We have combined the unique, long-term data sets collected by SDRP to determine how reduced prey affects behavior, physiology, health, and survival of bottlenose dolphins. The results of our efforts will help conservation managers predict how reduced foraging caused by human activities (such as noise exposure as a disturbance) will affect dolphin populations.
When individual animals respond to a stressor (anything that may cause an animal to change its physiology or behavior), what impact will such changes have on an entire population, and how will those changes occur? Those are two questions that have become increasingly important for conservation as the threats to marine mammals have become ever more subtle and pervasive. In addition, there is a need to know how exposure to multiple, seemingly-benign stressors can accumulate in an animal’s body and eventually affect reproduction and even survival. In particular, the Office of Naval Research (ONR) is interested in understanding how exposure to noise affects individuals, and how those effects are carried over to the population.
One of the critical behavioral changes we might see in animals exposed to sound is reduced foraging effort. In particular, bottlenose dolphins have little-to-no fat reserves that could buffer against lost foraging, making them (and species like them) particularly vulnerable. While we do not want to perform experiments that would actually result in lower reproduction or survival, we can use data about natural disturbances that may create the same effect. In Sarasota Bay, we are investigating how red tide (which reduces prey availability) affects dolphin behavior, health, survival, and reproduction. We have found that the number of prey calories available to dolphins during the winter is reduced when red tides are more severe and longer. Mother-calf separation (an indication of weaning) is more likely during that year, and the repercussions of the red tide persist through the following year. Survival of juvenile and adult female dolphins declines the year after a red tide event, with evidence of a decrease in lipid stores at the end of that year.
Knowing the connection between survival and lipid stores as well as how mother-calf separation relates to lost foraging will aid in understanding the relationships we might see for species, or even other bottlenose dolphin populations, for which we have very little data. In addition, the study will help determine the most effective type of data to collect to evaluate the population consequences of disturbance.
This article appeared on pages 5-6 in the December 2015 issue of Nicks n Notches.