New Delhi: Scientists have measured the reaction of dolphins to military sonar for the first time, revealing that the marine animals are far more sensitive to such noise than was once believed. The study, by UC Santa Cruz researchers, published on October 23 in the Royal Society Open Science, reports that dolphin responses happened at sonar levels substantially lower than what was expected by regulatory standards.
The research team from UC Santa Cruz and the other collaborating institutions surveyed 34 groups of dolphins, amounting to thousands of individuals, off the coast of Southern California. Under both simulated and actual sonar conditions, the dolphins exhibited significant changes in their behaviour: they avoided the source of sound persistently and intensively and changed their direction and their formation pattern. Lead author Brandon Southall, a research associate at UC Santa Cruz, said that the responses are good evidence for acoustic sensitivity, and dolphins respond at far less than current regulatory impact levels. These results imply that dolphins are highly vulnerable to the effects of military sonar and that there may be other similar threats to the species that are not fully considered by current regulatory assessments.
Monitoring with Advanced Techniques
In order to capture a wide range of dolphin activities, the researchers used a number of effective methods. These were aerial drones, underwater recorders, and observers on the shore, which gave a multi-perspective analysis of the dolphins’ reaction. Photogrammetry using drones, a technique developed by John Durban, a senior scientist at Southall Environmental Associates (SEA), enabled measurements of the movement and formation patterns of the dolphins. This new integration of monitoring methods provided the scientists with a much-needed opportunity to observe the effects of sonar on dolphins without interference with the animals.
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Effect on Conservation of Marine Life
The findings of the study are important in view of continuing debates over the effects of sonar on the marine environment, especially on cetaceans that depend on sound signals for calling, foraging, and orientation. Mid-frequency sonar, particularly the kind that is frequently utilised by naval forces, has been linked to mass strandings and distress in many species of marine animals. Other vulnerable species include dolphins that live in large pods along the coast of California and in other places. Co-author Caroline Casey, a researcher at the University of California, Santa Cruz, stressed that studying these responses would help to preserve dolphins, as these animals can be stressed or disrupted by routine naval operations.
The research was a collaborative effort among scientists from the University of California, Santa Cruz, the Cascadia Research Collective, SeaLife Response, Rehabilitation, and international organisations such as the Royal Netherlands Institute for Sea Research. They also recommend that current regulatory sonar impact standards should be reviewed in order to protect dolphins and other sea creatures.
