Collected Evidence: Collected Evidence: Scare birds from fish farms One before-and-after study from Israel found that the population of pygmy cormorants in the area increased after birds were scared away from fish farms, possibly due to lower persecution. One of two studies that examined fish stocks found that fewer fish were taken from a farm when heron distress calls were played. The other study, a literature review, found no evidence for the effects of scaring birds on fish stocks. Two replicated studies from Belgium and Australia found that using foot patrols to disturb birds from fish farms did not reduce the number of birds present or fish consumption. Ten of eleven studies from across the world, three controlled, found evidence that playing distress calls or using other acoustic deterrents (some with flashes of light) reduced the number of birds at fish farms, or changed bird behaviours. One of these involved underwater broadcasting. One study found effects were only temporary and five found that birds became habituated to noises. Four studies, one replicated and controlled, two before-and-after, found that acoustic deterrents were not effective in scaring birds. Five of seven studies, one controlled, found evidence that visual deterrents (including inflatable ‘Scarey Man’ scarecrows) reduced the number of birds at fish farms. Three found evidence for habituation to deterrents and three studies found no evidence that visual deterrents were effective. Two studies examined other deterrents, finding that trained raptors were effective but that the effects of helicopters and ultra-light aircraft were either inconclusive or very temporary.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F244https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F244Wed, 18 Jul 2012 11:00:04 +0100Collected Evidence: Collected Evidence: Disturb birds at roosts One controlled study from the USA investigated the effects of harassment on fish predation, and found there were fewer double-crested cormorants Phalacrocorax auritus on, and fewer fish were taken from, fish ponds near roosts which were harassed, compared with undisturbed roosts. A review found that there was a reduction in the number of cormorants foraging near roosts after night-time disturbance. Four studies, two replicated, from the USA and Israel, found that cormorants moved away from roosts where they were disturbed at night. One study found that this effect was only temporary.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F245https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F245Wed, 18 Jul 2012 11:42:12 +0100Collected Evidence: Collected Evidence: Use electric fencing to exclude fish-eating birdsTwo before-and-after studies from the USA found that electric fencing reduced the use of fish ponds by great blue herons Ardea herodias and great egrets Casmerodius albus.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F247https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F247Wed, 18 Jul 2012 11:52:28 +0100Collected Evidence: Collected Evidence: Use netting to exclude fish-eating birds Two replicated studies from Germany and the USA found that netting or closely-spaced string barriers reduced losses of fish or deterred fish-eating birds from fish ponds. A review concluded that excluding birds was an effective way to reduce damage. A series of tests in the Netherlands found that netting or nylon lines over ponds did not prevent birds from landing, but did alter behaviour, whilst a before-and-after study from the USA found that fewer great blue herons Ardea Herodias landed at fish ponds with netting, but that they stayed longer. Two replicated studies from Germany and Israel found that some birds became entangled in netting or closely-spaced string barriers over fish ponds. The Israeli study found that dark, small meshed netting entangled fewer birds than other netting types.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F248https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F248Wed, 18 Jul 2012 12:00:45 +0100Collected Evidence: Collected Evidence: Disturb birds using foot patrolsTwo replicated studies from Belgium and Australia found that using foot patrols to disturb birds from fish farms did not reduce the number of birds present or fish consumption.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F249https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F249Wed, 18 Jul 2012 12:05:00 +0100Collected Evidence: Collected Evidence: Use ‘mussel socks’ to prevent birds from attacking shellfishA randomised, replicated controlled experiment in Canada found that fewer medium-sized mussels were taken from mussel socks with a protective ‘sleeve’, compared to un-sleeved socks. There were no differences for small or large mussels.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F250https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F250Wed, 18 Jul 2012 12:11:31 +0100Collected Evidence: Collected Evidence: Translocate birds away from fish farmsA study from the USA cited in a review found that translocating birds away from a fish farm appeared to reduce the number of birds at the farm. A study from Belgium found that translocating herons did not seem to be an effective way to reduce bird numbers at fish farms.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F251https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F251Wed, 18 Jul 2012 12:15:27 +0100Collected Evidence: Collected Evidence: Increase water turbidity to reduce fish predation by birdsA randomised trial in France found that little egret Egretta garzetta foraging efficiency was lower in turbid water than clear.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F252https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F252Wed, 18 Jul 2012 12:45:59 +0100Collected Evidence: Collected Evidence: Provide refuges for fish within pondsA controlled cross-over trial in the UK found that great cormorant Phalacrocorax carbo foraging success was lower in a pond with artificial refuges, compared to a control pond.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F253https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F253Wed, 18 Jul 2012 12:49:06 +0100Collected Evidence: Collected Evidence: Use in-water devices to reduce fish loss from ponds 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.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F254https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F254Wed, 18 Jul 2012 12:54:38 +0100Collected Evidence: Collected Evidence: Spray water to deter birds from pondsA replicated study from Sweden found that a rotating water spray deterred birds from fish ponds, but that birds often became used to the spray.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F255https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F255Wed, 18 Jul 2012 12:57:49 +0100Collected Evidence: Collected Evidence: Deter birds from landing on shellfish culture gear using spikes on oyster cagesA replicated and controlled study from Canada found that significantly fewer birds landed on oyster cages with spikes attached, compared to control cages.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F256https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F256Wed, 18 Jul 2012 13:00:33 +0100Collected Evidence: Collected Evidence: Deter birds from landing on shellfish culture gear by suspending oyster bags under waterA replicated and controlled study from Canada found that significantly fewer birds roosted on oyster bags suspended 6 cm below the water, compared with non-submerged bags. Birds roosted on bags suspended 3 cm below the water as frequently as control bags.  Collected Evidencehttps%3A%2F%2Fconservationevidencejournal.com%2Factions%2F257https%3A%2F%2Fconservationevidencejournal.com%2Factions%2F257Wed, 18 Jul 2012 13:31:25 +0100
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What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

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