CCAMLR

This paper presents an analysis prepared by the  Secretariat and Korea to provide the context to the more variable and anomalously high CPUEs of the two Korean ships the Insung No. 2 and the Insung No. 7 while participating in CCAMLR exploratory fisheries. The operational characteristics of these ships showed distinct differences to the other ships that have participated in longline toothfish fisheries in Divisions 58.4.1, 58.4.2 and subarea 48.6. These differences are reflected in CPUEs with large mean and high variability, arising from periods of repeated low/zero catches and highly spatially and temporally aggregated sets with the largest catches reported across the fleet.

To infer important prey resources for Antarctic toothfish (Dissostichus mawsoni) in the south of SSRUs 881.J and 881.L in the southern Ross Sea, their lipid composition was determined and compared tolipid profiles of fish and invertebrate species taken as bycatch in the fishery or collected from stomachs of toothfish. Stable carbon and nitrogen isotope ratios were also determined to further identify feeding relationships between these species. The aim of this study was to establish the feasibility of tracking main dietary items of pre-recruit Antarctic toothfish by comparing results of biomarker analysis and conventional diet analysis. Sampling collections were made during a longline survey of pre-recruit toothfish from research vessel in February 2012. Results of fatty acid (FA) and stable isotope analyses from this study provide evidence that a combination of these two techniques can delineate the main prey items of Antarctic toothfish and trophic structure of the toothfish-related fish food web in the southern Ross Sea ecosystem. Similarities in total FA compositions and the FA profiles in muscle tissue of Antarctic toothfish and Pleuragramma antarctica, Pogonophryne barsukovi, Dacodraco hunteri, and Trematomus loennbergii indicated a trophic connection between toothfish and these fish species. Meanδ¹⁵N values of Antarctic toothfish were higher than those of P. antarcticum, P. barsukovi, and T. loennbergii, indicating a higher trophic position of thetoothfish. In contrast, similar δ¹⁵N values between Antarctic toothfish and icefish (D. hunteri) suggested that they occupy the same trophic position. Overall results of this survey are consistent with the frequency and percentage occurrence of prey in Antarctic toothfish stomachs. Further collection and subsequent biomarker analyses for more pelagic and benthic biota are needed to better understand entire food web structure in the southern Ross Sea.

The research fishing proposal for Dissostichus spp. in Subarea 48.6 and Divisions 58.4.1, 58.4.2 and 58.4.3a is resubmitted following paragraph 3.24 of WG-SAM-12. In the present proposal, we firstly showed information of catch, efforts, tagging experimental results based on the CCAMLR C2 data, and secondly showed the results of biological features with some discussion of life history in data-poor fisheries mainly using CCAMLR Biological data. Finally we made the proposal for the operations in the 2012/13 season for all vessels.

Catch and efforts were active in two areas in the north of Subarea 48.6, two areas in the south of Subarea 48.6, one area in Division 58.4.2, five areas in Division 58.4.1 and one area in Division 58.4.3a. In these areas, number of tags available for recaptures in 2013 was also higher. Recaptures were made also within these areas but those for D. mawsoni were scarce, especially in Division 58.4.2. Nominal CPUE in terms of weight of D. mawsoni in the south of Subarea 48.6 is two times higher than those in other areas.

According to the distribution of CPUE for small size groups, the west of Prydz Bay region seemed to be an important area for pre-adult D.mawsoni as reported previously. From the seasonal variations in development of GSI, the north of Subarea 48.6 is one of important spawning grounds for D. mawsoni, however, self-sustaining population may not exist in these areas because of very small proportion of immature fish. Highest GSI for D. mawsoni in March over years was observed in the shelf area at approximately 100°E (SSRU 58.4.1 C), which is consistent with previous report. The increase in abundance of fish with small sizes in SSRUs B and C of the south of Subarea 48.6 speculated the extension of the Weddell Sea population. The clarification of life history in data-poor fisheries may need more information of biological features in the wide areas including Weddle Sea and Ross Sea regions.

