Abstract
Abstract As part of a larger project on the feeding ecology of large pelagic predators off the Bay of Biscay, this study analyses the diet of the swordfish, Xiphias gladius. Stomachs were collected from 86 swordfish. The diet was analysed in terms of prey occurrence, relative abundance, reconstituted mass, and size distribution. It consisted mainly of fish, 40.5% by mass (%M) and cephalopods, 59.3%M; crustaceans, 0.2%M, were considered secondary prey. When considering only the fresh fraction to allow for differential digestion rates, these figures were 77.3%M, 22.7%M, and trace amounts, respectively. Lanternfish, including Notoscopelus kroeyeri and Symbolophorus veranyi, were abundant, but paralepidids, Atlantic pomfret (Brama brama), and the squid Todarodes sagittatus, Ommastrephes bartramii, and Gonatus steenstrupi, dominated the diet by mass. The overall prey size range was 11–1420 mm, but sizes of 60–360 mm accounted for 80% of the distribution by number and of 140–760 mm for 80% of the distribution by mass. Intraspecifically, larger swordfish ate larger prey as a result of a change in species composition of the diet. The swordfish appears to show feeding plasticity both between different areas and between animals in the same area.
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