Assessing Non-Lethal Seal Deterrent Options: Fishing Trials Technical Report
Abstract: The use of the ASD resulted in a 74% increase in catch
(weight) in the test net compared with the control.
A mackerel fishery in Torbay was selected for undertaking the trials, involving two
vessels using gill nets. An early prototype Acoustic Startle Device (ASD) developed
by Genuswave, which uses Targeted Acoustic Startle Technology (TAST), was
selected for use in the trials. On each fishing trip, each vessel deployed a ‘control’
net that was fished normally without any ASD, and a ‘test’ net with one or more ASD
to test the effectiveness of the device at reducing seal depredation compared with
the control net. Test nets were deployed with one to three devices set on separate
anchors as close to the net as possible; the combined duty cycles of devices
(percentage of time that the device emits a sound) deployed with test nets was
between 1.2% and 4.2%. Some technical problems occurred in the prototype ASDs
throughout the trials, resulting in reduced source levels, and/or truncated (shorter)
pulses for some trials. These errors were accounted for in the data analysis where
possible.
The results indicate that, despite the range of technical errors that occurred,
deployment of the ASD shows promise for reducing seal depredation in fisheries in
inshore waters, although testing has only taken place in a limited range of conditions
and gears types (water depth, net length etc). Generalised linear mixed models
(GLMM) (with logarithmic link function) estimates indicate that even when no other
factors are considered, the use of the ASD resulted in a 74% increase in catch
(weight) in the test net compared with the control. However, the data also indicate
that an appropriate adjustment of the duty cycle and the number of deployed units
could allow this positive effect in catch to be increased further.
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