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Deep-sea red crab - South East Atlantic
Marine Resource  Fact Sheet
Stock status report 2019
Deep-sea red crab - South East Atlantic
Fact Sheet Citation  
Deep sea red crab
Owned bySouth East Atlantic Fisheries Organisation (SEAFO) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Chaceon geryons nei, fr - Géryons Chaceon nca, es - Geriones Chaceon nep
Geographic extent of Deep-sea red crab - South East Atlantic
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Regional
Management unit: Yes        Reference year: 2019
 
 
Biological State and Trend
State & Trend Descriptors
FIRMS
Exploitation rateUncertain/Not assessedGray
Abundance levelUncertain/Not assessed
History
 

The SEAFO deep-sea red crab fishery started in 2001 when a Spanish vessel first reported red crab catches of less than 1 tonne. Since then the fishery has been accessed by Japanese, Namibian, Portuguese and Korean flagged vessels respectively. The depth range of the SEAFO deep-sea red crab fishery has been recorded to be between 280 to 1150 meters. Specifications of the fishing vessels that were fishing deep-sea red crab are outlined in Table 1.


Table 1. Vessel specification of each year of fishing for deep-sea red crab
Year Vessel Name Flag Callsign IMO Code Gear Type Length
2005 KINPO MARU 58 JPN JFXB   LL, Pot 62.6
2007 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61
2010 SEIRYO MARU NO1 JPN JNNI 8617586 LL, Pot 37.06
2011 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61
2012 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61
2013 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61
2014 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61
2015 MERIDIAN NO8 KOR DTBX5 9230646 LL, Pot 54.55
2017 NOORDBURG KALAPUSE NAM V5WO 7121736 LL, Pot 48.9
2017 SEIRYO MARU NO1 JPN JNNI 8617586 LL, Pot 37.06
2018 CRAB QUEEN 1 NAM V5XD 8909628 LL, Pot 49.61

* LL = Longline * NAM = Namibia * JPN = Japan * KOR = Republic of Korea * IMO = International Maritime Organisation

The Namibian, Korean and Japanese vessels’ gear setup (design & set deployment) are very similar. Japanese beehive pots are used (Fig. 1). The beehive pots are conical metal frames covered in fishing net with an inlet shoot (trap entrance – Fig. 1) on the upper side of the structure and a catch retention bag on its underside. When settled on the seabed the upper side of the trap are roughly 50cm above the ground ensuring easy access to the entrance of the trap. The trap entrance leads to the kitchen area of the trap – which is sealed off by a plastic shoot that ensures all crabs end up in the bottom of the trap.


Figure 1. Deep-sea red crab fishing gear setup (set deployment and design) and illustration of a Japanese beehive pot (shown in enlarged form on the right).



One set or pot line consists of about 200-400 beehive pots, spaced roughly 18 m apart, on a float line attached to two (start & end) anchors for keeping the gear in place on the seabed (Fig. 1). The start & end points of a set are clearly marked on the surface of the water with floats and one A5 buoy that denotes the start of a line. Under this setup (i.e. 400 pots at 18 m intervals) one crab fishing line covers a distance of roughly 7.2 km (3.9 nm) on the sea floor and sea surface.
Habitat and Biology
Climatic zone: Temperate.   Bottom type: Unspecified.   Depth zone: Slope (200 m - 1000 m).   Horizontal distribution: Oceanic.   Vertical distribution: Demersal/Benthic.  


One species of deep-sea red crab has been recorded in Division B1, namely Chaceon erytheiae (López-Abellán et al. 2008) and is thus considered the target species of this fishery. Aside from the areas recorded in catch records the overall distribution of Chaceon erytheiae within the SEAFO CA is still unknown. Further encounter records documented through video footage during the 2015 FAO-Nansen VME survey in the SEAFO CA indicate that deep-sea red crab are distributed across a major part of the Valdivia seamount range, as well as the Ewing and Vema seamounts (DOC/SC/22/2015).

Preliminary results from genetics studies, based on Mitochondrial DNA, indicate that the Deep-sea red crab targeted by the pot fishery on the Valdivia Bank is confirmed as C. erytheiae (López-Abellán pers. comm.).


