Estimating Variation in Shark Predation Risk to Bottlenose Dolphins in a Rapidly Developing Coastal Marine Ecosystem

ABSTRACT

The extent to which small odontocete populations are affected by predators remains poorly known but may vary with the extent of human impacts to ecosystems. Here, we analyzed six years of photo‐identification data to quantify the occurrence of shark‐inflicted injuries on bottlenose dolphins ( Tursiops sp. ) in Biscayne Bay, Florida. We tested (1) whether dolphins inhabiting northern, more urbanized waters, experienced lower predation risk (inferred from injuries) than dolphins inhabiting the less impacted and more seagrass‐dominated southern portion of the bay and (2) if ongoing habitat degradation and apparently increasing shark populations present an increasing risk to dolphins. Of 320 unique individuals identified, 69 (21.6%) had definitive shark‐inflicted injuries while 16 additional individuals had evidence of injuries that may have been inflicted by sharks. The prevalence of likely shark‐inflicted injuries was greater on northern dolphins (37.4%) than southern community individuals (24.6%), suggesting spatial variation in predation risk or risk‐taking by dolphins. There was also evidence for increased predation risk between 2017–2020 (19.3%) and 2021–2023 (31.1%). The drivers of this observed variation remain poorly understood, but seagrass loss leading to habitat degradation might be a driver of greater risk‐taking by dolphins or the turbid waters of northern Biscayne Bay may enhance risk.