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Spring 2012
Management of double-crested cormorants to improve sport fi sheries in Michigan: three case studies
Brian S. Dorr USDA/APHIS/WS National Wildlife Research Center, [email protected]
Shauna L. Hanisch Michigan State University
Peter H. Butchko U.S. Department of Agriculture
David G. Fielder Michigan Department of Natural Resources, [email protected]
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Dorr, Brian S.; Hanisch, Shauna L.; Butchko, Peter H.; and Fielder, David G., "Management of double- crested cormorants to improve sport fi sheries in Michigan: three case studies" (2012). USDA National Wildlife Research Center - Staff Publications. 1123. https://digitalcommons.unl.edu/icwdm_usdanwrc/1123
This Article is brought to you for free and open access by the U.S. Department of Agriculture: Animal and Plant Health Inspection Service at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USDA National Wildlife Research Center - Staff Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Human–Wildlife Interactions 6(1):155–168, Spring 2012 Management of double-crested cormorants to improve sport fi sheries in Michigan: three case studies BRIAN S. DORR, U.S. Department of Agriculture, Wildlife Services’ National Wildlife Research Center, Mississippi Field Station, P.O. Box 6099, Mississippi State, MS 39762, USA brian.s.dorr@ aphis.usda.gov. SHAUNA L. HANISCH, Michigan State University, Department of Fisheries and Wildlife, 13 Natural Resources, East Lansing, MI 48824, USA PETER H. BUTCHKO, U.S. Department of Agriculture, Wildlife Services, 2803 Jolly Road, Suite 100, Okemos, MI 48864, USA. DAVID G. FIELDER, Michigan Department of Natural Resources, Alpena Fisheries Research Sta- tion, 160 E. Fletcher, Alpena, MI 49707, USA
Abstract: Impacts of double-crested cormorants (Phalacrocorax auritus) to fi sheries have been documented, but evaluation of the process and outcomes of cormorant management to reduce impacts on fi sheries is lacking. We provide a synthesis of adaptive management of double-crested cormorants in the Les Cheneaux Islands (LCI), Brevoort Lake, and Drummond Island, Michigan from 2004 to 2007. The LCI management focused on reducing numbers of nesting cormorants in the region as a means of improving the yellow perch (Perca fl avescens) population and fi shery. At Brevoort Lake and Drummond Island, management focused on lethal and nonlethal harassment of spring migrating cormorants to reduce their foraging on spawning walleye (Sander vitreus) and yellow perch and to improve those fi sheries and increase fi sh populations. At each location, management efforts reduced cormorant foraging, and fi shery data indicated increased abundance of sport fi sh species. The 3 locations combined provided evidence for the underlying hypotheses that cormorants can infl uence mortality of local sport fi sh populations and that short-term management goals have been met. Continuation of adaptive management and monitoring programs will determine whether the improvement of targeted sport fi sheries through cormorant management is sustainable.
Key words: adaptive management, cormorants, culling, fi sheries, harassment, human– wildlife confl icts, predation
Populations of the double-crested prior to and concurrent with management cormorant (Phalacrocorax auritus; hereaft er, actions. cormorant) increased substantially throughout In the United States, nearly all bird species are the 1980s and 1990s, most notably in the eastern protected by the Migratory Bird Treaty Act of United States and Canada and the Great Lakes 1918, and the conservation of their populations (Hatch and Weseloh 1999, Wires et al. 2001). is a responsibility of the U.S. Fish and Wildlife Corresponding to this increase in numbers Service (USFWS). The USFWS revisited its were increases in the level of concern over policy for cormorant management when the real and potential damages associated with increasing abundance of cormorants and cormorants (Taylor and Dorr 2003). A growing concomitant upward trend in resource confl icts body of evidence in the United States and brought them to the forefront of migratory bird Canada demonstrates the reality of impacts management priorities. In keeping with the that abundant cormorant populations can have National Environmental Policy Act, the USFWS on their environment (Shieldcastle and Martin and the U.S. Department of Agriculture, Wildlife 1999, Taylor and Dorr 2003, Rudstam et al. 2004, Services (WS) cooperated on the development Hebert et al. 2005, Fielder 2008). The degree of an environmental impact statement (EIS) to of signifi cance for all categories of resource address the environmental eff ects of potential damages (e.g., ecological, economic, and policy revisions. In August 2003, aft er 4 years, 22 aesthetic) associated with cormorants varies public meetings, and >12,000 public comments, considerably from site to site. This variability in the USFWS published the fi nal EIS (USFWS actual and perceived impacts is the impetus for 2003a). much of the need for research and evaluation The most signifi cant regulatory change that 156 Human–Wildlife Interactions 6(1) came out of the fi nal EIS was the public resource depredation order (PRDO). This regulation authorizes offi cials of state wildlife agencies, WS, and Native Les Cheneaux Islands American tribes to control cormorants to protect fi sh, wildlife, plants, and their habitat in 24 states, including Michigan (USFWS 2003b). The PRDO’s purpose is to protect natural resources that are managed by public agencies for public benefi t (USFWS 2003b). The fi rst year of im- Figure 1. Les Cheneaux Islands archipelago of northern Lake Huron, Michigan, site of cormorant breeding colony management from 2004 to plementation of the PRDO 2007. Brevoort Lake and Drummond Island, Michigan, sites of spring on the northern