Meeting Abstract
Female bottlenose dolphins exhibit seasonal reproduction with peak mating and calving in spring and summer. However, analyses of tooth rake marks indicate female dolphins in the St. Johns River (SJR; Jacksonville, FL) receive more aggression during the non-breeding season. Here, we examine seasonal group composition and behavior of SJR females to explain this pattern. Photo-identification surveys were conducted from Mar. 2011-May 2012 (508 sightings; 290 individuals) and separated by season (winter: Dec-Feb; spring: Mar-May; summer: Jun-Aug; autumn: Sep-Nov). Females were identified by the consistent presence of a calf in infant position; all others were unknown sex. Groups were sorted into three categories: females only (F), females with unknown sex (F+U), and unknown sex only (U). Analyses used G tests of independence. Of group types, F+U were consistently most prevalent (mean=0.59). Yet, relative proportions of each group type varied seasonally (p=0.02). U were least prevalent (0.15) during summer, when F+U were most prevalent (0.67). Within group types, behavior did not differ across seasons (F, p=0.39; F+U, p=0.09; U, p=0.45). Travel was consistently the predominant behavior of F (mean=0.67) and F+U (mean=0.65). Yet, F and F+U behavior differed (p<0.001). Foraging was more common for F (mean=0.31) than F+U (mean=0.18). F were never observed socializing compared to 0.14 of F+U; there was also a trend towards more socializing in winter. These data suggest that females associate with unknown sex (presumed males) year-round, socialize only in mixed sex groups and primarily in winter, supporting the hypothesis of herding outside of summer.
