CCAMLR

Studies on DNA microsatellites and a tagging programme both provide information on the degree of interchange of Dissostichus eleginoides (Patagonian Toothfish) between two sites 40 nautical miles apart near Macquarie Island. Five DNA microsatellite loci were identified that showed polymorphism levels appropriate for population structure analysis, and two of these gave results that suggest samples from the two sites are not homogeneous at the 5% probability level. While the other three loci did not demonstrate significant spatial heterogeneity, combined results across all five loci again indicated heterogeneity at the 5% probability level. Results from tagging experiments support the inference from the genetic analyses that interchange of fish between the two sites is very low. Of 469 recaptures at both sites combined, only one fish had moved between sites. As the DNA analysis has so far only been performed on small numbers of fish and loci these results must be regarded as preliminary, but if confirmed by further study the implication of very localised stocks of D. eleginoides will have a great effect on the management of commercial fisheries for this species.

Results of published studies on the biology, biomass and distribution of the Antarctic toothfish (Dissostichus mawsoni) were reviewed. The review focused on those aspect of the species which are of importance for the assessment of its biomass and identification of its stocks. The trophodynamics of D. mawsoni are mentioned only in brief. Most published materials refer to studies conducted in the 1970-1980s. References in current publications on new studies of this species are scarce. A list of references is appended.

Various elements of the Generalized Linear Model (GLM) used to standardise toothfish CPUE in Subarea 48.3 are investigated. Problems with crossover between the essentially summer fishery of 1992-1993 prosecuted by Russian vessels and the winter fishery of 1995 onwards prosecuted by other nationalities, coupled with the existence of the experimental fishery in 1994, lead us to suggest that future analyses should be restricted to GLMs based on winter data alone. Unfortunately, this does result in there being no data for 1993, one of the most successful summer seasons. The relationship between CPUE and depth is also explored, and tins leads to some suggestions about the distribution of toothfish of different sizes on the shelf slope. A winter GLM is described which includes a depth factor, and is used in a discussion of the recent declines in CPUE seen in Subarea 48.3.

Satellite telemetry was used to identify the foraging zones of Shy Albatrosses Diomedea cauta breeding at two sites off Tasmania, Australia (Albatross Island in western Bass Strait and Pedra Branca to the south) to assess their level of interaction with longline fisheries. Adult birds from both colonies fed locally both in and outside the breeding season. Breeding birds from Albatross Island foraged over the Australian continental shelf or slope waters off northwest Tasmania, while those from Pedra Branca foraged between the colony and the southeastern edge of the continental shelf. The distances travelled by the birds and the duration of their foraging trips varied during the breeding cycle and tended to decrease as eggs approached hatching. Adults which were tracked near the end of the breeding season (March-April, n = 7 birds) deserted their chicks prematurely, and while dispersing further than incubating or brooding birds, they remained over the continental shelf and slope waters off southeast Australia. Home range analyses indicated 41 % overlap between foraging zones of birds during successive breeding stages. Dispersal during the postbreeding period extended the foraging zones with less overlap between individuals (10% for Albatross Island and 19% for Pedra Branca). The recent contraction of the Japanese Southern Bluefin Tuna longline fishery to the south and east coasts of Tasmania has resulted in extensive overlap with adult Shy Albatrosses from Pedra Branca, but appears to pose a minimal threat to adult birds from Albatross Island. Coupled with the concomitant increase in the Australian domestic tuna longlining industry, adult Shy Albatrosses from southern Tasmania (Pedra Branca and the Mewstone) are vulnerable to incidental capture throughout their annual cycle.

Long term fisheries observer data were used to analyse the influence of a range of environmental variables and mitigation measures upon catch rates of seabirds in the Japanese pelagic longline fishery. In the Australian Fishing Zone (AFZ) seabirds were most likely to be caught on longlines that were set during summer, in southern areas of the zone, and during daylight hours. However, interpretation of changes in catch rates resulting from the use of mitigation measures or from weather effects were problematic due to the interrelationships between the many measured factors. Interpretation and accurate assessment was further complicated by ongoing changes to fishing practices and equipment, and due to changes of the priority that fisheries observers placed on the collection of seabird data. The data relating to factors affecting seabird bycatch which is currently collected incidentally by fisheries observers are not sufficiently robust to allow confidence in statistical assessments alone to examine the efficacy of mitigation measures. Dedicated observations may allow for more confident determination of the reasons why seabirds were or were not caught, and to what degree mitigation measures are effective. The use of these observations in combination with the analyses suggested seabird bycatch rates may be lowered by the use of bird lines, bait throwing machines and thawed baits. However, appropriate use and deployment of these measures are critical if they are to be effective. Further work is required to better understand the effect of these measures, and their effect upon the catch rate of target and non-target species.

Large numbers of seabirds are killed each year within the Australian Fishing Zone (AFZ) by Japanese longline vessels targeting tuna. In recent years the estimated rate of seabird bycatch in the AFZ has been in the order of 0.15 birds 1000 hooks, translating to mortalities of 1000-3500 birds per year. These estimates are absolute minima because not all birds killed remain on hooks to be observed hauled aboard the vessels. The observed seabird catch rate varies annually, seasonally and spatially. Most birds are killed: (a) during the summer fishing season (October to March), even though most fishing effort occurs in winter; (b) when longlines are set during the day; (c) in the waters around southern Australia. Uncertainties in the observed catch rates prevent confident assessment of trends, but seabird catch rates do not appear to be showing a sustained decrease. The process of the incidental collection of seabird bycatch data (by observers whose priority is to fish sampling tasks) renders the seabird bycatch data inadequate for reliable assessment of trends in total numbers of birds killed over time. Sixteen seabird species of birds killed on longlines in the AFZ have been identified. These include black-browed (Diomedea melanophris), shy (D. cauta), grey-headed (D. chrysostoma), yellow-nosed (D. chlororhynchus) and wandering albatrosses (D. exulans), flesh-footed shearwaters (Puffinus carneipes) and white-chinned petrels (Procellaria aequinoctialis).Seventy-four per cent of birds killed were albatrosses and the species composition of the bycatch varied with seasons and areas. Most species of birds killed were characterised by unequal representation of sex and age cohorts. and these unequal representations were not consistent between fishing grounds or seasons.