Ontogenetic and seasonal variations in the feeding ecology of Indo-Pacific sailfish, <i style="mso-bidi-font-style:normal">Istiophorus platypterus</i> (Shaw, 1792), of the eastern Arabian Sea

Abstract

<span style="mso-bidi-font-weight:bold" lang="EN-GB">Present study consists the studies on the stomach contents of Indo-Pacific sailfish, <i style="mso-bidi-font-style:normal">Istiophorus platypterus </i>(Shaw, 1792), caught during tuna longline survey conducted in the western Indian EEZ (eastern Arabian Sea) between 2006 and 2009 to investigate the sexual, ontogenetic and seasonal effects in the diet. Stomachs of 290 specimens in the forklength range of 101-261 cm were examined, of which 38 (13.10%) were empty. Prey composition was assessed in terms of occurrence by number, frequency of occurrence, weight and Index of Relative Importance. Quantile regression techniques were used to determine the mean and upper and lower bounds of the relation between prey size and sailfish length. Diet was dominated by teleost fishes, followed by cephalopods while crustaceans were represented in limited instances. Purpleback flying squid, <i style="mso-bidi-font-style: normal">Sthenoteuthis oualaniensis</i>, was the most preferred prey species. Other important prey species identified were <i style="mso-bidi-font-style: normal">Euthynnus affinis</i>, <i style="mso-bidi-font-style:normal">Cubiceps pauciradiatus</i>, <i style="mso-bidi-font-style:normal">Gempylus serpens</i> and <i style="mso-bidi-font-style:normal">Onychoteuthis banksii</i>. Diet did not varied by sex, but the ontogenetic and seasonal variations in diet were significant. The maximum and mean size of prey increased with length of sailfish. However, relatively smaller prey constituted bulk of sailfish diet and even large specimens consumed small prey.

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