Kendrot, S.R. Restoration through eradication: protecting Chesapeake Bay marshlands from invasive nutria (Myocastor coypus)
Restoration through eradication: protecting Chesapeake Bay marshlands from invasive nutria (Myocastor coypus)
S. R. Kendrot USDA APHIS Wildlife Services. 2145 Key Wallace Drive, Cambridge, MD 21613, USA.
INTRODUCTION The eradication of invasive pests is increasingly being on Gosling’s recommendations, the task force focused attempted by conservation managers while the size and on eradication as the primary strategy for restoring and complexity of successful eradications has surpassed what protecting nutria-damaged marshlands in the Chesapeake was previously considered feasible (Donlan et al. 2003). Bay. Systematic trapping was identified as the primary Feral pigs and goats have been eradicated from several method for reducing nutria populations. large islands in the Galapagos (Cruz et al. 2005; Campbell In 1997, a partnership of federal and state agencies and and Donlan 2005) and the size of New Zealand Islands private interests was formed to develop and implement a from which Norway rats have been successfully eradicated pilot project with the ultimate goal of eradicating nutria has increased logarithmically (Clout and Veitch 2002). on Maryland’s Eastern Shore. The Nutria Control/Marsh The Delmarva Peninsula, which is bordered by the Restoration Pilot Project aimed to gather data on the Chesapeake and Delaware Bays and the Atlantic Ocean, population of nutria in CMNWRC, Fishing Bay Wildlife comprises the state of Delaware and parts of Maryland and Management Area (FBWMA), and Tudor Farms and Virginia (Fig. 1). The peninsula supports tidal wetland adjacent properties in Dorchester County. Information on habitats recognised as among the most important in the nutria population size, physiology, reproduction, behaviour, United States and as “Wetlands of International Importance” and movement were used to develop and test trapping under the Ramsar Convention Treaty (Tiner and Burke strategies to maximise removal. Two years were dedicated 1995). The wetlands are home to numerous fish and to the collection of baseline data (Phase I) and four years wildlife species, and support commercial and recreational (2002-2006) to test and implement eradication strategies fishing, hunting, trapping, bird watching, wildlife viewing, on the 24,300 ha encompassed by these areas (Phase and photography. II). In 2007, trapping of nutria began in neighbouring Nutria (Myocastor coypus), a tropical, aquatic South counties and the eradication zone was redefined to include American rodent, was introduced to the United States in all of Delmarva Peninsula. Although not an island per California in 1899 and to southern states in the early 20th se, the peninsula is sufficiently isolated from mainland Century for fur farming and weed control (Evans 1970; nutria populations that the risk of recolonisation through Willner et al 1979; LeBlanc 1994; Hess et al. 1997). After immigration is thought to be near zero. their introduction to Delmarva Peninsula in 1943, numbers This paper describes the methods used to reduce nutria of nutria increased to at least 50,000 in the early 1990s populations to near zero densities from 2002- 2009 as part (Carowan pers. comm.). In the Delmarva marshes, nutria of a campaign to eradicate the species from the Delmarva mostly feed on the roots of Olney three-square bulrush Peninsula. (Scirpus olneyi), a native emergent grass that grows 1-1.5 meters above water and supports a submersed root mat in MATERIALS AND METHODS highly erodible sediment. When nutria excavate roots, they expose the sediment to tidal erosion and brackish wetlands Project management and staffing to salt water intrusion (Haramis and Colona, unpublished). An eight member management team of senior-level Wetlands are converted to open water, removing all habitat representatives from U.S. Fish and Wildlife Service, U.S. benefits of the marsh for native species. On the Blackwater Department of Agriculture (USDA), Maryland Department National Wildlife Refuge (CMNWRC), for example, nutria of Natural Resources (MDNR), U.S. Geological Survey destroyed more than half of its original marsh (2833 ha). (USGS), and Tudor Farms oversaw the project and was Efforts to control nutria on Delmarva through primarily responsible for securing funding, obtaining commercial and recreational trapping did not prevent political support, and providing technical support to damage to three-square bulrush marsh. Maryland officials field operations. A full-time wildlife biologist managed then consulted Dr. L.M. Gosling who, after several decades operations and supervised staff members, which included of research, failed attempts and effective trials, led a 17 full-time wildlife trapping specialists, one full-time team of 24 trappers to successfully eradicate nutria from maintenance worker who maintained vehicles, boats Britain over six years in the 1980s (Gosling 1989). Based and trapping equipment, and a part-time administrative assistant. Pages 313-319 In: Veitch, C. R.; Clout, M. N. and Towns, D. R. (eds.). 2011. Island invasives: eradication and management. IUCN, Gland, Switzerland. 313 Island invasives: eradication and management
Fig. 1 Distribution of wetland habitats on Delmarva Peninsula and population status by subwatershed in May, 2011.
