CCAMLR

The Age-Structured Production Model (ASPM) presented to previous meetings is refined to allow the estimation of a selectivity-at-age function that decreases at larger ages. This is, in particular, to accommodate the view of the August 2003 meeting of the Subgroup on assessment methods that 0.2 yr-1 is likely the largest value of natural mortality M that is plausible for toothfish. Catch, catch-at-length and GLM standardised CPUE data are all extended for one further year. Despite model refinements, the CPUE data and catch-at-length data remain sharply inconsistent within the modelling framework considered. The former suggests the resource to be heavily depleted, whereas the latter suggests quite the reverse. Priority areas for further investigation to attempt to resolve this inconsistency are suggested. In the meantime, based upon a cautious interpretation of projections over the wide range of current stock status that can be argued from these analyses, it is suggested that annual catch levels should not exceed a few hundred tonnes.

This year the Subgroup on assessment methods (SAM) requested that WG-FSA consider whether a shorter CPUE time-series would be preferable for use in its annual assessments. (WG-FSA-03/40 2003, paragraph 2.27). This paper explores some of the consequences of shortening the dataset in the application of the usual assessment method. In addition we investigate the incorporation of uncertainty in the standardised CPUE series into the method of Kirkwood and Constable (2000) via Monte Carlo simulations of the CPUE series. Truncation of the standardised series from WG-FSA 2002 results in only slight modification to the median escapement but will generally diminish the probability of depletion as the dataset is truncated towards the more recent years. The use of the standardised series from the GLMM of Candy (2003) shows a more pronounced consequence of reducing the time series, such that the escapement level increases while the depletion probability decreases as the time series is reduced to recent years. In contrast, the explicit incorporation of uncertainties in the CPUE series in the overall assessment shows that truncation of the CPUE series could have a much greater effect on the final assessment, depending on the model used. These results indicate that the procedure for incorporating CPUE into the assessment process needs to be generally evaluated as to the consequences of its use in providing assessments that will meet the objectives of CCAMLR.

Operational interactions between marine mammals and the Patagonian toothfish (Dissostichus eleginoides) fishery were assessed in southern Chile through 7 surveys with observers on board industrial vessels between April 2002 and March 2003. Sperm whales (Physeter macrocephalus) occurred in higher frequency than any other species during fishing operations. In 60% of all monitored sets sperm whales were present, while orcas (Orcinus orca) were found in only 10% of these. When cetaceans were present, evidence of damaged catch included lips, heads and trunks and a total of 121 lips, 16 heads and 3 trunks were recovered. Mean rate of predation was 3% (± 2% CI 95%; n=180 sets) and ranged between 0% and 100%. Considering that in 153 (84%) of the effectively monitored sets no interaction whatsoever was recorded and that the mode and median of the predation rate was 0, the global impact of cetaceans over the fishing yield is considered to be low. When mixed sightings of orcas and sperm whales were encountered (n=12) the rate of predation decreased to 0%. Upon detecting orca presence, sperm whales modified their surface behaviour, grouping into tight parallel formations. This suggests that orcas prefer attacking aggregated sperm whales instead of the line. High sperm whale densities were found associated to different hotspots which had high fishing yields. This relationship tends to support the hypothesis that the richest fishing grounds are also traditional feeding grounds for sperm whales. Monetary loss associated with operational interactions associated with predation reach USD$92,684 (C.I. 95% USD$47.302 - $153.745) for the whole fleet, with a mean loss per set of USD$138 (C.I. 95% USD$74,76 - 249,3).

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.