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6-1-1997

Bird Predation and Its Control at AquacultureFacilities in the Northeastern United States

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Bird Predation and Its Controlat Aquaculture Facilities in theNortheastern United States

United StatesDepartment ofAgriculture

Animal andPlant HealthInspectionService

APHIS 11–55–009

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Photo credits: The images on the cover andin figure 3 were taken by APHIS photogra-pher Laurie Smith. Figures 1 and 2 weretaken by Cristopher Crowley and IsidorJeklin, respectively, of the Cornell UniversityLaboratory of Ornithology and are used bypermission. APHIS Animal Damage Control(ADC) employee Jim Glahn, the author of thisbrochure, took the photograph in figure 4, andADC wildlife biologist Erica Egan took thephotograph in figure 5.

The work reported in this publication wassupported in part by the Northeast RegionalAquaculture Center through Grant No. 93–38500–8391 from the Cooperative StateResearch, Education, and Extension Serviceof the U.S. Department of Agriculture(USDA). Findings, opinions, and recommen-dations expressed herein are those of theauthor and not necessarily those of the North-east Regional Aquaculture Center or USDA.

USDA prohibits discrimination in its programson the basis of race, color, national origin,sex, religion, age, disability, political beliefs,and marital or familial status. (Not all prohib-ited bases apply to all programs.) Personswith disabilities who require alternativemeans for communication of program infor-mation (braille, large print, audiotape, etc.)should contact the USDA Office of Communi-cations at (202) 720–2791.

To file a complaint, write the Secretary ofAgriculture, U.S. Department of Agriculture,Washington, DC 20250, or call (800) 245–6340 (voice) or (202) 720–1127 (TDD).USDA is an equal employment opportunityemployer.

Issued June 1997Cover photo: The great blue heron isbelieved to inflict the most damage to theaquaculture industry in the Northeast.

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Bird Predation and Its Control at AquacultureFacilities in the Northeastern United States

The diversity of northeastern aqua-culture and the adaptability of bird spe-cies to exploit this resource has led tocorrespondingly diverse bird-predationproblems. Several integrated approachesare needed to alleviate these problems.

The following information will helpproducers identify and assess predationlosses caused by primary bird predatorsas well as suggest species-specificcontrol measures that are also costeffective for reducing these losses.

The northeastern aquaculture industry,centered in Pennsylvania and New York,consists primarily of trout production, butlocal facilities also produce a number ofwarm-water species, including bait fish,catfish, and goldfish. There are severaldifferent culturing methods for producingthese fish.

Although trout culturing occurs pri-marily in concrete and earthen race-ways, it also occurs in ponds that aresometimes used for pay-to-fish sites.Narrow concrete raceways are usuallyset in rows over a small rectangulararea, whereas earthen raceways aremore linear and resemble a series ofinterconnected ponds that can meanderover a large geographic area. Warm-water fish species are almost alwaysproduced in ponds. Aquaculture facili-ties vary in size from farms with a single0.1-acre pond to several acres of con-crete or earthen raceways to more than100 acres of ponds.

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×

×

×

=

Average number ofbirds seen per hour

Bird feeding rate(fish taken per hour)

Hours birds arepresent per day

Days birds arepresent per year

Fish consumedper year

Table 1—Estimating yearly fishconsumption by bird predators

Assessing Predation Losses

It is important to assess fish losses tobirds before implementing control mea-sures. Several approaches to assessingpredation losses exist, but they vary withthe number of birds, foraging rates, andsize classes of the fish consumed. Theformula in table 1 shows how to estimateyearly fish consumption by a particularbird predator by using species-specificinformation on bird feeding rates.

By using information on the sizes offish consumed by each species of birdand on the value of these fish, the annualeconomic loss to bird predation can beestimated. For accurate estimates, theinformation used in this formula must becarefully obtained and applied. Withmost species, bird numbers vary consid-erably both throughout the day andthroughout a given season. Therefore,several counts must be taken daily dur-ing the damage season.

Primary Bird Predators atNortheast Aquaculture Facilities

Great Blue HeronThe great blue heron (cover), one of

the most common and most numerousspecies at northeastern aquaculturefacilities, is considered to inflict the mostdamage to the industry. It is readilydistinguished from other species ofheron by its larger size (4-foot bodylength) and its slate blue coloration,which is more mottled in juvenile birds.Adult birds have a white head; juvenilesdo not have this coloration. The blueheron occurs in varying numbersthroughout the year and forages ataquaculture facilities primarily at dawnand dusk. Night foraging is rare.

