Use deterrents to reduce predation on marine and freshwater mammals by native species

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects of using deterrents to reduce predation by native species on marine mammals. The study was in the North Pacific Ocean (USA).



  • Survival (1 study): One controlled study in the North Pacific Ocean found that neither boat motor sounds nor the presence of humans reduced Galapagos shark predation on Hawaiian monk seal pups, although shark presence was low throughout the study.


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 2009 at two small islands in the North Pacific Ocean, Hawaii, USA (Gobush & Farry 2012) found that two types of deterrent (boat motor sounds or a continuous human presence) did not reduce Galapagos shark Carcharhinus galapagensis predation on Hawaiian monk seal Monachus schauinslandi pups. The total number of predation events did not differ significantly when boat motor sounds were played (0 events) or when humans were continuously present (2 events) compared to when no deterrent was used (4 events). However, the authors state that shark presence was low at both sites throughout the study (12 sharks observed at one site, number not reported for the other).  In May–August 2006, the two deterrent treatments and a control (no deterrent) were rotated weekly between two sites. Deterrents were boat motor sounds played back through underwater speakers (with or without a boat anchored nearby) or 1–2 people camping on the island for ≥23 h/day. Surveyors recorded shark predation events (bite wounds, pups disappearing) at both sites every 1–3 days in May–August 2006. Video cameras recorded shark presence at one site for a total of 57 days.

    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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