Caribbean riverine fish assemblages are ecologically, economically, and culturally valuable, yet often lack the scientific understanding necessary for effective management and conservation. In particular, nearly all of the native freshwater fish in Puerto Rico are amphidromous. However, very little is known about amphidromous fishes and much less about amphidromous fish migration effects on riverine fishes. The purpose of this study was to provide insight on the possible effects of amphidromous fish migrations by characterizing the composition of the riverine fish assemblage, assessing habitat associations of the most abundant species, describing the temporal dynamics of predator abundance, and documenting patterns of movement before and during a return migration of postlarval amphidromous fishes in the lower Río Grande de Arecibo in Puerto Rico. Fish were sampled using pulsed-DC boat electrofishing throughout the lower freshwater reach of the Río Grande de Arecibo (approximately 1.5 to 3 km upstream of the river mouth to the first upstream barrier). All fish were weighed, measured, and injected with a passive integrated transponder (PIT) tag to estimate movement from recaptures.
Results/Conclusions
Of the 24 total fish species sampled, the freshwater riverine fish assemblage was numerically dominated by six species that comprised over 90% of the total individuals sampled. The most frequently caught predators (Common Snook Centropomus undecimalis, Tarpon Snook C. pectinatus, Bigmouth Sleeper Gobiomorus dormitor, American Eel Anguilla rostrata) were more abundant at the first upstream barrier and deeper outside river bends, compared to shallower habitats. At the first upstream barrier, Common Snook, American Eel, and Tarpon Snook increased in abundance prior to and during the peak migration of postlarval fishes. Recapture data indicated nearly all (88.9%) Bigmouth Sleeper remained at original capture locations, whereas recaptures of Tarpon Snook and Common Snook always occurred in outside river bend habitats but consistently at different sampling stations than original captures. Our results suggest that temporal and spatial patterns in the structure of the Río Grande de Arecibo fish assemblage may be variable among apex predators over a short temporal duration and is likely influenced by the postlarval fish migration and barrier presence. Future research efforts may consider the role of natural and man-made barriers on the migration and predation of amphidromous fishes to guide management of sport fishes and conservation of native fishes.