of pelagic armourhead (Pseudopentaceros richardsoni) from the SEAFO CA. Data reported by SEAFO CPs and other flag states reporting to SEAFO, and from FAO.
|Nation ||Namibia ||Russia ||Ukraine ||South Africa ||Spain ||Cyprus ||Rep. of Korea |
|Management Area ||B1 ||B1 ||UNK ||B1 ||B1 ||UNK ||B1 |
|Fishing method ||BT ||BT ||BT ||BT ||BT / LL ||BT ||MT |
|Catch details ||(t) ||(t) ||(t) ||(t) ||(t) || (t) ||(t) |
| ||Catch ||Discard ||Catch ||Catch ||Catch ||Discard ||Catch ||Discard ||Catch ||Catch ||Discard |
|1976 || || ||108 || || || || || || || || |
|1977 || || ||1273 || || || || || || || || |
|1978 || || ||53 || || || || || || || || |
|1993 || || ||1000 ||435 FAO || || || || || || || |
|1994 || || || || || || || || || || || |
|1995 ||8 || || ||49 ||530 || || || || || || |
|1996 ||284 || || ||281 ||201 || || || || || || |
|1997 ||559 || || ||18 ||12 || || || || || || |
|1998 ||N/F || || || || || || || || || || |
|1999 ||N/F || || || || || || || || || || |
|2000 ||20 || || || || || || || || || || |
|2001 ||N/F || || || || || ||<1 || || || || |
|2002 ||N/F || || || || || || || || || || |
|2003 ||4 || || || || || ||3 || || || || |
|2004 || || || || || || ||3 || ||22 || || |
|2005 || || || || || || || || || || || |
|2006 || || || || || || || || || || || |
|2007 || || || || || || || || || || || |
|2008 || || || || || || || || || || || |
|2009 ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||N/F || |
|2010 ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||688 ||0 |
|2011 ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||135 ||0 |
|2012 ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||152 ||<1 |
|2013 ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||13 ||0 |
|2014*** ||N/F || ||N/F ||N/F ||N/F || ||N/F || ||N/F ||N/F || |
N/F = no fishing; UNK = Unknown; Blank fields = No data available; ***
Provisional (July 2014); FAO =
values from FAO; TB = Bottom Trawl; TM = Mid-water Trawl; LL = Longline;
Populations of P. richardsoni
, particularly the adult exploited fraction, have patchy distributions. The species occurs in a restricted depth stratum on the summit of seamounts and oceanic banks. Simple analyses of catch per unit of effort (CPUE) in the recent fisheries may be used as an indicator of biomass and may reveal temporal abundance trends. However, provided that sufficient input data are available, the pattern of distribution makes the use of local depletion analysis a potentially useful tool to evaluate the status of the population in specific areas. In the case of the SEAFO CA the actual fishing grounds in the recent fishery were primarily located in a small area of about 200 km2
on Valdivia Bank . If sufficient length data are available, cohort analyses based on length may be possible.
Processes and discussions in previous SC sessions are available in the Scientific Committee reports (SEAFO SC Report 2012 pages 21-23; SEAFO SC Report 2013 pages 17-18). In 2014 the exploration of different approaches continued. Depletion estimators were recalculated and the Gulland approach adopted to estimate maximum sustainable yield (MSY) based on the estimate if initial biomass derived from the depletion model. Also, the SC considered length-based analyses as potentially complementary approaches to evaluate exploitation status, but due to the shortage of length data, that exploration was abandoned.
Depletion estimators are widely used in fish and wildlife studies to estimate population abundance (Seber, 2002; Hilborn and Walters, 1992). These estimators assume a simple linear relationship between CPUE and cumulative effort (DeLury, 1947) or cumulative catch (Leslie and Davis, 1939). Data available suggest that prior to 2010 the stock was unexploited and consequently the Gulland (1971) method may be an approach to estimate MSY.
Geo-referenced data on catch and effort were available from haul-by-hauls observer reports for the entire time-series of the recent Korean fishery (2010-2013). Logbooks were not available.
No survey data from the period of the fishery was available from the area fished commercially or any other area of the SEAFO CA.
In 2014 the SC reviewed length data collected by observers on Korean fishing vessels mainly operating in Valdivia Bank (Subdivision B1) in the period 2010-2013. No fishery has been conducted as of September 2014.
Due to insufficient sampling, it was impossible to derive reliable length compositions of the catches (see below). Length frequency distributions and length data (e.g. ranges and mean lengths) presented in 2013 or earlier SC reports are considered invalid.
