Using Fish As Biological Samplers to Gain New Insights into the Distribution, Diversity, and Abundance of Prey Resources in Open Ocean Environments

Cephalopods are known to serve as prey to a diversity of predators. However, quantitative and species-specific data on their ecological roles is scarce, particularly in offshore environments.  We used predators as biological samplers as an alternative method to gain insight into cephalopod ecology. Stomach contents from 14 species of fish predators caught in offshore waters of the western Atlantic and the Gulf of Mexico (GOM) between 2007 and 2012 yielded data on 25 species of squids and 5 octopods. The most important cephalopods across predator diets by number and frequency of occurrence included species from the families Ommastrephidae, Argonautidae, Histioteuthidae, and Onychoteuthidae. Results are in agreement with mid-water and bottom trawl surveys that ommastrephid and histioteuthid squids are some of the most abundant cephalopods in epipelagic and mesopelagic waters of the western Atlantic and GOM. In contrast, argonauts appear to be widely available and important forage, yet they are rarely caught in nets. Comparisons of cephalopods occurring in predator diets and surveys can help identify species that may be selectively captured (or avoided) by predators and nets. Further, information from predators should be considered to supplement records on species that are not targeted by fisheries or regularly caught by surveys.