Use ‘mammal-safe’ nets to capture and release mammals trapped in fishing structures
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Marine and freshwater mammals may enter fixed fishing structures, such as herring weirs, and become trapped. This intervention involves the use of specially designed nets, e.g. made with buoyant materials and a larger mesh size, to capture and release mammals instead of conventional fishing nets. This may reduce the risk of injury or death during release.
Supporting evidence from individual studies
A controlled study in 1992–2001 at coastal fishing sites in the Bay of Fundy, Canada (Neimanis et al. 2004) found that using specialised ‘marine mammal nets’ with a large mesh size to release harbour porpoises Phocoena phocoena from herring weirs resulted in lower porpoise mortality compared to when conventional nets were used. Overall porpoise mortality rates were lower when released from weirs with ‘marine mammal nets’ (6 of 240 porpoises, 3%) than with conventional herring nets (44 of 239 porpoises, 18%). Porpoises trapped in herring weirs were captured and released using two types of purse-seine net: ‘marine mammal nets’ (buoyant polypropylene with mesh size 7.5 cm; 240 porpoises) and conventional herring nets (mesh size 0.75–1.25 cm; 239 porpoises). Herring weirs (comprising 1-cm nylon mesh strung between wooden stakes in a kidney-shape, 3–20 m deep) were built near the shore to catch Atlantic herring Clupea harengus. Trapped porpoises were enclosed within the purse-seine nets, transferred to boats and released outside of the weirs. Researchers recorded porpoise deaths during each of the 479 release attempts in 1992–2001.Study and other actions tested