| Summary: | An important prerequisite of sustainable fisheries management is knowledge about the spatial structure of fish populations. Such information provides a basis for understanding population dynamics and connectivity as well as posing questions around a speciesˈ resilience to ongoing fishing pressure. For Antarctic toothfish (Dissostichus mawsoni), a bentho-pelagic fish species with a spatial distribution that encompasses much of the Southern Ocean south of about (60°S), aspects around population structure and connectivity are still uncertain. The basis of this study was to gain a better understanding of Antarctic toothfish population structuring across spatially discrete fishing areas located around the Antarctic continent. The primary aims were therefore to determine whether patterns of connectivity between these areas were evident and whether source or sink areas for toothfish existed across its Southern Ocean distribution which would be a key understanding towards effective management of toothfish populations. To that end, this study used fish otoliths (ear bones) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) to determine life history aspects of Antarctic toothfish. The first research chapter (Chapter 2) tests the efficacy of otolith microchemistry techniques by determining if otolith edge chemistry (corresponding to recent capture) could distinguish toothfish fishery grounds. Fish otoliths were obtained by scientific observers on board longline vessels operating across spatially discrete fishing areas in the Ross Sea (RS), Amundsen Sea (AMS), Southern Atlantic Ocean (SAO) and Southern Indian Ocean (SIO). Based on four elements (Al, Mg, Ba and Sr), significant spatial heterogeneity was shown among most regions indicating the water masses were quite different. The strongest patterns of separation were between the RS and SAO where significantly lower Sr compositions in the Ross Sea corresponded with a lower salinity water regime consistent with large scale freshening events within the Ross ...
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