Quiet-List 1997

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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 
relevant text:


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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