CCAMLR

Since the commencement of commercial fishing in Australian waters on the Heard Island plateau in 1997 an annual random stratified trawl survey (RSTS) has been conducted to assess the stocks of Patagonian toothfish (Dissostichus eleginoides) and mackerel icefish (Champsocephalus gunnari). The 2007 survey had two main aims:
• to assess the abundance of juvenile and adult Dissostichus eleginoides on the shallow and deep parts of the Heard Island Plateau;
• to assess the abundance of Champsocephalus gunnari on the Heard Island Plateau.
The survey had the same design as the 2006 RSTS survey in the number of stations chosen for sampling in each stratum. This paper describes the conduct of the survey on the FV Southern Champion during June to July 2007 and the resulting catches and biological sampling. The most abundant species in the catch was D. eleginoides, followed by Lepidonotothen squamifrons, Channichthys rhinoceratus, C. gunnari and Macrourus sp. Catches of these 5 main fish species were very similar to those in 2006, with the exception of Lepidonotothen squamifrons which was much more abundant in 2007. Holothurians, poriferans, medusae and anemones were the most common invertebrate biota caught in the net.

Scientific observers aboard vessels in the Australian fisheries in 58.5.2 have collected Dissostichus eleginoides otoliths since the fishery commenced in the 1996/97 season. This program has yielded data which has assisted with understanding age structure and growth rates of toothfish in this Division. This paper summarises the otolith collection housed at the Australian Antarctic Division, including individuals collected during research and commercial fishing, tag recaptures, and those individuals which have been processed by the Central Ageing Facility to provide size-at-age estimates. Over 21000 otoliths have been collected from toothfish in 58.5.2, and more than 2500 otolith pairs have been collected from recaptured tagged fish. More than 3200 otoliths have been processed to provide size-at-age estimates from fish captured between 1997 and 2003. A growth model based on these size-at age data is currently used in the assessment to predict growth and assign length-at-age to catch-at age, however an alternative method to assign catch at age is age-length keys. Relatively few otoliths have been collected or aged from the annual trawl survey or the longline fishery, making constructing historical season by season age-length keys for these fisheries impossible. It is likely that sufficient otoliths have been collected from the main trawl ground to construct age-length keys, however the feasibility and benefit of proceeding to age-length keys in terms of precision of stock assessment requires simulation analysis.

In 2006 the CCAMLR scientific committee noted several features of exploratory Dissostichus fisheries in the southern Indian Ocean (58.4) which gave cause for concern as to the status of the resource in this area, and the lack of a scientific basis for setting catch limits in these areas (SC-CAMLR XXV, paragraphs 4.184-4.192).
In its management advice for this and other exploratory fisheries, the Scientific Committee requested urgent consideration by Members of methods for collecting data and of assessing these stocks.
At its meeting in July 2007, WG-SAM agreed that fine-scale analysis of catch and effort would be a useful way of progressing an assessment of BANZARE fishery (WG-SAM 2007, paragraphs 3.1-3.7), including:
• Identification of grounds through analysis of spatial pattern in catch and effort;
• Exploration of standardising CPUE series for each ground; and
• Analysis of CPUE of Dissostichus spp. to provide initial estimates of biomass and rates of depletion in each ground.
This paper develops further the initial exploration of the C2 fine scale catch and effort data held by CCAMLR for the fishery in this Division presented to WG-SAM in 2007, as well as descriptive analyses of the B2 biological data submitted by scientific observers aboard vessels in the BANZARE fishery.
Data were too few, or with insufficient overlap between seasons, to permit meaningful standardisation for depletion analysis. However, these preliminary analyses indicate there is strong evidence for depletion of toothfish at the scale of individual fishing grounds in 2004/05 and 2005/06 seasons. There are also several inconsistencies noted between historical catch rates and catch compositions and those reported in the 2006/07 season, with Patagonian toothfish dominating in catches in one ground for the first time, and some observers reporting no biological information on important bycatch groups reported in the vessels catch records.
We recommend that WG-FSA evaluate management options in 58.4.3b, including the lowering of catch limits commensurate with the rapid and unsustainable depletion seen in the fishery, the development of SSRUs to better represent the concentrated nature of the fishery in 58.4.3b, commensurate management of areas that are obviously depleted, and the design of a longline survey to attempt to verify some of the trends in catch rates and catch composition seen in the main fishing areas.

