DOUBLE-CRESTED IMPACTS TO COMMERCIAL AND NATURAL RESOURCES

JlMMY D. TAYLOR II, USDA , APHIS , Wildlife Services , National Wildlife Research Center , Mississippi Field Station , P.O. Drawer 6099 , Mississippi State, MS 39762 , USA BRIAN S. DORR , USDA , APHIS, Wildlife Services, National Wildlife Research Center , Mississippi Field Station , P.O. Drawer 6099, Mississippi State , MS 39762 , USA

Abstract: The North American population of double-crested (Phalacrocorax auritus) has increased at an annual rate of 6.8% since 1966, with regional growth exceeding 20%/year since 1990 in Ontario and states bordering the Great Lakes. Population numbers , though operating under biological carrying capacity , have exceeded acceptance capacity with several wildlife stakeholder groups throughout Canada and the United States. Stakeholder concerns predominantly focus around social , ecological , and economic values associated with habitat destruction , changes in recreational fisheries , and loss of production at facilities. We describe perceptible impacts to these commercial and natural resources , and discuss current research and management efforts focused on reconciling discrepancies between stakeholders acceptance and biological carrying capacities.

Key words: aquaculture , biological diversity , carrying capacity , double-crested cormorant , Phala crocorax auritus, recreational fisheries

Proceedings of the I 0th Wildlife Damage Management Conference. (K.A . Fagerstone, G.W. Witmer , Eds). 2003

INTRODUCTION changes and increase in the presence of Anthropogenic impacts to the North human population growth , urban expansion , American landscape are linked to local, and extensive habitat alteration . regional , and complete extinction of numerous The double-crested cormorant flora and fauna . Conservation awareness and (hereafter , cormorant) is the most numerous cooperation between c1t1zens, private and widely distributed of the 6 North organizations , and state and federal agencies American cormorants (Hatch and Weseloh have championed successful efforts that have 1999). Human persecution in the nineteenth restored viable populations to their historic and early twentieth centuries , coupled with ranges throughout the continent. However , environmental contamination through the many species are terminally affected by large­ early 1970s (Hatch 1995; Hatch and Weseloh scale habitat alteration and continue to decline 1999), severely reduced population levels of despite intensive management efforts. Natural cormorants throughout North America resource managers rarely are challenged with (Ludwig 1984; Hatch and Weseloh 1999; controlling over-abundant populations, but Wires et al. 200 I). Response to increased rather plan for maintenance or recovery of human environmental awareness (i.e., populations. Ironically, one waterbird in reduction of environmental contaminants and North America has drawn a tremendous regulatory protection) over the past 3 decades amount of attention in the last 40 years for its facilitated a population resurgence of ability to respond positively to environmental cormorants in North America , particularly in

43 the interior region, with numbers in some cormorants. However, birders represent a areas doubling in < 5 years (Hatch and stakeholder group still interested in viewing Weseloh 1999, Glahn et al. 2000). Changes in cormorants in their natural environment fish communities on the breeding (Hatch and (Vermeer 1970, Conniff 1991, Bedard et al. Weseloh 1999) and wintering grounds (Glahn 1995) and which consider such observations et al. 2000) also may have contributed to an positive events. increase in cormorant numbers. Conservative Reports of cormorant guano estimates of the total population of cormorants destroying vegetation and cormorant colonies in the United States and Canada are > 1 having an unpleasant odor are not new events million individuals (Tyson et al. 1999), but a (Lewis 1929). However, Lewis (1929) true population estimate is likely closer to 2 reported that cormorants dwelled in secluded million (Hatch and Weseloh 1999). places and had no effect on those who did not While the overall rate of growth in seek them. Today, some homeowners