Interannual variation in summer habitat utilization by juvenile southern bluefin tuna (Thunnus maccoyii) in southern Western Australia
The spatial habitat utilization of juvenile southern bluefin tuna in southern Western Australia was investigated using automated acoustic receivers with acoustic transmitters implanted in tagged fish during three austral summers (2004/2005, N = 79 fish, 2005/2006, N = 81, 2006/2007, N = 84). Seventy acoustic receivers were deployed at three cross-shelf lines and three coastal topographic features (lumps) between December and May. We observed markedly different patterns of habitat utilization between the three seasons: (i) aggregation at lumps in 2004/2005 and 2006/2007, and (ii) wide distribution over the continental shelf (i.e., few occurring at lumps) in 2005/2006. Vertical profile by conductivity-temperature-depth casts showed these spatial shifts were caused by interannual changes in the presence of sub-Antarctic water. The sub-Antarctic water was present in the subsurface layer close to the continental slope only during 2005/2006, and the area had higher chlorophyll-a concentrations than the coastal areas, including at the lumps. These environmental characters, related to the nutrient rich sub-Antarctic water, appear to have a strong influence on fish distributions in 2005/2006, and may occur generally during La Niña events. Interannual fluctuations in habitat utilization will influence detection of fish in recruitment monitoring surveys and thus bias the resulting juvenile abundance indices.
Document Type: Research Article
Affiliations: 1: CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, Tas. 7001, Australia 2: Institute for East China Sea Research, Nagasaki University, Taira-machi, Nagasaki 2213, Japan 3: Field Science Center for Northern Biosphere, Hokkaido University, Minato-cho, Hakodate 041-8611, Japan 4: Graduate School of Environmental Science, Hokkaido University, Minato-cho, Hakodate 041-8611, Japan 5: National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Shimizu, Shizuoka 424-8633, Japan 6: National Research Institute of Fisheries Engineering, Fisheries Research Agency, Hasaki, Kamisu 314-0408, Japan
Publication date: 2010-05-01