While present at trout-rearing facili-ties, each heron consumes on average2.2 live trout per hour. Average prey is9 inches long, but trout up to 14 inchesin length may be consumed. At warm-water facilities, great blue herons con-sume smaller, but proportionally more,fish. At these facilities, herons arethought to consume about 0.5 pound offish per day.

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Other HeronsThe black-crowned night heron is

not widely occurring but can be numer-ous at northeastern aquaculture facili-ties. These herons have a chunky bodyand a short neck; they are about 2 feetlong, with black back and head andwhite stomach. The black-crowned nightheron typically arrives at dusk to startfeeding and may continue to feedthrough the night. At western aquacul-ture facilities, where they are a morecommon problem, it has been estimatedthat black-crowned night herons con-sume 1.2 live trout per hour apiece, andthey consume trout averaging 7.5 inchesin length. However, more limited datafrom the Northeast suggest that troutaveraging 6 inches in length are thepreferred prey size of the black-crownednight heron. Because of their nocturnalforaging habits, it may be difficult todetermine the presence and the extentof predation of this species.

The green-backed heron (fig. 1) isthe only other commonly occurring heronspecies that frequents northeastern

aquaculture facilities. One of the small-est herons, it has a chunky body, andshort neck and averages 1.5 feet inlength. It has a dark-olive back andstreaked breast with relatively shortbright-orange or yellow legs. Because itis primarily a solitary bird, it usually occursat very low densities and is typicallyseen from dawn to dusk. Observationsat northeastern aquaculture facilitiessuggest that the green-backed heroneats about 3 live fish per hour, and theyaverage 4 inches in length.

Common GrackleThe common grackle, a frequent

predator at northeastern aquaculturefacilities, exerts an impact primarily inthe spring months, when large breedingcolonies form and small trout fingerlingsinitially are placed in outside raceways.After fingerlings exceed 5 inches inlength, grackles shift their diet to inverte-brates and grains and sometimes leavethe hatchery altogether.

The common grackle is one of thelargest members of the blackbird family

and measures approximately 16 incheslong. Males are slightly larger thanfemales and are iridescent black.Females have brownish plumage. Dur-ing daylight hours, grackles sometimesforage in large flocks. At northeasterntrout-rearing facilities during the spring,grackles consume about 3 live trout perhour at an average length of 3 inches.At warm-water facilities, grackles aresometimes present but have not beenobserved to consume fish.

MallardThe mallard is a common species of

waterfowl that frequents northeasternaquaculture facilities. However, thepredation problems it poses occur inisolated situations. Where predationsituations do occur, mallards achieveextremely high densities throughout theday and have adapted to feed in troutraceways stocked with high densities ofsmaller fish. In these situations, mal-lards generally consume 4 fish per hour,with the fish averaging 4, but sometimesreaching 6, inches in length. In other

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situations, mallards may feed on onlyaquatic vegetation or fish feed, so carefulobservations are essential to determinewhether losses of fish are occurring.

Belted KingfisherThe belted kingfisher (fig. 2) is seen

at many northeastern aquaculture facili-ties throughout the year. However, thetypically low densities at which it occursand the smaller fish it consumes lessenits potential impact on the industry.Approximately 1 foot long, the beltedkingfisher is easily recognized by thewhite band separating the dark headfrom the gray body. An efficient predatorof small fish, the belted kingfisher for-ages throughout the day by plungingdirectly into the water to capture fishnear the surface and then rapidly flies offwith its prey. It consumes fish averaging3 inches in length at a rate of almost2 fish per hour.

Figure 1— The green-backed heron is one ofthe smallest herons and a common predatorin the Northeast.

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OspreyAn efficient predator of larger, more

valuable fish, the osprey achieves onlylow to moderate densities during thespring and fall migratory periods. Com-monly called the fish hawk, the ospreyresembles a large hawk with a 2-foot-long body and a wingspan of 4.5 to 6feet. However, white on breast andhead distinguishes it from other birds ofprey. Although it may appear for only afew weeks of the year, its impact can besubstantial in terms of the size of the fishit consumes. Ospreys take about 2 fishper hour that average 12 inches longand can consume fish up to 24 incheslong.

Figure 2— The belted kingfisher, an efficientpredator of small fish, brings its prey back tothe nest.

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sumed at least $1,800 worth of goldenshiners at an Arkansas minnow farmover a 3-month period. Similarly, atMississippi catfish farms, heron popula-tions averaging 1 bird per 15-acre pondwere estimated to inflict losses worth$182 per pond per year.

