Abstract
Many anthropogenic actions have an impact on coastal dolphins, with bycatch being one of the main threats. We describe the distribution patterns of common bottlenose dolphins Tursiops truncatus and periods of higher entanglement risk by the artisanal gillnet fishery in the Patos Lagoon estuary and along the adjacent coast of southern Brazil. A total of 136 dolphin groups and 187 gillnets were encountered in 69 surveys conducted between September 2006 and July 2009. Data were analyzed in relation to environmental, spatial and temporal variables using generalized additive models and a spatially adaptive local smoothing algorithm for model selec- tion. In both areas, dolphin densities increased as distance to the estuary mouth decreased. For the estuary area, water salinity and temperature influenced dolphin distribution. Along the adjacent coast, dolphin densities were higher with distance to shore as well as in the north area during the warm period. Patterns of dolphin distribution were probably a response to the presence of pre- ferred prey or avoidance of human-related disturbance. Kernel density showed that fishing effort was distributed along the entire surveyed area inside the estuary, while along the adjacent coast it was higher in the south compared to the north area in the warm period. The overlap between gillnets and dolphins increased considerably from the cold (33.8%) to the warm (48.6%) period. Seasonal variation in fishing effort and distribution affect the overlap and the risk of dolphin entanglement. Based on the findings of this study, a fishing exclusion area aimed at reducing bycatch was established by the Brazilian Environmental Agency.
Highlights
The coastal habitat of many dolphin populations overlaps with human activities, and these populations face the impacts, for example, of competition with fisheries, pollution, habitat degradation, coastal development and increasing underwater noise (Reeves et al 2003, 2013)
In this study we aimed to investigate the distribution patterns of bottlenose dolphins in Patos Lagoon estuary (PLE) and the adjacent marine coast, to determine the extent to which their distribution overlaps with artisanal gillnet fisheries, and to identify variables that might explain these patterns
The smooth curves showed that bottlenose dolphins were more likely to be found in areas closer to the estuary mouth and occurred at all ranges of surface salinity and temperature (Fig. 4A−C)
Summary
The coastal habitat of many dolphin populations overlaps with human activities, and these populations face the impacts, for example, of competition with fisheries, pollution, habitat degradation, coastal development and increasing underwater noise (Reeves et al 2003, 2013). In fine-scale studies, it is often challenging to collect and analyze the prey availability data required to understand this relationship (Acevedo-Gutierrez & Parker 2000, Heithaus & Dill 2002, 2006). Habitat features such as depth, slope and distances from rivers, estuaries or coast might trigger oceanographic processes that enhance local productivity or favor prey capture Ballance 1992, Parra 2006, Pirotta et al 2011) These variables are often considered useful proxies for prey availability, and dolphins preferred habitats have been identified without direct prey distribution data These variables are often considered useful proxies for prey availability, and dolphins preferred habitats have been identified without direct prey distribution data (e.g. Torres et al 2008, MacLeod et al 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
