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A modified longline system with a net sleeve and weight on the secondary vertical line was tested in the Chilean Patagonian toothfish fishery. A net sleeve that deploys to cover the fish/hook when hauled and a weight were attached to the vertical hook line. The net sleeve significantly reduced depredation of fish by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). The weighted line also was able to reduce seabird bycatch deaths to zero.  

Odontocete (i.e. toothed whale) interaction with longline fisheries is a global phenomenon that threatens the status of some populations and the economic viability of longline fisheries. This review paper summarizes the trend and geographical extent of interactions, the potential impact on odontocetes and fisheries, and describes potential acoustic and physical mitigation solutions. 

Two devices were designed to prevent odontocetes from depredating caught fish and putting themselves at-risk of becoming bycatch. One device used physical deterrence by shouding the fish with a barrier and the other used psychological deterrence by utilizing prior negative experiences of temporary entanglement in fishing gear. Both devices fit on a branchline at a distance from the hook and descend towards a caught fish using a line tension trigger mechanism. All interactions occurred on control branchlines that were not fitted with a deterrent device, suggesting the potential of this technology to deter depredating odontocetes. The impact on fish catch rates, size, and survival was negligible. 

An acoustic device designed to deter false killer whales from approaching longlines by reducing the whales' echolocation performance capabilities was tested on a trained false killer whale. The device, Longline Saver, produced a series of complex, broadband signals (1-250 kHz) at high intensity levels (up to 182 dB). The whale was asked to detect a target in the presense or abscence of the acoustic device. Initially, the device reduced the whale's echolocation performace to chance levels, however subsequent trials demonstrated improvement in echolocation.  

A study was conducted aboard the Cornish inshore gillnet fishery to determine if pingers could reduce porpoise and bottlenose dolphin bycatch, whether habituation to the pingers would reduce their effectiveness and how quickly porpoises and dolphins recolonise a pingered site after their removal. Vessels were equipped with passive acoustic monitoring systems that can recognize and log each animals click and AQUAmark 100 pingers were spaced 200 m apart on the nets.  Control nets with no pingers were also used.  There was a significant difference in the number of porpoise clicks between nets with and without pingers.  There was no significant difference in the proportion of loud clicks logged when pingers were active and so the extent of displacement by pingers cannot be determined. In addition, there was no evidence of habituation to the pingers.  It appears that porpoises take at least 7 hours to recolonise a pingered site. There were too few encounters with dolphins to determine the ability of pingers to reduce their bycatch or to determine how long recolonization will take.

The Patagonian toothfish longline fishery has high levels of depredation by killer and sperm whales, which puts the whales at risk of being bycatch. Observations from 2003 to 2008 revealed significant variations of interaction rates with killer whales between vessels, suggesting the influence of operational factors on vessel interaction and depredation. When killer whales were absent at the beginning of the line hauling process, short lines (<5,000 m) provided higher yield and were significantly less impacted by depredation than longer lines. The authors also recommend that when facing depredation, vessels should leave the fishing area and travel distances > 40 n miles to prevent killer whales from finding them within a few hours. 

Acoustic pingers, Fumunda F3 (2.7 kHz) for humpback whales and F10 (10 kHz) for dolphins, were used on sharks nets within the Queensland Shark Control Program.  Sound from the acoustic pingers was present for around 1.5 km beyond the nets. Humpback whales and dugons were able to hear the F3 pinger 90 m from the net and its two harmonic overtones (5.4 and 8.1 kHz) 10 and 210 m from the net respectively. The F10 pinger was audible to both species up to 130 m from the net. Dolphins could hear the F3 pinger 45 m from the net and it's two overtones 10 and 110 m from the net.  The F10 pinger could be detected by dolphins up to 40 m from the net. Shark nets are currently fitted with 3 to 4 pingers per 200 m length of net and therefore appear to be adequate for detection by marine mammals swimming straight at the net and at a top speed.

A study was conduceted to test the effect of SaveWave acoustic deterrent devices on target fish catch and bottlenose dolphins in the North Carolina Spanish mackerel gillnet fishery. Observations were carried out on commercial vessels and focal visual and acoustic follows of dolphins were conducted. Fish catches were significantly lower when dolphins were observed interacting with gillnets. The SaveWave device did not affect fish catch. Dolphins were less likely to interact with gillnets and more likely to echolocate when SaveWaves were present. However, SaveWave devices were not sufficiently durable to be deployed in this fishery.

Experiments were carried out aboard vessels in the Danish North Sea hake gillnet fishery to determine if increasing the spacing of Aqutec AQUAmark100 pingers could be done without negatively impacting the effectiveness of the pinger. Control nets without pingers were tested alongside nets with pingers spaced at 455 m and 585 m. The control nets had a bycatch frequency of 0.54 incidents/haul for harbour porpoises. Nets with pingers spaced at 455 m had an incidence rate of 0 and nets with pingers spaced at 585 m had a bycatch frequency rate of 0.12. Bycatch indences were significantly different between the control and two experimental groups. This suggests that the spacing of pingers may be increased without significantly impacting their ability to reduce bycatch of harbour porpoises. 

Fumunda acoustic alarms were tested in the absence of nets to determine their ability to modify the behavior of Australian snubfin and humpback dolphins, with possible applications to gillnet fisheries. The alarms emitted a regular interval pulse of 300 ms every 4 seconds at 10 kHz frequency.  The behavior of the animals changed slightly when the alarms were used but the likelihood of them leaving the area was not significantly different from the control.  This suggests this type of acoustic alarm may not be useful as a bycatch mitigation measure for these species.