Noise impacts and collisions
Maritime traffic has been identified to harm cetaceans in many ways. Underwater noise has the potential to mask acoustic communication signals or to reduce hearing capabilities. It can permanently deter animals or their potential prey from critical habitats such as breeding or feeding areas. In the Canary Islands, there is e.g. a high density of daily and year-round ferry traffic. Next to regular ferries operating at acceptable and apparently non-invasive speeds, there is a growing number of fast and high-speed ferries which cross the habitat of resident short-finned pilot whales. Their noise impacts largely remain unknown.
Vessel maneuvers can alter cetacean behaviour at the water surface. As an extreme case, collisions with whales and dolphins can severely injure or even kill individuals by propeller or hull strikes. Due to the increase in marine traffic during the last decades researchers have observed an increase in vessel-whale collisions around the globe. Recent research in the Canary Islands has shown that short-finned pilot whales are regularly involved in collisions. It remains unknown why the animals are not able to avoid approaching ferries. Reasons might be their fast approach speed and an acoustic underwater signature which is hard to detect by the animals.
Underwater noise of the high-speed ferry trimaran 'Benchijigua Express' transiting from San Sebastian (La Gomera) to Valverde (El Hierro). The ferry approaches with a speed of 36 knots (= 67 km/h) from a distance of 0.9 nautical miles (= 1.67 km) in the beginning of the sample. During the loudest part, the ferry passes the recording vessel at a distance of 0.27 miles (= 500 m).
(.mp3 file with 6.1 MB)
Underwater noise of the fast monohull ferry 'Volcan de Taburiente' transiting from San Sebastian to Los Cristianos (Tenerife). This ferry approaches with a speed of 21.5 knots (= 40 km/h) from a distance of 0.7 nm (= 1.3 km) in the beginning of the sound sample. During the loudest part, this ferry passes the recording vessel at a distance of 0.19 miles (= 350 m).
(.mp3 file with 9.6 MB)
Underwater noise of a single whale watching vessel maneuvering in close proximity to a pilot whale group. During the beginning of the recording you hear short-finned pilot whale calls and clicks. After a while the vessel starts its engine and the main audible sound impact results from propeller noise.
(.mp3 file with 1.6 MB)