CCAMLR

Mackerel Icefish Champsocephalus gunnari Lönnberg is an important component of the ecosystem at South Georgia where its diet is dominated by Antarctic Krill Euphausia superba, it is an important prey species for a number of upper trophic level predators, and is the target of commercial fisheries. Data on the frequency and size structure of C. gunnari in the diet of Antarctic fur seals Arctocephalus gazella and gentoo penguins Pygoscelis papua at Bird Island, South Georgia from 1991-2002 were used to examine the trophic interactions and evaluate the potential impact of predators on the C. gunnari population. C. gunnari occurred in 20 – 40 % of scats from Antarctic fur seals and comprised 48% of the diet by mass of gentoo penguins. The length-frequency distributions of C. gunnari indicated a dominant mode at 180-200 mm total length (1+ age class), with strong cohorts entering the population in 1993, 1996, 1999 and 2001. A recruitment index based on the contribution by mass of the 1+ age-class in the diet of gentoo penguins indicated a higher degree of variability in recruitment than in considered previously. Estimates of consumption of C. gunnari by Antarctic fur seals and gentoo penguins (c. 138 000 tonnes per annum) exceed standing stock estimates (17 –67 000 tonnes). A deterministic population model of cg from 1991 – 2002, using a variable mortality rate scaled by the inverse of krill abundance, replicated the fluctuations in C. gunnari shown by trawl surveys. Changes in the South Georgia ecosystem over the past 2 decades may have increased the level of predator consumption of C. gunnari providing a potential ecosystem based explanation for the lack of a recovery of pre-exploitation population size

Currently, three Australian commercial fisheries operate around Heard and McDonald Islands in CCAMLR Statistical Division 58.5.2. These comprise a trawl and a longline fishery for the Patagonian toothfish, Dissostichus elegionoides and a trawl fishery for mackerel icefish, Champsocephalus gunnari. This paper presents available by-catch information for the three fisheries including estimates of total removals by fishing season and ground, and length composition of rajids and macrourids. Preliminary results from a rajid tagging program are also presented. Total removals of by-catch in the trawl fisheries are estimated to be very low. From 1996/1997 to 2002/2003, a total of 115 tonnes of by-catch was caught in the D. eleginoides trawl fishery and 107 tonnes in the C. gunnari trawl fishery. These values represent less than 1% and 2% respectively, of the total catch weight (target and non-target species) in each fishery. During the 2002/03 season of the longline fishery for D. eleginoides, 23 tonnes of by-catch was caught representing 8% of the total catch. The length range of macrourids and rajids caught in the trawl and longline fisheries is discussed and compared to the length range of the population sampled by research surveys. Eight Bathyraja eatonii have been recaptured to date, resulting in a recapture rate of 1.9% for this species. Tagged rajids exhibit little movement between release and recapture with distances travelled ranging between 1 and 7 nautical miles. The time at liberty varied between 208 and 823 days, with most skates at liberty for approximately one year. Estimates of growth were very low, with average increments of 12 mm per year in total length, 17 mm per year in disk width and 0.1 kg per year in weight. The results presented here, indicate that this species is likely to be very slow growing and/or that the trauma of capture results in at least one year of very slow growth. Growth estimates were lower than those estimated for similar sized species from the northern hemisphere.

Based on data on movements of Patagonian toothfish derived from tagging experiments and analysis of toothfish DNA from Heard Island and McDonald Islands (HIMI), Kerguelen, Crozet and Marion/Prince Edward Islands regions a possible metapopulation model for the region is postulated. In this model some or all of the subadult fish at HIMI migrate northwestwards to Kerguelen and Crozet. Larval fish spawned to the north-west of HIMI then return to HIMI in the Antarctic Circumpolar Current. If such a model is valid, this will have significant ramifications for management of fisheries around these islands, which are at present managed independently.

