CCAMLR

The rate of foraging attempts by black–browed albatross on baited hooks during Spanish-system (demersal) longline setting operations, and a range of environmental and operational variables were used to investigate the relationship between their foraging behaviour and their mortality level. Logistic regression highlighted that a complex range of environmental and operational variables and black-browed albatross abundance combined to determine their mortality level. Our results suggest that, examined over a relatively short time period with minimal environmental variation, the rate of black-browed albatross foraging attempts during line setting significantly affects their level of mortality. However, as a range of variables influence mortality, until targeted experimental studies are conducted, we suggest that caution should be exercised using the rate of black-browed albatross foraging attempts as an index of their mortality.

Specifically tasked seabird observers recorded seabird interactions during shooting, trawling and hauling operations for 157 days onboard finfish trawlers in the Falkland Islands in 2002/03. It is estimated that >1,500 seabirds, predominantly black-browed albatross (Thalassarche melanophris), were killed by finfish trawlers during this period. Significant levels of mortality were also recorded on the Patagonian Shelf, north of the Islands. Birds were killed after being dragged underwater by the warp cable, while feeding on factory discharge at the stern of the vessel. An unknown proportion of these birds become impaled on a splice in the cable, which was situated on average around 50-100m from the waters surface, and are subsequently hauled onboard. In over 600 observed hauls in 2001-03 no birds were observed to become impaled on splices during hauling operations

This paper presents a protocol for the tag and release of toothfish (Dissostichus sp.) by fishers operating in the Ross Sea longline fishery in 2003-04. The protocol describes tag types, tag treatments and data recording requirements for the programme. Examples of reporting forms for release and recaptures are appended.

The monitoring program of demersal fish at inshore sites of the South Shetland Islands has continued in Potter Cove from 2000 to 2003, covering a continuous sampling period of twenty years and in 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 already reported for the period 1983-1999, is still evident. At Potter Cove, higher catches of N. rossii were obtained from 1991 to 2000, but the actual levels of relative abundance of this species and of G. gibberifrons are well below those found in the early 1980s. At Harmony Cove, the relative abundance of N. rossii showed an increase in years 2002-2003, whereas G. gibberifrons was absent in the catches. No recovery of the stocks of these two fish species was still observed, more than two decades after the end of the commercial fishery. However, the increase observed in the catches of N. rossii in some years since 1997 might be indicative of events of higher recruitment, not yet confirmed by the offshore scientific surveys carried out in the region. The results are consistent with diet information of the piscivorous Antarctic shag Phalacrocorax bransfieldensis in the South Shetland-Antarctic Peninsula area obtained from the early 1990s.

The elemental structure of growth increments in the otoliths of fish reflects the composition of water passing across the gills: as a result, elemental signatures can potentially be used to reconstruct the environmental history experienced by fish. To test whether the otolith elemental signatures of Patagonian toothfish (Dissostichus eleginoides) can discriminate spatial differences, we compared signatures from the outer edges (which are laid down during the interval leading to capture) of otoliths taken from toothfish sampled from management areas off southern Chile, the Falkland Islands, South Georgia, Kerguelen and Macquarie Islands. Edge Ba/Ca values were higher for toothfish caught south of the Subantarctic Front (SAF) in 1996 and 1997 compared to those captured off the South American continent, whereas Mn/Ca values were lower. Edge signatures also showed differences between samples taken south of the SAF, both across the Polar Front and across ocean basins. A sample taken west of South Georgia in 1998 showed similarities to the samples taken in 1996 and 1997 off South America, but very different Mg/Ca concentrations from all other samples.With further development, otolith elemental signatures show promise for identifying the site of capture of sampled toothfish, and for use as retrospective spatial markers to trace toothfish population structure and movement.

Using the High Resolution laser-ICPMS at Old Dominion University, we sampled the edge of otoliths from Patagonian toothfish (Dissostichus eleginoides), and examined whether the elemental signatures could discriminate between geographic locations along the Scotia Arc and along the eastern South American continental shelf near the Falkland Islands. Furthermore, we examined the elemental signatures of material in the otolith nuclei, formed during the early life history: similar nucleus signatures can be expected between fish which were spawned on the same spawning ground, even if the samples have subsequently been taken from different locations. We found signatures on the otolith edge of fish from South Georgia and Shag Rocks showed distributions characterized by lower levels of Mn/Ca than samples from the FOCZ. Signatures from the nucleus showed separation between the fish from South Georgia and Shag Rocks, and fish caught further west, implying a stock boundary. Although fish caught off the eastern North Scotia Ridge showed nucleus signatures similar to FOCZ fish, the distribution of their edge signatures was similar to South Georgia fish, suggesting that the elemental signature is due to an environmental effect rather than a genetic one.

To obtain a representative sample of the catch taken by toothfish longliners, CCAMLR observers are recommended to sample a quota of the first 30 fish that are caught during a sampling session. Since toothfish are often aggregated on a line, this means that fish within aggregations are sampled with less catch effort than those outside; or more generally, sampling effort is applied in inverse proportion to toothfish density on the line. The present recommendation therefore indicates sampling with unequal probabilities which, if unaccounted for, can lead to serious biases in estimates of population vital rates. To resolve this, either the probabilities need to be incorporated in the analysis of sampling data, or sampling effort should be proportional to catch effort. As vessels generally record the number of baskets taken while hauling a line, observers can use this to establish a point at which to start a session. Because there is little evidence of a consistent trend in fish sampled over a line, it does not particularly matter if an observer starts sampling before or after the correct basket arrives; but, preferably, the observer should start as close as feasible, and not be consistently late or early.

Water transported by the Antarctic Circumpolar Current (ACC) in the Southern Ocean may provide opportunities for Patagonian toothfish (Dissostichus eleginoides) to move downstream between island groups with little energetic cost, and may constrain movement in other directions, influencing population structure and richness. To test whether toothfish stocks were connected or segregated, we used an integrated experimental design to compare age-at-length data sampled at similar times from longline fisheries off the southern South American continent around the Falkland Islands north of the Sub-Antarctic Front of the ACC, and off Kerguelen and South Georgia Islands, situated respectively in the southern Indian and Atlantic Oceans to the south of the Polar Front. We fitted von Bertalanffy (VB) models representing segregation and coupling between management areas to the data, and tested between the models using a likelihood method. Toothfish showed significant differences in VB parameters between the Falkland Islands and both South Georgia and Kerguelen, but no differences between South Georgia and Kerguelen. This evidence suggests that, consistent with the dynamic-physical structure of the ACC, toothfish off the Falkland Islands are segregated from toothfish caught in the other two management areas, but that toothfish stocks at South Georgia and Kerguelen may be connected. Taken with the published genetic data, this evidence strongly suggests that toothfish population structure is related to the physical structure of the ACC and its fronts; that some toothfish populations may be connected between the major Southern Ocean basins; and that consequently, changes in toothfish population dynamics within one management area may have broader impacts through the Southern Ocean.