THE INTERCAFE CORMORANT MANAGEMENT TOOLBOX 4 CORMORANT MANAGEMENT TOOLS Limiting the interaction between 4.1 Scaring Cormorants Away combination. If these deterrents are cormorants and fish can be From A Fishery used in conjunction with highly- achieved in a number of ways, visible human presence, this will each falling into one of four broad The basic philosophy behind increase their overall efficacy but categories of action: techniques to scare birds away may reduce their cost-effectiveness. from a fishery is that cormorants As with many other techniques, 1. Scaring cormorants away from a are startled sufficiently to move to it seems best to operate these fishery. another foraging site by means of deterrents before or as soon as birds 2. Protecting the fish — by auditory, visual or even chemical arrive at a site — thus preventing preventing cormorants from deterrents. Clearly, the effectiveness them from getting used to the area reaching them. of these techniques relies on: (1) as a foraging site in the first place. 3. Altering fish availability to the deterrents being sufficiently Once birds have learned that a site cormorants — by making frightening to cormorants to make is good for foraging or breeding, it a fishery less attractive as a them move elsewhere; and (2) there will be much harder to deter them foraging site. being a ‘better’ alternative site for from coming to it. 4. Reducing overall cormorant them to move to. numbers — for example, by 4.1.1 Auditory deterrents killing cormorants locally to The main drawback of these reinforce scaring at specific techniques is that cormorants A number of commercially sites, killing them more eventually (often quite quickly) produced noise-generating bird intensively, or reducing their realise that they offer no real threat scarers are available — for example, reproductive efficiency. and the birds become ‘habituated’ through local agricultural suppliers. to the noises, sights or smells, These vary considerably in their In addition, under some ignoring them thereafter. However, price and complexity, from simple circumstances cormorant-fishery there is good evidence that birds humming tapes to relatively conflicts can be addressed through are scared consistently by human sophisticated, automatic devices the use of financial or other presence if they perceive that such as gas cannons. A general compensation measures. humans are associated with danger. consideration with all these devices Where this is not the case, the is noise nuisance, and any national The Toolbox aims to summarise birds can sometimes be approached and local controls on their use must information on each category of at close quarters and show no be taken into account. action with regard to the methods apparent fear of man. available, their efficacy, the 4.1.1.1 Gas cannons constraints on their deployment The key to the successful use of Gas cannons are deterrent devices or use, and the relative costs. auditory and/or visual deterrents that produce loud banging noises The aim is to provide a broad seems to be to make them as by igniting a mixture of gas (either overview of the effectiveness of unpredictable as possible by acetylene or propane) and air different management options for changing their location and under pressure. The frequency of different cormorant-fishery conflict frequency of use, and by using detonation can be regulated by situations. a number of techniques in adjusting the gas feed or with an [12] THE INTERCAFE CORMORANT MANAGEMENT TOOLBOX Gas cannon. Photo courtesy of Thomas Keller. automatic timing device. Most produced by a cannon is similar to migrating fish such as Atlantic cannons produce a single bang at the noise of a shotgun and causes a Salmon (Salmo salar) smolts, or pre-set, timed or random intervals, startle reflex, thus prompting birds in the vicinity of obstructions or but some devices can produce in the vicinity to take flight. Their barriers in rivers that may cause double or triple bangs, and rotators efficacy is reportedly heightened fish to congregate and hence are available so that the noise can where birds have had prior increase their vulnerability to be aimed in different directions. experience of shooting to kill. predation. Some are regulated by computer to produce a random length of the Gas cannons are widely used The effectiveness of gas cannons volley and with random intervals throughout Europe at aquaculture depends on how they are used, the between volleys, or they may facilities and to protect inland size of the site to be ‘protected’, incorporate light detectors to allow fisheries, particularly at smaller and the availability of alternative the device to be turned off at night. sites. They have also been feeding areas for the birds close deployed at specific locations by. Local conditions, such as A gas cannon is relatively or for particular times at larger wind direction and strength, can expensive and prices vary, sites — for example, to protect also affect the intensity of noise. depending on whether it is fishing gear (e.g. fixed nets), or Cannons are more cost effective electronic or mechanically ignited; to restrict local damage for short, at smaller fishery sites, and the whether it is a single, double or highly sensitive periods. These cost of sufficient numbers to cover multi-bang device; and whether might include the draining and a large area may be prohibitive. features such as a rotator or harvesting of Common Carp Researchers have suggested that mechanical or electronic timer (Cyprinus carpio) ponds, during one cannon can protect 1.3–2.0 ha are fitted. The unexpected noise aggregations of breeding or at aquaculture facilities, if www.intercafeproject.net [13] THE INTERCAFE CORMORANT MANAGEMENT TOOLBOX ‘A cannon firing repeatedly without any variation in timing or direction quickly loses its potential to scare birds’ Vehicle-mounted gas cannon. Photo courtesy of Thomas Keller. reinforced with other techniques. The general consensus of opinion is away by it, especially if they have A survey of catfish(Ictalurus that gas cannons are most effective no experience of shooting to kill. spp.) farmers in the USA indicated when moved every few days, have A cannon firing repeatedly without varying levels of satisfaction with variable firing intervals and are any variation in timing or direction the use of gas cannons to deter deployed in combination with other quickly loses its potential to scare Double-crested Cormorants: scaring techniques. For example, birds. In such circumstances, around 10% of respondents felt placing a cannon in a hide used by cormorants have even been they were ‘highly effective’ and shooters, and frequently moving reported to use gas cannons as about half found them ‘somewhat it between hides, may prolong the perches. Although cannons can be effective’; others regarded them as scaring effects of both the shooting effective if the firing frequency and ‘ineffective’. and the cannon. Gas cannons direction are varied, these scarers employed at fish-rearing ponds in may be socially unacceptable near A simple field experiment carried Israel have also been mounted on residential areas due to public out in the Czech Republic recorded wheeled carriages or on vehicles to concern about noise nuisance, the reactions of cormorants to make them highly mobile, where especially if left to fire at night. the firing of a gas gun. A number their effectiveness is reinforced However, pointing cannons away of cormorant responses were by human presence and shooting. from houses and constructing recorded: (a) no reaction; (b) taking Products are also available that simple straw baffles around them fright; (c) diving; (d) soaring and combine visual and acoustic stimuli allows the devices to be placed at circling; and (e) flying out of the to scare birds — the ‘Rotating approximately half the distance pond. These were found to be Hunter’ consists of two propane of cannons without baffles, with correlated with the distance of the cannons and the metal silhouette of no increase in noise nuisance. As birds from the gas gun. Typically, a person that swivels with the force sounds tend to be heard at greater birds up to 300 m away displayed of each bang. distance at night, gas cannons near an active response (e.g. soaring and human settlements should be turned circling, flying out of the pond), The main reason for cannons off or programmed to stop at night, suggesting that this method would losing their effectiveness is unless Night Herons (Nycticorax be particularly effective on smaller habituation — birds get used to nycticorax) or other nocturnal birds fish ponds. the noise and are no longer scared are also a problem. [14] THE INTERCAFE CORMORANT MANAGEMENT TOOLBOX Gas cannons may also have an crackers, screamer shells, whistling also require little manpower — undesirable effect on other wildlife and exploding projectiles, bird these are simply lengths of slow (e.g. birds and mammals) and bangers, flash/detonation cartridges burning fuse with bangers inserted humans (e.g. fishermen or fish farm and flares. These can be fired from at intervals to produce a series of workers), and they may also need modified pistols (with a range of loud explosions at approximately to be located in secure locations approximately 25 m) or shotguns 20-minute intervals. Placing them to guard against theft. One must (range of 45–90 m) and can produce inside clean, empty oils drums also be aware that the cannon noise noise levels of up to 160dB. As the can enhance the noise of the may be mistaken for gunshots, direction and intensity of firing can explosions, but particular care is and it would be prudent to inform be controlled to suit the bird species needed to ensure this is done safely. the police, wildlife rangers and, and location, an advantage of this Weather conditions can affect the in some countries where they may technique is that deterrence can be burning speed of the rope and there be deployed near national borders, targeted and disturbance of non- is also a danger of creating a fire the military about their presence.