breeding harassment of double-crested cormorants evaluated in 2005-2007 and grounds occurred in 2004 2004–2007, respectively. in New York, Vermont, and Michigan. In this Islands (LCI), Brevoort Lake, and Drummond paper, we discuss the cormorant management, Island, Michigan (Figure 1). monitoring, and research activities conducted by the WS program in Michigan (WS-MI), WS, Background and methods National Wildlife Research Center (NWRC), Les Cheneaux Islands Michigan Department of Natural Resources Cormorants have made a remarkable (MDNR), U.S. Forest Service (USFS), U. S. comeback in Michigan since they were placed Geological Survey (USGS), and Lake Superior on the state’s endangered species list in 1976 State University from 2004 to 2007. We evaluate (MDNR 2005). By 1986, >1,000 cormorant nests management actions in an adaptive format were documented in the state (MDNR 2005). By (Holling 1978, Walters 1986, Lee 1993) to link 1997, Wires et al. (2001) estimated Michigan’s learning with policy and implementation. cormorant abundance at > 30,000 breeding pairs. Specifi cally, we focus on research and The LCI population trend mirrors that of the state management eff orts in the Les Cheneaux as a whole. In 1980, cormorants established the
Figure 2. Number of nesting pairs of cormorants in the Les Cheneaux Islands, Michigan, 1980–2007. The vertical line indicates when control activities began. Cormorants • Dorr et al. 157
fi rst colony in the western part of the LCI at St. accounted for the contin-ued high total annual Martins Shoal (Diana et al. 1997). Cormorant mortality rate. Fielder (2008) concluded that numbers in the LCI increased nearly 6-fold from cormorant predation explained the greatest the early 1990s to a local breeding population of amount of variation in yellow perch abundance >5,500 nests in 2002 (Figure 2). of the explanatory factors evaluated. Wildlife The LCI is an archipelago of at least 23 named Services–Michigan (WS–MI) implemented a islands, located in northern Lake Huron. cormorant damage management program in Since the early 1900s, the yellow perch (Perca the spring of 2004, in light of the substantiation fl avescens) fi shery has been one of the main of fi shery and fi sh population declines for natural resources att racting visitors to the LCI the LCI and in response to stakeholder (Diana et al. 1987, Fielder 2008). Starting in concern (Dorr et al. 2010a, Fielder 2010). the late 1970s, the LCI yellow perch fi shery underwent a decline, remained relatively stable Drummond Island and Brevoort Lake through the mid-1990s, then fell to the point of Fielder et al. (2007) made community near total collapse in 2000 (Fielder 2004, Fielder assessments of fi sh communities in the St. 2008). Many residents of communities in the Mary’s River from 1975 to 2006 (including region believed that increasing cormorant Potagannissing Bay, which is adjacent to numbers were the cause of the yellow perch Drummond Island and the source of the crash, given the simultaneous decline and Potagannissing River; Figure 1). A 2002 study collapse of the fi shery and the signifi cant revealed that yellow perch and walleye (Sander increase in the abundance of nesting cormorants vitreus) abundance in Potagannissing Bay had in the LCI (Diana et al. 1987, Belyea et al. 1999, declined relative to previous surveys (Fielder et Fielder 2004). al. 2003). While not defi nitive, the fi shery survey Diana et al. (2006) reported on the degree and angler reports of fi shery declines were to which cormorant predation on yellow consistent with potentially higher mortality perch competed with anglers. This study caused by increased predation on yellow perch examined the diet of cormorants and evaluated and walleye by cormorants. A program of yellow perch population data from April to nonlethal harassment, supplemented by limited October 1995. Diana et al. (2006) estimated lethal take of spring migrating cormorants, was that cormorants consumed 270,000 to 720,000 implemented by WS-MI in 2004 with the goal of yellow perch in 1995, but concluded that the improving the yellow perch and walleye fi shery overall impact of cormorant predation was low. at Drummond Island (Dorr et al. 2010b). This fi nding was due partly to a high estimate Walleye abundance, survival, and recruitment of overall abundance of yellow perch in their in Brevoort Lake have been monitored study and because most perch consumed regularly since 1984 by the USFS and MDNR. were less than the minimum length limit of Prior to 1984, the walleye fi shery in Brevoort the sport fi shery (Belyea et al. 1999, Diana et Lake was maintained by stocking walleye fry al. 2006). Alewives (Alosa pseudoharengus) also and fi ngerlings, resulting in a sustainable sport were relatively abundant, possibly acting as a fi shery (USFS, unpublished data). In 1984, a buff er to cormorant predation on yellow perch spawning reef was constructed by USFS and (Fielder 2008). MDNR that greatly increased natural walleye Although Diana et al. (2006) concluded reproduction (Bassett 2006) and allowed that cormorant predation in 1995 was not a walleye stocking to be discontinued. Numbers signifi cant factor on the perch fi shery and of adult walleye declined steadily aft er 1991, that overall perch mortality was relatively resulting in resumed walleye stocking in low, the fi shery collapsed by 2000 (Fielder 1997 (Dorr et al. 2010b). Fishery assessments 2004). Yellow perch total annual mortality from 1994 to 2005 indicated unusually high was 88% in 2000, despite the near absence mortality of walleye occurring between fall-age of recreational fi shing activity (Fielder 2004, (0) and spring-age (3), and walleye numbers Fielder 2008). Fielder (2008) evaluated the data did not rebound (Dorr et al. 2010b). The decline related to the yellow perch decline in the LCI in the walleye population occurred despite and determined that