From the number of tags available for recaptures, a total of 12 blocks (aggregation of 1° longitude x 30’ latitude box) for research is produced over the data-poor fisheries area for all vessels. The research should be fundamentally conducted within the blocks. However, in case research hauls in the blocks along the ice-shelf area cannot be done sufficiently due to sea-ice and small number of fish caught etc., the vessel may operate at neighboring available area and accumulate tagged and released fish to clarify the migration of fish, biological feasters such as distribution of developmental and maturity stages, sex ratio, age-length relationship, and catch rate which help the progress in assessment of stock status.

Estimations on expected numbers of recaptures suggested that the increase of current catch limits may be needed to increase in success of the mark recapture research for D. mawsoni in the south of Subarea 48.6 and Divisions 58.4.1 and 58.4.2.

Following the advice from the CCAMLR Working Group in WG-SAM in 2012, a preliminary assessment of stock status of D. eleginoides in SSRU C in Ob-Lena Banks was made using a CASAL catch-at-length model. In this preliminary assessment, the model was started in 1990 and catch, proportions at length in the catch, and recapture data from SSRU C from 2007/08 to 2011/12 were fitted in the model. The MPD estimate of B₀ was 741 tonnes, and current biomass was 625 tonnes (84.4 % of B₀). MPD fits suggest suitable fits to the data, however, there appears to be a pattern of increasing YCS over the time, which is unlikely. Therefore, model where all of the YCS are fixed at 1 should be considered next time. MCMC plots and diagnostics suggest low mixing of the MCMC chain. Hence, the MCMC results are not yet robust. The reasons for this need to be investigated, and may require that the chain will need to be run for much longer (e.g. 10e6 iterations), and subsampled less frequently. The MCMC estimate of B₀ was 1 455 tonnes, and current biomass was 1 275 tonnes (87.6 % of B₀). An additional uncertainty in the current model is the historical IUU catch. The current model only includes the catch history since 2007/08 but there is a history of IUU catches for the whole Division starting from 1996/97. To provide a more realistic B₀ to consider the inclusion of IUU catches for this SSRU into the model. Possible approaches for this should be discussed during WG-FSA-2012.

A tagging survey in SSRUs B and C in Division 58.4.4 a & b was conducted in the 2011/12 fishing season with the aims of providing the data required for assessments of the population structure, size, movement and growth of Dissostichus spp. in the centred area of Division 58.4.4 a & b. An approximate stock biomass level of Dissostichus spp. in the survey area was tentatively estimated using Lincoln-Petersen and CPUE comparison methods. The medial estimate using Lincoln-Petersen (1 725 ton) was smaller than that 1 928 tonnes estimated in the WG-FSA meeting in 2011 (SC-CAMLR XXX, Annext 4, paragraphs 5.19-21).CVs of 20 % achievable from the biomass estimates may be achieved within three years with an annual research catch of approximately 50 tonnes. The estimate (976 tonnes) using CPUE comparison method was smaller than that using Lincoln- Petersen. We would continue the mark-recapture experiments in the 2012/13 season changing the targeted area from SSRUs B and C to SSRUs C and D due to avoid the huge loss of catch from killer whales in SSRU B. The catch biomass level in SSRUs B and C was calculated as 86 tonnes using Lincoln-Petersen and 54 tonnes using CPUE comparison at 5 % of exploitation rate. Because mean CPUE (67 kg /km) in SSRUs C and D was higher than that (62 kg /km) over the four year’s cruises (two year’s cruises for SSRU D), the proposed sample size as existing 70 tonnes for the next 2012/13 survey seems to be appropriate for the newly targeted area. To apply mark-and recapture studies, tagging rate of ≥ 5 fish / ton will be conducted. Only Trot line system will be used for all 71 hauls. However, if sufficient numbers of fish suitable for tagging are not captured using the normal trotline system, we would increase the comparison tests with trotline and Spanish line systems. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in SSRU B and C of Division 58.4.4a & b (Ob Lena Banks) from April 15 to May 19, 2012. Total catch (excluding tagged and released fish) of Dissostichus eleginoides was 28.3 tonnes in the survey area in 70 longline sets. Mean CPUEs of D. eleginoides was 48.3 kg / km (CV = 79.1%) in terms of weight. The mean CPUE in terms of weight in SSRU B (32.1 kg / km) was rather lower than that (50.5 kg / km) in the same SSRU in 2010/11. A total of 172 individuals of toothfish with good physical condition and single-hooked were tagged and released during the survey, and 3 D. eleginoides, which were tagged and released in SSRUs B and C from the 2007/08 to 2010/11, were recaptured in the same SSRUs, respectively. Fish with good physical condition and single-hooked contributed 50 % to the total among fish caught by Spanish line system, while this kind of fish contributed 14 % to the total among fish caught by trotline system. A total of 133 killer whales（Orcinus orca）were observed at the 30 hauls. All of whales occurred in SSRU B. The vessel tried to avoid killer whales as in the previous surveys but could not escape from them effectively in SSRU B. Seventy-nine % of sets to the total were affected by killer whales in SSRU B in 2010/11 and 2011/12. On the other hand, no set was affected by killer whales in SSRU D in 2007/08 and 2009/10. Generalized additive model analysis indicated that the presence of killer whales leads to huge loss (ca. 40 %) of catch of D. eleginoides in SSRUs B and C.

