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Trophic ecology of the shortfin mako Isurus Oxyrinchus (lamniformes: Lamnidae) in the eastern Pacific ocean

Abstract:

Shortfin mako sharks Isurus oxyrinchus are important organisms in the pelagic ecosystem. In spite of their vulnerable status, they are captured by fishermen in the Eastern Pacific Ocean. The proper management and conservation of this population in the Pacific is critical and thus, more biological knowledge of this species is needed. In this work, the trophic habits and consumption of key prey by I. oxyrinchus were studied through stomach content analysis of samples collected off the coast of Ecuador, and a literature review of its feeding habits was conducted for the eastern Pacific. The index of relative importance of prey items, and the consumption of key prey were calculated for the three areas. The diet was composed of 78 prey taxa, and cephalopods were the main prey items in the north and central areas, with the jumbo squid Dosidicus gigas being the most important prey. For the southern area, I. oxyrinchus fed on fish with the bigeye cigarfish Cubiceps pauciradiatus being the most important prey species. The trophic niche of I. oxyrinchus was composed of squids and fish as the main prey items. The niche breadth for the three areas was reduced, and the trophic level calculated with stomach contents and stable isotopes of δ15N showed values of 3.68 to 4.44 suggesting that this shark is a tertiary predator in the ecosystem. The jumbo squid D. gigas and fish of the family Scombridae were described as key species in the diet of I. oxyrinchus. The consumption estimate from 2000 to 2013 was 39 128 tons, with 55.8% of this consumption represented by D. gigas. These results demonstrate that I. oxyrinchus is an active and top predator in the trophic webs of the Eastern Pacific, with opportunistic feeding habits on the more available and abundant prey species.