Occurrence of depredation by common bottlenose dolphins (Tursiops truncatus) on reef fish captured and released by rod and reel fisheries in the northeastern Gulf of Mexico

Abstract

In the northeastern Gulf of Mexico, depredation by common bottlenose dolphins (Tursiops truncatus) on rod and reel fishing gear leads to increased costs for anglers and serious injury and mortality for dolphins. I analyzed data collected from the Florida Fish and Wildlife Conservation Commission fisheries-dependent monitoring at-sea observer program to determine contributing factors to, spatial distribution of, and frequency of interactions for bottlenose dolphin depredation from 2009-2020. The dataset included 110,575 observations, of which 269 were recorded depredation events. I chose potential predictive factors from the dataset based on their known or hypothesized influence on dolphin behavior and used a generalized linear model to examine relationships between instances of depredation and these predictive factors. The number of anglers fishing, two geographic areas (Panama City and Destin, FL), years 2015 and 2017-2019, and captured fish families Lutjanidae (snapper family), Carangidae (jack family), and Serranidae (grouper and sea bass family) were significant predictive factors in the model. These results, as well as the results of a spatial analysis and an examination of the frequencies of these predictors suggest that food provisioning in the Florida panhandle is a driver of depredation and that the incidence of depredation is increasing over time. Bottlenose dolphins from the Gulf of Mexico northern and eastern coastal stocks have become conditioned to exhibit a range of low cost foraging techniques such as scavenging and begging, and depredation is an augmentation of those behaviors. Lutjanidae species were observed in 78% of depredation events and the family was the most significant factor in the model, revealing a regional prey preference for snapper. This study can help inform management and mitigation of bottlenose dolphin depredation in the Gulf of Mexico and provides a baseline for future scientific study.