Bird predators cause significant losses of commercially produced aquaculture products in the southeastern United States. A wide variety of species are implicated, depending on the location and type of farm.
Cormorants, wading birds, pelicans, and even ducks and blackbirds forage at commercial catfish, crawfish, baitfish, ornamental fish, and trout farms.
Most birds are protected by state and federal laws, so most fish farmers must rely primarily on nonlethal techniques to accomplish control objectives.
Although much is yet to be learned about controlling bird damage at aquaculture facilities, producers can optimize current control efforts by understanding and considering the logic, costs, and limitations of different techniques and by developing integrated strategies for their use.
Factors in deciding on control:
Producers should first determine whether birds are causing economic losses in order to decide whether control is economically justified. It is important to identify the species of bird predators using the facility and to determine the size and species of fish available in ponds.
Herons, egrets, and other wading birds cause significant losses at some trout, baitfish, and ornamental fish farms. For instance, at trout-rearing facilities, foraging by great blue herons can result in production losses up to 39 percent.
However, at some catfish farms great blue herons and great egrets may have a negligible impact on catfish production because they forage primarily on wild noncommercial fish or sick catfish.
Likewise, although cormorants and pelicans cause significant losses at many catfish and other large pond culture farms, when shad are abundant in ponds, cormorants prefer and, appear to feed almost exclusively on, these species.
Potential damage is greater for some species of birds than for others. For example, a double-crested cormorant requires approximately 1 pound of food per day; a great blue heron requires 2 /3 to 3 /4 pound; a great egret about 1 /3 pound, and a white pelican 1 to 3 pounds per day.
Additionally, potential losses may be higher than one would estimate by consumption alone because birds often wound fish that they do not eat. The importance of birds as vectors of fish diseases has yet to be determined.
Where only a few birds are present, aggressive scaring programs may not be economically justified unless there is a risk that more birds will be attracted to the facility by the ones already present, or there is a limited, but particularly high value, crop that must be protected.
Physical characteristics of farms or production facilities must also be considered when determining appropriate control strategies. Size of ponds or production units is an important factor in determining whether exclusion or frightening techniques would be more cost effective.
For example, birds can be economically excluded or deterred from most concrete raceways or small ponds by using netting or barrier wires, but such measures will generally be too expensive on larger ponds and facilities. In such situations, frightening programs usually must be used to control bird damage.
On facilities with large ponds and heavy bird predation, an effective frightening program can require continuous harassment of bird predators by one or more employees driving pond levees. Pyrotechnics and/or live ammunition are fired from vehicles to scare birds away.
Recorded distress calls and/or electronic noises can be broadcast from vehicle-mounted speaker systems to supplement scaring efforts. One person can usually cover up to 500 acres if ponds are located in one contiguous complex and levee roads are in sufficient condition to allow continuous traffic.
An all-terrain vehicle may be necessary if levees are easily damaged or wet weather hampers access. A scaring program must be consistent and aggressive to be successful. When the potential for bird predation is at its worst, bird patrols should be conducted seven days a week from morning to evening.
When birds come to the farm only during certain periods of the day such as morning and evening, employing scaring efforts only during those periods may be adequate. Scaring programs to deter pelicans, night herons, and to a lesser degree, great blue herons may have to be conducted at night as well as during the day because these species feed at night.
Scaring programs should be started when birds first arrive, before they establish feeding habits at aquaculture ponds. On facilities that suffer chronic cormorant depredation in winter, a scaring program should be started in the fall when the first birds arrive.
Cormorants have reportedly stopped coming to some farms for a month or more after initial aggressive scaring efforts. Birds arriving later in the season often follow those that are already present to feeding areas. Conditioning the early birds to avoid production ponds may thus reduce damage by later arrivals.
Control measures may have to be applied throughout the season at farms located in major daily flight paths of fish-eating birds or near large roosting areas.
Cormorant roost dispersal programs:
Dispersing cormorants from night roosts can reduce depredation at nearby aquaculture farms. The number of cormorants visiting fish farms near roosts can be reduced by 70 to 90 percent when roost dispersal programs are implemented.
Dispersing birds from night roosts can be logistically difficult because it requires from one to eight people firing pyrotechnics for approximately 2 hours as birds arrive in the evening. Cormorants usually abandon roost sites, at least temporarily, after 2 or 3 consecutive nights of harassment with pyrotechnics.
For best results, night roosts should be patrolled weekly to prevent birds from returning, and all roost sites within a 15-mile radius of fish production areas should be harassed simultaneously.
Roost dispersal will not eliminate the need to harass birds on ponds, but it will substantially reduce the amount of harassment needed on farms where birds are causing severe problems.
Gary A. Littauer , James F. Glahn , David S. Reinhold and Martin W. Brunson