Copyright (c) 2007 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/nwrccormorants Recent documents in Symposium on Double-Crested Cormorants: Population Status and Management Issues in the Midwest en-us Sun, 11 Feb 2007 01:45:35 PST 3600 http://digitalcommons.unl.edu/nwrccormorants/18 http://digitalcommons.unl.edu/nwrccormorants/18 Fri, 09 Feb 2007 08:22:37 PST Authors' affiliations http://digitalcommons.unl.edu/nwrccormorants/17 http://digitalcommons.unl.edu/nwrccormorants/17 Fri, 09 Feb 2007 08:18:39 PST Populations of double-crested cormorants (DCCO's, Phalacrocorax auritus) have increased dramatically in North America during the past 2 decades (1978-98), especially in the Great Lakes region and Southeastern United States. Concern about the impact, real or imagined, of DCCO's on economics and ecosystem health has risen in parallel to the increase in cormorant numbers. A daylong symposium on this subject was opened by Stephen Lewis and D. V. (Chip) Weseloh, who introduced the audience to the general problems associated with cormorants in the Midwest. The moderators identified the following symposium objectives: (1) to provide current information on the status and biology of the DCCO; (2) to review scientific evidence related to the impacts of cormorants on sport fish, aquaculture operations, vegetation, and other colonial waterbirds; (3) to discuss options available to resolve human-cormorant conflicts; (4) to identify information needs (monitoring and research) related to cormorant management; and (5) to enhance communication and coordination among all entities concerned about cormorants and the resources they potentially affect. Francesca J. Cuthbert http://digitalcommons.unl.edu/nwrccormorants/16 http://digitalcommons.unl.edu/nwrccormorants/16 Fri, 09 Feb 2007 08:16:24 PST Double-crested cormorant (DCCO) research needs and data gaps were identified in the early 1990's by Erwin (1995) and Nisbet (1995). Erwin (1995) recommended four areas of research: (1) large-scale banding and marking to determine age- and sex specific survival and fecundity, (2) studies of movements during migration and winter, (3) assessment of limiting factors such as contaminants and disease, especially in light of recent Newcastle disease in cormorants, and (4) evaluation of economic impacts of cormorants on cultured fishes and ways to reduce predation by fish-eating birds. D.V. (Chip) Weseloh http://digitalcommons.unl.edu/nwrccormorants/15 http://digitalcommons.unl.edu/nwrccormorants/15 Fri, 09 Feb 2007 08:14:13 PST Modeling indicated that lowering the doublecrested cormorant population from 17,361 to 10,000 pairs could be attained only by a combination of techniques: culling breeding birds in arboreal colonies to lower breeding stock and egg spraying in accessible ground nests to lower recruitment. The 5-year program was launched in 1989; culling was halted 4 years later because the population had fallen below the threshold of 10,000 breeding pairs. A greater vulnerability of males to shooting (203:100) probably accounted for the faster-than-predicted drop in numbers. Egg spraying spanned the entire 5-year period, during which 25,095 nests were treated with inert mineral oil. As predicted by the model, spraying lowered recruitment, but only after a 2-year lag. Culling should be considered a last-resort form of intervention whenever softer techniques (egg spraying, mechanical nest destruction, and carefully planned disturbances to the nesting colonies to enhance predation and abandonment) are not sufficient or practical to produce population control. Population control should be based upon careful planning (including detailed censuses, population modeling, and prior communication with the public) and be conducted under close scientific supervision. J. Bedard http://digitalcommons.unl.edu/nwrccormorants/14 http://digitalcommons.unl.edu/nwrccormorants/14 Fri, 09 Feb 2007 08:11:00 PST We prepared this review of the status and management of double-crested cormorants (Phalacrocorax auritus) in Ontario, with management options, in response to concerns expressed about possible negative impacts of large numbers of the birds on fish stocks, and vulnerable, threatened and endangered species. Double-crested cormorants are native to Ontario and were first recorded breeding on Lake of the Woods in northwestern Ontario in the late 1700's. The birds spread eastward to colonize all of the Great Lakes by the 1930's. A decline in cormorant populations on the Great Lakes from the 1950's to the 1970's has been attributed mainly to chemical contaminants and resulting lower reproductive success. Populations on the Great Lakes have increased dramatically since the 1970's in response to reduced contaminant levels and increased abundance of small forage fish. There were an estimated 36,000 breeding pairs on the Canadian Great Lakes in 1997, with increasing numbers found on inland water bodies. Double-crested cormorants are protected in Ontario, and there are no population control programs. With increasing numbers of the birds, population management options were