Globally, by-catch is recognised as one of the most significant issues affecting fisheries management. The Commission for the Conservation of Antarctic Marine Living Resources (the Commission) has adopted an ecosystem approach to managing fisheries which takes into account the direct and indirect impacts of harvesting on non-target taxa. There are many approaches to reduce by-catch. Current approaches to managing by-catch focus on by-catch avoidance and mitigation measures, setting of precautionary catch limits and encouraging research programs that focus on non-target taxa.
Through summarising current approaches to by-catch management and activities across non-target taxa and examining the range of protection afforded to by-catch taxa (seabirds, marine mammals, elasmobranchs, bony fish and benthic invertebrates) it became evident that the application of these approaches is not consistent across by-catch taxa. CCAMLR has developed a comprehensive system for mitigation of seabird incidental mortality, but equivalent measures are not as well developed or implemented for bony fish, benthic invertebrates, and particularly the elasmobranch populations that are particularly vulnerable to harvesting as they have low fecundity, potentially greater longevity and slow growth rates.
Within CCAMLR, the impetus for action and application of approaches to minimise by-catch needs to be consistent where possible across non-target taxa. A consistent, integrated approach to by-catch could assist the development of measures for vulnerable species such as skates and rays and some fish species. Such an approach would identify and prioritise the areas that need to be addressed based on a preliminary evaluation of risks. This would facilitate agreement on a program of work. Such an approach could provide the basis for a comprehensive and integrated approach to managing by-catch issues in CCAMLR.

Further data arising from the tagging programme on Patagonian Toothfish at Heard and Macquarie Islands are presented, along with a summary of results since the beginning of the programme. Results from the programme of archival tagging of toothfish are also presented.

This review paper summarises available information on the Somniosus (sleeper shark) subgenus, comprising three species; S. microcephalus, S. pacificus and S. antarcticus. Taxonomy, distribution, life history, biological characteristics and exploitation by fisheries is discussed. Somniosus antarcticus is caught as by-catch in Australian subantarctic fisheries at Heard and McDonald Islands (Division 58.5.2) and Macquarie Island. Based on present by-catch rates, a risk assessment for this species concluded that there is unlikely to be a serious risk to the stock. A tagging program and continued monitoring of by-catch of this species is ongoing.

The Australian-flagged longliner Eldfisk was approved by CCAMLR to undertake an exploratory fishery for D. mawsoni in Division 58.4.2 in the 2002/03 season. The results of the fishery involving 140 sets between 5 February and 25 March 2003 are summarised. Total catch from the three SSRUs fished was 111.8 tonnes, of which 88.7% overall was D. mawsoni. Principal bycatch species were macrourids (10.2% overall), skates (0.34%) and Muraenolepis sp. (0.27%). The length range of D. mawsoni caught was between 500mm and 1650mm total length, and most fish were in gonad state 1 to 3. Length at first maturity is estimated at 1000mm for males and 1300mm for females.
There were marked differences between the SSRUs in catch composition and D. mawsoni length frequency.

Molecular markers were employed to investigate the fine-scale stock structure of Patagonian toothfish in the west Indian Ocean sector of the Southern Ocean. Four collections of toothfish from the Kerguelen (n=1), Crozet (n=1) and Prince Edward and Marion (n=2) Islands were typed genetically using two fragments of mtDNA and seven nuclear microsatellite loci. MtDNA haplotype diversity was moderate; ranging from 0.331 to 0.343. Allelic variation at the seven microsatellite loci was widespread with observed heterozygosities per locus per collection ranging from 0.000 to 0.900 and allele counts from 1 to 21. There was no evidence for significant mtDNA heterogeneity among the four collections and only weak and inconsistent heterogeneity (based on minor allele frequency differences) at several microsatellite loci among the four collections. Both mtDNA and microsatellite FST values indicated no population sub-structuring among the collections. Genetic variance estimates of both mtDNA (?ST=-0.016) and microsatellites (?ST=-0.005) indicated all variation was seen within the toothfish collections. Comparisons with previously collected genetic data from Heard and McDonald Island collections (n=4) also showed a lack of genetic differentiation among the geographic groups, indicating significant gene flow among west Indian Ocean sector fishing locations.