CCAMLR

Distribution, relationship between sizes and depths, sex ratio, size composition and maturity condition for Dissostichus eleginoides and D. mawsoni were investigated on Banzare Bank, using the biological data sampled by a Japanese commercial fishing vessel during austral summer from 2006/07 to 2008/09 fishing season. D. eleginoides was mainly caught in the shallower bank <1000 m, while D. mawsoni was mainly caught in the deeper slope >1500 m. The separation of the two species by depths may be related to the physical intolerance to the cooler temperature by the lack of antifreeze for the former species. The mean total length (TL) of females was significantly larger than that of males for both species. The proportion of males to the total adults decreased significantly with the depths with gradual slope for both species. Male D. mawsoni showed a significant correlation between depth and the TL with gradual slope. The size structure varied among the fishing seasons and showed the polymodal distribution in D. eleginoids, while the size structure was very similar among fishing seasons and showed the unimodal distribution in D. mawsoni. D. eleginoides showed resting stage in sexual maturity, while D. mawsoni was in running ripe condition. In both species, small fish contributed low proportion in abundance, which suggest that substantial recruitment does not take place on Banzare Bank and the population may consist primarily of adults migrating from other area

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in Division 58.4.4a & b (Ob Lena Bank) by using a commercial bottom longline vessel, Shinsei Maru No. 3, from April 30 to June 20. The survey was undertaken according to the decision in the 28th CCAMLR Meeting of the Commission (28th CCAMLR report paragraph 4.43). This report described the results preliminarily during the survey in four SSRUs of Ob Lena Bank. The catch amounted the total allowable catch of 60 tonnes in 94 longline sets, which corresponded to 83 % to the total allocated fishable 113 sets. D. eleginoides contributed 80.1 % in numerical number and 96.1 % in weight to the total samples in SSRUs. Mean CPUEs of D. eleginoides for 71 hauls where only Trot line system was adopted were 13.1 indiv. / 1,000 hooks in number and 138.9 kg / 1,000 hooks in weight. These values were larger than mean CPUEs of 11.0 indiv. / 1,000 hooks and 108.0 kg / 1,000 hooks in the same Division in the 2007/08 season. D. eleginoides caught showed a broad polymodal composition for each SSRU, but the proportion of smaller fish caught in eastern SSRUs tended to be lower than that caught in the western SSRUs, as observed in the previous 2007/08 survey.

In accordance with the Conservation Measure 41-07 (2009), a survey was conducted in order to collect information for the stock status and biological information on toothfish in the southeast sector (24 allocated points) of Division 58.4.3b (Banzare Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from December 1 to 13, 2009. Shinsei Maru Trot line system was used as fishing gear. Total catch (excluding released weight) of Dissostichus spp. And the other by-catch species was 15.9 tonnes in the SE sector, where the catch limit of 18 tonnes was set. Dissostichus spp. Made up 16 % in number and 87.5 % in weight of the whole fish caught, while Macrourus spp. Made up 81% in number but only 11 % in weight to the total. Among two species of toothfish, Dissostichus mawsoni was dominant (82 % in number and 88 % in weight to the total). Mean CPUE of D. mawsoni was 3.4 indiv. / 1,000 hooks in number and 111 kg / 1,000 hooks in weight. D. mawsoni showed a broad modal composition at approximately 130-150 cm. Total of 60 individuals of toothfish were tagged and released during the survey. One male D. eleginoides was recaptured.

From March, 23 till April, 1, 2010 during the cruise of the Russian crabber vessel "Tamango" in CCAMLR zone, the searching operations were carried out in the area of the Southern Orkney Islands (subarea 48.2) according to the Conservation Measure (C.) 52-02. Experimental harvest regime for the exploratory fishery for crab by traps was carried out for the first time in statistical subarea 48.2. Judging by insignificant catch crabs, state of benthic fauna and very small fish by-catch in traps, one can assume that highly expressed seasonality is present in vital activity of benthos in the area of the Southern Orkney Islands. Probably, the absence of crabs at the in March was connected to their seasonal migration to other depths. At the end of March, biological productivity of this area is extremely low; and it is economically inexpedient to conduct fisheries for bottom organisms at this time. The present article is a brief report on the executed work.

Length-frequency data are routinely collected in CCAMLR’s fisheries and used as inputs to stock assessments. In CCAMLR’s new and exploratory fisheries, stock assessment techniques are still in development and robust conclusions on stock status based on length-frequency data alone have been difficult. In this paper, we show that length-frequency data on their own have little inherent conclusive information about stock status. While length-frequency data can be useful in assessments when integrated with other more informative estimators for stock abundance and productivity, interpretation of trends in length-frequency data can be misleading and should be avoided.

In stocks that have been depleted by overfishing, the benefits of additional fisheries removals for research purposes need to be evaluated against the risks that such catches may contribute to delaying the recovery of such stocks. Through simulating a Dissostichus eleginoides stock that has been subjected to varying levels of overfishing and research catches, this study show that stocks can take decades to recover even in the absence of fishing, and apparently low levels of research catches can significantly delay the recovery of a stock. Research catches in excess of 0.6% of B0 should be avoided to ensure that research doesn’t significantly impact on the recovery of depleted stocks in the long term.