Mallards and common grackleshave also been reported to cause signifi-cant economic losses at trout-rearingfacilities in Pennsylvania, averaging$725 and $969 per raceway pool,respectively, per year.

Although managers considering thecosts of bird predation should focusprimarily on the value of the fish con-sumed, other costs need to be exam-ined, too. These costs include bird-related fish scarring that cause thesefish either to die or to be unusable (fig.3). Birds also have the potential tospread disease at the facility, resulting inmore costs. Although estimates rangeup to 773,530 fish lost per year at Penn-sylvania hatcheries, few estimates con-sider all forms of loss. In controlledexperiments comparing raceway pools

Economics of Bird Predation

Although a recent survey of northeasternaquaculture facilities indicated that about80 percent were experiencing some formof bird-predation problem, the extent ofthe problem varied considerably. Gener-ally, larger facilities experienced moresevere problems with regard to the num-ber of predators involved; in two instances,annual losses of about $500,000 weredocumented. However, annual lossesranging from several hundred to severalthousand dollars were more typical.

As many as 75 great blue heronshave been documented at 1 trout-rearingfacility in Pennsylvania, where they wereestimated to consume roughly $300worth of trout per day. Smaller numbersof these predators, typically one or twogreat blue herons, may proportionallyrepresent a serious economic concern totrout producers. Although not limited totrout-rearing facilities, heron predation ispoorly documented at warm-water pro-duction facilities in the Northeast.

Elsewhere in the United States,mixed flocks of around 100 herons andegrets were estimated to have con-

with and without exclusion, losses oftrout primarily due to great blue heronsranged from 9.1 to 39.4 percent over a3- to 4-month period. On average,another 2 percent of the fish inventoriedfrom the unprotected pools had punctureholes from heron spearing. In oneinstance, a higher incidence of “straw-berry” disease was also reported fromunprotected pools.

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Figure 3— This trout has suffered thespearing typical of heron predation.

Prevention and Control ofBird Predation

In the Northeastern United States, thediversity of culturing practices and avianpredators dictates the need for a varietyof damage prevention and control tech-niques used singly or in combination toprevent predation. The following meth-ods have been recommended for preda-tion problems in the Northeast and inmost cases have been observed in usein either the Northeast or elsewhere.

Fish HusbandryAlthough changes in the design of

fish culturing facilities and fish manage-ment are often recommended for reducingpredation losses from birds, the diversityof situations where predation problemsare observed raises doubt about theoverall utility of this approach. Recom-mendations for changes in facility designto reduce heron predation include deep-ening ponds and earthen raceways to aminimum of 3 feet and maintaining steepbanks on ponds and raceways to reducewading activity. Similarly, for concreteraceways, a minimum depth of 3 feet isrecommended, but the water level

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predation increases when fish areattracted to the surface with floatingfeed. Although floating feed helps theproducer monitor fish health, the valueof this practice should be weighedagainst its potential for increasing preda-tion. Similarly, low concentrations ofdissolved oxygen in these ponds forcefish to the surface, making them morevulnerable to predation. Regular moni-toring and more timely aeration of pondscould be helpful.

ExclusionExclusion—the complete enclosure

of ponds or raceways with screens ornets—is sometimes, but not always, apractical means of preventing predation.Pond culture, particularly with pay-to-fishsites, does not lend itself to exclusion,but certain raceway configurations maybe better suited to using exclusion.

Exclusion systems vary from simple,temporary netting applied directly overindividual raceway pools to elaboratepermanent systems that completelyenclose the entire facility. Although total

facility exclusion may be the only com-pletely effective method for preventingpredation by most species of birds, tem-porary exclusion, if properly installed,may be a more cost-effective alternative.Because of its cost, total facility exclu-sion is best suited for situations wherebird sightings and economic analysisdemonstrate a significant long-termproblem caused by a number of predatorspecies. In some situations, excludingbirds from selected raceways may bemore cost-effective if integrated withother control measures. For example,selectively covering raceways containing3- to 5-inch fish could prevent predationby grackles, kingfishers, and mallards;other methods could be used to protectlarger fish.

Care must be taken when selectingand designing both temporary and per-manent exclusion systems. Failure to doso can result in systems that are ineffec-tive, cumbersome to work around, and ahazard to either the birds or the fishenclosed.

should be at least 2 feet below the top ofthe perimeter walls.

