Feeding habits of the Pacific Porgy Calamus brachysomus (Teleostei: Sparidae) in the central Gulf of California, Baja California Sur, Mexico

Abstract

The Pacific Porgy (Calamus brachysomus) is a commercially important fish in Baja California Sur, Mexico, where it reproduces year-round. The feeding habits of fishes can change during reproductive stages in response to changes in energetic demand. The objective of this study was to characterize the trophic habits of the Pacific Porgy and how these varied by sex, reproductive stage, and season. Monthly samples were obtained from July 2015 to July 2016 in the central Gulf of California. The stomach contents of 235 specimens (108 males and 127 females) were analyzed. The trophic spectrum comprised 90 prey items, including 58 mollusks, 14 echinoderms, 13 arthropods, 2 chordates, 1 annelid, 1 poriferan, and algal remains. According to the prey-specific index of relative importance (%PSIRI), the most important prey items were the bivalves Transennella spp. (7.24%), Argopecten spp. (6.94%), Anadara spp. (6.25%), Septifer zeteki (6.19%), and Tivela spp. (6.1%). The trophic spectrum varied significantly by season but not by sex or reproductive stage. There were no significant interactions between sex and season or sex and reproductive stage. According to the Levin index, C. brachysomus exhibited a narrow trophic niche (Bi = 0.31). Costello graphs indicated the dominance of a few species, with shifts in the relative abundance of prey species. Based on the trophic analysis, C. brachysomus was classified as a tertiary consumer (3.18). Therefore, C. brachysomus represents an important link between upper and lower trophic levels. Based on these results, we inferred that the Pacific Porgy is an opportunistic predator that feeds actively during all reproductive stages. Thus, the energetic requirements needed for reproduction appear to be covered by the prey that comprise the trophic spectrum of C. brachysomus without this species needing to switch to more energy-rich prey.