and North American cormorant populations business owners in the Great Lakes region slowed during the early 1990s (Tyson et al. may find the sight and smell of cormorant 1999), significant population increases colonies offensive and aesthetically occurred in some areas. In the Great Lakes, unpleasing (J. Henke , Oneida Lake where cormorants reached a low of around Association, unpublished report). Some 200 nesting pairs between 1968 and 1973 outdoor enthusiasts in the Great Lakes region (Ludwig 1984), nesting pairs of cormorants and private land owners along the St. increased from 38,000 in 1991 (Weseloh et al. Lawrence Estuary also are aesthetically 1995), to 93,000 in 1997 (Tyson et al. 1999) opposed to cormorants roosting in wooded and to 115,000 in the 2000 breeding season areas ( e.g., Presqu ' ile Provincial Park, (D.V.C. Weseloh , unpublished data). Ontario) due to the unsightly loss of native flora (Ontario Parks 2002, unpublished) . STAKEHOLDER PERCEPTIONS Ecological Values Social Values Environmentalists, naturalists , natural For centuries , cormorants have been resource managers, and scientists perceive associated with unpleasant things and have ecological value in cormorants. As with all taken the common names "crow duck" , "eel living organisms , cormorants are intrinsically crow" , "lawyer", "shark", and "water turkey" valuable as members of a complex food web. (Lewis 1929). Conniff ( 1991) reported use of They fill a niche as consumers of small fish in the word "cormorant" in classical literature marine and freshwater environments, representing greed and gluttony. Yet despite generally taking fish at depths ::::8 m (Hatch their aversion to some, cormorants remain and Weseloh 1999). In natural waters, aesthetically pleasing to others. Lewis (1929) cormorants may support maintenance of estimated 26,586 breeding cormorants aquatic species diversity and stabilize the throughout North America. During that era, relationship between predatory fish and their cormorants provided a sense of wilderness prey (Glahn et al. 2000). Conversely, . and fascination and were welcomed at cormorants may decrease local avian diversity summer cottages and near scenic tourist areas on the breeding grounds through direct (Lewis 1929). Today, facing a continental competition for nesting sites (Jarvie et al. population approaching 2 million birds (Hatch 1999, Shieldcastle and Martin 1999). and Weseloh 1999), people in general are Cormorants also may decrease local plant perhaps more aware and less tolerant of diversity at breeding colonies (Weseloh and

44 Ewins 1994, Bedard et al. 1995, Jarvie et al. groups. 1999, Shieldcastle and Martin 1999) and The noise and smell of cormorant winter roost sites (G. Ellis, Wildlife Services, breeding colonies, coupled with the personal communication) through deposition appearance of dying trees, distract from the of excreta. appearance of an area, resulting in potential abandonment by recreational users and loss of Economic Values profit by business owners. Destruction of tree During the 19th and early 20th nesting cover and competition for space in centuries, cormorants were a subsistence item traditional breeding colonies impacts other in the Great Lakes region and generous colonial birds such as black-crowned night . bounties were paid for their meat (Lewis herons (Nycticorax nycticorax) [ Jarvie et al. 1929). Near the north shore of the Gulf of St. 1999, Shieldcastle and Martin 1999], great Lawrence, cormorant eggs were collected and blue herons (Ardea herodias), great egrets eaten, whereas young cormorants were killed (Ardea alba), and snowy egrets (Egretta and used to feed dogs and captive foxes thula) [Shieldcastle and Martin 1999]. Given (Lewis 1929). On occasion, cormorant meat their ability to switch to ground nesting once was eaten by local inhabitants, explorers, and trees are destroyed, cormorants may settlers (Lewis 1929). competitively exclude other colonial Today, cormorants are protected by waterbirds from traditional sites in the federal and international laws as migratory absence of control efforts. birds and there is no evidence that cormorants possess a positive economic value for food or Catfish Production