CCAMLR

In the beginning of February 2005, during the hauling of bottom-set longline in the Ross Sea (East Antarctic) from the depth of 1480 m to the surface a very large squid taken a large individual of Antarctic toothfish D. mawsoni (Norman, 1937) with a size of 160 cm and weight of 58 kg caught by a longline hook, was hauled up to the board of longliner VOLNA. Squid was very active and did not release its prey until under command of fish master it was beaten off by gaffs. Squid was not lifted aboard but it was registered with the use of photo- and video cameras. This allowed to determine its species belonging and size. On the opinion of the most competent specialist on squids in the Southern Hemisphere Yu.A. Philipova and our comparative observations this was giant squid Mesonychoteuthis hamiltoni (Robson, 1925).

Otolith nucleus chemistry resolved the population structure of Patagonian toothfish (Dissostichus eleginoides), an exclusively marine species, along the Patagonian Shelf and North Scotia Ridge out to South Georgia in the Southern Ocean. Concentrations of 55Mn, 88Sr, and 137Ba, ratioed to 42Ca, showed a sharp population boundary in the vicinity of the Polar Front, between South Georgia and the North Scotia Ridge. These results validated otolith nucleus chemistry as a technique for examining population structure in Patagonian toothfish, demonstrating that otolith nucleus chemistry can discriminate between populations even in fully marine environments. Moreover, the nucleus chemistry indicated population heterogeneity not previously detected, suggesting the possibility of more than one South American population; and also suggested some South American-caught fish had moved from South Georgia.

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