Even if these changes are accom-plished, the large repertoire of feedingbehavior exhibited by the great blueheron, including jumping into deep waterto take fish, makes the prospect for theiroverall effectiveness doubtful.

Possible modifications of fish-management strategies offer more pos-sibilities for at least a partial reduction infish predation. Where grackles are aproblem, a delay in moving the finger-lings outside in the spring would clearlybe beneficial. If such a delay is notpractical, temporarily covering the fishwith netting is an alternative. Studieshave shown that birds are more likely tofeed in ponds that are heavily stockedwith fish. Thus, reducing the amount ofstock may lessen the attractiveness ofponds to depredating birds. However,reducing stock may be contrary to thegoals of fish production.

Observations of herons feeding atcatfish ponds and other warm-wateraquaculture situations suggest that

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Selection of proper materials is ofcritical importance. Use small (1- to 2-inch mesh) wire or net to exclude allbirds, but avoid finely textured nettingthat may entangle birds on contact.Although relatively inexpensive polypro-pylene netting is available for this use,the usable lifespan of this netting is 3–5years. Framing for temporary coversused on concrete raceways should bestrong and durable but also lightweightso it can be easily moved. Althoughwood is typically used, framing consist-ing of 1.5-inch polyvinyl chloride (PVC)pipe makes these covers easier tomove.

To be completely effective, tempo-rary netting or screens must totally coverraceway pools and must be properlysupported. Birds, particularly heronsand mallards, will quickly find any gapsin the system and breach the barrier.Center supports of the netting suspendedover earthen raceways are important toprevent heron predation. The weight ofherons walking on unsupported nettinghas been observed to cause the net to

sag and allow herons to spear fishthrough holes that they develop in thenetting. Nets sagging into the water alsopresent a hazard to fish.

An important consideration in thedesign of exclusion systems is the abilityto perform routine fish maintenance andharvest operations. Where this is aprime consideration, more elaborate,permanent exclusion systems that allowpersonnel and equipment to work underthe exclusion system may be preferable.With permanent systems, particularattention must be given to winterweather conditions. If ice forms on net-ting, the whole exclusion system cancollapse. That has happened in Penn-sylvania. To avoid this problem, con-sider designing the system so workerscan remove netting before impendingstorms.

Other Barrier SystemsOther barrier systems include over-

head wires and perimeter fencing, bothof which have been shown to be selec-tively effective for excluding certain

species of birds. These systems are noteffective against smaller birds like grack-les and kingfishers but may be morecost effective than exclusion systems forpreventing predation by larger birds.

Overhead Wire Systems— Overheadwire systems (fig. 4), consisting ofmonofilament and stainless steel wire,can be a durable, all-weather alternativeto netting for excluding aerial avianpredators such as gulls, ospreys, andcormorants from both ponds and race-ways. However, when combined withperimeter fencing or netting, a durable,all-weather, cost-effective system can becreated to deter herons as well. Forexample, the Limestone Springs hatch-ery in Pennsylvania has successfullyexcluded both great blue herons andblack-crowned night herons by using aperimeter chain-link fence to support anoverhead monofilament line systemspaced at 6-inch intervals. Wire spacingof 10 inches may be adequate. To pre-vent these birds from landing on thechain-link fence and dropping through

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Figure 4— Overhead wires can make adurable, all-weather exclusion system.Attaching such a system to a tall fence makes

the wires, an electric fence was installedalong the top of the chain-link fence.

Where a chain-link fence is costprohibitive, some barrier such as nettingat the sides and ends is recommendedfor preventing both herons and aerialpredators from entering to enhance thebarrier’s effectiveness and to minimizebird injury, streamers or other materialsshould be hung from lines to make themmore visible.

Perimeter Fencing and Netting—Perimeter fencing and netting systemscan deter herons and other wading birdsfrom visiting both ponds and raceways.The most effective system evaluateduses two-strand electric fencing (fig. 5).At earthen raceways and ponds thewires are suspended 12 and 16 inchesabove the water from fenceposts posi-tioned in the water approximately 1 footfrom the water’s edge. On concreteraceways, fenceposts are positioned inholes drilled in the center of the racewaywalls.

it easy for facility personnel to workunderneath.

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The use of nonlethal levels of elec-tric current to shock birds quickly trainsthem to avoid the area. In some cases,however, herons can learn to avoid thefence by flying directly into the center ofthe pond or raceway. This happensmost often when pond or raceway depthis shallow or raceway flow is low.