subsistence. Rather, cormorants are most In a national survey of catfish often associated with economic loss. In fact, producers , 69% reported wildlife-caused most impacts associated with cormorants can losses of catfish with cormorants as the most be viewed from socioeconomic perspectives. frequently cited predator (Wywialowski 1999). Glahn and Brugger (1995) predicted CORMORANTIMPACTS wintering cormorants in the Delta region of Mississippi required an average of 504 Habitat Destruction g/bird/day (22% of their body mass) from Cormorants are notoriously destructive November to March, resulting in an annual on the breeding grounds. During nest loss of $2 million (US$) in replacement costs building, cormorants defoliate tree canopies for 1989-90 and 1990-91. With winter roost by stripping leaves and breaking branches. counts in Mississippi more than doubling Throughout the breeding season, cormorants from 1990 to 1998, Glahn et al. (2000) deposit vast amounts of guano in and around projected economic losses due to cormorant nest sites. Ground-nesting cormorants prevent predation on catfish at $4.8 and $4.9 million establishment of ground cover and woody in 1997-98 and 1998-99, respectively. Total growth, while tree-nesting cormorants cause estimated cost oflosses to all North American death to upper and mid-canopy vegetation as catfish producers in 1996 was $12 million , well as ground flora. The resulting habitat though the added costs of wildlife damage destruction is highly visible (Weseloh and prevention may have increased total cost to Ewins 1994, Bedard et al. 1995, Jarvie et al. >$17 million or 4% loss of total sales 1999, Shieldcastle and Martin 1999), resulting (Wywialowski 1999). in an array of social, ecological, and economic Economics of the catfish market are impacts perceived differently by stakeholder more complicated than offsetting catfish loss

45 with fingerling replacement cost, because cormorants did not impact game fish on Lake production is largely a function of total Erie and Lake Ontario, respectively. biomass at harvest (Tucker et al. 1992). However, cormorants have been shown to Using enterprise budgets , Glahn et al. (2002) impact fisheries during stocking, when small estimated net returns on a commercial-scale fish are released into rivers and lakes pond using a single-batch cropping system (Blackwell et al. 1997, Derby and Lovvorn ranging from $1189 .29/ha without cormorant 1997, Ross and Johnson 1999). predation to $-132 .12/ha with predation. Further research in the Great Lakes Calculations by Glahn et al. (2002) including region revealed that cormorants may impact compensatory growth of surviving catfish , recreational fisheries by reducing specific size suggested that previous estimates of catfish classes of sport fish. Schneider et al. (1999) · production loss in the Mississippi Delta region found that cormorant diets in the eastern basin may have been underestimated 5-fold. Thus , of Lake Ontario included 3- to 5-year old impacts of cormorant predation on catfish smallmouth bass (Micropterus dolomieui) production in 2000 were approximately $25 when alewife and other prey species million or 8.6% of total sales (Glahn et al. populations were low. VanDe Valk et al. 2002). While 4-9% loss may seem low, (2002) estimated that cormorants consumed production loss is not dispersed equally 49% of age-1 , 26% of age-2, and 13% of age- among catfish producers (Duffy 1995) and 3 and older yellow perch present in Oneida varies spatially with respect to cultural Lake, New York in 1997. Furthermore, they practices (i.e,, stocking density, size class of reported that cormorant depredation of sub­ fish, and cropping system) and adjacency to adults (ages 1 and 2) was a larger source of cormorant roost sites (Mott et al. 1992, King mortality than angler harvest, while et al. 1995). Impacts also vary temporally , depredation of adults (2:3 years) was with 50% of catfish losses projected to occur comparable to angler harvest (VanDeValk et in February and March in the Mississippi al. 2002). Delta (Glahn and Brugger 1995). Concern over depredation of recreational fisheries in the cormorant's Recreational Fisheries winter range is overshadowed by