Background information and definitions
Predation by birds at aquaculture facilities (e.g. fish ponds, raceways and shellfish farms) can cause significant commercial loss (Draulans 1987). With increasing protective wildlife legislation, demand for non-lethal, environmentally safe methods of bird exclusion and scaring have increased. Most fish farmers now rely primarily on non-lethal techniques to accomplish control (i.e. to reduce abundance or exclude fish-eating birds in and around the vicinity of fish farms). Control efforts may be optimized by compiling evidence relating to deterrent or exclusion device efficacy, taking into account costs, practicality of use and the possibility of developing integrated strategies (i.e. combining more than one deterrent method). Avian deterrents can be categorised as auditory, visual, chemical, exclusion, habitat modification and lethal (Bishop et al. 2003). Lethal deterrents are not considered here (except where, very rarely, used as part of an integrated approach).
Bishop, J., McKay, H., Parrott, D. & Allan, J. (2003) Review of international research literature regarding the effectiveness of auditory bird scaring techniques and potential alternatives. Department for Environment Food and Rural Affairs.
Draulans, D. (1987) The effectiveness of attempts to reduce predation by fish-eating birds: a review. Biological Conservation, 41, 219–232.
Supporting evidence from individual studies
A replicated study from Limburg, Belgium, over 49 nights in 1982-3 (Draulans & Van Vessem 1985), found that using foot patrols to disturb grey herons Ardea cinerea from 12 fish ponds did not necessarily reduce fish consumption. Low frequency disturbance (e.g. 3-5 farmer visits/night) caused a significant decrease in heron numbers but became less effective as heron numbers increased. Reduced numbers did not necessarily reduce fish consumption, as maximum predation occurred soon after bird arrival and disturbance mostly discouraged only well-fed birds from returning.Study and other actions tested
A replicated trial in New South Wales, Australia (Rowland 1995), found that hanging gill nets in fish ponds and using harassment patrols to deter cormorants Phalacrocorax spp. from fish farms was not effective. This study is discussed in ‘Use in-water devices to reduce fish loss from ponds’.Study and other actions tested