CCAMLR

Observer data collected on longliners between 2003 and 2009 was analysed to look at the levels of depredation caused by killer whales (Orcinus orca) and sperm whales (Physeter macrocaphalus) around South Georgia. Since 2003 cetaceans have been observed on 3000 out of 14644 observed lines (20.5%) with killer whales present on 562 lines (3.8%) and sperm whales on 2588 lines (17.7%). By comparing the catch per unit efforts (CPUEs) with and without the presence if cetaceans, the amounts lost were also examined and varied from 0.9% to 5.8% of the TAC per year over the time period. Additional work was also conducted which looked at the behaviour of cetaceans around fishing vessels in the area. To aid identification and give an idea of population size, a photographic catalogue of individual animals was developed. To date, a total of 35 killer whales and 65 sperm whales have been seen, with re-sightings occurring both in season and between years. Hydrophones deployed on longlines recorded both vocalisations of cetaceans and noises made by the vessels, generated by propeller cavitations, gearing and drive shafts, the hydraulics of line machinery and the fishing gear itself. Distinctive acoustic patterns were seen both when winches were engaged and when the drive on the vessel was engaged during hauling. Recordings made from a distance of 3.4nm away were picked up by the hydrophones and it is thought that these acoustic cues could be responsible for attracting the cetaceans.

Stomach contents were identified from 206 Antarctic skate (Amblyraja georgiana) that were collected during three groundfish surveys (winter 2007, 2008 and summer 2009) around the island of South Georgia, Southern Ocean. The diet of A. georgiana varied with skate size and between years. Preferred prey included fish (particularly for larger individuals) and Antarctic krill, as well as amphipods, polychaetes and other benthic fauna. The Antarctic skate appears to be an opportunistic predator and the clear presence of Antarctic krill in this skate’s diet indicates a benthic habit of this euphausiid species, which has hitherto been considered as occupying a purely pelagic niche.

An attempt to use reported catch and CPUE data based on data of observers in the assessment of Antarctic toothfish stock in Division 58.4.1 is made. Unlike some previous results obtained for this division (e.g. Agnew et al., 2008), the assessment was intended to be independent of estimates of toothfish stock biomass in the Ross Sea. As a result of implementation of an age-structured and a dynamic production models, current stock biomass in this division is estimated as about 12000 t, while the estimate of carrying capacity for this stock is found to be about 29000 t. Initial stock biomass is estimated as 19000 t.

On the basis of the analysis of the biological material collected by one of the authors during fishery for Antarctic toothfish from 2002 till 2008 on different grounds of the Antarctic Zone (Collaboration Sea, D’Urville Sea, Ross Sea and Amundsen Sea), the assumption was advanced regarding the long spawning period of deep-water icefish Chionobathyscus dewitti during spring-and-summer period of the southern hemisphere. Higher numbers of individuals in prespawning and spawning state were noted on underwater mountains and banks on depths more than 1000 m, than on the continental slope grounds of similar depth. The data on fecundity were obtained, the absolute individual fecundity can be 2.3-6.1 thousand of eggs and the relative one is 3-12 eggs per 1 g of body weight. The structure of the envelope of maturing oocytes allows considering icefish to have bottom eggs. Keywords: deep-water icefish, body length, gonad weight, GSI, sex ratio, spawning, depth, area, season, vitellogeneous oocytes, yolk vesicle stage, yolk globules stage, emptied follicles, residual oocytes, fecundity.