concern over Perceived impacts of cormorants on impacts to aquaculture; however, 2 studies recreational fisheries pre-date those of have examined food habits of cormorants in aquaculture (Lewis 1929, Mendall 1936), natural waters of the southern United States. though they also vary spatially and In a Texas study of 8 public reservoirs, shad temporally. Food habits studies on the (Dorosoma spp.) and sunfishes (Lepomis spp.) breeding grounds in the Great Lakes region accounted for 90% of the total food items by revealed that cormorants forage primarily on number in 420 cormorants sampled. small forage fish such as alewife (Alosa Similarly , Glahn et al. (1998) found shad and pseudoharengus), emerald shiners (Notropis sunfish to be the most common food items in atherinoides ), gizzard shad (Dorosoma 142 and 51 cormorants feeding on lakes in cepedianum) , sculpins (Cottus spp.), and Mississippi and Alabama, respectively. sticklebacks ( Gasterosteus spp. and Pungitius pungitius) [Lewis 1929, Craven and Lev MANAGEMENT OF IMPACTS 1987, Ludwig et al. 1989, Weseloh et al. 1995, Bur et al. 1999, Ross and Johnson Breeding Grounds 1999]. Furthermore , Bur et al. (1999) and Measures to control cormorants on the Ross and Johnson (1999) found that breeding grounds are applied locally to reduce

46 local impacts and usually consist of multiple most immediate effect on reducing local techniques. Common combinations of control impacts; however , it is generally the least include egg-oiling, nest removal, harassment , socially acceptable method of control. and (killing adults and/or chicks) . Unlawful shooting of cormorants on the Egg-oiling is an effective technique breeding grounds is well documented (Hobson for reducing reproductive success in et al. 1989, Ewins and Weseloh 1994, Keith cormorants while preventing or delaying re­ 1995), though the effects on impact reduction nesting attempts within breeding seasons and population growth are unknown. (Bedard et al. 1995, Farquhar et al. 2002, Dorr Bedard et al. (1999) initiated a 5-year et al. 2003); however , nests must be oiled culling /egg-oiling program in 1989 to halt the multiple times throughout the breeding season population increase of cormorants in the St. to ensure successful management. Nest Lawrence River Estuary and reduce damage removal also may reduce reproductive to unique forest habitat. This lethal/non-lethal success , though adults often re-nest combination exceeded expected goals and immediately in the same vicinity . Thus , to be reduced populations numbers faster than effective , management must be extended model predictions, likely due to a greater throughout the breeding season to remove vulnerability of males (203:100) to shooting successive nests. Moreover , egg-oiling and (Bedard et al. 1999). Nevertheless , the nest destruction must reduce local impacts efficacy of the program on impact reduction to (e.g., number of fish eaten , number of trees forest habitat was not reported. killed) and be cost effective; however , no published studies have evaluated their Wintering Grounds efficacy in reducing impacts. Measures to control cormorants on We found no published studies that wintering grounds focus almost exclusively quantified the effects of breeding season on reducing local impacts on catfish haras sment on reducing impacts of cormorants aquaculture facilities in the southeastern U.S. and speculate that it may be cost-prohibitive Ironically , the least-used methods on breeding in many circumstances. Furthermore , grounds are the most used on wintering cormorants often breed in close proximity to catfish ponds: harassment and shooting. less abundant bird species, which may be Physical barriers are a management option for negatively affected by harassment events. small-scale fish production ( e.g., tropical fish) Chipman et al. (2000) successfully used or hatcheries where fish are grown in combinations of boat chases , pyrotechnics , raceways (Parkhurst et al. 1987, Brugger mylar ribbon , human effigies , propane 1995, Pitt and Conover 1996); however , cannons , and electronic scare devices to exclusion devices such as nets and wires are harass post-breeding and migrating not practical for large-scale