Coastal Research Section

Reef Fish Survey (RFS)
Marine Resources Monitoring, Assessment, and Prediction (MARMAP) &
Southeast Area Monitoring and Assessment Program South Atlantic (SEAMAP-SA)

Diet Studies

RFS biologist Kevin Spanik examining stomach content specimens in the survey's diet laboratory.

The analysis of fish diet composition has become a common discipline of fisheries ecology. Information that can be gained from diet studies such as habitat use, ontogenetic shifts, and natural mortality help researchers learn more about the biology and life history of individual species, while other information such as trophic interactions and resource overlap are essential to ecosystem modelling efforts.

The RFS initiated a diet study program in 2008, and to date over 450 unique prey items have been identified in the diets of over 2,500 predator specimens in our lab. Target predator species collected vary every few years and are determined by data needs and management priority. Recently studied species include Black Sea Bass, Red Porgy, Gray Triggerfish, Red Snapper, White Grunt, Vermillion Snapper, and several species of grouper.

A typical diet laboratory setup includes a dissecting microscope, an analytical balance, and calipers. Various glassware and utensils are also used for sorting taxa and manipulating specimens.

Upon capture of a target predator, whole stomachs are removed and preserved at sea, and then transported back to the laboratory. Back in the lab, all contents from each individual gut are sorted, identified to the lowest possible taxon, counted, measured, and weighed. Diet composition is quantified using a number of different metrics including percent by weight, percent by number, and percent frequency of occurrence.

An unidentified gobioid fish specimen, consumed by a Black Sea Bass. Fish from predator stomachs can quickly lose morphological features necessary for their identification using taxonomic guides. More modern techniques such as DNA barcoding can sometimes be used in such situations to provide species-level resolution. A rough elbow crab, Platylambrus fraterculosis, eaten by a Squirrelfish. A hyperiid amphipod of the genus Phronima consumed by a Vermillion Snapper. These amphipods commonly occur in the zooplankton as an endoparasite of pelagic salps.