cormorant predation substantial natural reproduction, stocking 158 Human–Wildlife Interactions 6(1) of fi ngerlings, and regulatory protection of of the LCI breeding colonies, contravening walleye <38 cm in length. Concurrent with the desired management outcomes? How would decline in the walleye fi shery was an increase in a sustainable endpoint for management be the numbers of cormorants foraging at Brevoort recognized and measured? Are the appropriate Lake during the cormorant’s spring migration cormorants being targeted for management? (Basset 2006). Consequently, increased walleye These questions identifi ed some of the mortality was att ributed largely to an increase risks that were addressed through research in predation by spring migrating cormorants and monitoring eff ort associated with the of vulnerable spring spawning walleye and implementation of cormorant management yellow perch (Bassett 2006). A program of in the LCI. The NWRC collaborated with nonlethal harassment supplemented by limited MDNR Fisheries Division, USGS, and LSSU in lethal take of spring migrating cormorants was monitoring and evaluating management eff ects implemented by WS-MI in 2005 as a means to on cormorants, the targeted fi sh populations, improve the walleye fi shery (Dorr et al. 2010b). and fi shery response. To determine if control eff orts were reducing Management and monitoring cormorant numbers and foraging, WS–MI Les Cheneaux Islands and NWRC conducted nest counts on the The LCI cormorant management program colonies and aerial surveys of cormorants in was part of an eff ort to investigate the feasibility the LCI and surrounding areas (Dorr et al. of reducing cormorant foraging in the LCI as 2010a). In addition to surveys, research and a means of improving yellow perch survival evaluation eff orts included food habit studies and, ultimately, improving the yellow perch and evaluations of cormorant movements fi shery (Dorr et al. 2010a, Fielder 2010). A and distribution associated with management principal criterion in the determination of how activities using VHF telemetry (Dorr et al. cormorants would be managed was the desired 2010a). Rather than set a specifi c numerical outcome of a sustainable and satisfactory goal for nesting cormorants, an end-point for yellow perch fi shery commensurate with pre- cormorant management was determined as the collapse abundance, catch, and harvest, and a point at which the yellow perch population and viable cormorant population. fi shery recover to approximately pre-collapse Research began during initial planning levels. Although a specifi c goal for cormorant of cormorant management in the LCI. numbers was not set, historical cormorant Several factors were identifi ed that would counts and fi shery data indicated that a infl uence the management, research, and satisfactory yellow perch fi shery existed in the monitoring programs. Stage-based population late 1980s when cormorant numbers on all 5 models, coupled with lessons from previous colonies in the LCI were at about 1,000 nesting management eff orts in Canada, were used to pairs (Fielder 2010; Figure 2). determine the optimal management strategy Concurrent with cormorant management, the to reduce local cormorant numbers (Dolbeer MDNR conducted annual surveys of the fi sh 1998, Bédard et al. 1999, Blackwell et al. 2002). community and recreational fi shery in the LCI. This existing information suggested that a Fielder (2010) identifi ed 7 key metric, for yellow combination of egg-oiling and lethal take of perch population and fi shery metrics and adults from breeding colonies would best meet tested for signifi cant relationships with trends management goals (Dorr et al. 2010a). in cormorant abundance. The MDNR increased A number of questions arose and focused the sampling frequency of these data from once on how management would aff ect nesting every 3 to 5 years to annually to bett er inform and foraging numbers of cormorants in the and adapt management to changing yellow LCI. Would removal of cormorants on the perch population and fi shery demographics colonies produce a sink that would be fi lled (Fielder 2010). These data also provided by cormorants from other breeding colonies? information on yellow perch population and Conversely, would management activities fi shery metrics that could be used to evaluate cause abandonment and possible extirpation whether cormorant management was providing the intended results (Fielder 2010). Cormorants • Dorr et al. 159
Questions addressed through this research Walleye abundance in Brevoort Lake was and monitoring eff ort included if management monitored by spring trap-nett ing to estimate eff ectively reduced the number of nesting spawner abundance and fall electrofi shing to cormorants on managed colonies, targeted the assess spawning success, consistent with survey appropriate cormorants, aff ected a consequent methods since 1984 (Dorr et al. 2010b). Mark- reduction in foraging, and if the yellow perch recapture methods were used to determine fi shery responded, given the underlying walleye abundance and age specifi c growth and hypothesis that cormorants are a signifi cant mortality. The percentage of survival of stocked source of yellow perch mortality (Dorr et al. fi ngerlings was determined from population 2010a, Fielder 2010). estimates derived from mark-recapture analyses. Drummond Island and Brevoort Lake Periodic fi sheries assessments also were In 2004, WS launched a pilot project to conducted in the St. Mary’s River, including address potential impacts to spawning Potagannissing Bay at the mouth of the perch and walleye during spring migration Potagannissing River adjacent to Drummond when high numbers of cormorants forage Island (Fielder et al. 2003, Fielder et al. 2007). in the mouth of the Potagannissing River on The MDNR assessments in 2002, prior to Drummond Island (Dorr et al. 