Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (D. mawsoni) are widely sold in the North American market as Chilean sea bass. On the basis of genetic evidence, toothfish are managed as discrete stocks within sub-areas frequently corresponding to island groups under the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), and by neighboring national authorities. Management as discrete stocks assumes that each represents a closed population driven by its own births and deaths, and any vagrants are effectively lost. There is increasing evidence that toothfish can move considerable distances; however, rates of movement have proved difficult to examine. The elemental structure of growth increments in fish otoliths reflects the composition of water passing across the gills, and therefore the environment in which a fish is located; the growth increments also provide a chronological record of the life history up to capture. Otolith trace element signatures serve as a record of a fish's location in the past, and laser-based Inductively-Coupled Plasma Mass Spectrometry has been used by the principal investigators to examine elemental signatures in the otoliths of Patagonian toothfish (Dissostichus eleginoides), and to identify significant differences between management areas. Using this technique to sample the location on the otolith corresponding to the known date and site of capture, elemental signatures will be characterized over time and across the major areas of toothfish concentration in the Southern Ocean. Using toothfish taken recently, the elemental signatures recorded in the otolith during the life history will be compared with the corresponding spatial signatures determined in the ground-truthing analysis. Divergence between the two signatures will indicate that fish originated from outside the area of capture. The elemental data will then be used to estimate the proportion of fish currently in the population that have immigrated, and the life stage during which they migrated. By collecting otoliths and genetic samples from each fish, otolith microchemistry will be used to identify source populations and make effective use of multilocus data to not only characterize the distribution of genetically distinct stocks, but also to provide baseline data for estimating admixture proportions. By developing a set of chemical and genetic markers for both species, a comprehensive characterization of source populations and an accurate estimation of admixture proportions will be provided. As part of this research, international collaborations will include scientists working in the high Antarctic. This work will draw on these collaborations to further the integration of physical-biological components to clarify boundaries to the movement of toothfish. The project will provide scientific data will be of value in the Antarctic Treaty system on managing resources in the Southern Ocean. This proposal will also involve development of interdisciplinary studies that include minority and underrepresented, undergraduate, and graduate students.
