CCAMLR

The derivation of all parameters used in the assessments of toothfish using CASAL and the Petersen mark-recapture estimator in papers WG-FSA-05/16 and 17 are described.

The mark-recapture experiment continued at South Georgia in 2005. In total some 8000 fish have now been tagged in 48.3, and both tagging effort, fishing effort and recaptures were well – distributed over the whole of the fishable grounds in 48.3 this year. The Petersen mark-recapture estimator, which has been applied previously and described in detail by Agnew et al (2004) and Payne et al (2005), was recalculated for Subarea 48.3 based on updated parameter estimates and four different selectivity regimes: the historically used Kirkwood shallow selectivity, the single- and double- fleet selectivities estimates by CASAL (see WG-FSA-05/16), and a selectivity estimated directly from the tagging data.
Estimates from 2004 and 2005 were very similar to each other, whichever selectivity was used: about 62,000 t of vulnerable biomass using the Kirkwood shallow selectivity; 52-55,000 t using the CASAL derived selectivity functions; and 41,000 t using the tag-derived selectivity function. Current vulnerable biomass (BV2005) was (naturally) lower when CASAL determined selectivity and tag-derived selectivity were used, since these selectivity functions are more peaked than the Kirkwood shallow selectivity used in 2004. Estimates of sustainable yield, made adjusting mean recruitment in GYM so that BV2005 corresponded to the current estimates of vulnerable biomass, resulted in consistent estimates of sustainable yield of about 4,800 t, irrespective of the selectivity used.

The CASAL software has been successfully applied to an assessment of the stock of toothfish around South Georgia in Subarea 48.3. Both point estimate (“MPD”) and MCMC runs were carried out, with an extensive range of sensitivity tests and examination of diagnostics.
A baseline assessment model was selected to best represent the fishery and the available data sources. This incorporated two fleets with different selectivities, and fitted to catch length frequencies, tag recapture data, CPUE data, and the survey recruitment series (treated as a relative index). This produced excellent fits to the catch length frequencies, but a poor fit to the early CPUE data, for which a substantial process error CV was estimated (0.39). A possible alternative assessment model was also identified using a single fleet, as it is possible that overall trends in the CPUE series were not fully taken into account in the two fleet assessment. This alternative assessment produced worse fits to the catch length frequencies, and a poor fit to the CPUE data, for which an even higher process error CV was estimated (0.46).
For the baseline assessment incorporating two fleets, the 2005 vulnerable biomass was estimated to be 45,893 t, and the spawning stock biomass was estimated to be 120,360 t, around 67% of its unexploited level. For the alternative single fleet assessment, the 2005 vulnerable biomass was estimated to be 49,943 t, and the spawning stock biomass was estimated to be 100657 t, some 64% of its unexploited level. These estimates of current biomass are somewhat lower than the modified Petersen tagging estimates alone, which were 53,600 t and 55,600 t respectively (Agnew and Payne 2005: WG-FSA-05/17) but the confidence intervals for the estimates overlap.
The current implementation of CASAL is unable to reproduce all the features of GYM projections to estimate long term yields according to the CCAMLR decision rules. Using GY, the estimated long term yield is 4910 t for the baseline two-fleet assessment, while for the one-fleet assessment, the estimated long term yield is 4560 t.

At the request of the Scientific Committee, the Secretariat has prepared a single reference document which provides guidelines for the submission of meeting documents to the Scientific Committee, WG-EMM and WG-FSA (including ad hoc WG-IMAF).
In doing so, the Secretariat noted some Working Group-specific differences in relation to: submission deadline; exception to the deadline; and approach to accepting revised documents.
WG-EMM agreed that standardising the Working Groups’ guidelines in relation to the submission of meeting documents would simplify and unite the guidelines which participants to both WG-EMM and WG-FSA are required to follow. Standardisation would also simplify the Secretariat’s work in preparing information and documents for meetings. Consequently, WG-EMM agreed to a proposal to standardise the specific differences which related to the submission of documents to its meetings (WG-EMM-05/10).
WG-EMM also agreed to 3 changes to maximum size of meeting documents, submission of published papers, and availability of meeting documents in locked and unlock pfd. If WG-FSA adopted the changes agreed by WG-EMM, then the requirements for WG-FSA and WG-EMM would be identical and this would result in a standard set of guidelines for the submission of meeting documents to working groups.

