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Pelagic armourhead - South East Atlantic
Marine Resource  Fact Sheet
Stock status report 2014
Pelagic armourhead - South East Atlantic
Fact Sheet Citation  
Armourhead
Owned bySouth East Atlantic Fisheries Organisation (SEAFO) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Pelagic armourhead, fr - Tête casquée pélagique, ru - Рыба-кабан
Geographic extent of Pelagic armourhead - South East Atlantic
Main Descriptors
Considered a single stock: No        Spatial Scale: Regional
Management unit: Yes        Reference year: 2013
 
 
Biological State and Trend
State & Trend Descriptors
FIRMS
Exploitation rateModerate fishing mortality
High fishing mortality
Abundance levelLow abundance
History
 

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 40OS, 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.






Geographical Distribution
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.


Table 1 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


Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: No
Exploitation
 

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;


Assessment
 

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.
Data

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.


Table 3 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
Assessment Model
Length-weight relationships

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 (r2 = 0.96)
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.
Reproductive parameters

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

Maturity stage

Month

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).
Natural mortality

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).


Results
Reference Point
 

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
Management unit: Yes

Management Advice

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 Click to openhttp://www.seafo.org/media/00bfc878-a115-4573-a016-ee776f876332/SEAFOweb/pdf/SC/open/eng/SC%20Report%202013_pdf
SEAFO  “Report of the 8th Annual Meeting of the SEAFO Scientific Committee. SEAFO SC Report 2012.” 2012 Click to openhttp://www.seafo.org/media/deec2356-ae3d-4d46-94ad-393ad3a32dc2/SEAFOweb/pdf/SC/open/eng/SC%20Report%202012
Bibliography
 
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