2010b). In 2005, a management, and in 2006, 2 years aft er similar program was initiated on Brevoort Lake initiation of management, were used to evaluate due to documented declines in the walleye fi shery response to cormorant harassment at population and fi shery (Dorr et al. 2010b). The Drummond Island. Demographic measures of management programs at these 2 locations perch and walleye populations were abundance diff ered substantially from management in the indices determined by catch-per-unit-eff ort LCI. The depredation on sport fi sh was caused (CPUE) and mortality estimated by catch curve by spring migrating cormorants consuming fi sh analyses (Fielder et al. 2003, Fielder et al. 2007). prey during their spring spawning period. This Questions addressed through research and cormorant depredation occurred in relatively monitoring at both sites included whether small geographic areas over a short period cormorants were consuming targeted sport fi sh, relative to impacts of breeding cormorants in the biomass consumed, the relative proportion the LCI. The transitory nature of migrating of prey in the diet, whether harassment reduced cormorants at spring stopover sites, and their foraging, and the response of the fi sh population foraging on spawning assemblages of prey to management (Dorr et al. 2010b). fi sh presented unique management challenges. Although diff erent methods were used, all To address these challenges, a program of management actions had the goal of reducing nonlethal harassment with pyrotechnics and foraging by cormorants and, subsequently, the boat chases, combined with limited lethal mortality of sport fi sh species, thereby increas- shooting was initiated (Dorr et al. 2010b). ing recruitment to the associated fi sheries. To determine if control eff orts were actually Underlying these strategies was the hypothesis reducing cormorant foraging, WS and NWRC that cormorants are an important limiting trained and supervised volunteers to conduct mortality factor on those sport fi sh populations. counts of foraging fl ocks of cormorants at both The management goal in its simplest terms is a management areas (Dorr et al. 2010b). Surveys measure of a binomial outcome. The outcome of foraging cormorants were conducted from is the aff ected fi sh population’s abundance dawn to dusk in April and May 2004 to 2007 and survival increase aft er management on Drummond Island and on Brevoort Lake (goal att ained) or they decrease or there is no from 2005 to 2007 (Dorr et al. 2010b). In addition measurable change (goal not att ained). In all to surveys, research and evaluation eff orts management cases an adaptive framework included prey studies from samples collected of consideration of alternatives, prediction of concurrent with management to identify the outcomes, implementation of management, and proportion and biomass of fi sh in the cormorant monitoring and evaluation of goal att ainment diet (Dorr et al. 2010b). were pursued. 160 Human–Wildlife Interactions 6(1)
Results and discussion Data from VHF marked cormorants from LCI Les Cheneaux Islands colonies indicated a clear preference for use of Management of nesting cormorants by egg- the LCI relative to regions outside the LCI (Dorr oiling and lethal culling in the LCI contributed to et al. 2010a). Dorr et al. (2010a) hypothesized a large and rapid decline in nesting numbers in that reduced intra-specifi c competition the region (Figure 2). However, the total decline among cormorants and increased yellow in the number of nesting cormorants from all perch abundance may have created a positive LCI colonies over the same period was 37% feedback that resulted in a greater percentage more than the number culled (Dorr et al. 2010a). of the remaining cormorants from the LCI This rapid decline suggests that management colonies foraging in the LCI area. A positive may have caused some increased emigration feedback response in cormorant foraging may from managed colonies. Although rapid have implications for cormorant management decline and, possibly, increased emigration at other locations and at larger scales. If a was observed, cormorants did not completely positive feedback response is demonstrated at abandon nesting due to management and were other locations then management targeted at not extirpated from managed colonies (Dorr et larger scales (e.g., fl yway level management) al. 2010a). may not provide desired results at a local level. Dorr et al. (2010a) indicated that VHF- Fielder (2010) found that all yellow perch marked cormorants used the LCI area population and fi shery metrics for the LCI disproportionately more than in surrounding were signifi cantly correlated with changes in areas and that management was targeting the cormorant abundance. All metrics trended in appropriate cormorants. Aerial survey counts the direction expected, given the underlying of cormorants indicated a mixed response to hypothesis that cormorants are an infl uential management. While foraging in near shore mortality factor. Yellow perch abundance areas encompassing all the colonies declined increased (Figure 3), total mortality rate signifi cantly, foraging did not decrease decreased and the angler catch rate and harvest signifi cantly within the LCI proper (Dorr et in the recreational fi shery improved (Fielder al. 2010a). However, mean fl ock size declined 2010). Yellow perch growth rate declined, and in the embayments specifi c to the LCI area, mean age increased, which was consistent and aerial counts indicated a more dispersed with expected population density-dependent foraging patt ern over the study period (Dorr et eff ects associated with increased yellow perch al. 2010a). These aerial surveys also indicated abundance (Fielder 2010). Increased yellow that foraging numbers in the LCI were 5 times perch recruitment was documented during lower than indicated in the surveys conducted