CCAMLR

Otolith chemistry has been successfully used to reconstruct the environmental history experienced by estuarine-dependent teleost fish, including movement between estuaries and coastal areas. However, application has been more limited in species exposed exclusively to oceanic waters, where gradients in physical and chemical properties are less extreme. To test whether otolith elemental signatures record spatial information in an oceanic species, we sampled otoliths from Patagonian toothfish (Dissostichus eleginoides), and used an inductively coupled plasma-mass spectrometer (ICP-MS) coupled to a laser ablation system to target the outer otolith edges corresponding to the period immediately prior to capture. Using multivariate analysis of variance and multivariate discriminant analysis, we found edge signatures discriminated toothfish by geographic region with near complete success: only 5% of fish caught off South America and in the Antarctic were misclassified to sampling areas in the other region. Moreover, edge signatures showed strong differences between sampling areas within each region: fish captured off South America classified to sampling areas therein with 79-84% success, and Antarctic fish to sampling areas therein with 50-67% success. These results compare favourably with rates of classification for estuarine-dependent fish, demonstrating that otolith elemental signatures can discriminate the geographic provenance of oceanic as well as estuarine-dependent fish.

Otolith chemistry has been successfully used to reconstruct the environmental history experienced by estuarine-dependent teleost fish, including movement between estuaries and coastal areas. However, application has been more limited in species exposed exclusively to oceanic waters, where gradients in physical and chemical properties are less extreme. To test whether otolith elemental signatures record spatial information in an oceanic species, we sampled otoliths from Patagonian toothfish (Dissostichus eleginoides), and used an inductively coupled plasma-mass spectrometer (ICP-MS) coupled to a laser ablation system to target the outer otolith edges corresponding to the period immediately prior to capture. Using multivariate analysis of variance and multivariate discriminant analysis, we found edge signatures discriminated toothfish by geographic region with near complete success: only 5% of fish caught off South America and in the Antarctic were misclassified to sampling areas in the other region. Moreover, edge signatures showed strong differences between sampling areas within each region: fish captured off South America classified to sampling areas therein with 79-84% success, and Antarctic fish to sampling areas therein with 50-67% success. These results compare favourably with rates of classification for estuarine-dependent fish, demonstrating that otolith elemental signatures can discriminate the geographic provenance of oceanic as well as estuarine-dependent fish.

This paper follows preliminary work in 2005 and early 2006 in developing an integrated assessment for Patagonian toothfish in Division 58.5.2. It focuses on developing an integrated assessment using CASAL and demonstrates that all of the data available for assessments, including surveys, fishery catch-at-length data, standardised catch-per-unit-effort (CPUE) series for trawl grounds, and length-binned mark-recapture data, can be incorporated into the model. Earlier difficulties in using CASAL have been resolved. The results presented here indicate a general downward bias in the expected recaptures showing that the mark-recapture observations indicates a smaller stock size than the other datasets. This is consistent with the problems discussed of the potential bias of a single-area model in trying to cover a highly spatially structured stock. It is recommended that the mark-recapture data not be included in the assessment of D. eleginoides in Division 58.5.2 until the spatial structure of the mark-recapture program can be incorporated appropriately in the assessment. The assessment of long-term annual yield using CASAL, 2,306 tonnes, is less than that using the GYM, 2483 t. The reasons for this difference are discussed. We conclude that an integrated assessment using CASAL is possible for Dissostichus eleginoides in Division 58.5.2. However, as expected, the assessment will be sensitive to the inclusion of different datasets and to the choices of parameters used in both the stock assessment and projections. An important outstanding issue, relevant to stock assessments generally, is the need to provide an estimate of natural mortality. It is suggest that the assessment not include tagging data at this stage and that yields be estimated by integrating across uncertainties in natural mortality. It is also recommended that work be undertaken to understand the spatial dynamics of D. eleginoides in the region and, therefore, how best to incorporate mark-recapture data in the assessment. Until that time, recruitment surveys provide the best means of establishing current stock status.

