Spatial analyses of bottlenose dolphin–fisheries interactions reveal human avoidance off a productive lagoon in the western Gulf of Mexico

Abstract

Studying interactions between cetaceans and humans is fundamental to assess their ecological significance and the impact of human activities on marine wildlife. Delphinids have historically been associated with human maritime activities, and while evidence suggests that such interactions are becoming more frequent worldwide, these remain poorly studied. Areas of potential interaction and differences in dolphin affinity to interact with humans were used to test hypotheses about the spatial distribution and temporal variation in dolphin–fisheries interactions off the highly productive Alvarado lagoon, in the western Gulf of Mexico. Line-transect surveys yielded 928 dolphin, 980 vessel, and 320 fishing gear target records, the latter involving mostly the shrimp fishery. No temporal differences were found in daily relative abundance of dolphins ( = 8.1 h−1, SD = 9.7), vessels ( = 7.8 h−1, SD = 5.9) or fishing gear ( = 2.4 h−1, SD = 2.6) between two consecutive years. Non-random spatial distributions indicated higher target concentrations at the lagoon entrance; however, dolphins and fishers were found to evade each other, possibly to prevent competition; dolphins only interacted with gillnets (28.6% of vessels and 22.6% of fishing gear). We observed small areas of potentially intentional and random encounters outside the entrance of the lagoon and low or null potential for interactions elsewhere. Only 18.9% of dolphin schools (44.8% of the 172 photo-identified animals) interacted with fisheries mostly by chance. Resident individuals (N = 23) tended to avoid humans, likely in response to negative reinforcement caused by aggressions from fishers. Hence, the potential intentionality of a few individuals to interact with fisheries, show they bare higher risks while attempting to benefit from gillnetted prey. This research unveils the chronic and acute exposure of the dolphin community to artisanal fisheries within the area, having important reciprocal consequences on their distributions and activities.