Image: Gilles Lagne/Pixabay

In a new study published in the journal Royal Society Open Science, an international team sampled 34 groups of short-beaked and long-beaked common dolphins amounting to thousands of individuals, in experiments where simulated as well as operational military sonars were activated in carefully controlled conditions — or deliberately not played in experimental ‘”control'” conditions. The researchers then determined the types and likelihood of responses to known sonar exposures, which revealed unexpected behaviours.

A key observation was the different timescales over which behavioural changes occur from seconds (whistling), minutes (movement) and tens of minutes (group cohesion).

“We see clear evidence of acoustic responses — fine-scale changes in movement including directed, sustained, strong avoidance, and changes in group configurations,” said lead author Brandon Southall, a UC Santa Cruz research associate and senior scientist at Southall Environmental Associates (SEA). “While these behavioural changes occur and persist on variable time scales, they are surprising in that they collectively demonstrate responses at sound levels that are orders of magnitude lower than predicted in current regulatory impact assessments. These animals are clearly much more sensitive to noise exposure than we thought.”

To read the full paper https://royalsocietypublishing.org/doi/epdf/10.1098/rsos.240650