Geographical Distribution
Jurisdictional distribution: Straddling between High Seas and EEZ


In the SEAFO Convention Area fishing for deep-sea red crab is focussed mainly on Chaceon erytheiae on Valdivia Bank – a fairly extensive seamount that forms part of the Walvis Ridge. This seamount is located in Division B1 of the SEAFO Convention Area (CA) and has been the main fishing area of the deep-sea crab fishery since 2005. The spatial distribution of the catches aggregated to a 10 km2 hexagonal area for each year can be seen in Figures 2 to 9. Fishing occurred over a depth range of 280-1150 meters.


Figure 2. The 2010 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Figure 3. The 2011 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Figure 4. The 2012 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Figure 5. The 2013 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Figure 6. The 2014 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Figure 7. The 2015 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.
Figure 8. The 2017 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.
Figure 9. The 2018 catch distributions for Deep-sea red crab in Division B1 aggregated to a 10 km2 hexagonal area.


Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: Yes

Exploitation
 

Reported landings (Table 2) comprise catches made by Japanese, Namibian, Spanish, Portuguese and Korean-flagged vessels over the period 2001-2017. As is evident from Table 2 the two main players in the SEAFO crab fishery are Japan and Namibia, respectively, with Spanish and Portuguese vessels having only sporadically fished for crab in the SEAFO CA over the period 2003 to 2007. Spanish-flagged vessels actively fished for crab in the SEAFO CA during 2003 and 2004, whereas Portuguese-flagged vessels only fished for crab once during the 2007 season (Table 1).


Table 2. Catches (tonnes) of Deep-sea red crab (Chaceon spp. – considered to be mostly Chaceon erytheiae).
Nation Japan Korea Namibia Spain Portugal
Fishing method Pots Pots Pots Pots Pots
Management Area B1 B1 B1 UNK A
Catch details (t) Ret. Disc. Ret. Disc. Ret. Disc. Ret. Disc. Ret. Disc.
2001     N/F N/F     <1      
2002     N/F N/F            
2003     N/F N/F     5      
2004     N/F N/F     24      
2005 253 0 N/F N/F 54          
2006 389   N/F N/F            
2007 770   N/F N/F 3 0     35  
2008 39   N/F N/F            
2009 196   N/F N/F N/F N/F N/F N/F N/F N/F
2010 200 0 N/F N/F     N/F      
2011 N/F N/F N/F N/F 175 0 N/F N/F N/F N/F
2012 N/F N/F N/F N/F 198 0 N/F N/F N/F N/F
2013 N/F N/F N/F N/F 196 0 N/F N/F N/F N/F
2014 N/F N/F N/F N/F 135 0 N/F N/F N/F N/F
2015 N/F N/F 104 0 N/F N/F N/F N/F N/F N/F
2016 N/F N/F N/F N/F N/F N/F N/F N/F N/F N/F
2017 140 0 N/F N/F 7 0 N/F N/F N/F N/F
2018 N/F N/F N/F N/F 173 0 N/F N/F N/F N/F
2019 N/F N/F N/F N/F N/F N/F N/F N/F N/F N/F

N/F = No Fishing; Blank fields = No data available; UNK = Unknown;

(*) Provisional to September



Being a pot fishery, the Deep-sea red crab fishery has an almost negligible bycatch impact. To date only 5 kg of teleost fish discards have been recorded, during 2010, from this fishery. As of 2010, however, minimal to moderate bycatches of king crabs have also been recorded from this fishery.

Annual catches in relation to TAC can be seen in Fig 10.
Figure 10. Annual catches in relation to TAC for Deep-sea Red Crab in Division B1. No catches were taken elsewhere in the SEAFO CA.


Assessment
 

Currently the only data available for the assessment for C. erytheiae abundance within the SEAFO CA are the catch and effort data from which a limited catch-per-unit effort (CPUE) series can be constructed.

As part of the annual updating of the deep-sea red crab abundance index another attempt was made during 2018 at standardizing the CPUE index. Following the outcomes of the 2015 assessment that revealed “SoakTime” as an unreliable factor for consideration in the CPUE standardization, “SoakTime” was again omitted from the 2018 standardization of the annual CPUE from the SEAFO deep-sea red crab fishery. Table 3 outlines the number of sets used in the CPUE standardization.

