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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| Authors: | KENTARO HONDA ALISTAIR J HOBDAY RYO KAWABE NAOKI TOJO KO FUJIOKA YOSHIMI TAKAO KAZUSHI MIYASHITA |
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| Institution: | 1. Graduate School of Environmental Science, Hokkaido University, 3‐1‐1 Minato‐cho, Hakodate, Hokkaido 041‐8611, Japan;2. Wealth from Oceans National Research Flagship, CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tas. 7001, Australia;3. Institute for East China Sea Research, Nagasaki University, 1551‐7 Taira‐machi, Nagasaki, Nagasaki 851‐2213, Japan;4. Akkeshi Marine Station, Aquatic Research Station, Field Science Center for Northern Biosphere, Hokkaido University, Aikappu, Akkeshi‐cho, Akkeshi, Hokkaido 088‐1113, Japan;5. Graduate School of Science and Technology, Nagasaki University, 1551‐7 Taira‐machi, Nagasaki, Nagasaki 851‐2213, Japan;6. National Research Institute of Fisheries Engineering, Fisheries Research Agency, Ebidai, Hasaki, Kamishima‐gun, Ibaraki 314‐0421, Japan;7. Field Science Center for Northern Biosphere, Hokkaido University, 3‐1‐1 Minato‐cho, Hakodate, Hokkaido 041‐8611, Japan |
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| Abstract: | 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. |
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| Keywords: | acoustic tag inshore lumps size/age‐dependent distribution southern bluefin tuna southwest Australia |
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