Bottlenose dolphins and aquaculture: interaction and site fidelity on the north-eastern coast of Sardinia (Italy)

Abstract

Owing to the worldwide growth of aquaculture over the last years, new habitats have been created through the supplement of nutrients. This addition of nutrients affects the whole marine food web, resulting in predator species such as bottlenose dolphins becoming attracted to these areas. During this 5-year-long study that was carried out along the north-eastern coast of Sardinia (Italy), bottlenose dolphin’s history of exposure to aquaculture perturbations and their effects was documented. The interaction with a fish farm was assessed by studying the site fidelity, group dynamics, and seasonal and yearly occurrence. In all, 1,838 hours were spent in the field. Behavioural observations showed that the predominant activity (89 % of the time) in the fish farm was foraging (predation and depredation). The occurrence of bottlenose dolphins appeared to be related with the seasons and with the fish farm harvesting operations. Thus, the peak dolphin occurrence in the fish farm area throughout Fall coincides with the period in which they spend most of their time foraging. A relatively small community remained resident interacting with the fish farm over a long period of time. Hence, these individuals gained intimate knowledge on how to capitalize on the fish farm industry. This heterogeneity in site fidelity and residence patterns is highly relevant when coastal management initiatives are considered.