Bird predation of fish has become a major problem for fish farmers and is getting worse as problem bird populations increase. Most fish farmers already have experienced bird predation problems or will in the future that needs to be addressed for the sake of losing taxpayer money.
Most fish-eating birds are opportunistic feeders and take whatever food is most easily accessible, so most fish hatcheries serve as a buffet. There are several birds that prey on fish. These include the double-crested cormorant, great blue heron, green-backed heron, little blue heron, black-crowned night heron, great egret, snowy egret, American white pelican, belted kingfisher, osprey, bald eagle, gulls, terns, and merganser ducks. These birds, except the merganser ducks, are protected by federal law and cannot be killed without a special federal permit. The merganser ducks can only be hunted during duck season under regulations applying to general duck hunting.
Artificial rearing areas, heavily stocked during certain times of the year, attract these birds. Hatchery fish, having spent all their lives in protected environs, tend to be naive about predators. Although the fish are wary by nature, they may not, respond appropriately to a predator attack. When fish are stacked up in hatcheries, they are easier for birds to catch than are fish in a natural setting. Among the factors that affect the predator-prey relationship between fish eating birds and hatchery-reared fish are the size of the fish and the hatchery location. Hatcheries located near nesting sites, flyways, or estuaries routinely have severe avian predator problems. Coastal hatcheries in general have greater problems than inland hatcheries with fish lost to avian predators. Locations with naturally occurring populations of fish attract fish eating birds, and fish hatcheries are usually constructed near natural concentrations of fish. This results in an obscene amount of loss revenue for hatcheries that are unable to manage the wildlife and detour the birds from gorging on their profits.
The most effective frightening device is increased human presence, which can also be the costliest. Some of the better scare devices are shellcrackers, whistle cartridges, bird bangers, screamer sirens, shotgun shells fired into the air, propane blast cannons, rope firecrackers, recorded bird distress calls, pop-up scarecrows that emit a loud noise as they are inflated, and balloon or other types of scarecrows that move in the wind. Any scarecrow or noise device must be moved around the facility for it to maintain effectiveness. Control measures must consider the type of predator they will be used against. Some measures are useful for a wide range of pests and others are useful only for specific types. Physical Devices can be designed for specific types of predators. If the predominant loss has occurred from wading birds such as herons, electric fences or low-level netting are effective deterrents. Some hatcheries have been successful in deterring herons by lowering the pond water level so that the birds cannot reach the fish. Some hatcheries have vertical walls with undermined walkways, these coupled with water level manipulations prohibit the birds from perching on the walls or wading into the ponds and reaching the fish. Where predators attack fish by diving from the air or from a perch, lines or wires placed over the tops of ponds are effective. These devices break up the flight pattern, although occasionally a bird is killed by the lines. Cormorants are difficult to keep away from large ponds. They have been known to swim under netting suspended at or below the water surface to get to fish. Some losses are so high that netting can be placed several feet below the surface of the water to give the fish protection. Physical control measures must be designed specifically for the hatchery as well as for the predator.
With the population of wild fish such as salmon and trout decreasing with the demand of human consumption hatcheries are becoming more and more popular and needed to sustain healthy populations of fish. With this demand it seems to be apparent that the war between hatcheries and birds of prey is not going anywhere anytime soon. For more information, please fill out the fields below and someone from Loomacres Wildlife Management will contact you.
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