CCAMLR

Over 9,000 skates have been tagged and released in the Ross Sea over a period of seven years, and 47 (0.5%) have been recaptured. The recapture of tagged Amblyraja georgiana after up to four years at liberty shows that some skates survive and recover from being hauled out of depths of around 1,000 m and tagged. In-water tagging greatly reduces the incidence of broken jaws in skates, and probably increases the survival of released animals. Unfortunately, this means that length at release can not be determined, so no useful data were gathered for estimating skate growth rates. Amblyraja georgiana moved very little, even after four years at liberty. There was no movement between SSRUs, and the maximum distance travelled was less than 70 km. The distance travelled did not increase with period at liberty for skates at liberty more than nine months. It appears that this species makes only small-scale movements along depth contours.

Biological parameters were reviewed and updated for the two main species of skates taken as bycatch in the Ross Sea toothfish fishery: Amblyraja georgiana and Bathyraja cf. eatonii. Differences in length-weight relationships among regions raise doubt about the conspecificity of A. georgiana from the Ross Sea and South Georgia, and of B. cf. eatonii from the Ross Sea and Heard Island and the MacDonald Islands. The taxonomy needs to be resolved before biological parameters derived from populations outside the Ross Sea can be applied to Ross Sea skates. Length-weight regression relationships for male and female A. georgiana and B. cf. eatonii from the Ross Sea are provided. Male and female relationships differ significantly for both species. Male A. georgiana attain 50% maturity at 92 cm total length (TL). The length at maturity of females is not well determined but is probably in the range 95–100 cm TL. Length at maturity of B. cf. eatonii is poorly determined, but is about 90–100 cm TL for males and 100–110 cm TL for females. The best available, but unvalidated, growth curve for A. georgiana for both sexes combined is: TLt = 101.3(1 ? e?0.308[t+1.30]). The best estimate of longevity in A. georgiana is 14 years. However this may be a considerable underestimate, and true longevity may exceed 20 years. Age at sexual maturity for A. georgiana is estimated to be about 6–7 years for males and 8–13 years for females. The most plausible range for the natural mortality rate, M, for A. georgiana is probably 0.15–0.25. No growth curve, longevity estimate or age at maturity estimate is available for B. cf. eatonii.

This paper reviews the distribution of seabird species with the WCPFC Area. From a review of the distributions of 99 species of albatross and petrel, 16 species of albatross and 60 species of petrel occur within the area of the WCPFC, and are potentially vulnerable to fisheries bycatch. These include species with IUCN classification of Critically Endangered (n = 1), Endangered (n = 7), Vulnerable (n =26) and Near Threatened (n = 7). The remaining 30 species are classified by the IUCN as Least Concern. This paper, having identified key risks, is intended to assist with the development of advice on mitigation of seabird mortality in fisheries in the WCPFC Convention Area. Recommendations on future approaches to mitigating risk are made.

The exploratory fishery for Antarctic toothfish (D. mawsoni) has been operating for nine years in Subarea 88.1 and for five years in Subarea 88.2 with a large amount of data collected on toothfish and the associated bycatch. All SSRUs in the two subareas except for 881D and 882C have now been fished. The 2006 D. mawsoni catch was the second highest on record with a total of 3388 t against a combined catch limit of 3451 t. The subarea catch limit was almost reached in both Subarea 88.1 and 88.2. The management of the SSRUs within the two subareas was changed for the 2006 season as part of a 3-year experiment (SC-CAMLR-XXIV). One of the aims of the experiment was to simplify the administration of the fishery by having fewer catch limits. This appeared to be moderately successful, with only one catch limit being slightly exceeded in the 2006 season. Concentration of effort within a smaller spatial area also increased the recovery of tags by over 50% (Dunn & Hanchet 2006).
Interesting patterns are beginning to emerge concerning the size distribution of fish from the different areas in Subareas 88.1 and 88.2. The occurrence of large adult fish from relatively shallow waters on the Ross Sea Shelf as well as the occurrence of small juveniles in much deeper water on the continental slope in Subarea 88.2 suggests that depth alone does not explain all the variation in toothfish length in the areas. Further sampling from along the continental slope of the continent is needed to determine the extent of these small fish.

This project evaluated the prevalence and intensity of an ectoparasite Eubrachiella antarctica as a marker for stock discrimination of Antarctic toothfish in the Ross Sea. New Zealand Ministry of Fisheries Observers on four toothfish longline vessels recorded the number of E. antarctica on the fins and in the buccal cavity of 621 large D. mawsoni (mostly 120-150 cm). Up to five D. mawsoni per set were examined for parasites in Small Scale Research Units (SSRUs) 88.1C, 88.2E and 88.2F; and two fish per set in SSRUs 88.1H - 88.1J. Up to 15 E. antarctica, one from each of the first fifteen sets in each SSRU, were dissected out and stored in ethanol for laboratory identification. All of the preserved copepod parasites were identified as female or male E. antarctica. D. mawsoni from 88.1H had a higher prevalence of E. antarctica compared to D. mawsoni from 88.1C, 88.1I, and 88.1J (and to 88.2E) and higher intensity compared to D. mawsoni from 88.1C, 88.1I, and 88.1J. However, neither intensity nor prevalence were significantly different between 88.1H and 88.2F. These area differences do not appear to be sampling artefacts produced by differences in host length structure, sex ratio, seasonality, or observer experience, but represent a regional difference in prevalence and intensity of E. antarctica on D. mawsoni. The small-scale regional differences suggested by the parasite marker are inconsistent with the genetic and tagging studies which suggest homogeneity at small spatial scales. Genetic, tagging, and parasite studies measure different biological parameters and results from these independent studies provide a picture of toothfish movement over different time scales. The stability of this regional difference in prevalence and intensity of E. antarctica needs to be tested with large scale sampling in future years.