considered, ranging from no controls, to controls in specific local areas, to widespread controls. The latter does not appear to be justified because evidence suggests that cormorants have not had significant effects on sport, commercial or small forage fish on an ecosystem basis. Control measures in specific local areas may be justified for certain management purposes, such as protection of endangered species. C. Korfanty http://digitalcommons.unl.edu/nwrccormorants/13 http://digitalcommons.unl.edu/nwrccormorants/13 Fri, 09 Feb 2007 08:08:51 PST In the early 1990's, it became apparent that the rapid colonization of Tommy Thompson Park on Lake Ontario near Toronto by double-crested cormorants (Phalacrocorax auritus) would eventually affect the existing colonies of blackcrowned night-herons (Nycticorax nycticorax) owing to competition for nest sites and destruction of nest trees. As a result, monitoring of these two species was expanded in 1992 by individually marking all nest trees (using permanent metal tree tags) and by recording the numbers of heron and cormorant nests for all nest trees. In 1996, professional surveyors determined the exact locations of nest trees. We have developed a geographic information system (GIS) to plot the changes in the nesting distributions of cormorants and night-herons during 1992-97 on three peninsulas at Tommy Thompson Park. The GIS clearly illustrates the relationship between the expanding nesting areas of the cormorants and the receding nesting areas of the nightherons at the two shared colony sites. The GIS products will be helpful in any discussions of local cormorant management. S. Jarvie http://digitalcommons.unl.edu/nwrccormorants/12 http://digitalcommons.unl.edu/nwrccormorants/12 Fri, 09 Feb 2007 08:06:20 PST Recent survey data have shown the importance of West Sister Island National Wildlife Refuge, Lake Erie, to nesting waders. About 40 percent of all herons and egrets nesting in the U.S. Great Lakes are found there, including the Great Lakes' largest colonies of great blue heron (Ardea herodias), great egret (Ardea alba), and black-crowned nightheron (Nycticorax nycticorax), and the largest of two snowy egret (Egretta thula). West Sister Island's importance to Ohio has grown in recent decades with the loss of smaller mainland colonies of waders, especially the black-crowned night-heron. The double-crested cormorant (Phalacrocorax auritus) returned to Ohio as a successful nester in 1992 for the first time in more than a century. The effects of this species on wading bird colonies have been well documented in Canadian Lake Erie. Cormorants have successfully competed against great blue herons for nesting space and eliminated black-crowned night-herons through habitat destruction. Nest estimates made at the island since 1991 indicate that the night-heron has fallen to 37 percent of its historic numbers on the island and is dropping dramatically in the region. That species has been affected negatively as canopy height has increased with vegetative succession. A second concern is the cormorant, whose nest counts have increased from 0 to ~1,500 in 5 years. This rate of increase mirrors that on East Sister Island, a few kilometers northeast in Canada. To date, competition has not been a significant problem, but habitat degradation has been documented, with major leaf loss noted in 1995 on trees having cormorant nests and along the perimeter of West Sister Island. The Ohio Division of Wildlife and the U.S. Fish and Wildlife Service are concerned, both biologically and esthetically, about the future status of the island's colonies in light of habitat succession and the addition of the cormorant. Mark C. Shieldcastle http://digitalcommons.unl.edu/nwrccormorants/11 http://digitalcommons.unl.edu/nwrccormorants/11 Fri, 09 Feb 2007 08:03:10 PST Concurrent with the rapid growth of the Mississippi catfish industry during the 1980's, there was evidence of similar growth of double-crested cormorant (Phalacrocorax auritus) populations wintering in the delta region of Mississippi. Observational and food habits studies indicate that this expansive industry, incorporating more than 100,000 acres of ponds, provides an enormous food base for overwintering populations estimated in recent years to exceed 50,000 birds. As much as 75 percent of the diet in certain roosting areas of the Mississippi delta consisted of catfish, and according to bioenergetic models cormorants can exploit as much as 940 metric tons of catfish per winter. Despite these data, there has been little attempt to demonstrate whether exploitation of this food base has increased body condition and possibly survival of wintering cormorants that return primarily to the Great Lakes region to breed. To examine this possible effect, we analyzed monthly changes in body masses of wintering cormorants collected in the delta region of Mississippi and compared premigratory body masses and fat deposition of Mississippi cormorants with those from areas without extensive aquaculture production. With the exception of adult females, all sex and age groups of