Double-Crested Cormorant Damage to a Commercial Fishery in the Apostle Islands, Wisconsin
Total Page：16
File Type：pdf, Size：1020Kb
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln 2 - Second Eastern Wildlife Damage Control Conference (1985) Eastern Wildlife Damage Control Conferences September 1985 DOUBLE-CRESTED CORMORANT DAMAGE TO A COMMERCIAL FISHERY IN THE APOSTLE ISLANDS, WISCONSIN Scott R. Craven University of Wisconsin-Madison Esther Lev University of Wisconsin-Madison Follow this and additional works at: https://digitalcommons.unl.edu/ewdcc2 Part of the Environmental Health and Protection Commons Craven, Scott R. and Lev, Esther, "DOUBLE-CRESTED CORMORANT DAMAGE TO A COMMERCIAL FISHERY IN THE APOSTLE ISLANDS, WISCONSIN" (1985). 2 - Second Eastern Wildlife Damage Control Conference (1985). 11. https://digitalcommons.unl.edu/ewdcc2/11 This Article is brought to you for free and open access by the Eastern Wildlife Damage Control Conferences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in 2 - Second Eastern Wildlife Damage Control Conference (1985) by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. DOUBLE-CRESTED CORMORANT DAMAGE TO A COMMERCIAL FISHERY IN THE APOSTLE ISLANDS, WISCONSIN by Scott R. Craven and Esther Lev ABSTRACT eliminated perching and an old-fash- ioned scare-crow. National Park Service The endangered classification of policy precludes direct control of the double-crested cormorant (DCC) the increasing DCC population. in Wisconsin resulted in complete protection and significant management efforts in the 1970's., These efforts, INTRODUCTION probably coupled with reduced pesticide Double-crested cormorants loads, resulted in a resurgence of (Phalacrocorax auritus) have conflicted Wisconsin cormorant populations from with commercial fisheries along the a low of 66 pairs in 1972 to 1028 coast of Maine, in Wisconsin, in the pairs in 1982» The DCC was reclassified Great Lakes region in general (Matteson as a threatened species in 1982. 1983)> and perhaps in other areas. This apparent success story did not Such conflict was especially evident take into consideration the potential during the period 1920-45 and again negative impact of an abundant pisci- in recent years. Reports of cormorant vorous bird. In 1978 a colony of (DCC) depredations have been propor- DCC's became established on a remote tional to changes in cormorant numbers rocky island in the Apostle Islands throughout much of their North American National, Lakeshore, in Lake Superior. range. From 17 pairs in 1978 the colony in- Cormorants were abundant throughout creased to 289 pairs in 1985. By the Great Lakes region throughout 1982, commercial fishermen in the the 1800s (Lewis 1929). However, Apostle Islands began to complain there were no reports of DCC colonies about damage to the valuable catch in the Great Lakes in the early 1900s. of Lake Whitefish. They accused DCCs By the 1920s DCC numbers and colonies of feeding within pound nets and thus began to increase and as they did, causing sub stantial damage by gilling so did complaints from commercial and scaring captured whitefish. Annual fishermen. Persecution by fishermen loss was estimated at $5-10,000 distri- during the 1940s followed by the bio- buted amongst 3 fishermen. accumulation of DDT, DDE, DDD, PCB, The interaction of DCC's and the and other contaminants between 1950 whitefish fishery was studied from and the early 1970s combined to devas- 1983-84. Food habits data did not tate the DCC population of the Great suggest that commercial fish species Lakes. Subsequent protection and were important to the diet of DCC's management reversed these trends during in the Apostle Islands. Observations the 1970s. Vermeer and Rankin (1984) suggested that the attraction of pound present an excellent review of historic nets centered more on the use of net DCC population trends. support poles for perch sites than Prior to the 1890s DCCs inhabitated on the availability of food within the isolated and larger lakes of the the net. Nine abatement techniques northern and central parts of Wisconsin were tested. Damage was reduced for (Carr 1890). The number of colonies periods of up to 4 weeks by a combina- in Wisconsin increased substantially tion of structural modifications that between the 1920s and mid-1950s (Mat- teson 1983)o Between 1923 and 1966 ®Scott Craven, Extension Wildlife cormorant colonies were observed in Specialist and Associate Professor, 16 Wisconsin counties (Anderson and Department of Wildlife Ecology, Univer- Hamerstrom 1967, Scharf 1979). As sity of Wisconsin-Madison 53706 noted, by the mid-1960s the Wisconsin Esther Lev, Project Assistant, Depart- cormorant population was reduced by ment of Wildlife Ecology, University pesticide contamination, human perse- of Wisconsin-Madison 53706 cution and habitat loss. In 1972, 14 with a total state population of 66 the development of depredation abatement pairs (Matteson 1983)? the DCC was techniques. listed as an endangered species. We thank Bruce Swanson (WDNR) for Positive management practices such logistical support; Dennis Pratt (WDNR) as erection of artificial