Phases of Eradication Our nutria eradication campaign can be broken into six phases: 1) Survey: Define the distribution of nutria on the Delmarva Peninsula. 2) Knock-down: Rapid depopulation of metapopulations identified in the survey phase. 3) Mop-up: Targeted removal of residual nutria remaining after the knock-down phase is completed. 4) Verification: Population monitoring to confirm that eradication at the management unit level was successful. 5) Surveillance: Continued monitoring at the landscape level. 6) Biosecurity: Implementation of strategies to prevent the reinvasion of nutria. While the process outlined above was generally followed sequentially, we were frequently engaged in multiple phases simultaneously in different management units. In addition, the progression between phases was not always linear and the transition between phases was not always discrete. Removal methods Nutria were primarily removed through trapping, hunting and shooting. Trap devices used included rotating- jawed body-gripping traps (Conibear type) (Fig. 2), foothold traps (Fig. 3), cage/box traps, and cable restraining devices (snares). Traps were set on nutria trails, in ditches, along waterways and at approaches to natural and artificial (false) nutria beds and haul-outs, on floating support frames, and floating platforms. Methods used included: 1) “blind” sets in natural travel ways; and 2) lured sets using urine collected from captive animals, scats, anal gland lure, disturbed earth, and cut vegetation. Traps were typically set on sign of nutria presence. In low density areas, where nutria are more difficult to detect, trapping specialists used their understanding of nutria behaviour and movement to place sets where they were most likely to capture nutria
Fig. 2 A 17.8 cm body-gripping (Conibear) trap set on a floating platform. The trap triggers are spread to allow smaller non-target species to pass through the trap.
314 Kendrot: Chesapeake Bay nutria eradication moving through the area. Kill traps were checked within First, progressive sweeps were used in large contiguous 96 hrs and live traps within 24 hrs. Non-target captures blocks of marsh habitat. A continuous band of trapping of native mammals, birds and reptiles were minimised by units was established across the marsh, bridging non-nutria manipulating trap trigger and pan configurations, placing habitat (uplands or open water) on either side. Trapping jump sticks or obstructions to block non-target access to specialists used handheld GPS receivers to ensure that they traps, and selectively avoiding areas used by non-target were trapping assigned units. As nutria in each band of species. trapping units were reduced to very low density, trappers moved forward to the next un-trapped unit. When capture Hunting and shooting using small calibre rifles, shotguns, rates in a trapping unit slowed, traps were established in the and handguns, was conducted year round, but was most next adjacent trapping unit, leaving some traps behind to effective in winter when marshes and waterways froze and capture animals attempting to penetrate the trapping front. reduced escape routes for nutria and snow cover provided a A swath of continuous trapping activity was thus spread tracking substrate. Trained dogs were used throughout the across the marsh, three to four trapping units wide, with year to detect and remove nutria, particularly in previously trapping intensity highest at the leading edge. trapped areas. Second, a simultaneous blitz removal strategy was Use of toxicants (e.g., zinc phosphide) was considered used in smaller, isolated marshes that could be trapped during the planning phase of the programme, but rejected as a single unit. Such marshes typically bordered rivers because of concern over potential non-target impacts. throughout their tidal reach. Trappers were assigned to The high success of nutria removal through trapping and each section of river frontage and all marsh units were hunting, followed by spot removal using detection dogs, trapped simultaneously. has so far precluded any need to use toxicants. Trapping units were considered as depopulated after Initial Population Reduction Strategies two weeks without a nutria capture. Data collected included There are almost 200,000 ha of wetland habitats on the the number of trap nights, the location, age, and sex of each Delmarva Peninsula, which required a systematic trapping nutria removed, and the identity and location of all non- programme in manageable trapping units. A Geographic target captures. Information System (GIS) was used to overlay a 402 m x Hunting and shooting were used extensively during 402 m rectangular grid of trapping units on a wetland map winter, when freezing conditions impeded trapping efforts of the Delmarva Peninsula. Two removal strategies were and often caused nutria to aggregate. Areas that were implemented based on the spatial distribution of marsh heavily hunted were subsequently trapped once weather habitat. conditions permitted.