The purpose of this document is to inform CCAMLR of the results of a satellite tracking program on black-browed albatrosses and light-mantled sooty albatrosses at Heard Island (Division 58.4.2). This was the first time the movements of either species from the island had been studied. Ten black-browed albatrosses and five light-mantled sooty albatrosses were tracked between December 2003 and February 2004, yielding 90 and 28 foraging trips from each species, respectively. Black-browed albatrosses foraged on the shelf break within 150 km of Heard Island, and focused 75% of their foraging time in waters over submarine canyons on Gunneri Ridge, north east of the island. There was considerable spatial overlap between these foraging grounds and the Heard Island EEZ trawl and longline Patagonian toothfish fisheries. These fisheries have a history of a low incidental seabird by-catch (no fatalities recorded to date in the longline fishery), although in 2005 seven black-browed albatrosses were killed in the mackerel icefish trawl fishery. 17% of black-browed albatross foraging trips entered the Kerguelen EEZ and a further 5% went beyond either EEZ into the high seas north and east of Heard Island. In contrast, light-mantled sooty albatrosses foraged along the boundary of the continental shelf break and northern boundary of the pack ice 1200-1600 km south of Heard Island.

This purpose of this document is to inform CCAMLR of work-in-progress in the Australian eastern tuna and billfish fishery (ETBF) of potential relevance to the conservation of Convention area seabirds. The research plan includes (a) a line weighting experiment on a chartered tuna vessel to determine the effect of line weighting regimes and bait type on the sink rate of longlines. This experiment was completed in April 2005. (b) a manipulative experiment testing the effectiveness of various combinations of line weighting and streamer lines as deterrent to fleshy-footed shearwaters. This experiment is scheduled for October and November 2005 when fleshy-footed shearwaters (the main seabird species taken in the fishery) are most abundant on fishing grounds. A summary of findings of the line weighting experiment is presented below. The experiment examined the effect of bait type, swivel weight and bottom length (distance between weighted swivel and hook) on the sink rate of branch lines used in Australia’s ETBF.

This document seeks the approval of CCAMLR for a research plan to improve the seabird by-catch mitigation effectiveness of the Spanish system of longline fishing. The plan also aims to reduce the amount of fishing gear (and ghost fishing) lost in benthic habitats by Spanish system vessels in the Convention area and, potentially, in other fisheries where Spanish system vessels operate. A step-wise approach will be taken using a chartered fishing vessel in Chile to trial various line weighting systems, including replacing with steel sinker weights the bags of rocks that are traditionally used by Spanish system vessels. The objectives are to (a) reduce the degree of lofting in hook lines between line weights that occurs with the CCAMLR line weighting regime to expedite sink rates in surface waters, and (b) reduce the incidence of line weight hook-ups on the seabed. A line weighting system that improves sink profiles (and reduces frequency of line breakage) will then be trialled in normal fishing operations in southern Chile to determine effectiveness (along with use of streamer lines) as deterrent to black-browed albatrosses. The operational effectiveness of the new regime will also be determined. Assuming the new regime is practical to use, the intention will then be to seek permission from CCAMLR to trial the improved mitigation measures against white-chinned petrels in sub Area 48.3 at a high risk time of year.

Soon after longlining on Patagonian toothfish (Dissostichus eleginoides) started in the Southern Ocean in the second half of the 1980’s, interactions of cetaceans with these fisheries became apparent. The two species primarily involved were orcas (killer whales) (Orcinus orca) and male sperm whales (Physeter macrocephalus). Both species took substantial number of fish from the line primarily during day light hours. Catch rates of longliners declined to less than 50% when orcas occurred close to longline vessels while the loss to sperm whales was much less obvious. They were seen diving close to the line down to 400 m where they apparently took fish. Their impact on catch rates was much less notable. Sperm whales became frequently entangled in the line and part of the line was lost in a number of cases. Other cetaceans were rarely seen in the vicinity of longline vessels. They became entangled in the line only occasionally and one whale (presumably a minke whale) died.