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Two types of depredation mitigation devices (DMD) were designed and tested aboard pelagic longline fishing vessels targeting tunas and swordfish off the Seychelles. The DMDs were designed to reduce the damage and removal of fish from the fishing gear by predators such as toothed whales and sharks. The first DMD was termed "spider" and was made up of a 100 mm diameter plastic disc with sixteen holes in its outer range and a 37 mm diameter central hole.  Eight 1200 mm long hanging legs were created by placing four polyester strands into the outer holes and the entire system is triggered by a biting fish.  The second DMD, "sock", was designed to cover the fish to hide it from predators through either a net made up of fiberglass mosquito netting or of propylene fiber net.  Shark depredation was significantly higher throughout the surveys than toothed whale depredation, but toothed whales caused more damaged to fish through depredation events. The sock DMD did not affect the catch rates of targeted species or depredation events by either sharks or toothed whales.  These results for the spider DMD were not presented. Trigger rates for the two DMDs were up to 87.3% for the spider and 69.2% for the sock.  The protection rate was as high as 80% for spider but only 15.5% for the sock. Entanglement rates of the DMDs with the fishing gear were low for the spider (3.6%) and higher for the sock (17.8%).  In addition, the use of these DMDs significantly slowed down the fishing process, and therefore additional work into the design and application of DMDs needs to be explored.

Fisheries observers and skippers tested the effectiveness of the Dolphin Dissuasive Device (DDD) as a bycatch mitigation tool for porpoises and dolphins. This study was conducted aboard fishing vessels in the Cornish over-12m static net sector fishery in the waters of Southwest England. DDD's were placed at the end nets. The DDD's caught significantly fewer porpoises but no significant difference in dolphin bycatch was observed. When bycatch rates were separated between short (up to 4 km) fleets and long (larger than 4 km) fleets, there was no significant difference in porpoise bycatch in the long fleet but there was in the short fleet. 

Tests were conducted aboard small (<10 m long) static net fishing vessels targeting monkfish (Lophius americanus) off the coast of Britain to determine the response of cetaceans (largely harbor porpoise, Phocoena phocoena and bottlenose dolphin, Tursiops truncatus) to pingers.  AQUAmark 100 pingers were positioned at 200 m intervals on the net and acoustic click detectors (C-PODs) were placed at the end of 1 km tiers of the net to determine the response of cetaceans to the pingers.  Only one harbour porpoise was incidentally caught during these trials and there was a significant reduction in the number of porpoise clicks recorded at nets with pingers compared to those without.  Additional tests were conducted to determine habituation. For these tests, modified pingers, active for alternate seven hour periods, were attached below click detectors at one site with strong tides and loud ambient noise and one at a quite site.  The results of this part of the study showed the pinger effect was stronger at the quiet site and that were was no habituation.  In addition, there was evidence of exclusion of porpoises following pinger use for as much as seven hours.

A modified longline system with a net sleeve and weight on the secondary vertical line was tested in the Chilean Patagonian toothfish (Dissostichus eleginoides) 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 shrouding 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 (Pseudorca crassidens) 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 presence or absence of the acoustic device. Initially, the device reduced the whale's echolocation performance 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 (Phocoena phocoena) and bottlenose dolphin (Tursiops truncatus) bycatch, whether habituation to the pingers would reduce their effectiveness and how quickly porpoises and dolphins recolonize 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.

Pingers have been used on shark nets set along Queensland's beaches since 1992. Due to an increase in whale entanglements in 2009, new pingers (Fumunda F3 whale pingers and F10 dolphin pingers) were deployed between July and August 2010. Subsequently updated research on the use of these pingers was needed. For this study, the acoustic characteristics of pingers used on shark nets in Queensland Australia were measured and used to model sound propagation, estimate over what range marine mammals could detect the pingers, monitor ambient noise and to make recommendations on pinger deployment to the Queensland Shark Control Program (QSCP). The results of the sound propagation study indicate that the tones were a few hundred Hz less (2.6-2.8 Hz for F3 and 9.4-9.6 Hz for F10) than indicated. All pingers emitted multiple harmonics and fundamental tones. The power spectrum density levels varied up to 20 dB from angle to angle and pinger to pinger. The 1st harmonic of F3s was audible to all marine mammals over the longest ranges. Only 2 of the 6 tested pingers reached the manufacturer's listed audible range of 1-5 km. During testing, the ranges depended on the individual pinger and angle of the pinger toward the mammal. When animals travel alongside the net, a number of pingers should be set in a series. Based on the current configuration of 3-4 pingers per net of 200 m, humpback whales (Megaptera novaeangliae) would hear all of the pingers at any location along the net but dolphins would hear only 1-2 pingers. When animals swim straight at the net, maximum pinger spacing would need to be based on the animals swim speed. The current net/pinger configuration is adequate for humpback whales, dugongs (Dugong dugon) and dolphins swimming at normal travelling speeds. The current pinger spacing is insufficient for dolphins swimming straight at the net at high speeds.

A study was conduceted to test the effect of SaveWave acoustic deterrent devices on target fish catch and bottlenose dolphins (Tursiops trunactus) in the North Carolina Spanish mackerel (Scomberomorus maculatus) gillnet fishery in the United States. 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.