CCAMLR

During January 2000 a baited video camera system was deployed fifteen times at depths of 719-1518 m around the sub-Antarctic island of South Georgia. Four species of lithodid (Anomura: Lithodidae) crab (Paralomis formosa, P. spinosissima, Lithodes sp. and Neolithodes diomedeae) were attracted to the baits of which Paralomis formosa was the most abundant. Using arrival rate at baits, predictions of odour plume size and observations of walking speed the abundance of the stone crab Paralomis formosa was estimated. Numbers of crabs increased rapidly following bait emplacement, with total numbers observed in the 4.9 m2 field of view exceeding 50 within 200 minutes on three occasions. Current speed was used to predict the area of the odour plume, and by integrating the area to account for scavenger speed the effective area of the odour plume was obtained. The density of crabs, estimated from the increase in crab numbers per unit area of odour plume, averaged 8313 individuals km-2 (range 1100-25600). Density was not significantly correlated with depth, temperature or current speed and variability was attributed to substrate form.

During January 2000 a baited video camera system was deployed fifteen times at depths of 719-1518 m around the sub-Antarctic island of South Georgia. Four species of lithodid (Anomura: Lithodidae) crab (Paralomis formosa, P. spinosissima, Lithodes sp. and Neolithodes diomedeae) were attracted to the baits of which Paralomis formosa was the most abundant. Using arrival rate at baits, predictions of odour plume size and observations of walking speed the abundance of the stone crab Paralomis formosa was estimated. Numbers of crabs increased rapidly following bait emplacement, with total numbers observed in the 4.9 m2 field of view exceeding 50 within 200 minutes on three occasions. Current speed was used to predict the area of the odour plume, and by integrating the area to account for scavenger speed the effective area of the odour plume was obtained. The density of crabs, estimated from the increase in crab numbers per unit area of odour plume, averaged 8313 individuals km-2 (range 1100-25600). Density was not significantly correlated with depth, temperature or current speed and variability was attributed to substrate form.

The scavenging fauna of the South Georgia slope was investigated from 41 baited camera deployment at depths of 471-2235 m during research cruises in September 1997 and January 2000 and 2003. The scavenging fauna was dominated by lithodid crabs, with Patagonian toothfish seen at most deployments. Other scavenging fauna included grenadiers (Macrourus sp.), morids and skates. The data indicate toothfish are absent from depths greater than 1800 m and temperatures less than 1.3 C. The arrival rate of crabs at the bait can be used to estimate density, but the behaviour of toothfish precludes this approach to estimating their density.

On the basis of the results of the trawl-acoustic survey in February-March 2002, the microstructure analysis of otoliths of juvenile icefish of 5.5-13.3 cm in length was carried out. Fish studied represent a mixture of two year-classes of 1999-2000 and 2000-2001. The mean width of the daily growth zone in the first 100 days of fish life was 6 ?k at fish length of 4 cm. By the 200th day the daily growth zone was 4.2 ?k at fish length 7.2 cm, by the 300th day – 3.5?k at fish length 11 cm, by the 400th day – 3.1 ?k at fish length of up to 11.8 cm, by the 500th day – 2.8 ?k at fish length of up to 12.5 cm. The resulting age-length ratio can be used in separation of adjacent year-classes during juvenile fish surveys. The length of the young-of- the-year varies within a broad range as a result of prolonged spawning period and by the end of the first summer of fish life approaches 5.5 – 10.4 cm. This corresponds to the age of 120 – 250 days. The length of 1-year-old fish (1+) by the end of the second summer of fish life attains 12.5-13.3 cm, with the age of 477 – 533 days, and the first annulus radius of 0.7 – 1.3 mm. It was revealed that the period of eggs incubation and larvae hatching of the year-class 2000 – 2001 was about 4 months.

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.