Effects of Ocean Recreational Users on Coastal Bottlenose Dolphins (Tursiops truncatus) in the Santa Monica Bay, California

Abstract

Coastal bottlenose dolphins (Tursiops truncatus) have been observed in proximity to swimmers, kayakers, stand-up paddle boarders and surfers along near-shore corridors in the Santa Monica Bay, California. From 1997 to 2012, a total of 220 coastal boat-based focal follows of dolphin schools were conducted in this area to determine a) the type and proximity of encounters between ocean recreational users and coastal dolphins, and b) the effects of these encounters on bottlenose dolphins’ behavior. The majority of encounters involved dolphins and surfers (77.93%, n = 145 encounters), and overall, neutral reactions were observed in response to encounters (61.93%, n = 176 behavioral responses). Interactions between bottlenose dolphins and recreational users were recorded only once, and changes in dolphin behavior were observed more frequently when recreational users were at distances of less than three meters from a school. Although the current impact of human activities on coastal bottlenose dolphin behavior does not appear to be significant in the Santa Monica Bay, there is a need to: 1) adopt a precautionary approach in view of the increasing presence of ocean recreational users along this coastline, and 2) regularly monitor these encounters to determine potential changes in the type and proximity of encounters, as well as changes in dolphin behavioral responses.