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Summary:

Acoustic pingers placed in the rear of a pair trawl net in the United Kingdom bass pair trawl fishery did not reduce bycatch of common dolphins (Delphinus delphis). Multi-monofilament net, placed in the North Sea and West of Scotland gillnet fisheries, had no significant impact on harbour porpoise (Phocoena phocoena) bycatch when compared to traditional monofilament net. Thin twine monofilament nets (.4mm twine diameter, 90 mm mesh size) reduced bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to thick (.6mm twine diameter, 267 mm mesh size) monofilament nets. Barium sulphate nets had higher bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to traditional gillnets.

Summary:

Acoustic pingers placed in the rear of a pair trawl net in the United Kingdom bass pair trawl fishery did not reduce bycatch of common dolphins (Delphinus delphis). Multi-monofilament net, placed in the North Sea and West of Scotland gillnet fisheries, had no significant impact on harbour porpoise (Phocoena phocoena) bycatch when compared to traditional monofilament net. Thin twine monofilament nets (.4mm twine diameter, 90 mm mesh size) reduced bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to thick (.6mm twine diameter, 267 mm mesh size) monofilament nets. Barium sulphate nets had higher bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to traditional gillnets.

Summary:

Acoustic pingers placed in the rear of a pair trawl net in the United Kingdom bass pair trawl fishery did not reduce bycatch of common dolphins (Delphinus delphis). Multi-monofilament net, placed in the North Sea and West of Scotland gillnet fisheries, had no significant impact on harbour porpoise (Phocoena phocoena) bycatch when compared to traditional monofilament net. Thin twine monofilament nets (.4mm twine diameter, 90 mm mesh size) reduced bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to thick (.6mm twine diameter, 267 mm mesh size) monofilament nets. Barium sulphate nets had higher bycatch of harbour porpoise (Phocoena phocoena) and seals in the North Sea and West of Scotland gillnet fisheries when compared to traditional gillnets.

Summary:

Pingers were tested to reduce harbor porpoise (Phocoena phocoena) bycatch in bottom-set gillnets in the Swedish Skagerrak Sea. During the experiment, no harbor porpoise were caught in control or experimental gillnets, possibly as a result of a combination of factors including displacement of porpoise, high prey availability in other areas, or pingers acting as passive reflectors. Pingers did not affect the catch of target species, including cod (Gadus morhua) and pollock (Pollachius pollachius).

Summary: Harbour porpoise bycatch was significantly lower (p<0.01) in high-denisty Iron Oxide (IO) gill nets compared to control nets. There was no significant difference in the acoustic target strength of the IO and control nets, and both nets behaved similarly in flume tank tests. The authors conclude the reduction of harbour porpoise bycatch in the IO nets was a result of the mechanical properties of the nets.

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: Gillnets from the North Sea wreck net fishery equipped with pingers, had a 100% reduction in the bycatch of harbour porpoises, 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 harbour porpoises. 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. We 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 favourable 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.