Modelling distribution of the common bottlenose dolphin, Tursiops truncatus off the southwest coast of Puerto Rico

Abstract

Abstract Standardized sightings of the common bottlenose dolphin (Tursiops truncatus) from the south and west coasts of Puerto Rico were quantitatively analyzed to determine the spatio-temporal distribution patterns of sighting location, group size, composition and behavior in relation to key features such as distance from shore, depth and habitat type. Dolphin inhabit primarily the nearshore zone within 5 km of the coast, but they are also associated with edge and slope habitats of the platform and bank/islands off the west coast. Dolphins were rare both over the central portion of the western platform, characterized as a broad area of sand, as well as in deep waters outside the shelf edge zone. Although dolphins were sighted in various habitat types, the most predominant were sea grass beds (44%), sand (25%), and reef (22%). Only 17% of the sightings were in deeper waters, such as the shelf edge and mid platform, which were dominated by hard bottom. Multiple, multivariate correlations based on distance (DISTLM) showed that the only statistically significant predictor for dolphin relative abundances was Habitat Evenness (AIC = 250.89; R2 = 0.12; p = 0.003). On the other hand, for behavior data, DistLM showed that the only significant predictor was average rugosity (AICc = 551.21, R2 = 0.09, p = 0.02), where social behavior was more common in high rugosity areas, while traveling predominated in low rugosity areas. Given the predominately inshore distribution of bottlenose dolphins, their low abundance, and multiyear residency we believe the area off the west coast of Puerto Rico should be designated as a Critical Habitat.