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Summary: The authors tested the behavioural response of bottlenose dolphins (Tursiops truncatus) to gill nets equipped with active and control Dukane NetMark 1000 pingers. Although dolphins were observed significantly fewer times within a 100m circular buffer zone from the alarms, overall results showed no significant differences in the number of groups observed, or closest approaches by animals to the net, between active and control periods.

Summary: Gill nets fitted with Dukane NetMark 1000 pingers had significantly less bycatch of harbor porpoises than control nets and the fish size and catch rates of the target species were not affected.

Summary: A semi-flexible exclusion grid with a bar spacing of 15.5 cm reduced dolphin bycatch in the Pilbara trawl fishery by close to 50% and reduced the bycatch of sea turtles, large sharks and rays. However, the fate of the dolphins that encountered the grid and escaped is unknown.

Summary:

White Dukane pingers with a fundamental frequency of 10kHz and harmonies of up to 160 kHz, elicited the strongest response from Hector's dolphins (Cephalorhynchus hectori), compared to the black Pice and red Dukane pingers. More than half (62.5%) of the dolphins exhibited avoidance when exposed to the white pinger. However, no significant differences between pingers were found in the rate of echolocation clicks per dolphin or dolphin group, or among the peak frequencies of subset clicks.

Summary:

Gillnets from the North Sea wreck net fishery equipped with pingers had a 100% reduction in the bycatch of harbour porpoises (Phocoena phocoena) compared to nets with no pingers attached.

Summary:

Bottom set gillnets with pingers (LU-1, 8 signals, 145 dB, 300 ms, random signal intervals) attached were tested against standard nets and nets with dummy pingers (double blind) to determine if they could reduce the incidental capture of harbor porpoises (Phocoena phocoena). The proportion (number of nets with porpoises/number without) of harbour porpoise bycatch was reduced from 0.00229 and 0.00295 for nets with dummy pingers and no pingers respectively, to 0.00015 for nets with active pingers. The difference in bycatch rates between nets with active and dummy pingers was statistically significant but not between nets with dummy pingers and with no pingers.

Summary:

Small cetaceans are by-caught in salmon gillnet fisheries in British Columbia (BC) waters. In Canada, there is currently no generic calculation to identify when management action is necessary to reduce cetacean bycatch below sustainable limits. The researchers estimated potential anthropogenic mortality limits for harbour (Phocoena phocoena) and Dall’s (Phocoenoides dalli) porpoises and Pacific white-sided dolphins (Lagenorhynchus obliquidens) using quantitative objectives from two well-established frameworks for conservation and management (the United States’ Marine Mammal Protection Act and the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), which are similar to some management objectives developed for marine mammal stocks elsewhere in Canada. Limits were calculated as functions of (i) a minimum abundance estimate (2004–2005); (ii) maximum rate of population increase; and (iii) uncertainty factors to account for bias in abundance estimates and uncertainty in mortality estimates. Best estimates of bycatch mortality in 2004 and 2005 exceeded only the most precautionary limits and only for porpoise species. Future research priority should be given to determining small cetacean stock structure in BC and refining species-specific entanglement rates in these and other fisheries. The approach offers a quantitative framework for Canada to meet its stated objectives to maintain favorable conservation status of cetacean populations.

Summary:

Authors investigated the spatial and temporal responses of harbor porpoises (Phocoena phocoena) to simulated bottom-set nets equipped with periodically operating Dukane NetMark 1000 pingers. Pinger sound significantly reduced the median echolocation encounter rate by 50-100% at detectors placed up to 500m and reduced the sighting rate up to 375m from the simulated net. The average distance of approach also increased. When pingers were silent after being active for about two days, the return time of porpoises increased by several hours in comparison to a control. After about 50 days, habituation to the pingers was detected at two of nine stations. Pingers may affect harbor porpoises at greater distances than previously observed, but alternative solutions should be applied in ecologically important habitats and migration routes. 

Summary:

Acoustic harassment devices (AHDs) were tested in association with a marine fin-fish farm off the north-eastern coast of Sardinia, to determine their effectiveness on common bottlenose dolphins.  This was a controlled exposure experiment.  No significant or immediate effects on bottlenose dolphin presence, distance from AHD, group size or time spent in the fish farm area were caused by activation of the AHD. Thus, additional research is needed on their effectiveness in the marine environment before further deployment.

Summary:

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.