Attempts to estimate natural mortality, as a single constant M, simultaneously with other model parameters in integrated assessments via CASAL for the Heard and McDonald Islands (HIMI, CCAMLR Division 58.5.2) Patagonian toothfish (Dissostichus eleginoides) fishery have been unsuccessful. An alternative strategy was adopted whereby the catch-at-age and mark-recapture data were restricted to the main trawl ground in which the longest time series of catches and the great majority of releases and recaptures of tagged fish were available. Catch and releases by age class for this fishery were obtained using proportions-at-length and fishery and year specific age length keys (ALKs) for years 1998 to 2008. A large proportion of the recaptures of fish released in this fishery were aged and these were used to obtain recapture numbers by age class. Two alternative estimation models were programmed in R, based on alternative ordinary differential equations (ODE) for within-year population dynamics. These are the BODE model (Baranov ODE) and the CCODE model (constant catch ODE). Previous studies of the properties of these two models for estimation of M used simulation. In application to the data obtained for the HIMI main trawl fishery, the CCODE model, gave a well-behaved profile for the log-likelihood with the corresponding estimate of M of 0.155, however, the 95% confidence bounds of the estimate were very wide ranging from 0.055 to 0.250 (based on a Poisson over-dispersion estimate of 3). In contrast, the BODE model gave unrealistic estimates of M and the annual fishing mortality rates both when the model was or was not conditioned on the total numbers caught in each year.

A three‐year tagging study in the South of Subarea 48.4 was initiated in the 2008/09 fishing season with the aims of  providing the data required for assessments of the population structure, size, movement and growth of both Dissostichus eleginoides and Dissostichus mawsoni in the South of 48.4; A total of 186 D. eleginoides and 202 D. mawsoni were tagged and released in 2010, leaving a total of 794 tagged fish in the water, respectively. A total of 13 D. eleginoides and 22 D. mawsoni were recaptured in the latest season, including three and six within‐season recaptures, respectively. Macrourids and rajids again dominated bycatch, comprising 15.4% and 1.2% of toothfish catch, respectively. A total of 238 Amblyraja georgiana were tagged and released in 2010 and 3 were recaptured; Approximately 20% of sets were undertaken during daylight hours and no bird entanglements or mortalities were reported; Preliminary stock assessments by different methods estimate a lower stock size of Dissostichus spp. in the South than previously anticipated. In addition there are signs of significant stock depletion towards the northern boundary of the Southern management area. The UK proposes to complete the mark‐recapture experiment in the South of Subarea 48.4 in 2010/11 with a reduced TAC of 30 tonnes.

The target tagging rate of 5 fish per tonne was exceeded by both vessels, with 232 D. eleginoides tagged and released in 2009/10, bringing the total to 1,547 in all seasons; There were 18 D. eleginoides tag recaptures in 2009/10, a total of 72 in all seasons; The length-frequency of 2009/10 captures is consistent with the theory that the bulk of the biomass is dominated by a small number of cohorts. CASAL estimates a large recruitment event in early the early 1990s and faster growth rates than those currently assumed for the 48.3 population CASAL estimates of D. eleginoides population size in the North of 48.4 are very similar to that from the previous season with a B₀ of 1,123 t (compared to 1,127 t in the 2009 assessment) and B₂₀₁₀/B₀ of 92.8%. Sustainable yield calculated according to the CCAMLR decision rules is 41 tonnes. A lower than anticipated number of tag recaptures have come from 2007/08 releases. Removing these from the CASAL assessment reduced B₀ to 963 tonnes though had a minimal effect on B₂₀₁₀/B₀ (89.7%). Sustainable yield omitting 2007/08 tags is 37 tonnes.

In January 2010, the UK carried out the annual groundfish survey in CCAMLR Sub-Area 48.3 on the FV Sil. Seventy-five random hauls were completed with good coverage across the shelf, representing an increase in effort overall compared with surveys carried out in 2008 and 2009 on the same vessel. Catch-weighted length frequencies of mackerel icefish indicated that although 3+ sized fish dominated the population, 2+ and 1+ sized fish were also present, and in larger proportions than in 2009. A mean biomass of 52,329 tonnes was estimated for mackerel icefish, with a lower 1-sided 95% CL of 24,334 tonnes, an increase on the biomass estimate for 2009. Considering the anomalous environmental conditions and low availability of krill to mackerel icefish in the area (evidenced by dietary analysis) in 2009, this increase in biomass was unexpected. The importance of krill in the mackerel icefish diets was greater in 2010 than in 2009 but still remained low compared to historical data, and Themisto gaudichaudii dominated diets in Northern area strata where the largest numbers of mackerel icefish were caught. As seen during the 2009 survey, mackerel icefish remained close to the bottom and very few acoustic marks were observed in the water column during the survey. Catches of Patagonian toothfish were greater than in 2009, but still low compared with historical survey catches. There was however, the first evidence since 2003/04 of a recent recruitment of evident at Shag Rocks, with presence of putative age 2+ fish (29-39cm). Very large catches of marble rockcod were experienced during the 2010 survey, with increased catches across all areas of shelf surveyed around South Georgia and Shag Rocks compared with previous surveys. The mean biomass estimate was 173,223 tonnes, more than ten-fold the estimate for 2008. Catches and biomass estimates for Scotia Sea icefish and South Georgia icefish were also greater than estimates for 2008 and 2009. Exploration of historical marble rockcod catch data and environmental variables is underway, but careful monitoring of all three species should be carried out to determine whether these estimates represent population recovery.