Monitoring Following initial knock-down, trapping units were monitored every 3-12 months, depending on access and risk of reinvasion, for signs of nutria activity using: 1) intensive ground or shoreline searches documented with GPS tracks; 2) searches with dogs trained to find nutria; and 3) surveys of nutria sign at false beds. In order to reduce non-target impacts, traps were not used as monitoring devices unless sign was detected. Nutria population status was assigned to one of three categories for each trapping unit surveyed: Resident: Evidence of occupancy including well- used nutria trails, bedding and feeding activity and/or the presence of multiple sizes of fresh scats indicating the presence of different age groups of nutria. Set traps would have a high probability of capture. Transient: Evidence that a nutria passed through, but was not inhabiting the area. Usually a lone set of tracks or small amounts of scat of indeterminate age would be classified as transient. Set traps would have alow probability of capture. Absent: No evidence of nutria detected. With increasing size of the eradication zone, monitoring effort in previously trapped areas increased proportionately and competed directly with efforts to expand knock down efforts into new areas. In order to manage these competing needs, monitoring areas were prioritised for survey based on their risk of re-infestation as determined by prior occupancy, proximity to un-trapped areas, or presence of preferred habitat. High priority trapping units were monitored with increased frequency until failure to detect Fig. 3 A foothold trap set on an imitation nutria bed. The nutria after repeated visits warranted a reduction in priority. trap is wired to a one-way slide lock attached to a cable Mop-up trapping efforts were initiated upon the discovery anchored in deep water. This submersion set is designed of resident sign and discontinued after two weeks without to quickly drown captured nutria. Bamboo poles are placed a capture and failure to detect fresh sign. to reduce non target bird captures.
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Table 1 Total wetland area (ha) in Maryland counties and areas subject to nutria control in 2003-2008. No nutria control was conducted in Queen Anne, Kent, Cecil, and Worchester Counties (29,520 ha of marsh) and no new area received treatment in 2009. Avail. Area Percent County wetland 2003 2004 2005 2006 2007 2008 trapped available Dorchester 54,628 11,738 11,798 6607 10,254 2248 253 42,897 79% Somerset 42,715 0 0 0 0 6833 2901 9734 23% Wicomico 13,272 0 0 0 0 5473 0 5473 41% Talbot 5122 0 0 0 0 0 1482 1482 29% Total 118,448 11,738 11,798 6607 10,254 14,554 5407 60,358 41%
Table 2 Number of nutria removed and percent of first year removal from Initial Knock-down Areas (IKDAs) during eradication efforts on Delmarva Peninsula. IKDA 2003 2004 2005 2006 2007 2008 2009 Total 2003 4795 370 127 70 16 19 5 5402 % 100% 7.7% 2.6% 1.4% 0.3% 0.4% 0.1% 2004 3071 290 63 20 41 4 3489 % 100% 9.4% 2.1% 0.7% 1.3% 0.1% 2005 677 108 17 127 69 998 % 100% 15.9% 2.5% 18.8% 10.2% 2006 318 32 22 9 381 % 100% 10.1% 6.9% 2.8% 2007 812 79 88 979 % 100% 9.7% 10.8% 2008 1183 387 1570 % 100% 32.7% Total 4795 3441 1094 559 897 1471 562 12819
Table 3 Time required to achieve an approximate 100% reduction in nutria numbers in trapping units during initial trap out, and number of nutria removed. Data based on IKDAs trapped in 2003-2008. Trapping units reduced to near-zero density Nutria Removed Week Number % Cumulative % Number % Cumulative % 1 0 0.0 0.0 4584 51.1 51.1 2 145 11.4 11.4 1779 19.9 71.0 3 208 16.3 27.7 837 9.3 80.3 4 176 13.8 41.5 447 5.0 85.3 5 177 13.9 55.4 303 3.4 88.7 6 153 12.0 67.4 247 2.8 91.5 7 99 7.8 75.1 148 1.7 93.1 8 63 4.9 80.1 148 1.7 94.8 9 44 3.5 83.5 70 0.8 95.5 10 38 3.0 86.5 64 0.7 96.3 11 23 1.8 88.3 45 0.5 96.8 12 18 1.4 89.7 28 0.3 97.1 13-30 131 10.3 100.0 262 2.9 100.0 Total 1275 8962
