Behavioral repertoire of Lahille’s bottlenose dolphins that interact with artisanal fishers

Abstract

Many human cultures involve positive interactions with wildlife in the past and present. Lahille’s bottlenose dolphins (Tursiops gephyreus), for example, have developed tactics for coastal and estuarine foraging, which sustains a fishing practice known as “cooperative fishing” by traditional fishers in estuaries of southern Brazil. Here, we use aerial footage to describe the behavioral repertoire of the Lahille’s bottlenose dolphins and how it relates to the frequency of net casting by fishers in the Tramandaí Inlet. From nearly 8 h of footage from June 2017 to May 2018, we mainly observed dolphins foraging in the estuary inlet when fishers were present along the shoreline. Dolphins performed at least 27 clearly distinct behaviors and three types of movement patterns. A generalized additive model supported that the fishers interpret a subset of this repertoire (64%) as cues for casting their nets. The behavioral overview of the Lahille’s bottlenose dolphins presented here demonstrates not only a diverse repertoire for this population, but also its clear influence on fishers’ activities. Scientific and traditional perspectives should be integrated to better understand the ecological significance of this “cooperative fishing” for both dolphin populations and fishers that depend on them.

Significance statement

Interactions between different species can be very complex. It is a three-dimensional universe that comprises the behavioral and ecological characteristics of both sides, and then the dynamic they create together. In the case of the “cooperative fishing” between fishers and dolphins in southern Brazil, we still have one dimension to disclose in detail: the dolphins’ behavioral repertoire. Using aerial videos from a drone, we were able to shed light on how those dolphins behave and also how fishers coordinate their activity in response to the dolphins. We also showed that the dolphins’ behavioral repertoire is more diverse than assumed so far. Results suggest that the “cooperative fishing” seems to be based on the human’s perception of an extensive Lahille’s bottlenose dolphin behavioral repertoire during hunting. The knowledge provided here is essential to track the dynamic of this unique interaction in a given space and time.