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
2020	SEIRYO MARU NO1	JPN	JNNI	8617586	LL, Pot	37.06
2021	SEIRYO MARU NO1	JPN	JNNI	8617586	LL, Pot	37.06

* 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.

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).

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.

Figure 10. The spatial distribution of Deep-sea red crab during 2020 and 2021 in SEAFO Division B1. This catch position data shown here represents a single fishing trip that spanned the months of December 2020 and January 2021 - for this reason the data were presented on a single map (and not split into two separate maps - i.e. 2020 and 2021 maps).

Reported landings (Table 2) comprise of catches made by Japanese, Namibian, Spanish, Portuguese and Korean-flagged vessels over the period 2001-2021. No fishing for Deep-sea red crab took place during 2022. From Table 3 the two main players in the SEAFO Deep-sea red crab fishery are Japan and Namibia, respectively, with Spanish and Portuguese vessels having only sporadically fished for Deep-sea red crab in the SEAFO CA over the period from 2003 to 2007. Spanish-flagged vessels actively fished for Deep-sea red crab in the SEAFO CA during 2003 and 2004, whereas Portuguese-flagged vessels only fished for Deep-sea red crab during 2007. The only reported catch outside SEAFO Division B1 was made by Portugal in SEAFO Division A1 during 2007.


Table 2. Catches (tonnes) of Deep-sea red crab (Chaceon spp. – considered to be mostly Chaceon erytheiae).

Flag State

Japan

Rep of Korea

Namibia

Spain

Portugal

Research

Fishing method

Pots

Pots

Pots

Pots

Pots

Bottom Trawl

Management Area

B1

B1

B1

UNK

A

B1

Year (t)

Retain

Discard

Retain

Discard

Retain

Discard

Retain

Discard

Retain

Discard

Retain

TOTAL

2001

N/F

N/F

<1

<1

2002

N/F

N/F

0

2003

N/F

N/F

5

5

2004

N/F

N/F

24

24

2005

253

0

N/F

N/F

54

307

2006

389

N/F

N/F

389

2007

770

N/F

N/F

3

0

35

808

2008

39

N/F

N/F

39

2009

196

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

196

2010

200

0

N/F

N/F

N/F

N/F

200

2011

N/F

N/F

N/F

N/F

175

0

N/F

N/F

N/F

N/F

175

2012

N/F

N/F

N/F

N/F

198

0

N/F

N/F

N/F

N/F

198

2013

N/F

N/F

N/F

N/F

196

0

N/F

N/F

N/F

N/F

196

2014

N/F

N/F

N/F

N/F

135

0

N/F

N/F

N/F

N/F

135

2015

N/F

N/F

104

0

N/F

N/F

N/F

N/F

N/F

N/F

104

2016

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

0

2017

140

0

N/F

N/F

7

0

N/F

N/F

147

2018

N/F

N/F

N/F

N/F

173

0

N/F

N/F

N/F

N/F

173

2019

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

2020

31

0

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

31

2021

20

0

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

20

2022

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

<1

<1

2023*

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

N/F

TOTAL

2038

0

104

0

941

0

29

0

35

0

0

3147

* Provisional (August 2023); N/F = No Fishing; Blank fields = No data available; UNK = Unknown.

Annual catches in relation to TAC for Deep-sea red crab in SEAFO Division B1 and the remaining SEAFO CA are illustrated graphically in Figure 11.

Figure 11. Annual catches in relation to TAC for Deep-sea red crab in SEAFO Division B1 and the remaining SEAFO CA. The only reported catch outside B1 is that made by Portugal in SEAFO Division A1 during 2007 (see Table 3 for clarity).

Being a pot fishery, the Deep-sea red crab fishery has an almost negligible bycatch impact. To date only 5kg of teleost (Marine nei and European sprat) fish discards have been recorded during 2010 from this fishery. As of 2010, however, minimal to moderate bycatches of king crabs have been recorded (see Section 5.3 for additional information).

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 2021 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 2021 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.


Table 3. Number of sets per year for which catch and effort data are available for the CPUE standardization. No fishing was recorded during 2016 and 2019.

2005	2007	2010	2011	2012	2013	2014	2015	2017	2018	2020	2021
157	10	181	133	129	103	107	73	142	177	38	27

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.



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			1262	1546.83
Year	10	713.11	1252	833.72	< 2.2e-16 ***
Depth	17	30.79	1235	771.34	1.481e-14 ***
Zone	2	7.00	1233	755.13	1.316e-06 ***
as.factor(SEASON)	3	7.85	1230	736.44	7.668e-07 ***

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. 12). Plots of the residuals versus fitted values indicated evenly distributed data points, no overridingly skewed patterns in the plot (Fig. 12). Therefore, there is no evidence of non-constant error variance in the residual plot and independence assumption also appeared reasonable.

Figure 12. 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 the CPUE has fluctuated during the period 2005 to 2015. However, the confidence margins are fairly wide for the main part of the CPUE series (especially for 2013 and 2015 – Fig. 13), which indicates that the CPUE for these years (i.e. 2005, 2013 & 2015) are more comparable to each other than the CPUEs for the rest of the time series (Fig. 13). Furthermore, with the exception of 2010 - 2017 the CPUEs for the last two years of the data series were very close to zero (0.08 and 0.05 Kg/Pot, respectively) (Fig. 13).

Figure 13. Trends in catch CPUE indexes for catches per pot – with soak time as a categorical variable (factor) not included in the model. Standardized Index (black line) with the 95% Confidence Intervals (whiskers).