The stomach contents of 190 sub-adult (51-100 cm TL) Antarctic toothfish (Dissostichus mawsoni) captured by bottom longline in the western Ross Sea were analysed. Fish were sampled during the 2005 fishing (Dec 2004 to Jun 2005) season and caught in 398-1678 m depths. Sub-adult D. mawsoni are primarily piscivorous, feeding on a wide variety of small to medium sized fish. Icefish (Channichthyidae) were the most important prey by frequency, weight and IRI, while small notothens (Nototheniidae) were more numerous. Whitson’s grenadier (Macrourus whitsoni), dragonfish (Bathydraconidae), and eel cods (Muraenolepididae) were also important. Glacial squid (Psychroteuthis glacialis) were found in about 20% of stomachs, but only 6% by IRI.
Samples were collected mainly from the continental slope along the northern edge of the Ross Sea. Although the study provides an important comparison of diet of adult and sub-adult fish collected from the same area, the results may not reflect the diet of the main part of the subadult population which is thought to reside on the main shelf to the south. It is therefore recommended that further stomach samples be collected from further south on the Ross Sea shelf.

A toothfish species profile, covering aspects of the biology, fisheries and stock assessment of both toothfish species was completed by Everson (2002). Aspects of the biology of D. mawsoni were summarised by Hanchet et al. (2003), whilst more recent research has been reported in background documents to WG-FSA. The aim of the current work was to collate and summarise existing biological data on D. mawsoni. The report focuses primarily on data collected from the Ross Sea fishery because this is where most of the work has been carried out, but data from the other areas and fisheries have been included when available. It is intended that this report form the basis of a species profile of D. mawsoni as requested at the 2005 CCAMLR meeting (SC-CAMLR XXIV).

The long term monitoring program of demersal fish at inshore sites of the South Shetland Islands has continued at Potter Cove from 2000 to 2006, covering a continuous sampling period of twenty four years, and at Harmony Cove, Nelson Island, in the austral summers from 2001 to 2003. The decline in trammel net catches of fjord fishes of the species Notothenia rossii and Gobionotothen gibberifrons in relation to the non commercially fished Notothenia coriiceps, which was previously reported for the period 1983-1999, is still evident. At Potter Cove, despite an overall increasing trend of N. rossii catches from 1991 to 2006, the actual levels are half of those found in the early 1980s, while those of G. gibberifrons further declined and remain close to zero. At Harmony Cove, the relative abundance of N. rossii showed an increase in years 2002-2003, whereas G. gibberifrons was absent in the catches. These trends are consistent with those observed in scientific cruises on the offshore populations in a similar period. Commercial fishing off the South Shetland Islands in the late 1970s is the most likely explanation for the decrease in recruitment to the inshore sub-populations of N. rossii and G. gibberifrons. No recovery of the stocks of these two fish species was observed, even more than two decades after the end of the commercial fishery. Both, present results of inshore monitoring and those of the offshore cruises since 1998 show that the populations of N. rossii and G. gibberifrons in the South Shetland Islands region cannot, at present, sustain a commercial fishery.

Patagonian toothfish, Dissostichus eleginoides, collections (n-186) from three ocean basins were analysed for Hg concentration and comparisons were made by gender, total length (TL), wet weight (WW), and basin. There was no difference between TL-WW relationships by gender within any basin across the range examined. However, fish were significantly smaller within the Atlantic basin (mean=84.52 cm; 5.57 kg; n=142) than the Pacific (99.07 cm; 9.12 kg; n=15) and Indian (102.72 cm; 14.0 kg; n=29) basins, which were not different from each other. Similarly, Hg concentration did not differ by gender or size across the range examined and was less for Atlantic basin fish ) mean=0.23 ppm) than either Pacific (0.73 ppm) or Indian basin (0.80 ppm) fish, which did not differ.
The Pacific and Indian basin fish had Hg concentrations within the range found for other fish like shark, swordfish, tilefish, and king mackerel, that are considered high in Hg concentration by the U.S. Food and Drug Administration. In contrast, those from the Atlantic basin were found to have similar lower values in fish like haddock, halibut, cod, albacore tuna, and orange roughy.
Explanation of these geographical differences in Hg may be 1) the noted size differences among basins, or 2) the actual sample locations and associated hydrogeographical and oceanographical conditions. For example, sampling sites for the Pacific Ocean lie well outside the Antarctic Convergence whereas the Indian Ocean sites straddle the Convergence. The Atlantic sites lie well within the Antarctic Convergence, suggesting that the Polar Front may provide some type of hydrographic barrier, as suggested in other studies on Patagonian toothfish, to anthropogenic sources of contamination. With a steady global market demand for Dissostichus this could pose a human health risk that has yet to be adequately explored.

The new continuous krill fishing system uses both a small-meshed midwater trawl and a powerful pumping system for continuous pumping the catch out of the trawl bag. It was discussed the potential threats of new technology to Antarctic marine ecosystem. It was shown that application of this fishing technology may result in considerable by-catch of the juvenile fish and larvae in krill fishery.