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Age-dependent distribution of juvenile southern bluefin tuna (Thunnus maccoyii) on the continental shelf off southwest Australia determined by acoustic monitoring

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Juvenile southern bluefin tuna (Thunnus maccoyii, SBT) were monitored in nearshore waters off southwest Australia using acoustic tagging and monitoring over five austral summers (2002/2003–2006/2007) to determine patterns in age-based distribution of SBT. A total of 20–70 receivers were deployed in early December along one to three cross-shelf transects and at three inshore topographic features (lumps) where SBT are known to occur; and a total of 59–84 juvenile SBT (41–90 cm fork length) were tagged and released each year. After several months, receivers were recovered, and data extracted. In 2002/2003 and 2003/2004, 2-yr-old SBT were detected more frequently in nearshore areas than did 1-yr old fish. Similarly in 2004/2005 and 2006/2007, it was the larger 1-yr-old SBT that were detected more frequently at inshore lumps (>85% of detections) while small 1-yr-old SBT were detected more widely over the study area. In 2005/2006, although large 1-yr-old SBT were still detected more frequently at inshore lumps than small 1-yr old SBT, the percentage of all detections at lumps was lower at 31.5%, indicating wider distribution of both small and large age-1 fish. The observed age-dependent distribution pattern may be enhanced by the distribution of prey, which disperse or concentrate depending on the local oceanography.

Keywords: acoustic tag; inshore lumps; size/age-dependent distribution; southern bluefin tuna; southwest Australia

Document Type: Research Article


Affiliations: 1: Wealth from Oceans National Research Flagship, CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tas. 7001, Australia 2: Institute for East China Sea Research, Nagasaki University, 1551-7 Taira-machi, Nagasaki, Nagasaki 851-2213, Japan 3: Akkeshi Marine Station, Aquatic Research Station, Field Science Center for Northern Biosphere, Hokkaido University, Aikappu, Akkeshi-cho, Akkeshi, Hokkaido 088-1113, Japan 4: Graduate School of Science and Technology, Nagasaki University, 1551-7 Taira-machi, Nagasaki, Nagasaki 851-2213, Japan 5: National Research Institute of Fisheries Engineering, Fisheries Research Agency, Ebidai, Hasaki, Kamishima-gun, Ibaraki 314-0421, Japan 6: Field Science Center for Northern Biosphere, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611, Japan

Publication date: 2010-03-01

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