aquaculture cormorants from Oneida Lake, New York. operations (Mott and Boyd 1995, Price and Harassment was conducted in September Nick:um 1995, Littauer et al. 1997). (Chipman et al. 2000), following natural Many of the same harassment tools dispersal of common terns (Sterna hirundo ), a available for breeding cormorants are used species of concern in New York. during winter. Harassment programs must be Adult mortality affects reproductive aggressive and consistent to be effective output of cormorants more than nest (Littauer et al. 1997). They also must be treatments (Ewins and Weseloh 1994, adaptive and use multiple techniques to Blackwell et al. 2002). Culling of cormorants prevent habituation (Reinhold and Sloan on the breeding grounds also may have the 1999). The most common method of delivery

47 on southeastern catfish farms is via population in Bavaria, cormorants killed on harassment patrols (Wywialowski 1999, Bavarian lakes were quickly replaced by Wires et al. 2001 ), whereby farmers and migrating cormorants. Thus, they concluded employees actively scare birds when not that shooting was an inappropriate involved in other farm duties ( e.g., feeding, management tool for reducing impacts on fish harvesting, repairing equipment). Patrols use during cormorant migration (Keller et al. vehicles and pyrotechnics to disperse birds 1998). away from their facilities, thereby reducing One technique of non-lethal control immediate impacts. Farmers occasionally with merit among southeastern catfish stage unmanned vehicles on pond levees to producers is roost dispersal. Producers in deter bird use of nearby ponds. Mississippi use roost dispersal more than In 1986, the U.S . Fish and Wildlife other catfish producing states to prevent Service (USFWS) began issuing depredation depredation (Wywialowski 1999) and the permits to catfish farmers, which allowed USDA Wildlife Services Program coordinates them to shoot cormorants on their facilities . that effort in Mississippi at the request of the In 1998, USFWS issued a standing producers (Reinhold and Sloan 1999). depredation order (USFWS 1998; 50 CFR Numbers of cormorants observed visiting 21.4 7) that allows commercial freshwater catfish ponds may be reduced by 70-90% aquaculture producers in 13 states to take when nearby roosts are disturbed (Mott et al. cormorants without a permit, when found 1992, 1998). Thus, producers participating in committing or about to commit depredations a night roost dispersal program spend less to aquaculture stock . These events allow money to control cormorants than those that catfish producers to reinforce harassment with do not (Mott et al. 1998). lethal control (Mott and Boyd 1995, Reinhold and Sloan 1999). Wywialowski (1999) found FUTURE MANAGEMENT OF that shooting to harm or kill under USFWS CORMORANTS permits was the most frequently cited loss Perceptions of perceived and realized prevention method (57%) used by catfish impacts to natural resources are likely to producers. Similarly, Stickley and Andrews remain polarized by stakeholder groups. (1989) found that 60% of producers surveyed Given the extent of perceived impacts, it is patrolled their ponds and shot at cormorants. possible that a numerical decrease in Neither survey differentiated shooting to cormorant populations caused by density­ harass from shooting to kill, though it is dependent factors and/or wildlife damage suspected that firearms are used in some management may go unnoticed by some instances to scare birds instead of groups. Moreover, there are logistical pyrotechnics. problems associated with quantifying the Killing cormorants on catfish ponds to effects of management on impacts caused by reduce local or regional populations has not cormorants. For example , breeding been a management goal nor has it been cormorants that eat freshwater fish and breed investigated with scientific rigor. Keller et al. on Lake Ontario will continue to eat fish (1998) used lethal control in Bavaria , despite nest destruction or egg-oiling. Germany to reduce local populations of great Furthermore , age at first breeding in cormorants (Phalocrocorax carbo ), and cormorants is generally year 3 and most sub­ thereby reduce local fish depredation. adults do not return to their natal site until However , they found that despite killing the sexual maturity (Hatch and Weseloh 1999). equivalent of 50-100% of the mean cormorant Thus, there is a time lag (.::::.2years) in

