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

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

Effectiveness

30%
Certainty

27%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

This intervention involves using deterrents to reduce predation on marine and freshwater mammals by native species. This may be attempted when particularly endangered mammal populations are threatened by unsustainable levels of predation. Deterrents may include the presence of humans or playback of human-related sounds.

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).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

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.

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 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
Referenced paper
Gobush K.S. & Farry S.C. (2012) Non-lethal efforts to deter shark predation of Hawaiian monk seal pups. Aquatic Conservation: Marine and Freshwater Ecosystems, 22, 751-761.

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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