cormorant management, but, more importantly, in 1995 (Belyea 1997, Dorr et al. 2010a). This survival (longevity) of year classes improved decline was att ributed to management and the during cormorant management relative to elimination of nesting on a large colony due to pre-management year classes (Fielder 2010). the introduction of raccoons (Procyon lotor) just Analysis of cohort based mortality rate of prior to the initiation of management in the LCI yellow perch indicates a decline in mortality (Dorr et al. 2010a). Although the introduction during management to its lowest level since of raccoons complicated interpretation of 1996 (Fielder 2010). management eff ects, the number of cormorants Fielder (2010) showed improvement in foraging in the LCI was conclusively less than the yellow perch fi shery concurrent with that recorded by Belyea (1997) preceding cormorant management but concluded that the the yellow perch fi shery collapse (Dorr et al. long-term projection for the recovery of the LCI 2010a). yellow perch fi shery to pre-collapse levels was An initial concern regarding management still not clear. Numerically, the present yellow in the LCI was that management may create perch population (in 2007) likely does not equal a sink att racting cormorants from areas historical levels in the region (Fielder 2010). outside the LCI. Dorr et al. (2010a) suggested Although angler CPUE has increased to pre- that increased use of the LCI by cormorants collapse levels, fi shing eff ort and harvest have outside the management area was not an issue. not (Fielder 2010). In addition cormorants are Cormorants • Dorr et al. 161 only one of many potential factors aff ecting the initiation of the harassment programs (Figure yellow perch fi shery. Angler harvest, alewife 4). In addition, harassment deterred on average (Aloso pseudoharengus) abundance, changes in 90% of cormorant foraging att empts at both fi sh community structure, invasive species, locations (Dorr et al. 2010b). Because similar spring water levels, and temperatures can all patt erns of declining use over the study period impact the yellow perch fi shery (Fielder 2010). were observed at both locations, Dorr et al. Alewives, when abundant, may serve as a buff er (2010b) hypothesized that cormorants may for predation on perch by cormorants (Diana be exhibiting learned avoidance behavior to et al. 1997, O’Gorman and Burnett 2001), but harassment resulting in reduced use in years alewives can also be an infl uential predator on subsequent to initiation of harassment. This newly hatched larval percids (Kohler and Ney inter-annual decline in use of the harassment 1980, Wells 1980, Brandt et al. 1987, Brooking sites added to the eff ectiveness of the program et al. 1998). Fielder (2008) demonstrated that in reducing cormorant foraging. spring water levels and temperatures in the Paralleling the observed inter-annual decline LCI can infl uence yellow perch abundance. in numbers of cormorants was a decline in Lucchesi (1988) concluded that anglers in the harassment eff ort, lethal take, and use of LCI can aff ect the abundance and size structure associated pyrotechnics and shotgun shells of the perch population. The future of yellow (Dorr et al. 2010b). Lethal take of cormorants perch in the LCI will likely be infl uenced by was on average <5.4% of the cormorants a variety of ecological and environmental migrating through each site during the study factors, including cormorant abundance. period (Dorr et al. 2010b). The eff ectiveness of the harassment program in reducing cormorant Drummond Island and Brevoort Lake foraging, and the limited lethal take associated Dorr et al. (2010b) reported a signifi cant with the program, would likely make these (P < 0.05) inter-annual decline of 79% in the programs a viable option for managers where average number of cormorants at Brevoort the programs can be eff ectively applied. Lake and Drummond Island subsequent to At both locations, yellow perch were a pre-
Figure 3. Geometric mean gill-net catch of yellow perch/305 m of net for all the Les Cheneaux Islands sets combined and for Hessel Bay only, 1969–2008. Cormorant control was implemented in 2004 (from Fielder 2010). 162 Human–Wildlife Interactions 6(1)
A A
B
B B Mean daily cormorant count Mean daily cormorant
A B
B B Mean daily cormorant count Mean daily cormorant
Figure 4. (A) Mean daily counts (bars) of double-crested cormorants using the Drummond Island area of Lake Huron, Michigan, during spring migration 2004–2007. (B) Mean daily counts (bars) of double-crested cormorants using Brevoort Lake, Michigan, during spring migration 2005–2007. Vertical lines represent 95% confi dence interval estimates. Bars with different letters are signifi cantly different (p <0.05) from each other (from Dorr et al. 2010b). dominant prey item in terms of number and in signifi cantly reduced this age-specifi c eff ect of all years. Walleye composed a small proportion cormorant foraging and walleye abundance at of the diet at both locations. However, diet age 3 increased to near record levels in 2008 data reported by Dorr at al. (2010b) at Brevoort at Brevoort Lake (Figure 5). Additionally, the Lake indicated that cormorants target specifi c increased survival of walleye fully recruited walleye age classes and that observed numbers during the management period provides of cormorants could consume the majority of further evidence of a link between cormorant those age classes. Dorr et al. (2010b) reported predation and walleye survival in Brevoort that combined lethal and nonlethal harassment Lake (Dorr et al. 2010b). Cormorants • Dorr et al. 163 Number of age ≥3 walleye
Figure 5. Spring population estimates and 95% confi dence intervals (vertical lines) for age ≥3 year wal- leye in Brevoort Lake, 1985–2008. Double-crested cormorant management was initiated in spring 2005 (from Dorr et al. 2010).
