A recent study conducted by the Tursiops Association has found that bottlenose dolphins living around Ibiza and Formentera are exposed to more than double the underwater noise pollution experienced by dolphins inhabiting the protected waters of Cabrera National Park. The findings underline the growing impact of marine traffic, human-generated underwater noise, and increasing tourism on one of the Mediterranean’s most vulnerable marine species.

Using a network of underwater hydrophones, researchers monitored dolphin activity in Cabrera and successfully identified at least 82 individual bottlenose dolphins through their unique signature whistles, a distinctive vocalization developed during the animals’ first year of life that functions much like an individual name.

When compared with previous research carried out in Ibiza and Formentera, the results reveal a striking contrast. Scientists found no statistically significant relationship between human-generated noise and dolphin presence in Cabrera’s protected waters. In contrast, studies conducted around the Pityusic Islands showed a direct link between boat traffic, underwater noise pollution, and changes in dolphin behaviour.

According to Tursiops project coordinator Marga Cerdà, underwater noise levels around Ibiza and Formentera are more than twice as high as those recorded in Cabrera. Earlier research carried out in Es Freus and Cala Saona demonstrated that excessive boat noise dramatically affects dolphin communication. During August, the distance over which dolphins could communicate dropped by more than 70% in Es Freus, while communication range in Cala Saona was reduced by approximately 20%.

Protected Waters Offer a Quieter Marine Environment

The study highlights Cabrera National Park as one of the few remaining relatively pristine marine environments in the Balearic Islands. According to scientific director Txema Brotons, strict conservation measures—including a 10-knot speed limit for vessels and restrictions allowing boats to anchor only on eco-friendly mooring buoys—play a major role in reducing underwater noise.

Researchers deployed six hydrophones at depths ranging from 30 to 80 metres across the national park. Between December 2023 and February 2024, the monitoring system collected more than 213,000 underwater audio recordings, providing one of the most comprehensive acoustic datasets ever gathered for dolphins in the region.

Signature Whistles Reveal Resident Dolphin Population

By analysing the dolphins’ signature whistles, scientists identified 82 unique individuals. Of these, 58 dolphins were recorded multiple times, while one individual appeared in 193 separate recordings. The study also found that 12 dolphins remained in Cabrera throughout the year, providing strong evidence of a resident bottlenose dolphin population within the protected marine reserve.

The research further confirms that dolphin populations in the Gymnesian Islands (Mallorca and Menorca) remain genetically and acoustically distinct from those living around the Pitiusas Islands (Ibiza and Formentera). No matching individuals were found between Cabrera’s newly compiled acoustic catalogue and the existing database from Ibiza and Formentera.

Boat Traffic Remains One of the Greatest Threats

Researchers warn that underwater noise pollution, intense boat traffic, fishing interactions, and growing tourism continue to represent the most significant threats facing bottlenose dolphins in the Balearic Islands. While Cabrera currently offers a safer acoustic environment, conservation experts believe further protection could be achieved by extending the 10-knot navigation limit across the entire national park.

The study reinforces the importance of marine protected areas, sustainable boating practices, and stronger environmental regulations to preserve dolphin populations and safeguard the long-term health of the Mediterranean marine ecosystem.