CCAMLR

Between August and November 2001, two fishing vessels carried out exploratory and experimental surveys with semipelagic and different configurations of long line directed to the capture of Wreckfish (Polyprion americanus) and other fish species within the Uruguayan EEZ. Observers were trained in order to include Seabirds information along with their common tasks. Seabirds mortality associated with long line operation is analyzed, as well as species involved and mitigation measures application. Total mortality ranged: 3 birds/1 000 hooks, and main species captured were Procellaria aequinoctialis (50%), Puffinus gravis (27%) y Thalassarche melanophrys (21%). Bird species composition varied along the operation period. No significant differences in mortality were found between long line types, being higher in those with floats attached to the main line, and under daylight setting. Some species presence was consistent comparing their abundance during line setting and resulting mortality. Difficulties were found in mitigation measures application, specially to set during night only and avoiding bird scaring tangles with intermediate buoys. Although this fishery is no longer in Uruguay, the need to improve some information related to fishing gear and seabirds interaction is discussed, as well as the revision of current regulations.

The ASPM assessment of the Prince Edward Islands toothfish resource by Brandão and Butterworth (2004) that permitted annual fluctuations about a deterministic stock-recruitment relationship is updated to take account of further catch, GLM standardised CPUE and catch- at-length information that have become available for the year 2004. Twenty year biomass projections under the assumption of various constant annual catches are also shown. These suggest that maintenance of the present TAC of 500 tonnes is defensible.

This note describes the activities of an alliance of New Zealand government, fishing industry and environmental groups that has formed to promote fishing practices that avoid seabird capture by fishing fleets in the southern hemisphere.

Data on maturity, gonadosomatic index (GSI) and length weight of Antarctic Toothfish Dissostichus mawsoni were collected from Sub areas 88.1 and 88.2 in the 2002-2003 season by the New Zealand bottom longline vessels Janas, Avro Chieftain and San Aotea II operating in the Exploratory Fishery. The first fully mature female fish were found in December, three months earlier than in the previous season.
The onset of spawning in D. mawsoni is in December and continues until at least June, in both Sub-areas 88.1 and 88.2, and spawning occurs on isolated geographic features north of the main Antarctic shelf areas. One of the mature fish caught in Sub Area 88.2 had originally been tagged in McMurdo Sound Sub Area 88.1 in 1986.
A new 7 stage recording system is proposed for D. mawsoni to be agreed at WG-FSA.v

The CCSBT Ecologically Related Species Working Group held its 5th meeting in Wellington in February 2004. This report provides a summary of the discussion and outcomes of that meeting from the IMAF nominated observer at the meeting.

Two molecular methods, mitochondrial DNA and introns, were used to determine genetic relationships among Antarctic toothfish, Dissostichus mawsoni, samples from three CCAMLR areas 48.1, 88.1, and 58.4.2. D. mawsoni appeared to be characterized by low diversity; no genetic variation was detected with restriction enzyme digests of nine sub regions of the mitochondrial genome. Polymorphisms were found in four out of seven introns digested with the restriction enzymes, but there was no population differentiation among the three sea areas. While direct sequencing of cytochrome b (665 base pair) showed virtually no variation, sequences for ~600 bp of the left domain of the control region showed nucleotide variation with some haplotypes restricted to sea areas. The weak genetic differentiation is supported by oceanic gyres, which may act as juvenile retention systems, and by limited movement of adult tagged fish. It is recommended that the Ross Sea D. mawsoni be treated as a separate stock unit.

The stomach contents of 496 Antarctic toothfish (Dissostichus mawsoni) captured by bottom longline in the western Ross Sea during the 2003 summer fishing (from Dec 2002 to Jun 2003) season were analysed. Fish sampled were caught in 770-1890 m depths and ranged between 72–212 cm in total length. D. mawsoni feeds on a wide range of prey but is primarily piscivorous. The most important prey species was Whitson’s grenadier (Macrourus whitsoni), which dominated the overall diet. In continental slope waters, M. whitsoni, the icefish Chionobathyscus dewitti, eel cods (Muraenolepis spp.) and cephalopods predominated in the diet, while on oceanic seamounts M. whitsoni, violet cod (Antimora rostrata) and cephalopods were important.

Icthyoplankton sampling was carried out by the New Zealand bottom longliner Avro Chieftain in the Ross Sea Sub Area 88.1 in the 2002-03 fishing year. Four direct haul samples were taken with a UNESCO WP2 net to a maximum depth of 1620 m in areas where mature D. mawsoni had been observed. No Dissostichus eggs or larvae were observed. Larvae of Kreffichthys anderssoni and Electrona antarctica, and two unidentified egg types were found.

X-rays of vertebral half-centra, and X-rays and transmitted white light examination of caudal thorns, were used to estimate the ages of Amblyraja georgiana from the Ross Sea. Caudal thorns viewed with transmitted white light provided the clearest growth bands, but reading precision was low, producing uncertain age estimates. Furthermore, annual deposition of thorn bands has not been validated. The maximum age was 14 years, but this should be regarded as a conservative estimate of longevity because of the possibility that thorn growth ceases in large individuals. Von Bertalanffy growth curves are provided for females, males, and both sexes combined. There was no obvious difference between the sexes, so the curve for both sexes provides the best available representation of growth in the species: Lt = 70.8(1-e-0.308[t+1.10]), where Lt is the pelvic length (PL) in centimetres at age t. Applying this growth curve to the estimated lengths at maturity for males and females (64 cm and 66– 69 cm PL respectively) produced estimated ages at maturity of 6–7 years for males and 8–11 years for females. These estimates are near the middle to upper end of the range of ages at maturity for skates worldwide.