Thesis Part 1: Age and growth of the Antarctic toothfish (Dissostichus mawsoni) with radiometric age validation using 210Pb/226Ra disequilibria   

Abstract. Antarctic toothfish (Dissostichus mawsoni) are found in waters surrounding Antarctica, generally south of 60ºS. The Ross Sea, Antarctica is a primary Antarctic toothfish commercial fishery region. The Ross Sea is covered by sea ice year-round with the exception of the peak summer months of January and February when the sea ice breaks up enough to allow for commercial fishing operations. Since 1997 New Zealand has participated in an exploratory fishery for the toothfish during January and February when they can access the continental shelf and slope. A large international fishery has developed as a result of this exploratory fishery, with overall Antarctic toothfish landings increasing from 40 tons in 1998 to over 3500 tons in 2005. While landings increase, there is still very little published work on the age and growth of this species and no published validation studies. The most current age estimates indicate the Antarctic toothfish lives to at least 35 years of age, however this has not been validated. Because this fishery is still in its early stages, it is critical to obtain accurate age and growth estimates in order to better under the Antarctic toothfish’s life history and ensure sustainable fishery practices.

During the course of this study 1600 Antarctic toothfish otoliths will be processed according to the protocol established for Patagonian toothfish at the Center for Quantitative Fisheries Ecology (CQFE) at Old Dominion University. Otoliths will also be aged according to age estimation criteria established at the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) workshop for estimating age in Patagonian toothfish. Modifications to the protocols and criteria will be made when appropriate for catering to the differences between the otoliths of these two species. Once age estimates are obtained, radiometric age validation will be carried out using the disequilibria of lead-210 and radium-226 in the toothfish otoliths as a natural chronometer. Otoliths will be pooled according to discrete age estimates and processed to remove the core material (representing the first 3 years of growth). Radiometric ageing techniques using alpha spectrometry and TIMS or ICPMS will then be applied. This radiometric technique has a well recognized record of success as a tool for age validation and has been well established at Moss Landing Marine Laboratories (MLML). This technique has been applied at MLML for nine other species and continues to be modified and refined to pursue new species and to improve precision and accuracy. The resulting age data from this study will provide a greater understanding of Antarctic toothfish population age structure which will facilitate sustainable management of this valuable resource. This project is estimated to be completed by summer of 2007.

This project is funded through NSF Grant # 21-1509-3082 as part of the greater project “Collaborative Research: Age estimation of Toothfish in support of radiometric validation”

Sectioned toothfish otolith prepared according to CQFE methodology and viewed under reflected light. Growth increments are counted as shown above (photo from CQFE).	Typical ingrowth curve of the 210Pb:226Ra ratio. As the isotopes decay, 210Pb builds into secular equilibrium with parent isotope 226Ra over

Thesis Part 2: The relationship between Antarctic toothfish (Dissostichus mawsoni) distribution and megahabitat in the Ross Sea, Antarctica   

Abstract. The Antarctic toothfish (Dissostichus mawsoni) is one of the most important commercial species in the Southern Ocean. The Ross Sea, Antarctica, where the Antarctic toothfish is commercially fished, has been geologically characterized by a tectonics and glacial processes. These processes have created diverse habitat including distinct banks and basins. Antarctic toothfish habitat associations and spatial distributions are poorly understood yet may play a role in its distribution and abundance. In a preliminary study a habitat map was created for the Ross Sea, Antarctica in ArcGIS®. Toothfish catch data were placed over the map to understand the relationship between abundance and megahabitat. The resultant map showed that toothfish associate with the continental shelf megahabitat, with largest catches occurring towards the edge of the Ross Sea ice sheet. Since the preliminary study I have obtained higher resolution bathymetric data which will allow me to characterize the Ross Sea habitats in greater detail (at least meso-habitat resolution). The final product will show the relationship between toothfish age (obtained in Part 1 of my thesis) and habitat and provide insight into the spatial distribution of this species throughout their life history. This project is estimated to be completed by fall of 2007.

This project is funded through NOAA Grant # 25-1509-3599 in partial fulfillment of the Environmental Entrepreneurship Program (EEP)

Links:   

CCAMLR

CQFE

EEP