Naval sonar affects dolphins at shockingly low levels – Here’s why that matters

The research has significant implications for naval operations and marine mammal protection. While there’s no evidence that these behavioral disruptions lead to the kind of mass strandings seen in some whale species, the study suggests that current guidelines may need revision to better protect these marine mammals from unnecessary disturbance.

“Understanding how these animals respond to these types of acoustic signals is important for mitigating the impacts that this type of disturbance can have on social animals that rely on acoustics for communication, feeding, and other critical facets of their lives,” says study co-author Caroline Casey, a researcher at UC Santa Cruz.

The research team’s findings, supported by the U.S. Office of Naval Research’s Marine Mammals and Biology Program, open new avenues for understanding and protecting marine mammals. As human activities in the ocean continue to increase, this knowledge will be crucial for developing more effective conservation strategies while maintaining essential naval operations.

Paper Summary

Methodology

The research team pioneered an innovative approach combining multiple observation methods. They used “drone photogrammetry” – taking precise measurements from drone photographs – which allowed them to track dolphin movements with centimeter-level accuracy.

Underwater microphones recorded dolphin vocalizations, while shore-based observers tracked overall group movements. Each experiment lasted 30 minutes total, with 10-minute segments before, during, and after sonar exposure. They also conducted control experiments without sonar to ensure any observed changes were indeed related to the sonar exposure.

Key Results

The study documented clear acoustic and behavioral responses in both dolphin species. These included fine-scale changes in movement, sustained avoidance behaviors, and changes in group configurations. Importantly, these responses occurred at sound levels far below what current regulatory assessments predict would cause disturbance. The behavioral changes varied between species and persisted for different durations.

Study Limitations

The researchers faced several challenges, including the dolphins’ naturally dynamic movement patterns and the potential influence of environmental factors like prey presence or other vessels. The relatively short duration of the experiments may have limited their ability to detect longer-term behavioral changes.

Discussion & Takeaways

This research provides crucial new information about how common dolphins respond to military sonar in their natural environment. It emphasizes the importance of understanding how acoustic disturbances affect social marine mammals that rely on sound for communication, feeding, and other vital activities. The findings suggest that current regulatory guidelines may need significant revision to better protect these animals.

Funding & Disclosures

The research was funded by the U.S. Office of Naval Research’s Marine Mammals and Biology Program and conducted under various federal permits. The study involved collaboration between multiple institutions, including UC Santa Cruz, and the authors declared no competing interests.

Source: Study Finds

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Image: Picture of long-beaked common dolphin off Southern California taken during research authorized by permit #19091 from the U.S. National Marine Fisheries Service. (Photo by John Durban)