Although the cost of this system islow, regular maintenance is required toprevent the electric fence from ground-ing out. More elaborate nonelectrifiedperimeter fences and wires also havebeen shown to provide some protectionfrom heron predation. However, perim-eter netting suspended horizontally ordiagonally over the water surface isminimally effective. At best, perimetersystems do not deter all herons unlessadditional protection is provided by anoverhead wire system or netting.

Frightening the PredatorsTechniques to frighten predators

rely on visual and/or auditory stimuli toproduce fear and thus discourage birdsfrom remaining in the area. Although

Figure 5— Perimeter fencing and nettingsystems can deter herons and other wadingbirds from visiting both ponds and raceways.

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most northeastern aquaculture producershave consistently rated frightening asrelatively ineffective, it may be usefulwhere barrier systems and other tech-niques are impractical. To be effective,frightening procedures must be activelyand aggressively pursued in a carefullyplanned program. If possible, the regimeshould start before birds establish aregular feeding pattern at the site.

Many devices are commerciallyavailable for scaring birds, includingpyrotechnics, gas-operated exploders,electronic noisemakers, bird distresscalls, stationary and pop-up effigies,eyespot balloons, raptor models, strobeor flashing lights, reflective tapes, andwater-spray devices.

Although use of one technique mayproduce positive results in the shortterm, longer term results are bestachieved by using a combination ofmethods and by alternating the devicesused. Effectiveness of these devicescan also be enhanced if they are acti-vated upon arrival of the avian predator.Motion sensors or infrared beams can

be used to detect the predator and acti-vate many of these devices, thus increas-ing their effectiveness.

Pyrotechnic Devices— Pyrotechnicdevices are effective against most birds.They are fired with a breech-opening,open-bore 12-gauge shotgun or a spe-cially designed pistol. Shell crackers areshotgun shells that contain a firecrackerthat is projected 50 to 100 yards beforeexploding. This produces two loudnoises, one when the gun is fired andanother when the firecracker explodes.Because wads from the shell may stickin the gun, it is important to check thebarrel after each shot. Other pyrotech-nic devices called screamer sirens andbird bombs are fired from a 15-mm pistollauncher using .22-caliber blanks.Although the range of these projectiles isonly 35 to 75 yards, they are lessexpensive and more convenient to use.

Automatic Exploder— The automaticexploder is effective in deterring mostbirds if combined with other techniques.

Propane or acetylene gas is used tooperate this small cannon, which isequipped with an electronic timing device.The cannon emits loud explosions atadjustable intervals and can be heardover areas of up to 5 acres. For bestresults, exploders should be elevatedabove vegetation and moved to differentlocations every 1 or 2 days.

Alarm or Distress Calls —Broadcastingrecordings of alarm or distress calls hasbeen shown to be effective in frighteningblack-crowned night herons but not greatblue herons. For best results, distresscalls should be broadcast as birds beginto arrive, and the time interval betweenbroadcasts should be as long as possible.

Lights— Strobe lights, barricade lightsand revolving beacons have been usedto frighten birds. Of these, strobe lightsappear to be the most effective in fright-ening night-feeding birds, particularly theblack-crowned night heron.

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Water-Spray Devices— Water sprayfrom strategically placed rotating sprinklerscan deter birds from feeding. In somecases, water aeration systems can bemodified for this purpose. Best resultsare obtained when sufficient water pres-sure is used and sprinklers are operatedon an on–off cycle.

Human Effigies— Human effigies orscarecrows rely on the innate fear mostbirds have of humans. For this reason,effigies that best simulate humanappearance or that exhibit movementusually are more effective. Successfuluse of effigies at aquaculture facilitieshas been demonstrated when effigiesare periodically replaced with humansfiring live ammunition or pyrotechnics.

Dogs— The use of dogs to deter birds atnortheastern aquaculture facilities hasmet with variable success, depending onthe motivation, training, and tempera-ment of the dog. Physical characteris-tics of the facility, such as total size andlayout, also influence effectiveness. For

example, dogs obtained from animalshelters proved marginally effective inreducing predation at a large State facil-ity in New York.

Harassment Patrols— Harassmentpatrols by persons on foot or in vehiclesare widely used for frightening birds ataquaculture facilities, particularly largerfacilities. Such patrols typically involvethe use of pyrotechnic devices. Theeffectiveness of the technique is largelyrelated to the fear response birds haveto human presence. However, this tech-nique can become highly labor intensivebecause of the need for patrols through-out the day and night. For this reason,human effigies, automatic exploders,and other devices are needed to supple-ment these patrols when personnelcannot be present.

