Trophic ecology of a deep-sea fish assemblage in the Northwest Atlantic

Abstract

Understanding the trophic ecology of deep-sea communities provides valuable insight into deep-water ecosystem functioning, and can help inform fisheries management and conservation initiatives. However, few deep-sea food webs have been studied so far in the Northwest Atlantic. Here, stable isotope, gut content, and morphometric analyses were combined to explore trophic relationships in a deep-water fish assemblage off eastern Canada. While a weak depth effect was found on the isotopic composition of the species analyzed, isotopic and dietary records revealed the existence of two main, strongly coupled trophic pathways. The pelagic pathway either comprised pelagic fishes (e.g., meso- and bathypelagic species), primarily feeding on zooplankton and fish, or benthopelagic predators that showed a more pelagic-oriented diet. Such fishes displayed the lowest values of stable N and C isotope ratios. In contrast, demersal fishes representing the benthic trophic pathway had significantly higher values of δ15N and δ13C, and a taxonomically more benthic-oriented and diverse diet. Furthermore, smaller body sizes, larger mouths, and adaptations (e.g., bioluminescent structures and lures) prevailed in the pelagic species, consistent with living in a relatively food-poor environment. The largest average body sizes were found in the demersal fishes suggesting enhanced food intake and growth investment for the species. Only juvenile individuals of threatened species, such as Coryphaenoides rupestris and Rajella fyllae were caught, providing evidence of the vulnerability of such species to commercial fishing.