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Acoustic deterrence on salmon farms
A government report on the environmental risks of salmon aquaculture
(fish-farming) on the coast of British Columbia has just been released. It
does address a particular concern of mine, the use of underwater horns to
scare away seals. Although I think it's a mistake to focus on the effects
on whales and dolphins (as though the millions of other marine creatures
affected don't matter), the recommendation is encouraging. Here's the
B. Acoustic Deterrent Devices (ADDs)
Seventeen ADDs have been authorized for use at B.C. salmon farms. The
potential impact of these devices on non-target species has raised concern
to some. The SAR received submissions outlining these concerns based mainly
on local observations. The results of some scientific research on the
subject was made available to the SAR.
Conclusions reached by the SAR scientific advisors respecting impacts of
ADDs are that:
. Although ADDs are reportedly effective for up to two years, effectiveness
is variable among farm sites, and appears to diminish with time. Pinniped
(e.g., seal and sea lion) attacks occur even where ADDs are used. It is
thought that effectiveness is related to an animal's prior experience. It
is assumed that animals that continue to attack sites with ADDs have
experienced past success, and that these animals are sufficiently motivated
by previous success and hunger to withstand the intense ADD signals,
. Predator success depends on the predator net system or type of net pen,
net rigidity, material and mesh size, and the motivation of the predator,
which may be related to the availability of other prey choices,
. The long-term impacts of high intensity signals from ADDs marine mammals
are not conclusively known; however, pinnipeds (e.g., seals and sea lions)
that are not deterred by the devices may experience hearing damage at close
range. It is not known whether animals which continue to attack have
habituated to the signals, or have experienced hearing damage,
. ADD signals may interfere with animals' communication signals and with
passive listening abilities, due to "acoustic masking,"
. Harbour porpoise respond to ADDs by avoiding exposure to the ADD signal
by altering normal movement patterns. This could result in permanent
disruption of normal movements and appreciable loss of access to habitat,
. Declines in the number of sightings of baleen whales and killer whales in
the Broughton Archipelago have been reported and appear to coincide with
the introduction of ADDs to that area. It is not clear whether these two
events are related; however, observations in Newfoundland indicate that
humpback whales may vacate areas where ADDs are operating, and
. Based on the variable effectiveness among farm sites and diminishing
deterrence response with time, ADDs are not considered a long-term or a
desirable primary method of predation control.
Given these findings, particularly the finding on the inconclusive
effectiveness, ADDs present too great an environmental impact to allow
their continued use in B.C. Predator prevention through physical control
measures should be the priority-see above recommendation respecting
"predation prevention plans." ADD use should be phased out over a two-year
period to allow some time for salmon farmers to develop and implement
predation control plans with a focus on physical predation control
measures. Prevention plans should prohibit the use of ADDs.
Federal/provincial cooperation regarding implementation of this
recommendation will be necessary.
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