CCAMLR

An ongoing mark and recapture experiment for skates was commenced by New Zealand fishing vessels in the Ross Sea (CCAMLR Subareas 88.1 and 88.2) in 1999/2000. Based on preliminary results from this programme showing an unquantifiable degree of the survivorship of returned skates, the CCAMLR Scientific Committee gave approval in 2004 for licensed vessels to cut live skates from the line (while in the water) as an alternative to either retaining all aboard or discarding dead skates, as a skate mortality mitigation measure. Initial opinion when the skate tag and recapture programme was first implemented was that some form of in-water release would be the ideal to improve survival chances. Subsequently a number of problems have become evident with this method. The Working Group on Fish Stock Assessment (WG-FSA) noted in 2004, when recommending skate release as an option to the Scientific Committee, that it might be difficult to detect tagged rays skates if they are cut off at the sea surface rather than being brought on board. The WG-FSA recommended that should the tag identification rate be low, a relaxation of the requirement to cut all rajids from the line on specified vessels and/or for specified time periods be adopted. Consistent with this recommendation, commencing in the 2006/07 season, New Zealand fishing vessels were given permission by the New Zealand government as part of the national research plan, to trial an alternative technique. The new method (for simplicity in this paper called Method 2), required the crew to bring the skate aboard carefully, remove the hook and snood, take and record biological (and potentially other meristic data) from a sub-sample when possible, and release live skates in a timely fashion in a manner most likely to ensure survival. The advantages of this method have been the more effective scanning of the captured skate for existing tags, greater accuracy in the assessment of ideal candidates for live release, the capability to collect supporting meristic and biological data for release candidates, correct species and sex identification, and the ability to more accurately place tags on the skate body – improving the quality of skate tagging. Following favourable results aboard by New Zealand vessels using Method 2 during the 2006/07 season and following a discussion and recommendation from WG-FSA 2007 an amendment to CM 33-03 (2007) was made stating that: ‘Unless otherwise requested by scientific observers, vessels, where possible, should release skates and rays alive from the line by cutting snoods, and when practical, removing the hooks’. This paper documents the evolution of skate release methods both for tagging and for live release for New Zealand autoline vessels. It describes the current Method 2 systems in use for two New Zealand vessels. A brief analysis based on data collected from the skates treated in this manner during the 2007/08 fishery in the Ross Sea is included in the document to highlight the additional advantages in data collection possible using Method 2. This paper is intended to inform WG-FSA with additional information collected over the last two fishing seasons in preparation for the ‘Year of the Skate’ prior to a final decision on skate release protocols. A proposal is made for a comparative experiment using two tag types to inform a final decision on a standardised CCAMLR tag type for Rajid mark and recapture programmes carried out within CCAMLR Dissostichus spp. exploratory fisheries.

Ontogenetic, inter-annual and regional variations in diet were investigated in mackerel icefish, Champsocephalus gunnari, in three successive summer seasons around South Georgia. Stomachs from 2239 icefish (130-560 mm total length) were examined. A bootstrapping technique was used to calculate confidence intervals for an index of relative importance (% IRIDC) of prey categories. Diet varied significantly between years and age classes but there was little regional difference in diet. In general diet was dominated by krill, Euphausia superba and by the amphipod Themisto gaudichaudii. Smaller (younger) fish tended to prey on a higher proportion of T. gaudichaudii and small euphausids such as Thysanoessa sp. and took smaller quantities of E. superba. In a season of poor krill availability (summer of 2003-2004) the proportion of krill in the diet, stomach fullness and fish condition (indicated by length-weight relationships) were significantly lower than in the other summer seasons. The poor krill season was followed by a large reduction (> 80%) in the estimated annual biomass of C. gunnari the following year (2005). This may have been a result of mortality of age 2+ and 3+ fish, which were more krill dependent than 1+ fish. Younger fish appear to have survived, leading to an increase in the estimated population biomass in 2006.

