Juvenile dolphin behavioral development and survival strategies
By Katherine McHugh, PhD Student - University of California, Davis

The juvenile life stage is an extremely vulnerable and formative time for developing marine mammals, who must learn to find food and avoid predators in a complex underwater environment while forging social relationships and practicing skills critical for survival and reproductive success as adults. While bottlenose dolphins are among the best studied of all cetaceans, virtually no work has focused on understanding behavioral development between weaning and sexual maturity or determining the selection pressures acting on the juvenile life stage. Many factors remain poorly understood - for example, what are the major differences between the behavior of juvenile and adult animals? How do skills and relationships critical for adult survival and reproductive success develop through the juvenile period? What social, ecological, and behavioral factors influence survivorship of juvenile dolphins? Because of SDRP’s 36 year history of work on the bottlenose dolphin communities in the area, the “natural laboratory” of Sarasota Bay provides a unique opportunity to begin addressing such questions.

To this end, the main objectives of my dissertation project are to develop a better understanding of the social and behavioral development of bottlenose dolphins and to determine the major ecological and behavioral influences on survival strategies of free-ranging juvenile dolphins. I am starting to address these questions by combining long-term data from the dolphin population in Sarasota Bay with new information collected via boat-based surveys and focal animal behavioral observations on current juveniles. Preliminary fieldwork on this project began in Summer 2005, with the help of four college interns. In this first season, I was able to conduct 47 focal follows on 23 individuals (12 females and 11 males) in the Sarasota community ranging in age from two to ten years. I plan to continue observing these individuals over the next few years, which will allow for both a longitudinal and cross-sectional perspective on the social and behavioral development of juvenile dolphins in Sarasota Bay.

I am currently finishing data entry and working on preliminary analysis of both long-term and focal follow data. Initially, I plan to examine how dolphin association patterns, habitat use, ranging patterns, and activity budgets change from weaning to sexual maturity, looking for both between and within-sex differences in developmental trajectories as well as ways in which these behavioral patterns differ from adults. In addition, I will explore how juvenile dolphin behavior influences survival to adulthood by using long-term data to compare the ranging and association patterns of individuals who died before reproducing with those known to produce at least one offspring successfully. Such information will provide a more comprehensive understanding of dolphin life history, which may have implications for conservation and management of long-lived coastal cetaceans. Support for this project has come from NOAA Fisheries, the UC Davis Graduate Scholars Fellowship in Animal Behavior, and an NSF Graduate Research Fellowship.