CCAMLR

The integrated assessment of Patagonian toothfish, Dissostichus eleginoides, for the Heard and McDonald Islands (Division 58.5.2) was updated by replacing catch-at-length proportions from commercial catches with catch-at-age proportions by applying age length keys (ALKs) to gear- type/ground (i.e. sub-fishery) and year-specific length frequency (LF) data. A Poisson log-linear (contingency-type) analysis of the age-length frequency data suggested that ALKs could be pooled across sub-fisheries without significant loss of information. Pooling the ALKs in this way meant that all commercial catch data could be input to CASAL as catch-at-age proportions except for the 2009 catches. For 2006 and 2007 random stratified trawl surveys, ALKs were used to convert abundance-at-length to abundance-at-age data. Effective sample sizes for the commercial catch-at-age proportions, assuming a multinomial distribution, and the coefficient of variation (CV) for the abundance-at-age, assuming a lognormal distribution, each took into account uncertainty due to haul-level variability in catch-at-length proportions, ALK sampling error and random ageing error. CASAL allows a single ageing error matrix to be defined and applies this matrix to predictions of numbers-at-age and proportions-at-age. In other work, this matrix was found to depend on the readability score of the otoliths used for ageing, so the ageing error matrix was calculated as a weighted average of elements across nearest integer average readability scores for sub-fishery by year aged otoliths where the weights were the effective sample size for proportions-at-age. Compared to the assessment that did not incorporate catch-at-age or abundance-at-age data, the aged-based assessment dramatically lowered the CV for the recruitment series, from around 1.8 down to approximately 0.6. The other major differences to the a2-ess model of Candy and Constable (2007, CCAMLR Science 15, 1-34) were that catches and catch-at-age data for additional sub-fisheries (2 longline, 1 trawl) and pot fishing in the 2006 season were included since catches in these cases have become significant in recent years, and the CV of mean length-at-age was fixed at 0.1 and not estimated since the inclusion of age data has reduced the ability to successfully estimate this parameter. The long-term yield that satisfies the CCAMLR decision rules, using a split of the catch by sub-fishery corresponding to actual catches in 2008, was 2 565 t.

A random depth stratified bottom trawl survey of South Orkney Islands (CCAMLR Subarea 48.2) demersal finfish was completed during February-March, 2009 during the U.S. AMLR Program field season. Detailed information is presented for several of the most abundant demersal finfish species, including spatial distributions, size compositions, diet compositions, gonad development, and standing stock biomass within the 500 m isobath of South Orkney Islands. Spatial distribution of standardized finfish densities demonstrated substantial contrast across the shelf area, with most finfish biomass occurring on the northwest sector of the shelf area. The highest densities of demersal finfish occurred at stations north of Inaccessible and Coronation Islands, and the highest mean densities occurred within the 150-250 m depth stratum. Estimates of biomass for nine abundant species were generally low. Standing stock biomass of Champsocephalus gunnari, the primary species targeted by the commercial fishery from the late 1970’s through the 1980’s, has increased since the last survey conducted in 1999, though remains severely depressed, and has not recovered to pre-exploitation levels.

1. 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; 2. In 2008/09 a total of 214 D. eleginoides and 192 D. mawsoni were tagged and released. Two tagged D. mawsoni were recaptured in the first season. 3. Macrourids and rajids dominated finfish bycatch with discard weights at 19% and 0.8% of toothfish catches, respectively. These rates are similar to those experienced in the North of 48.4. 196 Amblyraja georgiana and 1 Bathyraja eatonii were tagged and released and none were recaptured; 4. Almost half (47%) of sets were undertaken during daylight hours and no bird entanglements or mortalities were reported; 5. The UK proposes to continue the mark-recapture experiment in the South of Subarea 48.4 in 2009/10 with a combined catch limit of 75 tonnes for Dissostichus spp. 6. It is proposed that tagging effort is restricted to D. mawsoni which dominates catches in the South of 48.4.

1. The bycatch TAC of 12 tonnes of macrourids was reached in 2008/09 triggering the early closure of the fishery with only 58.9 t of the 75 t TAC of D. eleginoides taken; 2. The target tagging rate of 5 fish per tonne was exceeded by both vessels, with 344 D. eleginoides tagged and released in 2008/09, slightly under the target of 375 for the full 75 tonnes of catch; 3. There were 29 D. eleginoides tag returns in 2008/09, bringing the total from all seasons up to 54 tag recaptures; 4. A total of 12 D. mawsoni and 269 rajids were tagged in all seasons combined though none were recaptured; 5. Evidence of gonad development in 2008/09 suggests that D. eleginoides may spawn in the North of 48.4 in some years; 6. Analysis of tagging and biometric data suggests that D. eleginoides at 48.4 have similar growth parameters to those of 48.3; though the bulk of the current vulnerable biomass may be composed of a limited number of cohorts. 7. CASAL confirms that the vulnerable biomass is dominated by a single cohort spawned in the early-1990s and that growth parameters are similar for D. eleginoides caught in 48.4 and 48.3. 8. CASAL estimates of D. eleginoides population size in the North of 48.4 agree with simple Petersen and local CPUE estimates, with a B0 of 1143 t and B2009/B0 of 85%. 9. The sustainable yield calculated according to CCAMLR decision rules is 47 tonnes.

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.