In April 2008 the UK undertook a bottom trawl survey of CCAMLR Sub-Area 48.3 on the FV Sil, with 70 bottom trawls undertaken giving good geographic coverage. Using 10 strata and the updated sea-floor areas and adjusting this for the low headline height of the UK trawl (see CCAMLR WG-FSA (2003), the biomass of mackerel icefish was estimated to be 80,426 tonnes, with a lower 1-sided 95% CI of 30,050. Catch-weighted length frequencies indicated that icefish population was dominated by 2+ and 3+ fish, with differences in the size between Shag Rocks and South Georgia and with few small fish in the NW South Georgia area. A preliminary short-term projection of the mackerel icefish stock was run using standard CCAMLR parameters in the GYM. Two scenarios were tested, both assumed that all the 2007/08 catch that remained after the survey (1709 tonnnes) will be taken. Scenario 1, which included the 1+ fish produced yield of 3445 tonnes in Year 1 (2008/09) and 2318 tonnes in Year 2 (2009/10). In Scenario 2, in which the 1+ fish were excluded and biomass adjusted accordingly, yields were 3372 and 2248 tonnes in Years 1 & 2 respectively. The Patagonian toothfish population was dominated by the same cohort that has been detected by surveys since 2003, with no evidence of new recruitment since. Biomass estimates and length frequencies are reported for other non-target species. Conducing the survey in April was successful. The icefish appeared to be dispersed, which is amenable to a random trawl survey. There was evidence that the September 2007 survey under sampled the 2+ fish, meaning that September is not an ideal time for a survey.

Results of the survey of entanglements of Antarctic fur seals Arctocephalus gazella at Bird Island, South Georgia for the 18th consecutive winter (April to October 2007) and 20th consecutive summer (November 2007 to March 2008) are reported here. During the reporting period of 1 April 2007 to 31 March 2008 a total of 36 entangled seals were observed. Sixteen and 20 entanglements were observed in the winter and summer periods respectively. Entanglements classed as Severe or Very Severe accounted for 25% of winter and 10% of summer entanglements. During winter, synthetic string/longline material was the most commonly found item forming neck collars (44%), whereas during summer the largest proportion of entanglements were in sections of fishing net (40%). Packing bands were the second most abundant entangling material in both summer (38%) and winter (25%). The majority of entanglements (78%) involved juveniles (including pups and sub-adults), comprising 88% in winter and 65% in summer. Data for the winter period showed a decrease in the number of entanglements compared to the high levels during the previous season, but levels were still above the long term winter median (1990-2006). Data for the summer period showed a small rise in the number of entanglements compared with the previous season, but levels were slightly below the long term summer median (1989-2007).

This report details the twelfth annual survey of the incidence of entanglements of Antarctic fur seals Arctocephalus gazella and eighteenth beach survey of man-made debris at Signy Island, South Orkney Islands. Data are reported for the period 14 November 2007 to 13 March 2008. Three seals were observed with neck collars formed from fisheries related debris. Beach surveys recovered a total of 56 items weighing 11 kg, representing an increase from 2006/07 of 11% (by number) and 33% (by mass). There was a decrease in the number of plastic packaging bands with only two found in the current season (both of which had been cut open), marking a break in the otherwise continued rise in packaging bands observed. Styrofoam and other plastic waste was predominant, making up 64% of all items recorded. Fishing related debris contributed 11% of all items (9% rope and 2% trawl net webbing). These results show that the longevity of plastics and other materials with a high resistance to degradation in the marine environment remains a problem. The need for continued monitoring to ensure that vessels are aware of, and comply with, regulations prohibiting the disposal of debris at sea is paramount.