Lethal ControlLethal control, usually by shooting,

is the selective killing of birds involved inpredation problems. Although mostwildlife-damage-management profes-

sionals consider lethal control appropri-ate and necessary as a last resort incertain situations, its use remains con-troversial. In the Northeast, lethal con-trol appears to be most appropriate andnecessary as part of an integrated pro-gram to control significant and wide-spread problems caused by great blueherons. Lethal control of grackles alsoseems appropriate, but it may not bepractical because of the large number ofindividuals usually involved. Lethalcontrol seems to be practical only whenthere are a limited number of individualsthat need to be removed. Typically,lethal control is recommended only toreinforce or supplement nonlethal tech-niques by removing a few individuals.

Another situation when lethal controlmight be used is to remove a limitednumber of herons that remain at aqua-culture facilities during the winter monthsafter temporary removal of netting.

Lethal control, involving either trap-ping or shooting birds, is illegal without apermit from the U.S. Fish and WildlifeService. State permits also may be

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required. An exception to this require-ment applies to the common grackle,which under Federal provisions can bekilled without an advance permit whenbirds are in the act of causing depreda-tion. However, State permits for gracklecontrol may be required. Inquiries aboutobtaining a permit should be madethrough the appropriate Animal DamageControl (ADC) office of the U.S. Depart-ment of Agriculture’s (USDA) Animal andPlant Health Inspection Service (APHIS).

Capture and Release TechniquesAlthough not a practical solution in

many cases, capturing and relocatingcertain birds may be a viable alternativeto lethal control in specific situations.This technique involves capturing birdsalive, transporting them some distance,and releasing them. It might be useful incontrolling mallard populations. Thechemical immobilization agent alpha-chloralose can be used to capture largenumbers of mallards. Use of alpha-chloralose is restricted to ADC personnelfor removing waterfowl from nuisance

and damage situations. But the translo-cation of waterfowl may be regulated orprohibited by specific State wildlife agen-cies. Contact the appropriate ADC officeconcerning possible use of this proce-dure.

Economics of Predation Control

When tracking control costs, aquaculturefacility managers need to consider notonly the prorated cost, including mainte-nance of the device or system over time,but also the additional cost of performingfish-maintenance procedures with thesedevices or systems in place. For tempo-rary exclusion systems, the labor cost ofthe latter has been documented toexceed the cost of buying, installing, andmaintaining the system itself. At north-eastern aquaculture facilities, 82 percentof producers reported spending $500 orless for controlling birds annually, possi-bly reflecting the large number of smallerfacilities sampled. In contrast, largeState and private trout hatcheries inPennsylvania have recently spent from$42,000 to $261,000 to erect total-facilityexclusion systems.

The cost effectiveness of controlmeasures should be considered at eachfacility before implementation. To accu-rately examine cost effectiveness, someknowledge of the cost of the controlmeasure and its expected effectivenessis needed. This knowledge, combined

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with knowledge about the cost of preda-tion, can be used to perform a cost–benefit analysis with the following for-mula:

Cost–benefit ratio = Control cost ÷Percentage effectiveness (decimalfraction) ÷ Predation cost

If this cost–benefit ratio is greaterthan 1, the cost of implementing controlwill exceed the savings realized fromusing it. In contrast, a ratio of less than0.1 clearly suggests that the controlmeasure will be beneficial. For example,the cost of a chain-link fence and over-head wire system erected at one trouthatchery was $19,340 to cover a rearingarea of approximately 22,000 squarefeet. Over the expected 20-year lifespanof this system, the annual prorated costincluding maintenance is $1,728. Duringits first year of use, this system was 100-percent effective in reducing losses fromgreat blue herons and black-crownednight herons, resulting in actual savingsof $459,453. The cost–benefit ratio of

the system in this situation is 0.04, but itis strongly influenced by the extremelylarge predation cost and the expectedlong life of this system. Considering itsdurability, this system has been pro-jected to be more cost effective thansimilarly priced total-facility exclusionwith netting, and it may be applicable toother situations where predation costsdue to herons are high.

For Further Information

In New York, contact

USDA–APHIS–ADC1930 Route 9Castleton, NY 12033–9653Phone (518) 477–4837

In Pennsylvania, contact

USDA–APHIS–ADC2301 N. Cameron StreetRoom 413Harrisburg, PA 17110–9405Phone (717) 238–4127