Data on sampling levels are provided in Figure 3 and Table 3. The majority of trawl tows were sampled by observers, but in all years the sampling level in terms of total number of fish sampled, and number of individual sampled/tow (and per tonne) was inadequate. The sampling level even declined during the period 2010-2013.
|Figure 3 Frequency distributions of sample sizes for individual trawl hauls, 2010-2013 in the Valdivia Bank trawl fishery for Pelagic armourhead. The source is observer reports submitted to SEAFO until September 2014. N = total number of hauls sampled; n = total number of boarfish sampled. |
Samples and sampling levels resulting from observer observations of the trawl on Valdivia Bank. Data on Pelagic armourhead only, as officially submitted to SEAFO until Sept. 2014.
|Year ||No. of trawl tows sampled ||Mean #ind. sampled/tow ||Min. #ind. sampled/tow ||Max. #ind. sampled/tow ||Mean #ind. sampled/tonne |
|2010 ||54 ||19.3 ||12 ||39 ||0.03 |
|2011 ||69 ||10.1 ||1 ||27 ||0.09 |
|2012 ||107 ||4.5 ||1 ||12 ||0.03 |
|2013 ||10 ||4.5 ||2 ||7 ||0.35 |
The weight-length relationship of pelagic armourhead (for the two sexes combined) derived from samples collected by observers in 2010-2012 was: W = 0.016 L3.048
Available abundance indices and estimates of biomass
Catch & effort data was available for the years 2010-2013 and used to calculate CPUE, as an indicator of stock biomass.
The frequencies of Pelagic armourhead by maturity stage and sampling month for the period 2010 – 2012 are shown in Table 4.
The fishing activity in SEAFO CA 2010-2012 was restricted to May and June, and the observer data suggest high proportions of pre-spawning and spawning stages (Fig. 4) and that spawning occurs after May but probably before September. This period is different from that observed in the Southwest Indian Ocean, i.e. between October and December (López-Abellán et al. 2007). However, in neither area were the entire year sampled.
A maturity ogive based on the above data suggests 44.1 cm FL as the likely size at 50% maturity (Fig. 5). Table 4
Annual number of fish by maturity stage of Pelagic armourhead (Pseudopentaceros richardsoni) in the SEAFO CA for 2010-2012. Source: observer samples from Korean fishery.
|Year || |
|Immature ||Developing ||Pre-spawning ||Spawning ||Spent |
|2010 ||Sep ||0 ||504 ||159 ||0 ||0 |
| ||Oct ||0 ||437 ||107 ||0 ||0 |
| ||Nov ||0 ||84 ||26 ||0 ||0 |
| || || || || || || |
|2011 ||Jan ||14 ||78 ||27 ||0 ||0 |
| ||Sep ||59 ||75 ||4 ||0 ||0 |
| ||Oct ||30 ||26 ||13 ||0 ||0 |
| ||Nov ||0 ||16 ||27 ||2 ||0 |
| || || || || || || |
|2012 ||May ||0 ||0 ||38 ||96 ||0 |
| ||Jun ||0 ||0 ||69 ||352 ||0 |
|Figure 4 The proportion of maturity stage by month of Pelagic Armourhead (Pseudopentaceros richardsoni) in the SEAFO CA for 2010-2012 (1: immature, 2: developing, 3: pre-spawning, 4: spawning and 5: spent). |
|Figure 5 The maturity proportion by length of pelagic armourhead (Pseudopentaceros richardsoni) on the Valdivia Bank in the SEAFO CA (Division B1). |
Empirical natural mortality estimates for Pelagic armourhead were calculated by different methods and using the estimates of growth parameters derived from growth studies on the same species from the Southwest Indian Ocean (López-Abellán et al. 2008a) and on Valdivia Bank during the Spanish-Namibian research surveys reported on earlier (López-Abellán et al. 2008b).
The growth parameters fitted were: K=0.27 year-1; Linf
=65.1 cm; and t0
=-0.34 year-1. The maximum observed age of the Pelagic armourhead in the Southwest Indian Ocean was 14 years.
The values of empirical natural mortality obtained using different methods were determined using the Fishmethods R package:
|Method ||M |
|Pauly (1980) - Length Equation ||0.457 |
|Hoenig (1983) - Joint Equation ||0.316 |
|Hoenig (1983) - Fish Equation ||0.300 |
|Alverson and Carney (1975) ||0.253 |
|Roff (1984) ||0.417 |
|Gunderson and Dygert (1988) ||0.089 |
The natural mortality M=0.3 for the Pelagic armourhead calculated using the Hoenig’s method was considered acceptable and used in the analyses below. The effect of using M=0.2 was illustrated. The average longevity for stocks in the data set used by Hoenig (1983) is the age at which about 1.5% of the stock remains alive (Hewitt and Hoenig, 2005).
Apart from the provisional estimate of MSY=128 t, no reference points have been estimated and found to be valid. The main reason is the shortage of basic data to carry out assessments. Harvest control rules have not been implemented, but a suggestion is provided by the SC in 2014.
In view of the current perception of the stock as being at a low level, the SC recommends that a harvest control rule is implemented and suggests as a candidate HCR the following:
Where ‘Slope’ = average slope of the Biomass Indicator (CPUE) in the recent 5 years; and
λu :TAC control coefficient if slope > 0 (Stock seems to be growing) : λu=1
λd :TAC control coefficient if slope < 0 (Stock seems to be decreasing) : λd=2
The TAC generated by this HCR is constrained to ± 5% of the TAC in the preceding year.
The application of the proposed HCR in the future requires a base level of catch in 2015.
