Pilot Whales Increase Call Volume to Overcome Shipping Noise in Strait of Gibraltar

Long-finned pilot whales in the Strait of Gibraltar increase the volume of certain calls to compensate for underwater noise produced by shipping traffic, researchers reported on May 7 2026. Milou Hegeman and Frants Jensen of Aarhus University in Denmark, along with an international team, attached suction-cup recorders to 23 pilot whales between 2012 and 2015.

The devices, mounted on a 6-meter pole, recorded the animals' movements, depth and acoustic environment for up to 24 hours before detaching and floating to the surface. The recorders captured 1,432 calls that the team classified into four types: short pulsed calls, high-frequency calls, low-frequency calls and two-component calls used for long-distance communication.

Background noise levels ranged from 79 to 144 decibels, comparable to the sound of a vacuum cleaner in a busy restaurant.

The whales raised the volume of their quieter high-frequency and short pulsed calls in response to increased vessel noise. However, the low-frequency and two-component calls, which are used after deep dives to locate group members, were already produced at maximum volume and could not be amplified further.

Jensen stated that the rising background noise reduces the effective communication range, making it harder for separated animals to find each other. The long-finned pilot whale is a highly social, matrilineal species that typically remains with the same group for life.

Many of their dives are synchronized to reduce separation risk, though individuals can still become separated at the surface or during dives.

Challenges in High-Traffic Waters Approximately

60,000 ships pass through the Strait of Gibraltar each year. The study found that prolonged exposure to shipping noise may increase the time whales spend searching for their group rather than foraging. This could affect survival and reproduction and reduce the population's resilience to other stressors such as disease outbreaks.

Jensen noted that the whales are unlikely to become completely lost because they can resume hearing each other once noise levels decrease. The long-finned pilot whale population in the strait is classified as critically endangered, making effective communication particularly important for group cohesion.

The findings illustrate a form of vocal plasticity known as the Lombard effect, previously documented in other marine mammals including beluga whales, orcas and right whales. In pilot whales the compensation is only partial, as some call types cannot be increased beyond their current maximum volume.