48 population response to treatments by the Midwest. United States Department of cormorants (Bedard et al. 1999) and the Agriculture , Animal and Plant Health Inspection Service Technical Bulletin 1879, fishery. Washjngton , D.C. Recently proposed changes to CHIPMAN, R .B ., M.E. RICHMAN, J.T. GANSOWSKI, cormorant management (Barras and Tobin K.J. PREUSSER, D.L. STANG, J. COLEMAN, 2004; 50 CFR Part 21, Volume 68) may AND D. SLATE. 2000 . Bada bang , bada further task natural resource managers and boom: Dispersal of fall migrating cormorants to protect sportfish on Oneida Lake , New expand their roles spatially and temporally in York . Proceedings of the Wildlife Damage reducing impacts by cormorants . Management Conference 9:46 . Nevertheless, managers must work closely CONNIFF, R . I 991. Why catfish farmers want to with research scientists throughout these throttle the crow of the sea. Srojthsonian processes and quantify the effects of local 22:44-55. CRAVEN, S.R. , AND E. LEV 1987. Double-crested management activities throughout the range of cormorants in the Apostle Islands , Wisconsin , cormorants. USA: population trends , food habits , and fishery depred ations . Colonial Waterbirds LITERATURE CITED I 0:64- 7 1. BARRAS, S.C. , AND M.E. TOBLN. 2004 . The role of DERBY,C.E. , ANDJ .R. LOVVORN. 1997. Predation on research in expanded regional management of fish by cormorants and pelicans in a cold­ double-crested cormorants. Proceedings of water river: a field and modeling study. the Wildlife Damage Management Conference Canadian Journal of Fisheries and Aquatic 10:87-94. Science 54: 1480-1493 . BEDARD, J., A. NADEAU, AND M. LEPAGE. 1995 . DORR, B.S., J.D . TAYLORII , S.J . WERNER, D .T. KING, Double-crested cormorant culling in the St. J.F. FARQUHAR, l.M . MAZZOCCHI, ANDR.D. Lawrence River Estuary. Colo nial Waterbirds McCULLOUGH. 2003. Effects of egg-o iling 18 (Special Publication I ):78-85. on double-crested cormorant movements in __ , , and 1999. Double-crested eastern Lake Ontario. New York Department corn10rant cullin g in the St. Lawrenc e River of Environmenta l Conservation Special Estuary: result s of a five-year program . Pages Report , March 2003. 147-156 in M. E. Tobin , technical coordinator. DUFFY, D.C. 1995. Why is the double-crested Symposium on double-crested cormorants: cormorant a problem ? Co lonial Waterbirds 18 population statu s and managem ent issues in (Special Publication I ):25-32. the Midwest. Uni ted States Department of EWINS, P.J ., AND D .V. WESELOH. 1994. Effects on Agriculture , Animal and Plant Health productivity of shooting of double-crested Inspec tion Service Technical Bulletin 1879 , cormorants on Pigeon Island, Lake Ontario , Washington, D.C. 1993. Journal of Great Lakes Research BLACKWELL, B.F ., W.B. KROHN, N.R. DUBE, ANDA.J. 20:761-767. GODIN. 1997. Spring prey use by double­ FARQUHAR, J.F ., R.D . MCCULLOUGH, AND I.M. crested cormorants on the Penobscot River , MAZZOCCHI. 2002 . Cormorant management Maine. Co lonial Waterbirds 20:77-86. activities in lake Ontario 's eastern basin . New __ , M.A . STAPANIAN, AND D.V . WESELOH. 2002. York Department of Environmental Dynamics of the double-crested cormorant Conservation Special Report , March 2002. population on Lake Ontario. Wildlife Society GLAHN, J. F., ANDK.E . BRUGGER. 1995. The impact Bulletin 30:345-353 . of double-crested cormorants on the BRUGGER, K.E. 1995. Double-crested cormorants and Mississippi delta catfish industry: A fisheries in Florida . Colonial Waterbirds 18 bioenergetics model. Colonial Waterbirds 18 (Special Publication 1): 110-117. (Special Publication I) : 168-175 . BUR, M.T. , S.L. TINNERELLO,C.D. LOVELL,AND J.F. --' J.B. HARRELL, ANDC. YYLES. 1998. The diet TYSON. 1999. Diet of the double-crested of wintering double-crested cormorants cormorant in western Lake Erie. Pages 73-86 feeding at lakes in the southeastern United in M. E. Tobin , technical coordinator. States. Colonial Waterbirds 21 :446-452. Symposium on double-crested cormorants: __ , M.E. TOBIN, AND B.F . BLACKWELL. 2000. A population status and management issues in science-based initiative to manage double-

