Collaborative Research: Radiometric Age Validation of the Patagonian and Antarctic Toothfishes (Dissostichus Eleginoides and D. Mawsoni)
Recent years have seen the re-establishment of large-scale marine resource utilization by humans in the Antarctic. In contrast to early sealing and whaling activity, the modern impact is directed on krill and finfish populations, most notably of the Patagonian toothfish (Dissostichus eleginoides), but also its congenor the Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea. Toothfish are a valuable resource and are likely to continue to command a high price in world markets. However, extensive illegal fishing has lead to considerable concern that Patagonian toothfish populations are being over-harvested. In other parts of the world, over-harvesting of larger, commercially valuable species has led to fishing down of marine food webs, leaving impoverished, less valuable ecosystems. The goal of the Convention for the Conservation of Antarctic Marine Living Resources, part of the Antarctic Treaty System, is to allow harvest while avoiding disruptions to the Antarctic ecosystem. To achieve this, the sustainable management of the fishery depends on reliable age data. Age data allow population age structure to be modeled, so that growth, mortality and recruitment rates can be estimated and used to understand population dynamics. Age data provides the basis to determine the life history pattern of a species, to model population dynamics, and to determine which age classes are vulnerable to over-exploitation under a particular set of environmental conditions. Current age and growth information for toothfish is based on age determination methodologies which are not validated and depend on the specific laboratory and principal investigator. Recently, the Commission of the Conservation of Antarctic Marine Living Resources has endorsed three preparation methodologies using otoliths and a common set of criteria for estimating age from otolith micro-structure. The CCAMLR Otolith Network has also been initiated as a medium for exchanging samples to ensure that age estimates are comparable between readers and laboratories. However, considerable work is needed to ensure that age estimates generated by the three methodologies are accurate. One technique that has been successful is radiometric age determination, which uses the disequilibria of lead-210 and radium-226 in otoliths as a natural chronometer. This proposal brings together an international collaboration to examine population age structure for both toothfish species, in an experimental design built around radiometric validation tests of age data generated by all three preparation methodologies. To integrate the validation component within an Antarctic-wide effort to examine toothfish population age structure, sub-samples for validation work will be drawn from sample sets taken for population age studies by research teams working in Australia, New Zealand, the United Kingdom and France, as well as the United States. Scientists at Moss Landing Marine Laboratories will use radiometric age determination to independently age otoliths from Patagonian and Antarctic toothfishes. Scientists at Old Dominion University will use a system already established for aging to generate validated age data, allowing growth, mortality, and longevity to be estimated by geographic areas. The project will provide validated otolith sample sets that can be used as a foundation for a unified and validated age estimation system for the toothfishes. This study will provide information which will be disseminated to the public, policy-makers and the international community. The project will provide opportunities for under-represented students at both universities.
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