Use in-water devices to reduce fish loss from ponds

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

34%
Certainty

35%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Cormorants Phalacrocorax spp. hunt by pursuing fish underwater. Putting nets or other obstacles underwater may reduce hunting effectiveness and so reduce aquaculture losses.

Study locations

Key messages

A before-and-after study from the USA found a 95% reduction in the number of double-crested cormorant Phalacrocorax auritus at two ponds in a fish farm following the installation of underwater ropes.
A replicated study at a fish farm in Australia found that hanging gill nets in ponds did not decrease the number of cormorants swimming in ponds.

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 before-and-after study at a channel catfish Ictalurus punctatus farm in Mississippi, USA, in January-April 1992 (Mott et al. 1995) found a 95% reduction in double-crested cormorant Phalacrocorax auritus on two ponds following the installation of parallel lengths of 9.5 mm yellow polyethylene rope with foam floats, 6.1 m apart (0.8-2.2 birds/min/day before installation vs. 0.03-0.08 afterwards). Eleven helium balloons also appeared useful in frightening cormorants habituated to ropes. During the week prior to addition 0.29 cormorants/min/day entered, whereas in the week after 0.02 entered. A 4.6 ha pond was monitored for 1,019 minutes before rope installation and 2,418 minutes after.
Study and other actions tested
Referenced paper
Mott D.F., Flynt R.D. & King J.O. (1995) An evaluation of floating ropes for reducing cormorant damage at catfish ponds. Proceedings of the Eastern Wildlife Damage Control Conference, 6, 93-97.
A replicated study at four silver perch Bidyanus bidyanus rearing ponds in New South Wales, Australia, found that hanging of gill nets and harassment patrols proved ineffective in deterring cormorants (great Phalacrocorax carbo, little black P. sulcirostris and little pied P. melanoleucos) from fishing in the ponds (Rowland 1995). Gill nets (large diameter mesh enabling young fish to swim through) were hung vertically in the water and harassment patrols (people walking around the ponds) were undertaken. Three ponds of 0.1 ha were stocked with fry (50,000-60,000 fish/ha) and one of 0.3 ha stocked with fingerlings (8,000/ha). Survival rates of fry in the three smaller ponds was 0.3%, 0.8% and 3.5% (average 1.5%), and survival of fingerlings 0.9%.
Study and other actions tested
Referenced paper
Rowland S.J. (1995) Predation of Bidyanus bidyanus (Teraponidae) in ponds by cormorants. The Progressive Fish-Culturist, 57, 248-249.

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Bird Conservation

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