Analysis We tallied the amount of effort required to reduce the Initial knock-down areas (IKDAs) were defined by the nutria population to near-zero by counting the number year in which knock down activities were initiated and the of weeks of trapping required and back-calculating area covered in that year. We determined the number of the percentage of the pre-existing population captured nutria removed from each IKDA during the year of initiation during each week of trapping, accepting that this slightly and compared the number of nutria removed during mop- overestimates percentage removed as an unknown number up efforts in the same areas in subsequent years. Traps of nutria remained un-trapped. By determining the total were only set when sign was detected during monitoring, number of nutria removed from a trapping unit during thus trapping effort was not applied equally across years initial removal and dividing that number into the weekly and catch per unit effort data was not compared. However, capture total, we were able to determine the percentage the reduction in number of nutria removed was evaluated of the presumed population that was taken during each to gauge the magnitude of the population reduction. successive week of trapping.
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Table 4 Number and percent of nutria removed by method during initial population reduction and clean-up phases of eradication. Knock-down Mop-up Total Method Number % Number % Number % Conibear 7457 67.9% 762 42.4% 8219 64.3% Shooting 1316 12.0% 101 5.6% 1417 11.1% Submersion foothold 927 8.4% 449 25.0% 1376 10.8% Dog 470 4.3% 344 19.2% 814 6.4% Foothold 460 4.2% 78 4.3% 538 4.2% Snare 105 1.0% 13 0.7% 118 0.9% Floating Conibear 97 0.9% 10 0.6% 107 0.8% Hand caught 66 0.6% 15 0.8% 81 0.6% Platform Trap (foothold) 62 0.6% 18 1.0% 80 0.6% Platform (conibear) 15 0.1% 2 0.1% 17 0.1% Cage 8 0.1% 4 0.2% 12 0.1% Spotlight/shoot 6 0.1% 0.0% 6 0.1% Grand Total 10,989 100 % 1796 100 % 12,785 100 %
Table 5 Trap nights and catch per unit effort (nutria/1000 trap nights) for top three trapping methods and total captures using non-trapping methods during initial knock-down and mop-up during eradication efforts on Delmarva, 2002-2008. Initial Knock-down Mop-up Method Trap nights Captures CUE Trap nights Captures CUE Body-grip 602,636 7462 12.38 56,917 746 13.11 Submersion 36,538 928 25.39 17,356 434 25.01 Foothold 13,160 460 34.9 1960 78 39.79 Shooting n/a 1316 n/a n/a 1417 n/a Dog n/a 470 n/a n/a 814 n/a
RESULTS Between 2003 and 2008, the campaign against nutria The most productive methods of nutria removal was conducted over nearly 61,000 ha of the 148,000 ha during the initial depopulation phase were body-gripping wetland habitat on Maryland’s eastern shore, as determined traps, shooting, footholds set on submersion cables, dogs, from National Wetland Inventory maps (Table 1). Knock- and staked foothold traps (Table 4). Staff accumulated down activities were initiated on new areas each year until 652,334 and 76,233 trap nights during knockdown and 2009, when verification and mop-up activities left little time mop-up trapping efforts, respectively. Body gripping traps for expansion into new areas. Nutria catches on IKDAs accounted for 92 % of trap nights and 84% of captures were used to track progress in population reduction (Table during knock-down trapping and 59% of trap nights and 2). In the third year following initial knock-down, mop-up 75% of captures during mop-up trapping. Submersion efforts yielded <3% of the population removed in the initial footholds accounted for 6% of trap nights and 10% of year of treatment for IDKAs 2003-2006. The exception captures during knock-down, but 23% of trap nights and was IKDA 2005, where an area was not trapped until 2008 35% percent of captures during mop-up trapping. Staked due to access restrictions imposed by a private landowner footholds accounted for 2% of trap nights and 6% of (Table 2). More than 100 nutria were removed from this captures during both knock-down and mop-up trapping property. In fact, many of the nutria captured in 2003 and phases. During initial knockdown, catch rates were lowest 2004 IKDAs during monitoring were trapped within 13 km for body-gripping traps and highest for staked foothold of this property, well within dispersal distances observed traps. These latter were marginally more effective during by GPS/radio-tagged nutria released as part of an ongoing mop-up trapping (Table 5). Judas experiment (not reported here). Populations that remained or developed after initial Nutria were encountered in approximately