cormorants collected in the delta during the winters of 1989- 90 and 1990-91 increased (P < 0.05) their body mass from November to April. Over all months, body masses of adult males and adult females were greater than that of subadults. Standardized by wing chord length, the premigratory body masses of Mississippi males and females differed (P < 0.0004) from premigratory males and females collected from Alabama in areas remote from catfish production. Premigratory fat deposition appeared to be responsible for the body mass increases, and omental fat mass was highly correlated (R = 0.721, P < 0.0001) with body mass and also differed (P = 0.0003) between Mississippi and Alabama birds. We hypothesize that the improved body condition of cormorants resulting from exploiting catfish has increased their survival and contributed to the population explosion of cormorants observed over the past decade. We suggest additional studies to substantiate our findings and to clarify the importance of southern aquaculture on improving body condition and survival of cormorants. James F. Glahn http://digitalcommons.unl.edu/nwrccormorants/10 http://digitalcommons.unl.edu/nwrccormorants/10 Fri, 09 Feb 2007 08:01:03 PST Double-crested cormorant (Phalacrocorax auritus) depredation throughout the Southeastern United States has been on the increase over the past 20 years. The increase in depredation coincides with the growth of the aquaculture industry and an expansion of double-crested cormorant wintering populations throughout the Southeast. The U.S. Department of Agriculture-Animal and Plant Health Inspection Service-Wildlife Services plays a major role in reducing double-crested cormorant damage. Nonlethal harassment on farms, dispersal from night roosts, and lethal control have reduced double-crested cormorant depredation at aquaculture farms in Mississippi. However, the efficiency and compatibility of current methods of reducing double-crested cormorant depredation must be improved. David S. Reinhold http://digitalcommons.unl.edu/nwrccormorants/9 http://digitalcommons.unl.edu/nwrccormorants/9 Fri, 09 Feb 2007 07:57:55 PST In response to concerns expressed by anglers, the U.S. Fish and Wildlife Service conducted an extensive review of published studies done throughout the United States and Canada on the impacts of double-crested cormorants (Phalacrocorax auritus) on sport-fish populations in open waters. The literature review indicated that fish species valued by sport and commercial anglers make up a very small proportion of the cormorants' diet and that these birds have a minor effect on fish populations compared to the effects of sport and commercial fishing, natural predation, and other mortality factors. The Service sent a questionnaire to State agencies, soliciting their biological information and professional opinions on the role of cormorants in regulating wild fish populations, affecting sport angler catch, and causing adverse impacts on tourism and other fish-related economies. Agency attitudes toward cormorant population control were also assessed. On the basis of literature review and the survey responses, it does not appear that a strategy of reducing double-crested cormorant populations to benefit sport fish is biologically warranted at this time. John L. Trapp http://digitalcommons.unl.edu/nwrccormorants/8 http://digitalcommons.unl.edu/nwrccormorants/8 Fri, 09 Feb 2007 07:54:24 PST Sport and commercial fishing interest groups are concerned about potential impacts double-crested cormorants (Phalacrocorax auritus) may have on fish species. Our objectives for this study were to determine the diet of the cormorant in western Lake Erie and the diet overlap and competition for resources with piscivorous fish, such as walleye (Stizostedion vitreum.) The stomach contents of 302 double-crested cormorants collected in western Lake Erie consisted primarily of young-of-the-year gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides,) and freshwater drum (Aplodinotus grunniens). In the spring, freshwater drum were the most frequently occurring food in the stomachs and constituted the greatest portion of the diet by weight. Young gizzard shad became the most abundant prey and made up the largest percentage of the diet by weight in the stomachs from the end of July through October. Emerald shiners were abundant in the diet during June, September, and October. The fish species that cormorants ate resembled, by proportion, the species mix found in trawl catches. The diets of cormorants and walleyes were similar from July to October with significant overlap. Results from this study suggest impacts of cormorants at current population levels in Lake Erie are not detrimental to sport and commercial fishing. Therefore, control for the purpose of reducing competition for prey fish with walleye is not warranted at this time. Michael T. Bur http://digitalcommons.unl.edu/nwrccormorants/7 http://digitalcommons.unl.edu/nwrccormorants/7 Fri, 09 Feb 2007 07:51:17 PST We examined 4,848 regurgitated digestive pellets of double-crested cormorants (Phalacrocorax