Double-Crested Cormorant Impacts to Commercial and Natural Resources

DOUBLE-CRESTED CORMORANT 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 cormorants (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 aquaculture 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

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