nesting for identification of fish; Scott structures were vigorously pursued Hulse (WDNR) for collection of fish; by the Wisconsin Department of Natural and Sumner Matteson (WDNR) for field Resources (Meier 1981). Only a decade assistance, constructive criticism, later the number of nesting pairs and a wealth of information. Commercial had increased to a minimum of 1028 fishermen Morris Boutin, Jack Erikson, and the bird's status was downgraded and Dean Halvorson were extremely to threatened. There are no documented cooperative and willing to test abate- explanations for the dramatic increase ment devices and provide catch data. in population, however, reduced pesti- James Selgeby (USFWS) assisted with cide loads in the environment, immigra- the identification of otoliths. The tion from other DCC populations, manage- NPS Apostle Islands National Lakeshore ment, protection, and other factors office, especially Park Ecologist are probably all involved. Merryll Bailey, provided valuable In 1978, 17 pairs of DCCs were logistical support. Terry Daulton found nesting on Gull Island in the deserves special thanks as a hard- Apostle Islands National Lakeshore working and dedicated field assistant (AINL) in Lake Superior under National in 1983 and 1984. Donald Rusch, Leader, Park Service jurisdiction,, By 1985 WCWRU, provided the boat that made the Gull Island colony had increased field work possible. J. Philip Keillor, to 289 nesting pairs and at least Sea Grant, provided many of the initial one satellite colony had been establ- ideas and contacts that led to this ished. In 1980, only 3 years after study. Financial support for this the Gull Island colony was discovered, research was provided by the U.S. commercial pound net fishermen in National Park Service and the Department the Apostle Islands began to complain of Wildlife Ecology, University of about cormorant depredations. Fishermen Wisconsin-Madison. claimed losses of 30-40$ of the white- fish catch in 1982 due to direct consump- STUDY AREA tion, scarring or gilling caused by The principal area of research DCCs (B. Swanson, pers. commun.). was the Apostle Islands National Lake- (Note: Gilling results when fish shore, Bayfield, Wisconsin (Fig. 1). become entangled in the pound net The 22 Apostle Islands, 20 of which mesh.) Five pound net fishermen were are part of the National Lakeshore, affected in 1982 and at least 40 pound are located off the tip of the northern nets which provided 60-70$ of the Wisconsin mainland in Lake Superior. commercial fisherman's income were The twenty islands comprise 15,778 involved in the depredation problem hectares of land, ranging in size (Mary Halvorsen, pers. commun.). from Gull Island (1.2 ha) to Stockton Thus the problem was viewed as serious Island (4,021 ha). The Apostle Islands by local resource managers. Fishermen lie in the transition zone between attempted to abate depredations with northern boreal coniferous forest rubber snakes, wind wheels, brightly- and deciduous forest. Sugar maple colored flags, eagle decoys, pieces (Acer saccharum), yellow birch (Betula of metal, and covered nets with no lutea), hemlock (Tsuga canadensis), success. red pine, (Pinus resinosa), white In response to National Park Service birch (Betula papyrifera), white cedar (NPS) concern about the AINL depreda- (Thuja occidentalis), balsam fir (Abies tions problem, we initiated a study balsamea) and black spruce (Picea of the DCCs in the Apostle Islands mariana)' are common trees (USNPS 1983). in 1983. Data were collected on the The understory of several islands food habits and ecology of DCCs and is dense Canada yew (Taxus canadensis). 15 METHODS colony, placed in plastic bags, and Field research was initiated on frozen for later identification. July 11, 1983» Prior data were col- Cormorant pellets were collected lected on the biology of the DCC in from Gull and Eagle Islands (Fig. 1). the Apostle Islands by USNPS biological Pellets are a mass of indigestible aids in cooperation with WDNR staff. material enveloped in mucus and expelled Collaboration between the Department by adult and subadult DCCs. Young of Wildlife Ecology, USNPS, and WDNR birds do not begin producing pellets personnel and 3 commercial fishermen until they are able to fly (Ainley continued throughout the study. Obser- and Kelly 1981). Cormorants typically vations of DCCs and data on their produce one pellet daily and these ecology, food habits and interaction pellets are comparable to regurgitation with the commercial whitefish industry samples as indicators of diet (Jordan were collected from May-October, 1983 1959). In many cases food remains and May-September, 1984. were digested to the point where fish Four aerial surveys of the Apostle species could not be identified by Island's cormorant population were gross examination. Thus, we used conducted between July 17 and September otoliths as a diagnostic tool (Ainley 2, 1983. Each 2-hour survey was flown and Kelly 1981). Fish otoliths (calcare- in the morning around all of the is- ous concretions in the inner ear) lands. Number of birds observed and were easily separated from pellets.