|Langston University Aquaculture|
Bird Predation On Fish
Glen E. Gebhart
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.
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.
Some birds, such as the bald eagle, feed primarily on dead fish and although they can be found on fish farms, they are not a significant problem to fish farmers. Two birds that cause major problems to fish farmers in Oklahoma are the double-crested cormorant and the great blue heron. The cormorant is a diving bird that captures the fish by diving and swimming after them. Cormorants usually travel in flocks and migrate south in the late fall or early winter about the same time as the major duck migration. Once cormorants find a prime feeding location, such as an aquaculture pond stocked with thousands of fish, they tend to stay through the winter unless cold weather forces them to migrate. Cormorants are especially devastating to fingerling fish, but they will eat and injure larger fish, as well.
The great blue heron is a shoreline wading bird that stalks and spears fish in shallow water. Herons generally fish alone or in small numbers rather than in flocks. Herons will live in the same area throughout the year unless ice cover forces them farther south. They primarily prey on fingerling fish and minnows, but they will eat or injure larger fish.
To illustrate the severity of fish predation, approximately 50 percent of 20,000 channel catfish fingerlings were lost to cormorants in one winter at the Langston University research facility. That same winter, 891 out of 900 rainbow trout were lost to cormorants in open pond experiments, while trout in covered cages at the same facility experienced essentially no mortality. It proved impossible to scare the cormorants out of the trout ponds by any means. The author has observed one great blue heron eat 23 fingerling hybrid bluegill in approximately one hour. Fish that are active feeders are especially vulnerable to heron predation, since the fish will come to the activity of the heron feeding on other fish.
One solution to the bird predation problem is to screen the birds out. This is feasible for holding tanks, raceways, and small pond facilities. Screening is not feasible on larger fish farms. The best solution may be a multiple method approach which scares birds off the facility before they become established. It has proven highly effective in some instances to intercept the birds on their way to the ponds and scare them off at that point.
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 in order for it to maintain effectiveness.
Stringing wires across the pond and along the shoreline has been effective for some fish farmers. This inhibits birds from landing and taking off from the water. Wires strung along the shoreline inhibit herons from landing on shore and wading into the water to feed. Electric fencing has been used around the edge of ponds to successfully prevent wading birds from fishing the shoreline. Wire methods have proven effective when strung close together, but they interfere with harvest operations and generally have to be removed during harvest.
Another solution is to scare the birds away from nearby roosting and nesting sites to encourage the birds to migrate elsewhere. This will generally require the aid of the local animal damage control officer. The animal damage control agent can assist you in solving a bird depredation problem and can be contacted through: USDA-APHIS, Animal Damage Control, 2800 N. Lincoln Blvd., Oklahoma City, OK 73105-4298, phone (405) 521-4039. For the address and telephone number of an Animal Damage Control office outside Oklahoma, call (301) 734-8281.
A final solution is to obtain a bird depredation permit from the U.S. Fish and Wildlife Service that will allow the permittee to kill a limited number of problem birds. This has proven necessary in a number of cases where birds have become acclimated to scare devices. To apply for a bird depredation permit, contact the Animal Damage Control office at the address listed above. They must recommend a depredation permit for your situation before the U.S. Fish and Wildlife Service will issue one.
The key solution is to move the birds before they discover the high density of fish and attract more birds to the pond. Use a variety of techniques to prevent establishment of a bird population and be aggressive in your efforts. Contact the Animal Damage Control office at the first sign of a bird depredation problem. It generally takes about two weeks to obtain a bird depredation permit if that becomes necessary. Fact sheets and a video are available which detail bird identification, frightening techniques, electric fencing, parallel and grid wire fencing, and other exclusion techniques along with cost estimates.
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