49 crested cormorant damage to southern crested corn1orant [Phalocrocorax auritus aquaculture . United States Department of auritus, (Lesson)]. Ph.D. Dissertation . Agriculture , Animal and Plant Health Corne ll University, Ithaca , NY , USA. Inspection Service Publication 11-55-0 I 0, LITTAUER, G.A ., J.F. GLAHN, D.S. REINHOLD, AND Washington , D.C., USA. M.W. BRUNSON. 1997. Control of bird __ , S.J. WERNER, T. HANSON, AND C.R. ENGLE. predation at aquaculture facilities: strategies 2002. Cormorant depredation losse s and their and cost estimates. Southern Regional prevention at catfish farms: economic Aquaculture Center Publication 401 . considerations. Pages 138-146 in L. Clark , Mississippi Cooperative State Extension editor. Human conflicts with wildlife: Service, Mississippi State , MS, USA. economic considerations. Proceedings of the LUDWIG, J.P. 1984. Decline, resurgence and Third NWRC Special Symposium, Fort population dynamics of Michigan and Great Collins, CO , USA. Lakes double-crested cormorants. Jack-Pine HATCH, J. J. 1995. Changing populations of Warbler 62:91-102. double-crested cormorants. Colonial , J.P. , C.N. HULL, M .E. LUDWIG, AND H.J. Waterbirds 18 (Special Publication 1):8-24. AUMAN. 1989. Food habits and feeding HATCH, J.J. , AND D.V . WESELOH. 1999. Double­ ecology ofnesting double-crested cormorants crested cormorant (Phalacrocorax auritus) in in the Upper Great Lakes , 1986-1989. Jack­ A. Poole and F. Gill, editors. The birds of Pine Warbler 67:115-127. North America. The Academy of Natural Mendall , H.L. 1936. The home-life and economic Sciences , Philadelphia , Pennsylvania , USA, status of the double-crested cormorant and The American Ornithologists Union, Phalocrocorax auritus auritus (Lesson). Washington, D .C., USA. Maine Bulletin 39: 1-159. HOBSON, K.A., R.W . KNAPTON, AND W. LYSACK. MOTT, D.F. , AND F.L. BOYD. 1995. A review of 1989. Population , diet , and reproductiv e techniques for preventing double-crested success of double-crested cormorants breedin g cormorant depredations at aquaculture on Lake Winnipegosis , Manitoba , in 1987. facilities in the southeastern U.S. Colonial Colonial Waterbirds 12:191-197. Waterbirds I 8 (Special Publication I): I 76- JARVIE, S., H. BLOKPOEL, ANDT. CHIPPERFIELD.1999 . 180. A geographic information system to monitor __ , K.J. ANDREWS,ANDG.A. LITTAUER. 1992. An nest distributions of double-crested eva luation of roost dispersal for reducing corn1orants and black-crowned night herons at cormorant act1v1ty on catfish ponds . shared colony sites near Toronto, Canada . Proceedings of the Eastern Wildlife Damag e Pages 121-130 in M. E. Tobin , technical Contro l Conference 5:205-211. coordinator. Symposium on double-crested __ , J.F. GLAHN,P.L. SMITH, D.S. REINHOLD, K.J. cormorants: population status and BRUCE, AND C.A. SLOAN. 1998. An management issues in the Midwest. United evaluation of winter roost harassment for States Department of Agriculture, Animal and dispersing double-crested cormorants away Plant Health inspection Service Technical from catfis h production areas in Mississippi . Bulletin 1879, Washington , D.C., USA. Wildlife Society Bulletin 26:584-591. KEITH, J.A. 1995. Management policies for PARKHURST, J.A ., R .P. BROOKS, AND D.E. ARNOLD. cormorants in Canada. Colonial Waterbirds I 987. A survey of wildlife depredations and 18 (Special Publication 1):234-237. control techniques at fish-rearing facilities. KELLER, T., A. VON LINDEINER,AND U. LANZ. 1998. Wildlife Society Bulletin 15:386-394. Cormorant management in Bavaria , Southern PITT, W.C., ANDM.R. CONOVER. 1996. Predation at Germany - shooting as a proper management lntermountain West fish hatcheries. Journal tool? Cormorant Research Group Bulletin of 60:616-624. 3: 11-15. PRICE, l.M ., AND J.G. N!CKUM. 1995. Aquaculture and KING, D.T ., J.F. GLAHN, AND K.J. ANDREWS. 1995. birds: the context for controversy. Colonial Daily activity budgets and movements of Waterbirds 18 (Special Publication 1):33-45. winter roosting double-crested cormorants REINHOLD, D.S ., AND C.A. SLOAN. 1999. Strategies to determined by biotelemetry in the Delta reduce double-crested connorant depredation Region of Mississippi. Colonial Waterbirds at aquaculture facilities in Mississippi . Pages 18 (Special Publication 1):152-157. 99-105 in M . E. Tobin, technical coordinator. LEWIS,H.F. 1929. The natural history of the double- Symposium on double-crested cormorants:

