CCAMLR

The population structure of black-browed (Thalassarche melanophris and T. impavida) and grey-headed (T. chrysostoma) albatrosses was examined using both mitochondrial DNA (mtDNA) and microsatellite analyses. mtDNA sequences from 73 black-browed and 50 grey-headed albatrosses were obtained from five island groups in the Southern Ocean. High levels of sequence divergence were found in both taxa (0.55–7.20% in black-browed albatrosses and 2.10–3.90% in grey-headed albatrosses). Black-browed albatrosses form three distinct groups: Falklands, Diego Ramirez/South Georgia/Kerguelen, and Campbell Island (T. impavida). T. melanophris from Campbell Island contain birds from each of the three groups, indicating high levels of mixture and hybridization. In contrast, grey-headed albatrosses form one globally panmictic population. Microsatellite analyses on a larger number of samples using seven highly variable markers found similar population structure to the mtDNA analyses in both black-browed and grey-headed albatrosses. Differences in population structure between these two very similar and closely related species could be the result of differences in foraging and dispersal patterns. Breeding black-browed albatrosses forage mainly over continental shelves and migrate to similar areas when not breeding. Grey-headed albatrosses forage mainly at frontal systems, travelling widely across oceanic habitats outside the breeding season. Genetic analyses support the current classification of T. impavida as being distinct from T. melanophris, but would also suggest splitting T. melanophris into two groups: Falkland Islands, and Diego Ramirez/South Georgia/Kerguelen.

1. Several albatross species, including the wandering albatross Diomedea exulans , have shown marked declines in abundance throughout their range. These seabirds are frequently taken as by-catch in longline fisheries and this mortality has been implicated in the population declines.
2. We developed a deterministic, density-dependent, age-structured model for assessing the effects of longlining on wandering albatross populations. We used demographic data from field studies at South Georgia and the Crozet Islands, data on albatross abundance from 1960 to 1995, and reported effort data from the tuna longline fisheries south of 30 S, to model estimated by-catch levels and other population parameters in the model.
3. The model used two alternative assumptions about patterns of at-sea distribution of wandering albatross (uniform between 30°S–60°S; proportional to the distribution of longline fishing effort between these latitudes).
4. Our model was able to predict reasonably closely the observed data from the Crozet Islands wandering albatross population, but the fit to the South Georgia population was substantially poorer. This probably reflects: (i) greater overlap in the Indian Ocean than in the Atlantic Ocean between the main areas of tuna longline fishing and the foraging ranges of wandering albatrosses from the Crozet Islands and South Georgia, respectively; and (ii) greater impact of poorly documented longline fisheries, especially the tuna fisheries in the south Atlantic and the Patagonian toothfish Dissostichus eleginoides fishery, within the foraging range of wandering albatrosses from South Georgia.
5. The model results suggest that the marked decline in both populations, and subsequent recovery of the Crozet Islands population (but not the continued decline of the South Georgia population), can be explained by the tuna longline by-catch. They further indicate that populations may be able to sustain some level of incidental take. However, the likely under-reporting of fishing effort (especially in non-tuna longline fisheries) and the delicate balance between a sustainable and unsustainable level of by-catch for these long-lived populations suggest great caution in any application of such findings.

Age based fishery population models require information on size at age of the fished population and the commercial catch. Age-length keys can be produced by standardised random sampling of the commercial catches. This information does not necessarily reflect the size at age of the fished population and may be seriously biased. Through the use of a model, and using the Patagonian toothfish as an example, a method is developed to estimate size at age of the population using information collected from the commercial fishery.

The fishery for Patagonian toothfish is one of the most valuable in the CCAMLR Area. Age based models are used to assess the status of the stocks of this species. Although age can be estimated using otoliths it has proven difficult for these to be validated. During a recent trawl survey the length density of juvenile toothfish in the catches had a clearly defined polymodal distribution. The age of each fish was estimated from the otoliths and the distribution of these ages matched closely the modal size groups. It is confirmed that one annulus, as seen on an otolith section, corresponds to one year’s growth.

Tristan da Cunha and Gough Islands in the central South Atlantic Ocean support globally important seabird populations. Two longline fisheries occur within Tristan's Exclusive Economic Zone: a pelagic fishery for tunas and a demersal fishery for bluefish and alfoncino. Fishery observers have accompanied all three licensed demersal cruises. Despite attracting considerable numbers of birds and setting lines during the day, only one bird (a Great Sheawater Puffinus gravis) was killed (mortality rate 0.001 birds per 1000 hooks). By comparison, the pelagic fishery for tuna, which exceeds demersal fishing effort, probably has a much greater impact. Observations aboard one vessel in mid-winter suggest a bycatch rate of> 1 bird killed per 1000 hooks; this could be even higher in summer when more birds are breeding at the islands. Stricter regulations are required for pelagic vessels, including routine placing of observers on board. The gravest threat posed by longline fishing to Tristan's seabirds comes from vessels fishing illegally in Tristan waters, as well as vessels in international waters that do not use basic mitigation measures. There is a pressing need for better policing of Tristan's waters.