one third of population reduction typically comprised small groups the trapping units inspected and were reduced to very low ranging in size from two to six animals, although one group numbers in 75 % of those within seven weeks of trapping of 41 animals eluded detection for three years. Analysis of (Table 3). A few units required up to 30 weeks to capture the sex and age distribution of the captured nutria led us to the last one or two nutria. Typically, more than half of conclude that this abnormal population arose from a small the original population was captured in the first week of group of three to six females that immigrated sometime trapping, 80% by the end of the third week, and more than during the third year following initial knock-down. 90 % by the end of the sixth week of trapping. In many trapping units, catching the last 5-10% of the population took as long as or longer than capturing the first 90-95 %.
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DISCUSSION restrict our access during the non-growing season, from September to the end of January, primarily because of We implemented a systematic hunting and trapping recreational hunting. programme that effectively reduced feral nutria populations within 16 ha trapping units to near zero within Damaged marshes often recovered rapidly after nutria four to eight weeks per unit. Progressive and sequential were removed. As nutria populations approached zero, treatment of trapping units across larger management units staff reported that nutria swim channels were reclaimed by (watersheds) enabled us to effectively eliminate nutria over rhizome growth from three square bulrush. The resulting >60,000 ha of sensitive coastal wetlands in the Chesapeake network of new roots trapped sediments that filled in swim Bay Watershed. Several mop-up sessions have been channels, thereby eliminating the primary route of erosion applied throughout this area, much of which is now in the for organic soils dislodged by nutria foraging habits. These verification phase. Nutria have not been detected in some anecdotal observations were corroborated by quantitative watersheds for several years and these sites are now in the vegetation studies conducted at Patuxent Wildlife Research surveillance phase. Center, which showed a dramatic recovery in areas Although the same removal methods were used during extensively damaged by nutria (e.g., Figs 4a, b; Haramis knock-down and mop-up trapping phases, the relative et al. 2006). importance of different trapping techniques was influenced This project was the first large scale attempt to eradicate by the needs of knock-down versus mop-up trapping nutria in North America. The type and distribution of strategies. For example, body-gripping traps accounted habitat on Delmarva differs significantly from nutria habitat for the largest number of animals in both phases, but in England. While the UK example provided valuable submersion footholds and detector dogs played a greater insights, the political, social, and ecological conditions role in removal during mop-up efforts. One possible dictated a different approach in Delmarva and yielded new explanation for the increased importance of submersion lessons including: footholds is that nutria at low densities move greater distances along waterways in search of other nutria and 1) Eradication is achievable at the trapping unit level are therefore more vulnerable to footholds set at false beds when integrated methods are applied systematically along waterways. In addition, specialists aided by dogs by skilled technicians. By replicating the process are more efficient at finding nutria in areas of low density progressively across management units nutria than specialists without dogs. We thus relied heavily on densities were reduced to near zero at the landscape detection dogs during mop-up phases. level. In England, catch per unit effort was used to indicate declines in population (Gosling and Baker 1987), but we did not detect significant changes in catch per unit effort between knock-down and mop-up trapping phases. Furthermore, box traps were used in England to allow the release of non-target species and a consistent trapping effort during consecutive trapping sessions. However, we set kill