In the study “Behavioral Responses of Common Dolphins to Naval Sonar,” researchers led by Brandon Southall investigated how short- and long-beaked common dolphins react to mid-frequency active sonar (MFAS) used in naval activities. This type of sonar emits sound waves in the 3–4 kHz range, which, although outside of dolphins’ most sensitive hearing range, can still be detected and may potentially disturb their behaviors. The researchers sought to determine if and how these dolphins might change their group dynamics, movements, and communication patterns when exposed to MFAS.

Given the challenges in observing dolphins in large, fast-moving groups, the team used an innovative approach combining drones, acoustic recorders, and visual observations to study these dolphins off the coast of Southern California. Controlled Exposure Experiments (CEEs) were designed to simulate realistic sonar conditions, involving sequences where dolphins were exposed to either simulated or actual Navy sonar.

One key finding was that short-beaked dolphins showed more noticeable responses to sonar than long-beaked dolphins, indicating species-specific sensitivity. For example, during sonar exposure, short-beaked dolphins often changed their group formation and movement patterns. This could include scattering or speeding up, responses that suggest an increase in stress or attempts to avoid the sonar source.

In contrast, long-beaked dolphins displayed more subtle or inconsistent responses to sonar exposure, likely due to differences in social behavior or environmental factors at the time.

Sign up for the Daily Dose Newsletter and get every morning’s best science news from around the web delivered straight to your inbox? It’s easy like Sunday morning.

The researchers also noted that sonar exposure caused a reduction in whistle communication, especially among short-beaked dolphins, which persisted even after the sonar exposure had ended in some cases. This suppression of whistling might indicate disrupted social communication among group members, which could affect their cohesion and coordination.

This study is significant as it provides the first experimental data on how common dolphins, which are frequently exposed to naval sonar, might react. The findings support that MFAS can disturb dolphin behavior, particularly for species like the short-beaked common dolphin. This insight is valuable for shaping sonar use guidelines to mitigate its impact on marine life, as Southall highlights: “These are the first experimental behavioral response data for these abundant dolphins to directly inform impact assessments for military sonars.“