Habitat use of the common bottlenose dolphin (Tursiops truncatus) in the Gulf of Guayaquil, Ecuador: Management needs for a threatened population

The habitat use by two neighboring coastal bottlenose dolphin communities (Posorja and El Morro) was evaluated in the western inner estuary of the Gulf of Guayaquil, Ecuador (3?S, 80?55 ' W). The study aimed to determine to what extent some environmental variables influence dolphins' distribution and behavior. The analysis included 344 dolphin groups recorded between 2014 and 2019. For both dolphin communities, 95% of home ranges were estimated (23.5 km(2) Posorja and 44.8 km(2), El Morro). Home ranges overlapped in an area of 11.2 km(2). No clear preference for areas to carry out specific activities was found, as dolphins used the same areas for multiple purposes. Multinomial logistic regression with four environmental parameters (distance to shore, depth, hour of day and tide) were used as predictor variables of behavior. A significant relationship between the tidal cycle and behavioral states was found with feeding occurring more frequently during the low tide, socializing and transit during high tide, and resting during mid-tide. Count models were used with environmental and behavioral variables to explore their relationship with dolphins' group size. Differences with respect to dolphin counts were associated with tide height and socialization. Depth is relevant for predicting dolphin counts mainly during high tide. We recommend that environmental authorities consider the dolphins' preference to carry out their activities within small home ranges, identify overlapping human activities and take steps to reduce potential conflicts, such as prohibiting all types of gillnets in areas of high concentration of dolphins. Likewise, regular assessments are required to detect future changes in both dolphins' habitat and human uses over time.

Automated summary

This study evaluated the habitat use of two neighboring coastal bottlenose dolphin communities in the western inner estuary of the Gulf of Guayaquil, Ecuador. It found that dolphins did not show a clear preference for specific areas for their activities and their behavior was influenced by the tidal cycle. The study also identified the relevance of depth and socialization in predicting dolphin group size. Recommendations were made for environmental authorities to consider the dolphins' preferences, reduce potential conflicts, and regularly assess changes in the dolphins' habitat and human uses.