Use a larger mesh size for fishing trap-nets

How is the evidence assessed?
  • Effectiveness
    50%
  • Certainty
    30%
  • Harms
    15%

Source countries

Key messages

  • One study evaluated the effects on freshwater mammals of using a larger mesh size for fishing trap-nets. The study was in the River Indal (Sweden).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (0 STUDIES)

BEHAVIOUR (0 STUDIES)

OTHER (1 STUDY)

  • Human-wildlife conflict (1 study): One controlled study in the River Indal found that a fishing trap-net with a larger mesh size in the first two sections had fewer grey seals feeding around it and less damage caused by seals.

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

  1. A controlled study in 2000–2001 at the mouth of the River Indal, northern Sweden (Lunneryd et al. 2003) found that a fishing trap-net with a larger mesh size in the first two sections had fewer grey seals Halichoerus grypus feeding around it and less damage by seals than a conventional trap-net. Fewer seals were observed surfacing (average 0.2 seals/h) and feeding on fish (0 seals) around the modified trap-net than a conventional trap-net (surfacing: average 1.6–4.1 seals/h, feeding: 0.1–0.3 seals/h). The modified trap-net had fewer holes caused by seals (total 6) than the conventional trap-net (total 269), although statistical significance was not assessed. Catches of target salmon Salmo salar and trout Salmo trutta were higher in the modified trap-net during one trial, and similar in modified and conventional trap-nets during two trials (see original paper for data). A modified and conventional trap-net were alternated between two fishing sites on opposite sides of a river mouth during three trials (each lasting 15–25 days). Both had a 100-m leader net with 3–4 funnel-shaped sections leading to a ‘seal-safe’ fish chamber. The first two sections had mesh sizes of 400 mm (modified trap-net) or 200 mm (conventional trap-net). Target fish catches and holes were recorded every other day during each of the three trials in June–August 2000. Seals were observed daily from the shore and with a video camera above each trap-net during two of the three trials in July–August 2001.

    Study and other actions tested
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

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Marine and Freshwater Mammal Conservation

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation
Marine and Freshwater Mammal Conservation

Marine and Freshwater Mammal Conservation - Published 2021

Marine and Freshwater Mammal Synopsis

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