Research-based New and Exploited fisheries have been conducted in order to collect information for the stock status and biology of toothfish in the Division 58.4.3b (Banzare Bank), using a Japanese commercial longline vessel Shinsei maru No. 3, during 2006/07 and 2011/12. Total number of hauls ranged from 22 to 148 during the six cruises. Total catch of Dissostichus spp. ranged from 9 to 108 ton. Predicted CPUE (catch/km) for D. eleginoides and D. mawsoni varied with years but showed no upward and downward tendencies with years. D. mawsoni mainly occurred in the shallower areas > 1 200 m but decreased in the CPUE as the depth decreased, while D. eleginoides mainly occurred in 600 – 1 000 m depths but rarely occurred in the deeper areas > 1 400 m. Progressed stages of GMI and high GSIs for D. mawsoni were observed in 2010/11 and 2011/12 when the researches were conducted in May and June, suggesting that Banzare Bank is one of important spawning grounds for D. mawsoni. On the other hand, such an apparent seasonal development of the maturity indices was not observed for D. eleginoides. Predicted trot line CPUE was significantly higher than Spanish line for D. eleginides, but no significant difference in the CPUE between gears was observed for D. mawsoni.

We would continue the survey focusing mark-recapture experiment in the 2012/13 season with a little modified spatial design. An approximate stock biomass level of Dissostichus spp. in the target stock area was estimated to be 8 444 tonnes, using CPUE comparison method. Applying a precautionary discount factor for biomass estimated of 0.3 and a precautionary exploitation rate of 0.01, catch biomass level was calculated as 84.4 ton. Thus the existing catch limit of 40 tonnes seems to be appropriate for the 2012/13 survey. We aimed the establishment of CASAL catch-at-age model for this Division by 2016/17.

Grenadiers Macrourus spp. are the main bycatch species in the exploratory longline fishery for toothfish Dissostichus spp. in the Ross Sea, Antarctica. Ongoing monitoring tools are needed to assess stock status of grenadiers in the Ross Sea and to ensure ecological relationships are maintained. There may be potential to use fisheries acoustic methods to obtain estimates of grenadier abundance. Acoustic data collected during New Zealand’s International Polar Year Census of Marine Life survey in February–March 2008 provide evidence that single targets close to the bottom over the Ross Sea slope are grenadiers. The acoustic target strength distribution of single targets was very similar to that predicted based on the measured size range of grenadiers. There are also positive correlations between acoustic backscatter and trawl and longline catches of grenadiers. Key uncertainties of the acoustic method are mark identification away from the bottom, and technical issues with low signal-to-noise ratio at depths greater than 1000 m and the acoustic dead-zone close to the bottom.

Updated software is presented for the automated production of standardised image plots of spatially referenced bottom fishing impact assessments. This software is submitted to WG-FSA as an R library to assist the Secretariat or CCAMLR Working Groups in the production of integrated bottom fishing impact assessments, including routine update of the circumpolar impact assessment originally described in SC-CAMLR-XXIX/4, Appendix E.