As noise in the marine environment is substantially increasing, it is important to understand the extent to which its inhabitants are able to compensate for this change – particularly for cetaceans, which rely on sound for vital activities such as foraging and communication. My dissertation research examines the effects of noise on various dolphin whistle characteristics with the aim of elucidating any adaptive mechanisms employed by these animals, which may have important management implications.
Documented responses to increased noise include increased signal redundancy through repeating calls or an increase in the number of syllables per call, increased call duration, and alterations in the frequency characteristics of the call. The effects of noise on these variables were examined using a linear mixed modeling approach on 12,497 bottlenose dolphin whistles recorded by four bottom-mounted acoustic sensors (DSG, Loggerhead Instruments Inc, Sarasota, FL). These sensors were deployed in Sarasota Bay during September 4th, 2012 – May 15th, 2013, at two different sites that differed considerably in the frequency of noise exposure (high noise vs. low noise sites). Analysis results revealed that bottlenose dolphins are able to compensate for increased noise in their environment using a wide range of strategies. These strategies include modifying the frequency characteristics of their whistles, increasing whistle duration, and increasing whistle redundancy via increases in the number of whistle elements, loops, and repetitions of the entire call. These strategies are employed in a singular fashion or in various combinations, depending on the frequency content of the noise, the noise source, the time of day, and, possibly, the frequency of noise exposure at the animals’ location. Much remains unknown, such as the limits to such adaptive ability. However, this study provides a solid foundation upon which such studies can be built.
This article appeared on pages 10-11 in the December 2015 issue of Nicks n Notches.