A key fi nding of Dorr et al. (2010b) was that, fi shery of Potagannissing Bay in 1999 (Fielder although walleye made up a small percentage of et al. 2002, Dorr et al. 2010b). However, harvest the cormorant diet at Brevoort Lake, cormorant by anglers and predation by cormorants was predation can still reduce cohort-specifi c not directly comparable because age classes survival. Historically, measures of cormorant taken by cormorants and anglers diff er. The impacts to fi sheries have focused on the level of cormorant consumption of yellow proportion of prey in the diet (Craven and Lev perch presents a possible allocation issue to 1987, Ludwig et al. 1989) or total biomass of fi sh fi shery managers (Dorr et al. 2010b). Eff orts to consumed relative to total abundance of prey limit angler harvest and maintain sustainable (Draulans 1988, Madenjian and Gabry 1995). fi sheries through regulatory means may be Results of these management actions suggest ineff ective if cormorant consumption negates the aforementioned approaches are inadequate, regulatory eff ects on angler harvest. Conversely, as cormorants do not randomly consume fi sh of cormorant management may re-allocate those all age and size classes, but, instead, consume a fi shery resources from cormorants to anglers limited range of prey age and size classes. This (Dorr et al. 2010b). foraging behavior may result in a cropping eff ect Mortality data for fi sh populations in and reduced recruitment to older age classes Potagannissing Bay were lacking, due to small (Rudstam et al. 2004, Dorr et al. 2010b, Fielder sample size or violation of assumptions in the 2010). This cropping eff ect results in a very estimation methods (Dorr et al. 2010b). This lack diff erent predator–prey population dynamic of reliable mortality estimates makes it diffi cult than random prey consumption proportional to evaluate management, as there may be more to age class availability. walleye and yellow perch, due to improved A pronounced decline in cormorant foraging reproductive success, lower mortality, or a was observed at Drummond Island aft er combination of these factors (O’Gorman and initiation of management (Figure 4), and Burnett 2001, Dorr et al. 2010b). both walleye and yellow perch abundance Harassment programs at Brevoort Lake and increased signifi cantly at Drummond Island Drummond Island have been successful to date post management (Dorr et al. 2010b). In the with respect to management goals of improving fi rst year of management at Drummond Island fi sh populations. Success at these locations (2004), the estimated biomass consumption of refl ects situations where a combination of yellow perch by cormorants exceeded the total factors made harassment a viable management reported harvested in the entire open water method. At both of these locations there were 164 Human–Wildlife Interactions 6(1) vulnerable spawning fi sh stocks, a relatively whether improvement of targeted sport fi sher- limited geographic area to be harassed, large ies is sustainable. Information gathered from numbers of migratory cormorants arriving these management actions can also provide concurrent with spawning, and a pool of further input for adaptive management dedicated and willing volunteers to undertake programs and to link learning and policy. the considerable harassment eff ort safely The cormorant management programs we and eff ectively (Dorr et al. 2010b). However describe in Michigan are just a few of several success at these locations does not mean that projects that have been implemented or are harassment programs will be successful in the being planned under authority of the PRDO long term or are applicable in all cases even if to address localized cormorant damage. With the aforementioned factors are present. the intensifi ed management of cormorants Management at each of the 3 locations taking place under the PRDO, the need for described in this paper had varying levels interagency cooperation, research, monitoring, of research and monitoring associated with and feedback on management programs has management, particularly with the fi sheries increased greatly. As more programs are put component. Brevoort Lake was the most in place, a means of monitoring fl yway or intensive eff ort using mark-recapture methods population level eff ects will be important to over time, providing age specifi c population evaluate cumulative impacts of local control. and mortality estimates. The methods used at The eff orts at LCI, Brevoort Lake, and Brevoort Lake provided the most information Drummond Island refl ect situations where with respect to evaluation of management long-term fi shery data were available and objectives but were also the most logistically there was strong stakeholder support and intensive. The LCI used indices of several concern. Additionally, expertise and resources population demographics and included cohort- and institutional commitment to a multiyear specifi c survival collected over time. This management and research program were method provided a reasonable alternative to confi rmed. These circumstances are not always the more intensive mark-recapture methods in present. In the absence of pre-existing data, evaluating management. At Drummond Island researchers and managers should att empt there was evidence of increased abundance of to develop clear and objective means of sport fi sh following cormorant management, identifying