Dolphins, it turns out, do not mix "work" and "rest." A new study has shown that these marine mammals use different parts of the ocean for communication and for finding food.
Scientists from Florida Atlantic University, led by Laurent Cherubin, conducted observations off the Atlantic coast of Florida for two months. Using an autonomous underwater vehicle — a solar-powered wave glider 3,7 meters long — they recorded 62 hours of sounds and collected data on temperature, salinity and other water parameters.
Dolphin signals were detected in more than 1600 recordings. Whistles, which serve for communication and maintaining contact within a group, were recorded more often in coastal waters. Rapid clicks for echolocation, by contrast, predominated in areas with a large number of sound-producing fish.
The analysis showed that the distribution of whistles is influenced not only by depth and temperature, but also by the level of background noise. Thus, dolphins apparently choose places for social interaction and for hunting with acoustic conditions in mind.
Interestingly, according to the recordings, fish fall silent when dolphins approach. This suggests that prey too are capable of "listening" to predators and reacting to their presence.
The discovery points to acoustic differentiation of habitats: dolphins use the same stretch of shelf differently depending on their behaviour. Such specialisation may be important for the species' survival in a changing environment.
The results have been published in the journal PeerJ. The authors note that effective conservation requires protecting not one type of habitat, but several different zones where the animals engage in different kinds of activity.
The researchers plan to continue their observations in order to understand how dolphins adapt to ocean warming, coastal development and other anthropogenic factors.