This report describes and quantifies occurrences of fishing gear, marine debris and hydrocarbons associated with seabirds at Bird Island, South Georgia for the period 1 April 2007 to 31 March 2008. It is the fifteenth such annual report. As in previous years, the majority of items (84%) of marine debris and fishing gear (mostly hooks and lines from longline fisheries) were found in association with wandering albatrosses Diomedea exulans, and very few in association with grey-headed Thalassarche chrysostoma and black-browed albatrosses T. melanophrys. Despite increased observer effort, a slight decrease was observed in the total number of items encountered (n=116) compared with the previous season. Two non-fatal entanglements involving a wandering albatross and a northern giant petrel Macronectes halli were observed, and in both cases the fishing gear was typical of that used in longline fisheries. There were no incidences of hydrocarbon soiling of seabirds during the reporting period.

During the seventeenth year of standardised beach surveys of man-made debris at Bird Island, South Georgia (covering the period 1 October 2006 to 30 September 2007) a total of 365 items were collected. This represents a reduction by 33% on the 544 items recorded in 2005/06 and a decrease in mass of 1.72 kg (32%). The distribution of debris between the summer and winter was similar to the five previous years: 73% during summer (265 items) and 27% during winter (100 items). After three consecutive years in which no fisheries related debris was observed, one nylon fishing line and one snood were found on the survey beach during the summer, plus another snood in winter (August). Both snoods were clearly identified as being the end of a multifilament line where a hook would have been attached. Five multifilament fishing lines (from longliners) were found on the beach, all during the winter fishing season. Six plastic packaging bands were recovered, suggesting that measures introduced by CCAMLR to control their use onboard fishing vessels have yet to prove entirely effective. Fifty-six pieces of trawl web were recovered, mainly during the summer period. Miscellaneous debris such as plastic sheeting, Styrofoam packaging and other plastic items comprised the greatest proportion of items removed from the study beach (96% of the total).

Preliminary analysed data obtained from bottom fishing in 1987, 1989 from Cosmonaut and Cooperation Seas. Presented frequency of occurrence of immature Dissostichus mawsoni in catches of bottom trawls and juvenile Dissostichus mawsoni in catches of mid-water trawls during krill fishing in the same regions. Some grounds of these seas are permanent feeding places of Dissostichus mawsoni.

The exploratory fishery for Antarctic toothfish (D. mawsoni) has been operating for eleven years in Subarea 88.1 and for six years in Subarea 88.2. This report summarises the large amount of data collected on toothfish and the associated bycatch by all vessels participating in the fishery. All SSRUs in the two subareas except for 88.1D and 88.2C have now been fished. The 2008 D. mawsoni catch was the fourth highest on record with a total of 2666 t against a combined catch limit of 3207 t. The management of the SSRUs within the two subareas was changed for the 2006 season as part of a 3-year experiment (SC-CAMLR-XXIV). One of the aims of the experiment was to simplify the administration of the fishery by having fewer catch limits. This appeared to be moderately successful, with only one catch limit being slightly exceeded in the 2006 season, two catch limits in the 2007 season, and none in the 2008 season. The catch limit was under caught in both Subareas 88.1 and 88.2 during the 2008 season, primarily as a result of the ice conditions. The length frequency data from the Ross Sea fishery have been very consistent over the past 3–4 seasons. There is no evidence of any truncation of the overall length frequency distribution, and no evidence for a reduction in fish length in any SSRU over time. Although moderate numbers of small fish are caught in some years (e.g., on the Shelf in 1999 and 2001), these year classes are not seen in large numbers in later years in the fishery. So at this stage there is no evidence for strong variation in year class strength in the fishery.

A previous study on the age and growth of Amblyraja georgiana in the Ross Sea suggested that these skates initially grow very rapidly for about five years, after which growth almost ceases (Francis and Ó Maolagáin, 2005). We present an alternative interpretation of age and growth in A. georgiana that is radically different from the published interpretation. By counting fine growth bands in the caudal thorns instead of broad diffuse bands, we have generated growth curves that suggest much slower growth, greater ages at maturity (about 20 years compared with 6–11 years) and greater maximum ages (28–37 years compared with 14 years). Several pieces of circumstantial evidence support the new interpretation, but a validation study is required to determine which growth scenario is correct.