resource confl icts associated with but evaluation of the management was less cormorants. In some cases (e.g., vegetation conclusive because age and size class specifi c damage), identifi cation of cormorant impacts information and particularly mortality estimates may be readily apparent. In other cases (e.g., were not available. fi sheries issues), identifi cation of cormorants The management goal of the Les Cheneaux as an infl uential factor can be diffi cult, at Islands, Brevoort Lake, and Drummond best. When the origin of suspected impacts Island cormorant management programs is poorly defi ned but considered important was to reduce cormorant caused sport fi sh enough to warrant management, adaptive mortality as a means of improving targeted management approaches off er the best means sport fi sheries by increasing fi sh survival for reducing uncertainty and risk associated and abundance. Each management program with management strategies. independently provides evidence that short- The information we present here, highlights term management goals have been met. The the importance of cormorants as a top tier strength of evidence varies for each location, predator in aquatic systems. Other scientists and in some cases was complicated by other have noted that cormorants and other fi sh- contributing factors. However, all 3 locations eating birds are a signifi cant infl uence on aquatic together provide weight of evidence for the food webs (Steinmetz et al. 2003, Rudstam underlying hypothesis that cormorants can be et al. 2004, Ridgway et al. 2006). Research an infl uential mortality factor on some local also has highlighted the cormorant’s role as a sport fi sh populations. Continuation of adaptive sentinel species with regard to contaminants management programs, if needed, and fi shery and ecosystem health (Weseloh et al. 1995, assessments at all locations will determine Ryckman et al. 1998). Although management Cormorants • Dorr et al. 165 may be prescribed in cases where cormorant Survey, Lake Superior State University, U.S. abundance causes confl icts, eff ectiveness of Forest Service, and the many volunteers and management should be evaluated in the context designated agents who contributed to the that cormorants are an important part of the research management and monitoring eff orts. ecosystems in which they exist. We thank K. C. Hanson-Dorr, F. Cunningham, M. Conover, and 2 anonymous reviewers for Management implications reviews of a previous draft of this manuscript. We described how researchers and managers through public and agency meetings, planning Literature cited and implementation of management, and Bassett, C. E. 2006. Decline of the Brevoort Lake collection and analysis of data, developed walleye fi shery: have cormorants played a role? and evaluated measurable objectives within U.S. Department of Agriculture, U.S. Forest the context of defi ned impacts of cormorants Service, Hiawatha National Forest, Escanaba, to sport fi sheries. We found that several key Michigan, USA. measureable objectives were important to Bédard, J., A. Nadeau, and M. Lepage. 1999. successful adaptive management: (1) are the Double-crested cormorant culling in the St. cormorants being managed the cormorants Lawrence Estuary: results of a 5-year program. that are impacting the resource?; (2) how much Pages 147–154 in M. E. Tobin, technical co- cormorant predation was occurring and what ordinator. Symposium on double-crested cor- was the response to management action?; (3) morants: population status and management what were the estimates of prey age and size issues in the Midwest. USDA-APHIS Technical class specifi c impacts by cormorants, including Bulletin 1879. Washington, D.C., USA. measures of prey mortality?; (4) what was the Belyea, G. Y. 1997. The impact of cormorant pre- prey response to cormorant management, and dation on yellow perch in the Les Cheneaux was that response consistent with cormorants Islands, Lake Huron. Pages 42–46 in J. S. as a limiting mortality factor?; and (5) were Diana, G. Y. Belyea, and R. D. Clark Jr. edi- desired management outcomes att ained? tors. History, status, and trends in populations A fl exible and responsive adaptive man- of yellow perch and double-crested cormorants agement program can address and adjust in Les Cheneaux Islands, Michigan. Michigan to uncertainty and risk associated with Department of Natural Resources Special Re- management actions. However, successful port 17, Ann Arbor, Michigan, USA. achievement of such programs requires con- Belyea, G. Y., S. L. Maruca, J. S. Diana, P. J. siderable commitment and coordination among Schneeberger, S. J. Scott, R. D. Clark Jr., J. all parties involved, as well as leadership from P. Ludwig, and C. L. Summer. 1999. Impact of managers willing to take risks (Riley et al. 2003). double-crested cormorant predation on the yel- The evaluation of management we described low perch population in the Les Cheneaux Is- here focused primarily on biological outcomes. lands of Michigan. Pages 47–59 in M. E. Tobin, We suggest research on the socioeconomic technical coordinator. Symposium on double- impacts of these management actions to further crested cormorants: population status and inform management and policy decisions. management issues in the Midwest. USDA- APHIS Technical Bulletin 1879, Washington, Acknowledgments D.C., USA. The data and results included in this synthesis Blackwell, B. F., M. A. Stapanian, and D. V. C. We- are the combined eff ort of many managers, seloh. 