The records from 2007 were excluded from the analysis as they were derived from an area not exploited in the remaining years, constituting only 10 sets, and were not comparable to datasets from the rest of the data series. In addition to this the 7 sets from a Namibian vessel that conducted some very uncharacteristic crab fishing operations during 2017 were also removed from the analysis as the data from this vessel was severely disparate (both in terms of total set number and catch) from all of the remaining data in the SEAFO database.

The following variables from each record were considered in the model:

Year- A 12-month period – explanatory variable (covariate).

SEASON- The seasonal cycle – explanatory variable (covariate).

VesselID- Identification code for a participating vessel – explanatory variable (covariate).

Zone- Identification code for a fishing area – explanatory variable (covariate).Co-ordinates where categorized into three smaller fishing zones reflecting the fishing records within Division B1.

Depth-Fishing depth – explanatory variable (covariate). Depth was categorized into 50 metre intervals covering the entire range of depths recorded by the fishery.

Pots- The number of baited pots used per set during fishing operations – explanatory variable (co-variate).

CPUE- Catch/number of pots – response variable.


Table 3. Description of the sets for which catch and effort data are available for the CPUE standardization.
2005 2007 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
157 10 181 133 129 103 107 73 - 142 177 -



Results from the CPUE standardization are presented below to illustrate some of the more important outputs and methods applied.

The maximum set of model parameters offered to the stepwise selection procedure was:

CPUE = β0 + β1 Year + β2 VesselID + β3 Depth + β4Zone + β5Season + β6Pots + ɛ

A stepwise backward model selection procedure was deployed in selecting the covariates, to the model. The model with lowest Akaike value (AIC - Akaike Information Criterion) was selected as the best model, since it has a better predictive power. The best model (outlined below) was then used for further analysis.



CPUE = β0 + β1 Year + β3 Depth+ β4 Zone +β5 Season + β6Pots + ɛ



Table 4 presents the estimates of the coefficients, standard error and t values for different levels of the factors entered into the selected model. Model, covariates year, depth, zone, season and pots all had very significance with p-values of 2.2*10-16, 1.037*10-9,3.766*10-4,5.084*10-4 and 2.2*10-16 indicating strong covariance with deep-sea red crab catch rates.


Table 4. ANOVA results for the CPUE model.
Covariates Df Deviance Residual Df Residual Deviance Pr(>Chi)
NULL     1115 1088.40  
Year 8 516.75 1107 571.64 < 2.2e-16 ***
Depth 13 30.79 1094 540.86 1.037e-09 ***
Zone 2 7.00 1092 533.86 0.0003766 ***
as.factor(SEASON) 3 7.85 1089 526.01 0.0005084***
Pots 10 47.34 1079 478.67 < 2.2e-16 ***

Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1



Model diagnostics of the best model were assessed. This involved checking for normality of the residuals and the spread of the residuals across the fitted values. A total of 82 outliers were removed (out of a total of 1198 data points – i.e. outliers removed equates to 6.8% of entire dataset) on the basis of residual skewness and Cook’s Distance disparity. After the removal of the outlier’s, diagnostic plots revealed improved distributions thus indicating that model assumptions were not violated. QQ plots of the residuals indicated that the model residuals were well within the excepted limits for data skewness (Fig. 10). Plots of the residuals versus fitted values indicated evenly distributed data points, no overridingly skewed patterns in the plot (Fig. 11). Therefore, there is no evidence of non-constant error variance in the residual plot and independence assumption also appeared reasonable.


Figure 11. QQ and studentized residual plots of the best lognormal fit model for retained catch CPUE (kg/pot).



Results from the standardized CPUE exercise suggest that CPUE has fluctuated during the period 2005 to 2018. However, the confidence margins are fairly wide for the main part of the CPUE series – which indicates that the CPUE hasn’t changed over the period 2011-2015, with the exception of 2010, 2014, 2017 and 2018 where the CPUE was very close to zero (Fig. 12).
Figure 12. Trends in catch CPUE indexes for catches per pot-hour of crabs – with soak time as a categorical variable (factor). Standardized Index: black line with standard deviation (error bars).


Data

The available SEAFO data (2005-2018) for purposes of considering possible assessment strategies are presented in Table 5.


