Caribbean estuarine predatory fishes provide valuable ecosystem services including recreational fisheries and food for humans. They also represent the upper trophic levels of Caribbean estuarine ecosystems. Therefore, documenting the diets of predatory fishes is essential knowledge for Caribbean fisheries management and for understanding estuarine trophic ecology. However, the diets of Caribbean estuarine predators are virtually unknown. In the Caribbean region, amphidromy is the dominant life history of native riverine fishes and shrimps. In this life history, postlarvae and juveniles must migrate through estuaries to reach adult riverine habitats and may face a predator gauntlet during migration. The objectives of this study were to quantify the diets of Caribbean estuarine predatory fishes and to determine the importance of migrating postlarval fishes and shrimps as forage for estuarine predators. We sampled predatory fishes at locations throughout the Río Grande de Arecibo estuary, Puerto Rico, during one week in July 2015. This sampling period encompassed a postlarval amphidromous fish mass migration event. Fishes were captured with a boat electrofisher and a beach seine. The stomach contents of captured predators were extracted with acrylic tubes and by stomach excision. Preserved diet items were identified to the lowest taxa feasible, enumerated, and weighed.
Eleven estuarine predatory fish species were sampled, however, four of these (Tarpon Snook, Common Snook, Burro Grunt, and Bay Whiff) made up 91% of the diets sampled, so detailed results are presented for these species. Postlarval shrimps were the most important components of the diets of both Tarpon Snook and Bay Whiff at 46% and 34% mean composition by weight, respectively. While postlarval Sirajo Gobies were the most important component of Burro Grunt diets at 33% mean composition by weight. Common Snook diets contained mostly unidentifiable fish at 36.7% mean composition by weight. Postlarval shrimps made up the second most important component of the diets of Common Snook and Burro Grunt at 16% and 19% mean composition by weight, respectively. While postlarval Sirajo Gobies made up the second most important component of the diets of Tarpon Snook and Bay Whiff at 27% and 23% mean composition by weight, respectively. In total, amphidromous postlarval fishes and shrimps are made up the majority of the diets of three of the four estuarine predators examined here. As such, migrating amphidromous postlarvae appear to be key components of the estuarine forage base and are central to Caribbean estuarine trophic ecology and fisheries management.