Preliminary results of testing of a PIT-D device for autonomous measurements of temperature and pressure at deepwater longline fishery of Antarctic toothfish D. Mawsoni in the Ross Sea during the fishing season of 2006/07 are presented. Diagrams of a Spanish-type longline sink rate at deployment and water temperature on various horizons are shown.

Experiments were carried out on two fishing trawlers to test whether mincing all waste to a paste before it was discharged reduced the number of seabirds around the vessels. The first trial was on a mid-water trawler targeting hoki (Macruronus novaezelandiae), and the experiment on this trip compared three treatments (1) mincing all waste (2) discharging unprocessed waste and (3) mealing all waste and reducing discharge to sump water. The second vessel was bottom-trawling for squid (Nototodarus sloanii). There was no meal plant on board and the mealed treatment was replaced with a batching treatment (4) where waste was held and discharged in batches. The response to the experimental treatments was determined by counting the number of birds within a 40m-radius semi-circular sweep zone behind the vessel stern. Results from the first experiment showed that mincing reduced the numbers of large albatross (Diomedea spp.) feeding around the vessel, but had no significant effect on other groups of seabirds. In contrast, mealing all waste had a marked effect on several of the bird groups. In particular, the abundance of small albatross (principally Thalassarche spp.) within the sweep area was reduced to 5% of the number that were there when unprocessed waste was discharged. On the second trial a smaller mincer was used. The vessel was bottom trawling, and there were problems with rocks going through the waste stream. The batched treatment was compromised by the limited ability of the vessel to hold waste, with only a 10 to 20 minute delay between discharge events being achieved. Despite low numbers of observations on the second trial, the minced treatment suggested a reduction in the numbers of all albatross within the observation area.

A preliminary field identification guide to the main fishes caught by toothfish longline boats fishing in the Ross Sea was prepared under the New Zealand Ministry of Fisheries Project ANT2005-02 and was used by Ministry of Fisheries observers and fishers during the 2006–07 season. That guide was revised in 2007 following comments and suggestions from the users and now covers 27 taxa. Mostly it provides information for identification to species but for liparids (snailfishes), zoarcids (eelpouts) and bathydraconids (dragonfishes) identification is at family level and for Muraenolepis (eel cods), and Pogonophryne (plunderfishes) identification is to genus. Identification to species for some fishes is difficult because of uncertain taxonomic status, e.g., Pogonophryne, or scarcity of field characters, e.g., liparids. Some species likely to be seen only in stomach contents of other fishes are included. Future revisions could be made as taxonomic issues are resolved, and more species are recorded from the Ross Sea. Data and images are stored on a relational database to facilitate revision and easy information retrieval.

The descriptive analyses of the toothfish tagging programme carried out in Subareas 88.1 and 88.2 since 2001 are updated, including data for the 2007 season for all vessels. This paper provides an update of the preliminary tag-release and tag-recapture data that were presented at the July 2007 meeting of WG-SAM by including revised data and data from non-New Zealand vessels that fished in 2007.
Overall, a total of 15 088 Antarctic toothfish have been reported as released and 458 recaptured, and 911 Patagonian toothfish released and 43 recaptured since 2001.
The number of tags recaptured in the Ross Sea in 2007 by New Zealand vessels was the highest annual recapture to date and double the number caught in 2006, although the nature of these recaptures suggests that assumptions of homogeneous mixing may need to be investigated. For the first time, long distance movements of Antarctic toothfish were observed from toothfish tagged by fishing vessels. Six fish moved 400–600 km from the slope fisheries in SSRUs 88.1H, 88.1I, and 88.1K to grounds off Terra Nova Bay and Ross Island in SSRU 88.1J. There was also some evidence that more fish are recaptured after a longer time at liberty on the slope than in the North. In addition, a Patagonian toothfish tagged near Macquarie Island was recaptured in the north of the Ross Sea, after 4 years at liberty.
Analysis of tag recapture rates suggested some evidence that rates between New Zealand and non-New Zealand vessels were different, and further, that the rate that tags were recaptured from vessels of different nations were different. The reason for these differences is unclear, but may related to different survival rates of fish tagged by different vessels, different detection rates of tagged fish on different vessels, and/or incomplete spatial mixing of the fish tagged by different vessels in different local regions. Further investigation is required.

