Critical foraging habitats of pantropical spotted dolphins (Stenella attenuata graffmani) in a tropical fjord: Golfo Dulce, Costa Rica

Abstract

Coastal pantropical spotted dolphins are commonly seen off the Pacific coast of Costa Rica, but their ecology remains poorly understood. This study examines their distribution and habitat relationship in coastal waters off Osa Peninsula and Golfo Dulce, southern Pacific coast of Costa Rica. Sightings records were gathered year-round for several years; 2001-2006 off Osa Peninsula (n= 1247) and 2005-2011 in Golfo Dulce (n= 102); we applied spatial analyses (Near Neighbor Index and Kernel Density Map) to examine the area use pattern in both locations, while critical foraging habitats were identified for the inner basin of Golfo Dulce through the analyses of behavioral data collected at first encounter and with a scan sampling protocol during group follows. The species display a preference for coastal-shelf marine ecosystem, with significantly non random clustered distribution (Osa Peninsula: NNI= 0.35, Z score= -44.08, p < 0.01; Golfo Dulce: NNI= 0.72, Z score= -5.43, p < 0.01). Off Osa Peninsula, the relative density and observed group sizes vary with season (Kruskal Wallis= X2: 6.98; p < 0.05), while in Golfo Dulce they remain stable throughout the year (Kruskal Wallis= X2: 0.091; p > 0.05), seemingly associated with key foraging habitats. We suggest that the mapped critical habitats be considered as areas of conservation importance and potential candidates for a Marine Protected Area (MPA) status, with designated zoning based on the modeled spatial probability of occurrence of foraging. These findings are of considerable importance in the context of regional management and conservation, where spotted dolphins represent a key resource for a local tourism industry that operates in a coastal ecosystem of high biodiversity value.