Protected Species and Marine Aquaculture Interactions

eported by the farmers as more effective deterrent measures.
In addition to the ADDs, Terhune et al. (2002) reviewed
other nonlethal interventions including harassment
by boat or with noise (such as underwater seal firecrackers),
aversive conditioning, predator (killer whales) models
or sounds, and the use of acoustic devices and relocation.
Often, harassment techniques are effective in the short
term, but may be less efficacious over time as animals become
habituated.
A three-month study at Chilean salmon farms reported
significantly lower sea lion predation after installation
of an ADD compared to a similar farm with no device
(Vilata et al. 2010). In 2007, 13.17t of salmon were
predated by sea lions from April to June 2007. In contrast,
for the same period of 2008, an ADD was used and just
7.75t were predated. This farm also had significantly lower
depredation in 2008 compared to a similar nearby farm
with no device installed (42.33t). However, at a nearby
farm, the same ADD was ineffective. The short span of
the study left doubts about the long-term effectiveness. Farm management was recommended
as being equally or more protective against predation. The researchers
also found interactions of the sea lions followed patterns linked to daily and annual
circa-rhythms, the intensity of the tidal flux, and prey size.
Effort has been focused in Scotland on understanding how pinnipeds interact
with farms and developing non-lethal control measures to deter them from fish farms
and other marine industry sectors. Only about half of Scottish farmers use ADDs,
with many relying heavily on farm management and husbandry practices to decrease
predation. Underwater video surveys at 13 farms provided extensive and detailed information
about individual behavior patterns of seals, how seals access the fish
through net holes, effectiveness of predator nets, net management issues that affect
predation success, patterns of seal attack on fish, the extent of predation across the
industry, timing of predation during the grow out cycle, geographic patterns of predation
occurrence and intensity, and review of ADD effectiveness (Northridge et al.
2013). This study also investigated the secondary effects of a previously untested
ADD on harbor porpoises which are protected and do not pose a predation threat to
salmon farms. There was little evidence of any significantly reduced porpoise activity
due to the ADD being turned on, but there was a weak trend indicating decreased
activity closest to the ADD. Another part of the study, tested signal characteristics of
four different transducers, finding only one was around 120kHz, the same frequency
band as harbor porpoise echolocation clicks.
Coram et al. (2014) conducted a comprehensive assessment of the design, effectiveness
and impacts of the variety of deterrent devices used in aquaculture and other
aquatic activities. Great uncertainty remains about just how effective ADDs are,
kARIN BEATE NøSTERuD
Norwegian salmon farm
Only about half of
Scottish farmers
use ADDs, with
many relying
heavily on farm
management
and husbandry
practices to
decrease
predation.
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