Effect of Anthropogenic Injuries on the Social Associations of Bottlenose Dolphins (Tursiops Truncatus) in Sarasota Bay, Florida

Abstract

Social connectivity is an important factor for measuring the survivability of bottlenose dolphins (Tursiops truncatus). Dolphins rely upon others for information transfer, protection from preda- tors, reproduction, and successful feeding. When an animal becomes injured, the association between individuals can potentially weaken, thereby threatening the survival of the animal. In Sarasota Bay, Florida, recreational boating and fishing have led to increases in the number of boat strikes and entanglements. These anthropogenic factors cause debilitating injuries to the animals and disrupt their group associations and social networks. Using long-term data sets available for the dolphin community in Sarasota Bay, we investigated how these injuries affect the social associations of dolphins by examining the differences before and after injury in (1) group size; (2) the number of strong associates (COA≥0.14); and (3) the closeness of associates. We further analyzed whether the type of injury, sex and age class of the injured animal, pres- ence of human intervention, and duration of human intervention affected these values. We found that while the size of the group a dolphin associates with does not change due to injury, injured dolphins have fewer strong associates within their individualized networks and form less tightly knit groups within one year of injury. This decrease in connectivity was not related to the age, sex, type of injury, presence of human intervention, or duration of human intervention. However, two years after injury, the decrease in the number of strong associates lessened, suggesting that injuries only appear to disrupt the social relationships of dolphins for a short period of time. Despite the fluctuation in individual associations of the injured animal, the strongest bonds, such as those between mothers and calves as well as male alliance partners, remained stable. Our findings suggest that injuries can potentially impact bottlenose dolphin social networks and underscore the need for further investigation into the ways humans are disrupting the social connectivity of wild bottlenose dolphin communities.