Foraging Behavior of Bottlenose Dolphins in the Shannon Estuary, Ireland as Determined through Static Acoustic Monitoring

Abstract

The Shannon Estuary in Ireland is home to a resident population of bottlenose dolphins (Tursiops truncatus) and is designated as a Special Area of Conservation under the EU Habitats Directive. It is an important industrial area, with numerous deep-water berths for shipping. Despite its high conservation value, there are few published studies on habitat use or foraging behavior of the Shannon dolphins throughout the year. The present study assessed the year-round presence and foraging activity of bottlenose dolphins at different locations in the middle and inner estuary using static acoustic monitoring. Dolphin presence was found to decrease with increased distance from the estuary mouth, i.e., where the estuary meets the Atlantic Ocean, while at the same time, foraging was found to be considerably higher in the upriver areas, suggesting the inner estuary was an important foraging area. Model predictions for seasonal, tidal and diel foraging were highly variable across locations, indicating that changes in dolphin behavior occurred over relatively small geographical scales. These results indicate that conservation efforts should consider the Shannon Estuary as a dynamic aggregation of habitats and future development initiatives should attempt to mitigate disturbance to the dolphins during important foraging periods on seasonal and diel scales.