Prey use by three deep-sea fishes in the Emperor Seamount waters, North Pacific Ocean, as revealed by stomach contents and stable isotope analyses

Abstract

We analyzed the stomach contents and nitrogen and carbon stable isotope ratios of three deep-sea fishes Pentaceros wheeleri (North Pacific armorhead), Beryx splendens (splendid alfonsino), and Allocyttus folletti (oxeye oreo)—to elucidate interspecific and intraspecific differences in prey use among demersal fishes in the Emperor Seamount waters (North Pacific Ocean). Principal component analysis using an index of relative importance revealed interspecific differences in prey use: P. wheeleri preyed on plankton and benthos; B. splendens on micronekton and plankton, and A. folletti on micronekton. The relationship between the index of relative importance in B. splendens and body length also indicated ontogenetic shifts in prey use. High percentage of empty stomachs and low stomach fullness index in P. wheeleri indicated this species’ limited feeding ability during its demersal life on seamount. Nitrogen isotope ratio analysis suggested that the trophic level of A. folletti was the highest, followed by large B. splendens, small B. splendens, and P.wheeleri. Variation in carbon isotope ratio values were small, indicating that primary producers were similar. Differences in nitrogen isotope ratio (trophic level) coincided with differences in prey use by the three fishes. Thus, these species are likely able to coexist in seamount waters by partitioning their use of benthos, plankton, and micronekton food resources. They might be supported by food supplied from the surrounding water columns by horizontal flux of plankton or vertical migration of micronekton in the deep scattering layer because except for the benthic prey of P. wheeleri they consumed plankton and micronekton.