Use ‘mammal-safe’ nets to capture and release mammals trapped in fishing structures

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

65%
Certainty

32%
Harms

0%

Calculating overall effectiveness category

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.

Study locations

Key messages

One study evaluated the effects on marine mammals of using ‘mammal-safe’ nets to capture and release mammals trapped in fishing structures. The study was in the Bay of Fundy (Canada).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Survival (1 study): One controlled study in the Bay of Fundy found that using ‘marine mammal nets’ with a larger mesh size to release harbour porpoises from herring weirs resulted in lower porpoise mortality compared to using conventional herring nets.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Neimanis A.S., Koopman H.N., Westgate A.J., Murison L.D. & Read A.J. (2004) Entrapment of harbour porpoises (Phocoena phocoena) in herring weirs in the Bay of Fundy, Canada. Journal of Cetacean Research and Management, 6, 7-18.

Please cite as:

Berthinussen, A., Smith, R.K. and Sutherland, W.J. (2021) Marine and Freshwater Mammal Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation

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Use acoustic devices on moorings Action Link	Trade-off between benefit and harms	8	Synopsis Link
Use bindings to keep trawl nets closed until they have sunk below the water surface Action Link	No evidence found (no assessment)	0	Synopsis Link