Killer whales (Orcinus orca), sperm whales (Physeter macrocephalus) and fur seals (Arctocephalus sp.) interactions with longlines fishing operations were reported by observers onboard of fishing vessels, catching Patagonian tooshfish in the Crozet and Kerguelen Exclusive Economic Zones, between 2003 and 2005. In Crozet waters, 71% of the 1308 longlines presented marine mammals interactions with killer whales and/or sperm whales. On the other hand, fur seals and/or sperm whales were present in 54% of the 6262 longlines monitored in the Kerguelen waters. Interactions occurred over the whole fishing areas even if contrasted situations regarding the marine mammal species are observed between localities. Depredation effect was assessed by comparing CPUEs of the longlines, in absence/presence of any marine mammals species alone or in association. In Crozet waters, the CPUE was found to be reduced by both killer whales and sperm whales presence by themselves or associated. An important photo-identification effort mainly dedicated to killer whales allowed to identify 103 individuals. However, few individuals are responsible for most of the interactions with the fishery. In Kerguelen waters CPUE tended to decrease in presence of sperm whales alones or in association with fur seals.

Protocol for observing warp strikes in trawl fisheries

Form used with protocol for observing warp strikes in trawl fisheries

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, CPUE, catch-at-age and tag-recapture data from New Zealand vessels. The updated reference case resulted in a much higher estimate of initial biomass, though this appeared to be almost entirely due to the impact of the catch-at-age data from the shelf fishery. Parameterising the model to better explain these data resulted in estimates of initial and current biomass that were very similar to those presented in 2005. The inclusion of the 2005 tag-release and the 2006 tag-recapture data had a small effect that slightly modified estimates from the models, suggesting that the new data had a similar pattern to that of previous years.
Preliminary models using tag-recapture data from all vessels are also presented. Inclusion of all vessels tagging data resulted in a more optimistic assessment, and was due to the increased numbers scanned but smaller increase in the reported numbers recaptured. The reason for this is unclear, however, a number of the recaptured tags were not able to be linked to a release due to non-availability of some release data from non-New Zealand vessels. Further investigation is recommended.
Overall, model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested little evidence of non-convergence. MCMC estimates of initial (equilibrium) spawning stock abundance (B0) for the preferred model were 80 510 t (95% C.I.s 59 920–119 920 t), and current (B2006) biomass was estimated as 87% B0. Estimated yields, using the CCAMLR decision rules, were estimated to be 3046 t.

The ASPM is an integrated modeling technique used in stock assessment of different D. eleginoides fisheries (Prince Edward Islands and Patagonian Shelf) and allows fitting to many different information sources, such as catch and age and size data from fishing fleet, surveys and others abundance indexes. Last results obtained from ASPM model used to assess the D. eleginoides biomass at CCAMLR Subarea 48.3 shows an acceptable fit to CPUE series and catch-length-proportions (WG-FSA-SAM 05/5 and WG-FSA-05/73). In this paper the methodology and assumptions for the 2006 TOP assessment at CCAMLR Subarea 48.3 using ASPM are presented.

The ASPM assessment of the Prince Edward Islands toothfish resource by Brandão and Butterworth (2005) 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 has become available for the years 2005 and 2006. The assessment allows for a second fleet to accommodate data from a pot fishery that operated in 2004 and 2005. Updated biological parameter values for Subarea 48.3 are incorporated and lead to less optimistic results. The resource is estimated to be at about 40% of its average pre-exploitation level in terms of spawning biomass. It is suggested that it would be prudent to restrict annual legal catches to 500 tonnes or less, unless a large proportion of the catch is to be taken by pots (which avoid the cetacean predation associated with longlining). Specific issues raised at WG-FSA-SAM 2006 about this assessment are addressed.

In this paper we analyse data on the distribution of catches, the size of krill and bycatch of larval fish taken by the Saga Sea fishing with continuous trawls in 2006, and the Atlantic Navigator which fished in 2005 using both continuous trawling and conventional trawling. The sizes of krill caught by both conventional and continuous trawling techniques appear to be very similar. Although there are few data for comparison, the bycatches of larval/juvenile fish in the continuous trawl also appear to be the same as those from conventional trawls.