50 population status and management issues in Technical Bulletin 1879. Washington , D.C. , the Midwest. United States Department of USA. Agriculture , Animal and Plant Health USFWS (U.S. FISH AND WLLDLIFE SERVICE). 1998. Inspection Service Technical Bulletin 1879 , Establishment of a depredation order for the Washington , D.C. double-crested cormorant. Final rule. Federal Ross , R.M. , ANDJ.H. JOHNSON. 1999. Fish losses to Register 63: I 0550-10561 . double-crested cormorant predation in eastern VANDEVALK,A.J. , C.M. ADAMS,L.G. RUDSTAM,J.L. Lake Ontario , 1992-97 . Pages 61- 72 in M. E. FORNEY, T.E. BROOKING, M. GERKEN, B. Tobin, technical coordinator. Symposium on YOUNG, ANDJ . HOOPER. 2002 . Comparison double-crested cormorants : population status of angler and cormorant harve st of walleye and management issues in the Midwest. and yellow perch in Oneida Lake, New York. United States Department of Agriculture, Transactions of the American Fisheries Animal and Plant Health Inspection Service Society 131:27-39. Technical Bulletin 1879, Washington , D.C. VERMEER, K. 1970. Some aspects of the nesting SCHNErDER, C.P., A. SCHIAVONEJR. , T.H. ECKERT, double-crested cormorants at Cypress Lake, R.D. MCCULLOUGH, B .F. LANTRY, D.W . Saskatchewan, in 1969: a plea for protection. EINHOUSE,J.R . CHRISMAN,C.M. ADAMS, J.H . Blue Jay 28:11-13. JOHNSON, AND R.M. Ross. 1999. Double­ WESELOH, D.V. , ANDP.J. EWINS.1994. Characteristics crested cormorant predation on smallmouth of a rapidly increasing colony of double­ bass and other fishes of the eastern basin of crested cormorants (Phalacrocorax auritus) in Lake Ontario: overview and summary. New Lake Ontario: population size, reproductive York State Department of Environmental parameters and band recoveries. Journal of Education Special Report , Albany , NY , USA. Great Lakes Research 20:443-456. SHJELDCASTLE, M.C. , ANDL. MARTIN. 1999. Co lonial __ , __ , J. STRUGER, P. MINEAU, C.A. BISHOP,S. waterbird nesting on West Sister Island POSTUPALSKY, AND J.P. LUDWIG. 1995. National Wildlife Refuge and the arrival of Double-crested cormorants of the Great double-crested cormorants. Pages 115-120 in Lakes: changes in population size, breeding M. E. Tobin , technical coordinator. distribution and reproductive output between Symposium on double-crested cormorants: 1913 and 1991. Colonial Waterbirds 18 population status and management issues in (Special Publication 1): 48-59 . the Midwest. United States Department of WIRES, L.R. , F.J. CUTHBERT,D .R. TREXEL, ANDA.R. Agriculture, Animal and Plant Health JOSHI. 200 I. Status of the Double-crested Inspection Service Technical Bulletin 1879, cormorant (Phalacrocorax auritus) in North Washington , D.C.. USA. America. Final Report to United States Fish STICKLEY,A.R .. JR.,ANDK.J. ANDREWS.1989 . Survey and Wildlife Service , Arlington , VA, USA. of Mississippi catfish farmers on means , WYWIALOWSKI, A.P. 1999. Wildlife-caused losses for efforts , and costs to repel fish-eating birds producers of channel catfish (lctalurus from ponds . Proceedings of the Eastern pun ctatus) in 1996 . Journal of the World Wildlife Damage Control Conference 4: I 05- Aquacu lture Society 30:461-472. 108. TUCKER, C.S., J.A. STEEBY,J.E WALDROP,AND A.B. GARRAND. 1992. Effects of cropping system and stocking density on production of channel catfish in ponds . Mississippi Agricultural and Forestry Experiment Station Bulletin 988 , Mississippi State , USA. TYSON, L.A., J.L BELANT, F.J. CUTHBERT, AND D.V. WESELOH. 1999. Nesting populations of double-crested cormorants in the United States and Canada. Pages 17-26 in M.E. Tobin, Technical Coordinator. Symposium on double-crested cormorants: Population status and management issues in the Midwest. United States Department of Agriculture , Animal and Plant Health Inspection Service

51