Retrospective analysis of bottlenose dolphin foraging: a legacy of anthropogenic ecosystem disturbance

Abstract

We used stable isotope analysis to investigate the foraging ecology of coastal bottlenose dolphins (Tursiops truncatus) in relation to a series of anthropogenic disturbances. We first demonstrated that stable isotopes are a faithful indicator of habitat use by comparing muscle isotope values to behavioral foraging data from the same individuals. δ 13 C values increased, while δ 34 S and δ 15 N values decreased with the percentage of feeding observations in seagrass habitat. We then utilized stable isotope values of muscle to assess temporal variation in foraging habitat from 1991 to 2010 and collagen from tooth crown tips to assess the time period 1944 to 2007. From 1991 to 2010, δ 13 C values of muscle decreased while δ 34 S values increased indicating reduced utilization of seagrass habitat. From 1944 to 1989 δ 13 C values of the crown tip declined significantly, likely due to a reduction in the coverage of seagrass habitat and δ 15 N values significantly increased, a trend we attribute to nutrient loading from a rapidly increasing human population. Our results demonstrate the utility of using marine mammal foraging habits to retrospectively assess the extent to which anthropogenic disturbance impacts coastal food webs.