Overall Assessment Results
The catches of P. richardsoni
were from a directed fishery on Valdivia Bank, in a very small area, where the species concentrate as adults. These two aspects make the species highly vulnerable to overfishing. The SC did not have valid size or age distributions allowing evaluation of trends in size-age structure of the stock through the time-series. No data on recruitment was available. Under the assumption of a 4-year recruitment age, it is expected that until 2015 the entries in the population come from year classes born prior to 2010, i.e. before the fishery started.
The current perception of the stock fished primarily on the Valdivia Bank is that it is reduced to a low level.
There is no information on recruitment processes and dynamics, and it is not known whether the concentrations of the species constitute a self-sustaining population or are sustained by immigration/influx of larvae and juveniles from other areas. The abundance of recruiting year classes is unknown due to lack of age data and pre-recruit data. It is therefore unknown if the present abundance level on Valdivia Bank is above or below a level at which recruitment is impaired.
Recovery of the stock and fishery on Valdivia will require that the fishing intensity is controlled and kept at a much reduced level to facilitate recruitment and a reversion of the negative CPUE trend. A recovery plan may be required.
The 2010-2013 fishery for armourhead was mainly conducted on the Valdivia Bank. A single catch was, however, also reported from a seamount in the NE corner of B1. In Figure 6 the generalized distribution area of the species was provided. However, the species is restricted to depths less than 800m and mostly less than 600m. The actual areas of suitable character and depth, i.e. shallower than 600m and north of 40N, are few and widely dispersed (Figure 6). Fisheries expanding into other areas also have to be closely monitored and regulated.
|Figure 6 Bathymetry of the SEAFO CA and locations with bottom depths of 600m or less. |
Management unit: Yes
In 2013 the Commission could not reach consensus on a TAC for Southern boarfish/Pelagic armourhead, consequently, the fisheries is open in 2014. The only CP fishing armourhead in the 2010-2013 fishery, i.e. Korea, declared that the precautionary approach would be respected and that a total catch of 300 tonnes in Division B1 would not be exceeded.
The Commission furthermore requested that the Scientific Committee assess the Southern boarfish/Pelagic armourhead and present a TAC in 2014.
The SC recommended that a TAC corresponding to the output level resulting from the HCR using the average catch in 2011 and 2012, i.e. 143 t.
Source of information
SEAFO “SC-SEAFO-2013. Report of the 9th Annual Meeting of the SEAFO Scientific Committee. SEAFO SC Report 2013.” 2013 http://www.seafo.org/media/00bfc878-a115-4573-a016-ee776f876332/SEAFOweb/pdf/SC/open/eng/SC%20Report%202013_pdf
DeLury, D.B. “On the estimation of biological populations. Biometrics, 3: 145–167.” 1947.
Garcia, S.M., Sparre, P., Csirke, J. “Estimating surplus production and maximum sustainable yield from biomass data when catch and effort time series are not available. Fish. Res. 8, 13-23.” 1989.
Gulland J.A. “The Fish Resources of the Ocean. Fishing News (Books), West Byfleet, 255 pp.” 1971.
Heemstra, P.C. “Pentacerotidae. p. 622-623. In M.M. Smith and P.C. Heemstra (eds.) Smiths' sea fishes. Springer-Verlag, Berlin.” 1986.
Hewitt, D. A., Hoenig, J. M. “Comparison of two approaches for estimating natural mortality based on longevity. Fishery Bulletin, 103(2): 433-437.” 2005.
Hilborn, R. and C.J. Walters “Quantitative Fisheries Stock assessment: Choice, Dynamics and Uncertainty. Chapman and Hall: 570 pp.” 1992.
Hoenig, J. M. “Empirical Use of Longevity Data to Estimate Mortality Rates. Fishery Bulletin 82:898-903.” 1983Bibliographic Entry Leslie, P.H. and D.H.S. Davis “An attempt to determine the absolute number of rats on a given area. J. Anim. Ecol., 8: 94–113.” 1939.
Gili, R., L. Cid, H. Pool, Z. Young, D. Tracey, P. Horne and P. Marriott. “Estudio de edad, crecimiento y mortalidad natural de los recursos orange roughy y alfonsino. FIP 2002-12. Informe Final. IFOP-SUBPESCA. 129 p. Age, growth and natural mortality of orange roughy and alfonsino. (Final report FIP N° 2000-12. 129 p. (In Spanish).” 2002.
López-Abellán, L.J., M.T.G. Santamaría and J.F. González “Approach to ageing and growth back-calculation based on the otolith of the southern boardfish Pseudopentaceros richardsoni (Smith, 1844) from the south-west Indian Ocean seamounts. Marine and freshwater Research 59: 269-278.” 2008.a.
López-Abellán, L.J., J.A. Holtzhausen, L.M. Agudo, P. Jiménez, J. L. Sanz, M. González-Porto, S. Jiménez, P. Pascual, J. F. González, C. Presas, E. Fraile and M. Ferrer “Preliminary report of the multidisciplinary research cruise on the Walvis Ridge seamounts (Atlantic Southeast-SEAFO). Part I-II: 191 pp.” 2008b http://hdl.handle.net/10508/370
Seber, G.A.F. “The Estimation of Animal Abundance and Related Parameters. Second Edition. Blackburn Press, New Jersey.” 2002.