Unanswered Forum Topics

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.

Blue sharks account for most of the bycatch in the Canadian pelagic longline swordfish fishery. Electropositive metals (e.g. lanthanide) oxidize in seawater and create electric fields, which can alter the behaviors of several species of sharks. Researchers deployed seven sets (6300 hooks) with three hook treatments (standard hooks, hooks with electropositive metals - neodymium/praseodymium - and hooks with lead weights) on the Scotian Shelf in the Northwest Atlantic. Electropositive metals did not reduce the catch of blue sharks or other common shark bycatch species.  

This paper is a global assessment of marine mammal (cetacean, pinniped, sirenian, and marine mustelids) bycatch in gillnets and other entangling nets from 1990 to 2011. The authors found that at least 75% of odontocete species, 64% of mysticetes, 66% of pinnipeds, and all sirenian and marine mustelids have been recorded as gillnet bycatch over the past 20 years. 

This paper is a global review of seabird bycatch in gillnets. The authors identified 148 seabird species as susceptible to bycatch in gillnets, of which 81 have been recorded incidentally caught. A review of reported bycatch estimates suggests that at least 400,000 birds die in gillnets each year. The highest levels of bycatch are reported in the Northwest Pacific, Iceland, and the Baltic Sea.  

Studies were conducted aboard beam trawlers in the North Sea to determine the performance of pulse beam compared to conventional tickler chain beam trawlers.  Overall the pulse beam trawl caught 68% less than the conventional trawls.  Specifically, the pulse beam trawl caught significantly fewer plaice and sole compared to the conventional beam trawl. There was no significant difference in catch rates of undersized plaice between the two gears but the pulse beam trawl caught significantly less undersized sole.