Skates are an important bycatch of the toothfish fishery in the CCAMLR area and have been identified as priority taxa for which assessments of status are required (e.g., SC-CCAMLR XXIII 2004, paragraphs 4.172, 4.177 and 4.199). While Dunn et al. (2007) and Agnew et al. (2007) have developed preliminary assessment models for skates, they also highlighted that further information was required before a full assessment can be carried out. In 2007, CCAMLR-SAM-WG recommended (CCAMLR XXVI WG-SAM paragraph 8.10) a review of data requirements and a “Year of the Skate” for 2008–09 whereby data collection effort on bycatch will be concentrated on skate species in that year in order to inform a full skate assessment.
This paper discusses improvements to the fishery derived data that may be required to better inform an assessment of Ross Sea skates. We propose options for the appropriate collection of such data from the fishery and a revised skate tagging protocol. These changes could be piloted in the 2007–08 season by all or a subset of vessels fishing in the Ross Sea. The results from the pilot study may be useful to inform modifications to data collection systems that would be required in 2008–09, for the “Year of the Skate”. Note that we do not consider other information requirements such as determining biological parameters.

The results of the histological analysis of the Antarctic toothfish (Dissostichus mawsoni) gonad structure, caught in December-February, 2004-2005, by longliner YANTAR in subareas 88.1 and 88.2 of the Ross Sea are presented. The morphological parameters and indices of maturity have been described. The histological criteria of the assessment of the ovary maturity stages, cytological parameters of oocytes and type of the toothfish oogenesis have been determined. The analysis of the histological state of toothfish testes has been made, and the abnormal primary fusion renal and generative tissues in testis have been revealed. It was shown that for Antarctic toothfish during the fishing period the females with ovaries on the early III stage of maturity were dominated (47.0%), and males with testis on III stage of maturity (85.7%).

We provide an update of the Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea (Subareas 88.1 and SSRUs 88.2A–B), using revised catch, catch-at-age, and tag-recapture data for the 2007 season. The updated reference model resulted in a slightly lower estimate of initial biomass than the 2006 base case. The inclusion of the 2007 recaptures of 2006 tags released had the most substantive impact on the model estimates.
Models using tag-recapture data from all vessels are also presented. Inclusion of all vessels tagging data resulted in a more optimistic assessment. The more optimistic estimate was probably due to the lower recapture rate by non-New Zealand vessels, particularly in the early years. The reason for this is unclear, and may be related to different distributions of fishing effort by different vessels, to poorer survival of tagged fish, or to poorer detection rates. However, if data from all vessels was restricted to 2007 recaptures of 2006 releases, then model estimates were more similar to the 2007 reference model.
Overall, model fits to the data were adequate, and, as in previous assessments, the tag-release and recapture data provided the most information on stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested little evidence of non-convergence in the key biomass parameters. MCMC estimates of initial (equilibrium) spawning stock abundance (B0) for the 2007 reference model were estimated as 71 200 t (95% C.I.s 59 570–87 900 t), and current (B2007) biomass was estimated as 81.9% (78.4–85.4%). Estimated yields for the reference case, using the CCAMLR decision rules, were 2700 t.
Similar estimates of initial biomass and yield were obtained for models where the north fishing selectivity was assumed to be logistic (median B0=78 480 t, yield=2988 t), and where the 2007 recaptures from all vessels were added to the New Zealand tag-release and recapture data (median B0=81 100 t, yield=3099 t). If tag-release and recapture data for all vessels in all years were used, then the estimated initial biomass was higher (B0=110 130 t), and corresponding yields were also higher (yield=4200 t).