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Free Content Feeding ecology of broadbill swordfish, Xiphias gladius, off eastern Australia in relation to physical and environmental variables

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Abstract:

We examined the feeding ecology of broadbill swordfish, Xiphias gladius (Linnaeus, 1758), from eastern Australian waters through the analysis of gut contents of 638 fish (size range 660–2450 cm orbit to fork length) collected between 1997 and 2005, the results of which were compared with a suite of oceanographic and environmental variables from the region. Cephalopods with an index of relative importance (%IRI) of 61.65% dominated the prey followed by fish (38.10 %IRI); crustacea were eaten rarely (< 1% IRI). A total of 56 prey taxa was identified, consisting mainly of cephalopods dominated by Ommastrephes bartramii (Lesueur, 1821). The main fish prey were from the families Nomeidae and paralepididae. Size of fish, year, area, and sea surface fluorescence were significantly correlated with feeding activity. In particular, swordfish taken in nutrient-rich offshore waters had a significantly higher prey mass than those from more oligotrophic inshore waters associated with the East Australia Current. Cephalopods dominated the prey offshore whereas fish were the main group in inshore waters. Stable isotope analysis indicated that δ15N increased significantly with fish size (r2 = 0.65), paralleling a change in diet from fish with low δ15N values to cephalopods with relatively high values.

Document Type: Research Article

Publication date: November 1, 2006

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  • The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.
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