2002. Dynamics of the double-crested researchers, and volunteers too numerous cormorant population on Lake Ontario. Wildlife to list individually. We thank contributing Society Bulletin 30:345–353. staff from USDA-National Wildlife Research Brandt, S. B., D. M. Mason, D. B. MacNeill, T. Center, Mississippi Field Station–Michigan Coates, and J. E. Gannon. 1987. Predation by Program, Starkville, Michigan, Field Station, alewives on larvae of yellow perch in Lake On- USDA Wildlife Services, Michigan Program, tario. Transactions of the American Fisheries Michigan Department of Natural Resources, Society 16:641–645. U.S. Fish and Wildlife Service, U.S. Geological Brooking, T. E., L. G. Rudstam, M. H. Olson, and 166 Human–Wildlife Interactions 6(1)
A. J. VanDeValk. 1998. Size dependent alewife Fielder, D. G. 2008. Examination of factors con- predation on larval walleyes in laboratory ex- tributing to the decline of yellow perch popula- periments. North American Journal of Fisheries tion and fi shery in Les Cheneaux Islands, Lake Management 18:960–965. Huron, with emphasis on the role of double- Craven, S. R., and E. Lev. 1987. Double-crested crested cormorants. Journal of Great Lakes cormorants in the Apostle Islands, Wisconsin, Research 34:506–523. USA: population trends, food habits, and fi sh- Fielder, D. G. 2010. Response of the yellow perch ery depredations. Colonial Waterbirds 10:64– in the Les Cheneaux Islands, Lake Huron to 71. declining numbers of double-crested cormo- Diana, J. S., G.Y. Belyea, and R. D. Clark Jr., edi- rants stemming from control activities. Journal tors.1997. History, status, and trends in popu- of Great Lakes Research 36:207–214. lations of yellow perch and double-crested cor- Fielder, D. G., D. J. Borgeson, A. K. Bowen, S. R. morants in Les Cheneaux Islands, Michigan. Koproski, S. J. Greenwood, and G. M. Wright. Michigan Department of Natural Resources, 2003. Population dynamics of the St. Marys Special Report 16. Ann Arbor, Michigan, USA. River fi sh community 1975–2002. Great Lakes Diana, J. S., C. A. Jones, D. O. Lucchesi, and J. C. Fisheries Commission, Ann Arbor, Michigan, Schneider. 1987. Evaluation of the yellow perch USA,
Lucchesi, D. O. 1988. A biological analysis of the tional Wildlife Refuge and the arrival of double- yellow perch population in the Les Cheneaux crested cormorants. Pages 115–120 in M.E. Islands, Lake Huron. Michigan Department of Tobin, technical coordinator. Symposium on Natural Resources, Fisheries Research Report double-crested cormorants: population status No. 1958. Ann Arbor, Michigan, USA. and management issues in the Midwest. US- Ludwig, J. P., C. N. Hull, M. E. Ludwig, and H. J. DA-APHIS Technical Bulletin 1879, Washing- Auman. 1989. Food habits and feeding ecol- ton, D.C., USA. ogy of nesting double-crested cormorants in Steinmetz, J., S. L. Kohler, and D. A. Soluk. 2003. the upper Great Lakes, 1986–1989. Jack-Pine Birds are overlooked predators in aquatic food Warbler 67:114–126. webs. Ecology 84:1324–1328. Madenjian, C. P., and S. W. Gabrey. 1995. Water- Taylor, J. D., and B. S. Dorr. 2003. Double-crested bird predation on fi sh in western Lake Erie: cormorant impacts to commercial and natural a bioenergetics model application. Condor resources. Pages 43–51 in K. A. Fagerstone 97:141–153. and G. W. Witmer, editors. Proceedings of the Michigan Department of Natural Resources. Wildlife Damage Managment Conference, Hot 2005. Double-crested cormorants in Michi- Springs, Arkansas, USA. gan: a review of history, status, and issues U.S. Fish and Wildlife Service. 2003a. Final en- related to their increased population,
BRIAN S. DORR is a research wildlife biolo- PETER H. BUTCHKO received a B.S. degree gist with USDA-Wildlife Services' National Wildlife in Natural Resources from The Ohio State Univer- Research Center, Mississippi Field Station, and is sity. He has been the State Director of the USDA- an adjunct faculty member with Mississippi State APHIS-Wildlife Services in Michigan since 1998. University. He received his B.S. degree from the Prior to his current position, he worked for Wildlife University of Arizona and his M.S. and Ph.D. de- Services in Mississippi, California, and Ohio. grees from Mississippi State University. His research is focused primarily on ecological relationships between avian predators and their environment, particularly as it relates to human–wildlife confl icts.
DAVID G. FIELDER is a fi sheries research biologist for the Michigan Department of Natural Resources (MDNR), specializing in the dynamics and stock assessment of cool water fi sh populations of the Great Lakes and works principally on Lake Huron. He has been with the MDNR since 1994. He holds a B.S. degree from Eastern Michigan Univer- sity, an M.S. degree from the University of Michigan, SHAUNA L. HANISCH is a Ph.D. student in and is presently a Ph.D. candidate at Michigan State the Department of Fisheries and Wildlife at Michigan University. State University where she is studying human di- mensions of wildlife health management. She spent 9 years as a biologist with the U.S. Fish and Wildlife Service's migratory bird program, mostly working on double-crested cormorant management. She has a B.S. degree in wildlife biology from the University of Montana and a Master of Public Administration degree from Boise State University.