Abstract
Loud hydroacoustic sources, such as naval mid-frequency sonars or airguns for marine geophysical prospecting, have been increasingly criticized for their possible negative effects on marine mammals and were implicated in several whale stranding events. Competent authorities now regularly request the implementation of mitigation measures, including the shut-down of acoustic sources when marine mammals are sighted within a predefined exclusion zone. Commonly, ship-based marine mammal observers (MMOs) are employed to visually monitor this zone. This approach is personnel-intensive and not applicable during night time, even though most hydroacoustic activities run day and night. This study describes and evaluates an automatic, ship-based, thermographic whale detection system that continuously scans the ship’s environs for whale blows. Its performance is independent of daylight and exhibits an almost uniform, omnidirectional detection probability within a radius of 5 km. It outperforms alerted observers in terms of number of detected blows and ship-whale encounters. Our results demonstrate that thermal imaging can be used for reliable and continuous marine mammal protection.
Highlights
Growing concerns that aquatic noise produced during naval exercises and offshore seismic surveys by the oil and gas industry may be harmful to marine mammals [1,2], have led an increasing number of regulating agencies to request mitigation measures when issuing permits for such surveys in their nations’ EEZ [3]
Several hundred whale blows were unambiguously identified within a range of 8 km, with most of the blows originating from a distance of less than 4 km range (Figure 2)
Using the automatic detection system on data from 7 expeditions, we identified more than 4500 whale blows at distances of up to 5500 m
Summary
Growing concerns that aquatic noise produced during naval exercises and offshore seismic surveys by the oil and gas industry may be harmful to marine mammals [1,2], have led an increasing number of regulating agencies to request mitigation measures when issuing permits for such surveys in their nations’ EEZ [3]. The most common measure is to implement a ‘‘marine mammal watch’’, a team of observers that scans the ship’s environs for signs of presence of marine mammals to trigger a shutdown of the hydroacoustic source when marine mammals are entering a predefined exclusion zone. Marine mammal observers usually scan the ship’s environs for whales using binoculars or the naked eye. In combination with the whales’ prolonged dives, sighting opportunities are rare, which, in addition to the limited field of view and finite attention span of human observers, renders this method personnel-intensive and difficult, even during fair weather and daytime.
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