auritus) over a 6-year period (1992-97) to estimate annual predation on sport and other fishes in the eastern basin of Lake Ontario. We found more than 51,000 fish of 28 species. Using a model that incorporates annual colony nest counts; fledgling production rates; adult, immature, and young-of-year residence times (seasonal); estimates of mean number of fish per pellet and mean fish size; and a fecal pathway correction factor (4.0 percent), we estimate total annual number of fish consumed by cormorants in the eastern basin of Lake Ontario to range from 37 million to 128 million fish for 1993-97. This fish loss equates to an estimated 0.93 million to 3.21 million kg (mean 2.07 million kg) of fish consumed per year, principally alewife (Alosa pseudoharengus, 42.3 percent) and yellow perch (Perca flavescens, 18.4 percent). Forage fish (alewife, cyprinids, trout-perch [Percopsis omiscomaycus], and other minor components) accounted for 65 percent of the diet, and panfish contributed 34 percent of the diet for the 5-year period. Game fish were minor components of the diet, in view of an average estimated annual consumption of 900,000 smallmouth bass (Micropterus dolomieui, 1.1 percent) and 168,000 salmonines (mostly lake trout, Salvelinus namaycush, 0.2 percent). Cormorant predation on lake trout fingerlings stocked in May 1993 and June 1994 was estimated through the use of coded wire tag recoveries from pellets collected on Little Galloo Island 1 and 4 days after stocking events. We estimated losses of 13.6 percent and 8.8 percent, respectively, of the fish stocked for the two events, an average of 11.2 percent. Such losses may be reduced through alteration of existing stocking practices. Robert M. Ross http://digitalcommons.unl.edu/nwrccormorants/6 http://digitalcommons.unl.edu/nwrccormorants/6 Fri, 09 Feb 2007 07:47:09 PST The Michigan Department of Natural Resources, in conjunction with the University of Michigan and the U.S. Fish and Wildlife Service, initiated a research study to determine the impact of double-crested cormorants (Phalacrocorax auritus) on the yellow perch (Perca flavescens) population in the Les Cheneaux Islands area of northern Lake Huron. Aerial and nesting colony counts were conducted to monitor cormorant abundance. Creel census counts and tagging of 8,400 perch were used to study perch abundance. We collected 373 cormorants to study food habits via stomach-content analysis. We found that (1) cormorants fed heavily on yellow perch in early spring, but over the entire season only 10 percent of their diet was perch; (2) alewives (Alosa pseudoharengus) and sticklebacks (Culaea inconstans, Pungitius pungitius, Gasterosteus aculeatus) made up the major portion of the cormorants' diet; (3) cormorants removed only 2.3 percent of the available perch biomass (v. 1.8 percent by anglers over the same period); (4) most fish taken by cormorants were less than 150 mm long; (5) total annual perch mortality was about 45 percent, of which less than 9 percent was due to cormorants; and (6) cormorants accounted for only 0.8 percent of the mortality of legal-size perch (&#8805;178 mm), whereas summer sport fishing accounted for 2.5 percent. Thus, although the impact of cormorants on the perch population may vary slightly from year to year, we conclude that cormorant predation had minimal impact on the local perch population. Glenn Y. Belyea http://digitalcommons.unl.edu/nwrccormorants/5 http://digitalcommons.unl.edu/nwrccormorants/5 Fri, 09 Feb 2007 07:42:03 PST We reviewed and summarized historical data and conducted population surveys from 1973 through 1997 to determine the breeding status and distribution of doublecrested cormorants (Phalacrocorax auritus) in Wisconsin. Breeding cormorants historically occupied large, isolated lakes and wetlands in northern Wisconsin, but there were no known nesting sites until 1919, when cormorants were reported nesting on Lake Wisconsin in south-central Wisconsin. From the 1920's to the 1950's, cormorants occupied 17 colony sites in 16 counties, though no more than 7 sites were occupied during any particular year. From the 1950's to the early 1970's, the number of cormorant nests and colony sites plummeted owing to bioaccumulation of dichlorodiphenyltrichloroethane (DDT) and its metabolites, human persecution at some colony sites, and habitat loss. The installation of 1,269 artificial nesting platforms at 13 locations in north-central, northeastern, northwestern, east-central, and southwestern Wisconsin, coupled with a decline in dichlorodiphenyltrichloroethane (DDE) levels in breeding birds, as well as protection as a State-endangered species, led to a marked recovery. Between 1973 and 1997, the State's breeding population grew at an annual rate of nearly 25 percent, from 66 nests at 3 colony sites to 10,546 nests at 23 colony sites. We estimated population trends for six geographic regions in the State determined by distinct distribution patterns of nesting birds. Cormorant populations for five of six regions increased during 1973 through 1997. Trends differed significantly among