Table 5. Description of the entire Deep-sea red crab database highlighting important datasets.
Year Flag State Data Type - Source Brief Description [NB Data Groups only]
2005 JPN Catch Data – Observer Report Set-by-Set data (vessel ID, set-haul positions & dates), Depth, Catch, Effort - (157 records).
2007 NAM Catch Data –Observer Report Set-by-Set data (vessel ID, set-haul positions & dates), Depth, Catch, Effort - (10 records - sets).
2010 JPN Catch & Biological Data – Observer Report Set data (vessel ID, set-haul positions & dates), Depth, Length, Weight, Catch, Effort - (Catch: 181 records, Biological: 5430 records).
2011 NAM Catch & Biol. Data – Observer Report Set-by-Set data (vessel ID, set-haul positions & dates), Depth, Length, Weight, Catch, Effort - (Catch: 133 records, Biological: 3990 records).
2012 NAM Catch & Biol. Data – Obs. Report & Captain’s Logbook [log sheet data] Set-by-Set data (vessel ID, set-haul positions & dates), Depth, Length, Weight, Catch, Effort - (Catch: 129 records, Biological: 3600 records).
2013 NAM Catch Data – Captain’s Logbook [log sheet data] Set-by-Set data (vessel ID, set-haul positions & dates), Depth, Catch, Effort - (Catch: 103 records, Biological: 3090 records).
2014 NAM Catch Data – Captain’s Logbook [log sheet data] Set-by-Set data (vessel ID, set-haul positions and dates), Depth, Length, Weight, Catch, Effort – (Catch: 107 records, Biological: 10660 records)
2015 KOR Catch Data – Fishing Logbook data Set-by-Set data (vessel ID, set-haul positions and dates), Depth, Length, Weight, Catch, Effort – (Catch: 73 records, Biological: 5554 records)
2017 JPN & NAM Catch Data – Fishing Logbook data Set-by-Set data (vessel ID, set-haul positions and dates), Depth, Length, Weight, Catch, Effort – (Catch: 142 records, Biological: 5554 records)
2018 NAM Catch Data – Fishing Logbook data& Biological Data (not from Observer Report) Set-by-Set data (vessel ID, set-haul positions and dates), Depth, Length, Weight, Catch, Effort – (Catch: 177 records, Biological: 17700 records)



Very limited fisheries-independent data on deep-sea red crabs exists for the SEAFO CA. A total of 479 deep-sea red crabs were sampled during the 2008 Spanish-Namibia survey on Valdivia Bank. The data was collected over a depth range of 867-1660 m. Additionally 127 deep-sea red crab samples were collected onboard the RV Fridtjof Nansen during the SEAFO VME mapping survey conducted at the start of 2015.

Sampling frequencies from 2010 to 2017 can be seen in Table 6.


Table 6. Sampling statistics from the deep-sea red crab commercial fleet within the SEAFO CA (2010-2018).
  2010 2011 2012 2013 2014 2015 2017 2018
Total number of sets 181 133 129 103 107 73 145 177
Total number of crabs sampled per set 30 30 30 30 100 136 100 100
Total number of crabs sampled 5430 3990 3600 3077 10654 32500 13500 17700


Assessment Model
Length data and frequency distribution

Available length-frequency data for crabs caught in the SEAFO CA over the period 2010-2018 are presented in Figure 13. Length-frequency data from all areas sampled in Division B1 were pooled as no significant differences were detected between areas.


Figure 13. Carapace width (mm) frequencies (in percentages) of crabs sampled from commercial catches [2010-2018]. Notes: “n” refers to sample size; “u” refers to the carapace width arithmetic mean for each sample as indicated.



For the period 2010-2018 there have been no significant changes in the female crab size distribution (Fig. 13). The male crab size distribution changed from a wider size distribution in 2010 and 2011, where larger male crabs were recorded, to a slightly narrowed size distribution in 2012-2014 of smaller crabs. During 2015 a lot more female crabs larger than 110 mm were recorded than any preceding years since 2010 (Fig. 13). Sex ratio from crab commercial samples fluctuated around 4:1 in favour of male crabs – a well-known bias of the commercial traps used in this fishery.

Length-weight relationship derived from catches on Valdivia Bank reveal the gender-specific growth disparity (Fig. 14). Male crabs grow at a faster rate than females and thus attain much larger sizes than female crabs. This species attribute, however, is not unique to Chaceon erytheiae and has been recorded for other crab species in the Chaceon genus (Le Roux, 1997). Data from the 2008 survey show a much more coherent length-weight relation for both male and female crabs (Fig. 15).


