Abstract
Bottlenose dolphin (Tursiops truncatus) strandings have been documented in Alabama since 1978, with enhanced data collection since 1996. Members of the public report sick, injured, and deceased marine mammals to the state stranding network and are asked to submit descriptions and/or photographs to confirm the species, location, and other necessary details of the stranding. One of these details is the sex of the stranded dolphin, which is vital to define mortality demographics and better understand underlying causes of death or at-risk members of a population through time. Sex identification can be difficult because dolphins lack external genitalia and internal examination (necropsy) of deceased individuals is not always possible due to scavenging, decomposition or inability to successfully salvage remains. To determine the effectiveness of the two most common sex identification methods, gross examination of photographs and necropsy, we compared sex ratios of 460 T. truncatus stranded in Alabama from 1996 to 2018. Sixty-eight percent (%) (n=313) were necropsied, of which 42% (n=131) were female, 54% (n=168) were male, and 4% (n=14) were unknown sex. Of the 147 carcasses that were not necropsied, 23% (n=34) were female, 40% (n=59) were male, and sex could not be determined for 37% (n=54) of individuals. We found that males were more easily distinguished via photograph than females because male genitalia are often distended during decomposition. The proportion of unknown sexes was lower and the proportion of female identifications was higher when animals were examined by necropsy (χ2= 67.98, p< 0.001 and p=0.003, respectively). These findings highlight the importance of necropsy and internal examination for sex determination in stranded dolphins and underscore the value of stranding response for obtaining complete demographic information needed to support cause of death determination and subsequent conservation actions.