regions, with a greater estimated increase in Great Lakes' sites (P < 0.01). In 1997, 81 percent of the State's breeding population occurred on four islands in Green Bay on Lake Michigan. Increasing Lake Michigan cormorant populations have raised concerns among sport and commercial fisheries about impacts on yellow perch (Perca flavescens), although recent studies indicate that alewives (Alosa pseudoharengus) predominate in cormorant diets. Summer W. Matteson http://digitalcommons.unl.edu/nwrccormorants/4 http://digitalcommons.unl.edu/nwrccormorants/4 Fri, 09 Feb 2007 07:37:33 PST Double-crested cormorants (Phalacrocorax auritus) are receiving increasing attention in North America because of depredations at aquaculture facilities and alleged impacts on sport and commercial fisheries. We obtained recent (most since 1994) estimates for the number of nesting double-crested cormorants in the United States and Canada from published references and by conducting telephone interviews with State and Provincial biologists. Using published data, we also determined annual rates of change in the number of cormorants since about 1990. The estimated minimum number of nesting pairs (colonies) of double-crested cormorants was 372,000 (852). Most cormorants nested in the Interior region (68 percent). Overall, double-crested cormorants increased about 2.6 percent annually during the early 1990's. The greatest decline (&#61485;7.9-percent annual change) was in the West Coast-Alaska region. The greatest increase (6.0-percent annual change) was for the Interior region. The increase there was primarily a consequence of a 22-percent annual increase in Ontario and U.S. States bordering the Great Lakes. These baseline population data are essential for monitoring trends in nesting populations and for developing informed management decisions. However, the completeness, quality, and timing of surveys varied substantially among jurisdictions. Population estimates and rates of change should, therefore, be used with caution. Methods and timing of future surveys should be coordinated among political jurisdictions (at least within regions) to improve accuracy of estimates and allow more meaningful comparisons of population status. Laura A. Tyson http://digitalcommons.unl.edu/nwrccormorants/3 http://digitalcommons.unl.edu/nwrccormorants/3 Fri, 09 Feb 2007 07:34:27 PST The natural history, behavior, and ecology of double-crested cormorants (Phalacrocorax auritus) predispose this species for conflict with human sport and commercial fisheries. Cormorants breed early in life, have large broods, are efficient predators even in marginal conditions, seem to be able to adjust colony sizes quickly in response to local conditions, and have limited requirements for feeding and nesting habitats. A survey of the past history of successes and failures in managing cormorants reveals that economic impact is greatest with aquaculture and least in sport fisheries. Research during the past 5 years suggests that some control methods like culling and egg spraying are effective but must be balanced against the actual impacts on humans. Douglas Siegel-Causey http://digitalcommons.unl.edu/nwrccormorants/2 http://digitalcommons.unl.edu/nwrccormorants/2 Thu, 08 Feb 2007 13:14:35 PST Populations of double-crested cormorants (Phalacrocorax auritus) have increased dramatically in the last 2 decades, particularly in the Great Lakes and the Southeastern United States. Their food habits and propensity for killing the trees in which they nest and roost have made cormorants the subject of much controversy. Cormorants affect--or are perceived to affect--sport fishing, aquaculture operations, vegetation, and other colonial waterbirds. Anglers, aquaculturists, resort operators, lakehome owners, politicians, and others are calling for a solution to these problems. This symposium was convened to provide information that will help conservation agencies and others make sound resource management decisions about cormorants. The objectives of the symposium were to: (1) provide up-to-date information on the status and biology of double-crested cormorants; (2) review scientific evidence related to the impacts of cormorants on sport fish, aquaculture operations, vegetation, and other colonial waterbirds; (3) discuss options available to resolve human-cormorant conflicts and biological, social, economic, and political issues related to cormorant population control; (4) identify information needs (monitoring and research) related to cormorant management; and (5) enhance communication and coordination among all entities concerned about cormorants and the resources they can impact. Our emphasis is on the Midwest, but it is clear that migrant cormorants from other areas pass through this region and that all of these birds mix on the wintering grounds in the Southern United States. Stephen J. Lewis http://digitalcommons.unl.edu/nwrccormorants/1 http://digitalcommons.unl.edu/nwrccormorants/1 Thu, 08 Feb 2007 13:12:31 PST Symposium on Double-Crested Cormorants: Population Status and Management Issues in the Midwest