The plan submitted to the WG-SAM-09 (Document 09/11) for fishing surveys on stock status and biological characteristics of Dissostichus spp. in Division 58.4.4 a & b has been revised according to the recommendations of the working group. The working group recommended the consecutive research focusing on tagging program for a period of 3-5 years to estimate current stock size accurately, and on fishing trials using both Trot line and Spanish line systems so that their properties can be better understood. We recalculated the necessary sample size as 120,000 kg for Dissostichus spp. for this division that includes 4 SSRUs, taking into account the conservative exploitation rate (less than 3.8 % of the total estimated biomass). Distributing research hauls across all SSRUs rather than concentrating the effort on a smaller subset of this Division is thought to be more reasonable in terms of minimizing localized impacts on the stock, avoiding predation of tagged and released toothfish by toothed whales, and accomplishing the objectives of the survey. To apply the mark-and-recapture studies, sufficient tagging rate was calculated to be 5 fish/ton, which can predict the CV of a Petersen estimate of population abundance to be sufficiently 0.31 when over-dispersion value is assumed to be 2.0. A total of 117 research hauls are allocated on 10-minute latitude x 20-minute longitude grid points, taking into account the need to deploy research hauls and tagging releases evenly throughout the survey area. A Trot line system will be employed for 88 research hauls in order to make an evaluation of the stock status and biological characteristics of Dissostichus spp. and to compare the information to be obtained in this survey with the information collected by the Trot line system used in the same Division in the previous research in 2007/08. In 29 hauls (a quarter of total sets), the experimental gear, which consists of three segments of Trot line system and Spanish line system respectively within one fishing line, will be used in order to standardize the CPUE of Trot line accurately in this Division and collect information on various properties of the two gears.

Examined the distribution and migration patterns of whales in the Southern Hemisphere. The presence of a new species of killer whale in the Antarctic, Orcinus nana, is shown. The impacts of extermination of whales in the Antarctic ecosystem are examined. Regions are defined which could be used as testing areas for whale survey methods.

In January 2009 the UK undertook a bottom trawl survey of CCAMLR Sub-area 48.3 on the FV Sil. A total of 71 random and representative 30 min tows were made giving good geographic coverage. The estimated mean biomass of Mackerel icefish (Champsocephalus gunnari) calculated using 10 strata, updated sea-floor areas and adjusting for the low headline height of the trawl (see CCAMLR WG-FSA (2003)) was 31,753 t with a lower 1-sided CI at 18,904 t. Catches of icefish across the region were dominated by a single length class whose mean length varied between South Georgia and Shag Rocks and were assumed to be 3+. Very few juvenile fish were observed except in the south eastern sector of the South Georgia shelf. Icefish diet was dominated by the amphipod, Themisto gaudichaudii with very low levels of krill, Euphausia superba found. This was likely to have been a result of the anomalous environmental conditions experienced at South Georgia during 2009. Biomass estimates and length frequencies are reported for other non-target species. There was evidence that the large cohort of juvenile Patagonian toothfish (Dissostichus eleginoides) observed an all surveys since 2003 had moved into deepwater and was no longer present at depths <300m. The estimate of biomass of the marbled rockcod, Notothenia rossii was considerably higher than estimated from the 2008 survey data.

For the first time in the history of deepwater longline fishing on Antarctic toothfish Dissostichus mawsoni (Norman, 1937) the experimental settings of deepwater vertical longlines was made from the Russian longliner Yantar in March, 2008 in the Amundsen Sea (subarea 88.2,D of the Pacific sector). The experiments proved that this species, one of the most valuable large commercial species of the South Ocean resided in bathypelagial as well as near the bottom.

Three aspects of current management of the “exploratory” Antarctic toothfish (Dissostichus mawsoni) fishery in Area 88 indicates that less-than-full precaution is being exercised in the face of climate-related environmental changes currently underway. These aspects are: 1) lack of knowledge about how environmental variability affects this species’ recruitment; 2) an inherent sensitivity of this species to climate-related factors; and 3) an increase in that sensitivity owing to the targeted removal of the oldest, most successful and most fecund toothfish. The current strategy is to deplete the pre-fished biomass slowly but ultimately by 50% by about 2025 (Pinkerton et al. 2007), i.e. not all at once. Based on information in the literature not available when the current CCAMLR Area 88 Antarctic toothfish management was formulated, we discuss why such a strategy is unlikely to result in a sustainable fishery, and we propose solutions to the problem.