Depredation by Coastal Bottlenose Dolphins (Tursiops truncatus) in the Southwestern Gulf of Mexico in Relation to Fishing Techniques

Cetacean-fishery interactions are a recurring problem. These interactions are conflict prone, especially between fishers and those seeking marine mammal conservation. In the southwestern Gulf of Mexico, a large fleet of artisanal fisheries operates using a range of different techniques. We recorded 90 fishing operations in two different fishing areas of Veracruz, Mexico, between 2009-2010 and 2014-2015, assessing whether dolphin interaction negatively affects fish catch and fish gear. These potential impacts were evaluated using three generalized linear models (GLMs) hypothesizing that (1) depredation decreases catch per unit effort (CPUE), (2) the predator presence modifies catch composition, and (3) prey species presence increases the likelihood of depredation. Of the gillnet hauls analyzed, 27 were subject to depredation by bottlenose dolphins, despite conditions and fishing methods varying among sites. Higher CPUE attracts larger pods, but a negative effect by depredation was not detected. We also found that depredation probability increased when there were higher capture volumes, when mackerels and jacks were present, and when operations were most southwesterly. Despite the short distance (< 80 km) between sites, we found that bottlenose dolphins on each site displayed different feeding behaviors towards fishing nets. Regarding conservation, bycatch caused by dolphins does not seem to be problematic. In fact, the increase in boat traffic and declining prey abundances due to overfishing could be the main causes of fishers' economic loss. Dolphin-fishery interactions may not represent an actual challenge for marine conservation managers, but stakeholders, fisheries, and governmental institutions should be aware that diminishing returns due to overfishing could exacerbate the apparently false notion of dolphins competing for the fish.