MEPS 222:253-264 (2001)  -  doi:10.3354/meps222253

ABSTRACT: Previous studies have proposed that seagrass habitats, by supporting diverse and abundant fish assemblages, are preferred by foraging dolphins in coastal systems. To test this hypothesis, we (1) examined the fine-scale behavior of bottlenose dolphins in relatively pristine and developed inshore sites near Clearwater Harbor, Florida, USA, and (2) used an otter trawl to sample potential fish prey in non-seagrass and seagrass habitats. In the pristine site, dolphins preferred dredged channel and spoil-island habitats, while least preferring shallow seagrass habitats. In the developed site, foraging dolphins preferred the natural channel habitat, but exhibited little further selection. Therefore, the hypothesis that dolphins prefer seagrass habitats while foraging was rejected. Feeding frequency was significantly associated with diel state, with foraging peaking at dawn and decreasing throughout the day. Dolphin group size was negatively correlated and nearest neighbor distance positively correlated with feeding frequency. Analysis of trawl data focused on the pinfish Lagodon rhomboides which dominates the diets of dolphins in west Florida. The relative abundance of pinfish was significantly greater and standard lengths significantly less in seagrass than in non-seagrass habitats. Dolphins therefore forage in non-seagrass habitats where fish prey is both larger and perhaps more available. Although seagrass habitats support greater abundance of smaller fishes, they also provide a structural refuge which obscures fishes both visually and possibly acoustically. Thus, the importance of seagrasses to the health of coastal dolphins is probably indirect, as seagrasses support fish populations on which dolphins rely.

KEY WORDS: Tursiops truncatus · Foraging strategy · Prey availability · Diel patterns · Pinfish Lagodon rhomboides