Figure 14. Length-at-weight data for Chaceon erytheiae as recorded from catches on Valdivia Bank (2008-2015). Red text show female length-weight relationship, blue text show male length-weight relationship.


Figure 15. Length-at-weight data for Chaceonerytheiae as recorded from the 2008 Spain-Namibia survey (López-Abellán et al. 2008).


Results
Reference Point
 

At this point in time it should be noted that no biological reference points exist for this stock in the SEAFO CA.

However, it is worthwhile to note that the C. erytheiae stock, based on the grounds of it being a long-lived and relatively stable stock, is a good candidate for an empirical Harvest Control Rule (HCR) similar to that applied to the Greenland halibut stock by the North Atlantic Fisheries Organization (NAFO). This is a simple HCR that merely considers that slope of an abundance index such as the CPUE and applies a catch limit to future years based in the current year’s TAC. The concept is as follows:



Slope: average slope of the Biomass Indicator (CPUE, Survey) in recent 5 years.



  • 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
  • TAC generated by the HCR is constrained to ±5% of the TAC in the preceding year.




For the interim this is considered to be a fairly good starting point, given the current status of the C. erytheiae resource, until such time that additional data are available for more advance stock assessment approaches.


Overall Assessment Results

The biological data series obtained from the SEAFO deep-sea red crab fishery, although short, is of relatively good quality. Nevertheless, important data such as growth parameter for the C. erytheiae stock, which will enhance the cohort analyses of the resource, was not available for the SEAFO CA and emphasis needs to be given in collecting this data for future assessments.


Management
Management unit: Yes

Management Advice

Fishing activities in 2018 providing required catch and effort data to update the CPUE series which form the basis for the application of the HCR as adopted by the Commission in 2015.The SC applying the HCR based on CPUE trend (Figure 16).


Figure 16. Comparison of the regression lines fitted to both the nominal and standardised CPUEs (2013-2018) for use in the Harvest Control Rule.





Considering that no catches were recorded outside Division B1 the 2019 TAC recommendations are only applied to Division B1.



TAC2019 = TAC2018* (1 + (2 * slope))



TAC2019 = 180 tonnes * (1 + (2 * -0.2989))



TAC2019 = 72 tonnes



The SC agreed to adopt the best estimate of the slope which is -0.2989. Under this scenario the HCR stipulates the use of “Rule 2” for setting the TAC.



The difference between the 2018 and proposed 2019 TAC is greater than the 5% limit stipulated by the HCR. SC therefore recommends a TAC for 2019 and 2020 be set at 171 tonnes for Division B1, and 200 tonnes for the remainder of the SEAFO CA.


Source of information
 
SEAFO “SC-SEAFO-2019. Report of the 15th Annual Meeting of the SEAFO Scientific Committee. SEAFO SC Report 2019.” 2019 Click to openhttp://www.seafo.org/media/578a3179-65a6-4778-ac48-c76ef891b4ed/SEAFOweb/pdf/SC/private/2019/eng/SC%20Report%202019%20-%20Final_pdf
SEAFO “SC-SEAFO-2017. Report of the 13th Annual Meeting of the SEAFO Scientific Committee. SEAFO SC Report 2017.” 2017 Click to openhttp://www.seafo.org/media/72e43665-5c43-4038-9f1f-96eebef05325/SEAFOweb/pdf/Meeting%20Files/2017/SC/SC%20Report%202017_pdf
SEAFO “SC-SEAFO-2016. Report of the 12th Annual Meeting of the SEAFO Scientific Committee. SEAFO SC Report 2016.” 2016 Click to openhttp://www.seafo.org/media/4ca98f5f-c111-4bcf-875b-36ac3213b8b7/SEAFOweb/pdf/SC/open/eng/SC%20Report%202016_pdf
SEAFO “CM 32/16 – Total Allowable Catches 2017.” 2016.
Bibliography
 
Le Roux, L. “Stock assessment and population dynamics of the Deep-sea red crab Chaceon maritae (Brachyura, Geryonidae) off the Namibian Coast. M.Sc. thesis, University of Iceland, Department of Biology. 88 pp.” 1997.
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.” 2008 Click to openhttp://www.repositorio.ieo.es/e-ieo/handle/10508/370?locale-attribute=en
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