Journal
FISHERIES OCEANOGRAPHY
Volume 18, Issue 4, Pages 237-254Publisher
WILEY
DOI: 10.1111/j.1365-2419.2009.00509.x
Keywords
archival tags; habitat characterisation; pelagic habitat use; seasonal migrations; south Indian Ocean; southern bluefin tuna
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Funding
- Japan Marine Fishery Research Resource Center (JAMARC)
- Commonwealth Scientific and Industrial Research Organisation (CSIRO)
- Australian Fisheries Management Authority (AFMA)
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Electronic tagging provides unprecedented information on the habitat use and behaviour of highly migratory marine predators, but few analyses have developed quantitative links between animal behaviour and their oceanographic context. In this paper we use archival tag data from juvenile southern bluefin tuna (Thunnus maccoyii, SBT) to (i) develop a novel approach characterising the oceanographic habitats used throughout an annual migration cycle on the basis of water column structure (i. e., temperature-at-depth data from tags), and (ii) model how the vertical behaviour of SBT altered in relation to habitat type and other factors. Using this approach, we identified eight habitat types occupied by juvenile SBT between the southern margin of the subtropical gyre and the northern edge of the Subantarctic Front in the south Indian Ocean. Although a high degree of variability was evident both within and between fish, mixed-effect models identified consistent behavioural responses to habitat, lunar phase, migration status and diel period. Our results indicate SBT do not act to maintain preferred depth or temperature ranges, but rather show highly plastic behaviours in response to changes in their environment. This plasticity is discussed in terms of the potential proximate causes (physiological, ecological) and with reference to the challenges posed for habitat-based standardisation of fishery data used in stock assessments.
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