Site fidelity of common bottlenose dolphins (Tursiops truncatus) in a highly industrialized area of the upper Galveston Bay estuary

Coastal common bottlenose dolphins (Tursiops truncatus) that inhabit urban estuaries are exposed to a myriad of anthropogenic threats. To manage and conserve these populations, it is imperative to understand their habitat use and residency patterns. In this study, we evaluated the site fidelity of common bottlenose dolphins in upper Galveston Bay (UGB), a heavily industrialized area of the Galveston Bay estuary. We aimed to identify groups within the population with varying affinity to UGB and to determine if there are resident dolphins in UGB. The Galveston Bay Dolphin Research Program conducted monthly photo-identification surveys in UGB between January 2016 and December 2019. We identified 442 distinct dolphins within UGB and used their sighting histories to calculate occurrence, permanence, and periodicity. These site fidelity metrics were incorporated into a cluster analysis that revealed three groups. Group 1 (n = 192, 43%) consisted of individuals with the highest site fidelity to UGB and were classified as year-round or seasonal long-term residents. Group 2 (n = 141, 32%) were transients and Group 3 (n = 109, 25%) were short-term users of UGB. This study identified resident dolphins in UGB, and we recommend that this group be monitored closely, as they are particularly vulnerable to stressors in the upper estuary.

Automated summary

This study evaluated the site fidelity of common bottlenose dolphins in upper Galveston Bay. Through photo-identification surveys, three groups were identified, with one group being resident dolphins in UGB. This study is important for the conservation of these populations and monitoring potential stressors.