Abstract:
The use of commercial echosounders for scientific and industrial
purposes is steadily increasing. In addition to traditional navigational
and fisheries uses, commercial sonars are used extensively for
oceanographic research, benthic habitat mapping, geophysical
exploration, and ecosystem studies. Little is known about the effects of
these acoustic sources on marine animals, though several studies have
already demonstrated behavioural responses of cetaceans to shipboard
echosounders. Some species of cetaceans are known to be particularly
sensitive to acoustic disturbance, including beaked whales. In 2011 and
2013, we conducted cetacean assessment surveys in the western North
Atlantic in which a suite of Simrad EK60 echosounders was used to
characterize the distribution of prey along survey tracklines.
Echosounders were alternated daily between active and passive mode, to
determine whether their use affected visual and acoustic detection rates
of beaked whales. A total of 256 groups of beaked whales were sighted,
and 118 definitive acoustic detections were recorded. Regression
analyses using generalized linear models (GLM) found that sea state and
region were primary factors in determining visual sighting rates, while
echosounder state was the primary driver for acoustic detections, with
significantly fewer detections (only 3%) occurring when echosounders
were active. These results indicate that beaked whales both detect and
change their behaviour in response to commercial echosounders. The
mechanism of this response is unknown, but could indicate interruption
of foraging activity or vessel avoidance, with potential implications
for management and mitigation of anthropogenic impacts.
Best wishes,
Danielle Cholewiak