traps only where evidence of nutria was documented during intensive sign searches. This targeted approach to removing residual populations enabled us to reduce impacts to non-target species by restricting trapping to areas occupied by nutria. Compared with experiences in England, our approach required a greater investment in alternative detection methods. Differences were recorded in the catch per unit effort of body-gripping versus foothold traps is likely due to the way in which traps are set. Body-gripping traps are often set as blind trail sets in higher trap densities to cover the myriad of trails available. Footholds, in contrast, are most often set selectively along waterways in conjunction with a false bed and/or urine or other visual or olfactory attractant. The difference between submersion and staked foothold efficiency is probably due to small sample sizes and the fact that staked footholds were only used during the first few months of knock-down trapping. The use of staked footholds was largely discontinued after submersion sets were approved as a lethal trapping technique, allowing us to increase trap check intervals from 24 to 96 hours. Monitoring the previously trapped populations remained one of the programmes biggest challenges. With 61,000 ha of depopulated habitat spread across five counties, returning to these areas on a regular basis required an exhaustive effort that precluded expansion into new areas. Yet, expansion into new areas was necessary to Fig. 4 (A) A wildlife specialist examines a nutria eat out in reduce the risk of reinvasion of the nutria-free zone. Thus, Monie Bay watershed, Somerset County, Maryland in May these priorities competed for limited staff resources and 2007. (B) the same marsh in May 2009, during the second time. Additionally, many private landowners continued to growing season following eradication of nutria.
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2) Cooperation of private landowners is important to Clout, M.N. and Veitch, C.R. 2002. Turning the tide of biological invasion: the potential for eradicating invasive species. In: Veitch, C.R. and Clout, putting every nutria at risk, although it is likely that M.N. (eds.). Turning the tide: the eradication of invasive species, pp. nutria residing in relatively small private in holdings 79-84. IUCN SSC Invasive Species Specialist Group, IUCN, Gland, can be trapped from the periphery. Switzerland and Cambridge, U.K. 3) Techniques used effectively during the knock- Cruz, F.; Donlan, C.J.; Campbell, K. and Carrion, V. 2005. Conservation down phase may not be sufficient to achieve final action in the Galapagos: feral pig (Sus scrofa) eradication from Santiago eradication once the population has been reduced to Island. Biological Conservation 121: 473-478. extremely low densities. Donlan, C.J.; Tershy, B.R.; Campbell, K. and Cruz, F. 2003. Research for requiems: the need for more collaborative action in eradication of 4) Staff must be prepared to develop and adapt tactics and invasive species. Conservation Biology 17: 1850-1851. strategies when new challenges reveal themselves. Evans, J. 1970. About nutria and their control. U.S. Department of the 5) Efficiency varies seasonally. Nutria are more Interior Bureau of Sport Fisheries and Wildlife, Denver. 65 pp. difficult to detect during the summer months when Gosling, L. M. and Baker, S.J. 1987. Planning and monitoring an attempt lush vegetation conceals evidence of occupancy and to eradicate coypus from Britain. Zoological Society of London. nutria movements appear to be minimal. Conversely, Symposia, No. 58: 99-113. late fall through early spring is an optimal period for detecting nutria as vegetation dies back and nutria are Gosling, L.M. 1989. Extinction to order. New Scientist 1654: 44-51. more active. Haramis, G.M.; O’Connell, A. and Kendrot, S. 2006. USGS Research to assist nutria eradication in Maryland: Detection and monitoring a 6) Nutria may restrict activity or abandon sites major need. [On-line] Available at: http://www.pwrc.usgs.gov/research/ subjected to intense daily human activity. Reducing scimtgs/2006/posters/Haramis_marsh_loss_new.pdf [Accessed 17 Jan the frequency of trap checks to 96 hours appeared to 2010] reduce incidence of site abandonment. Hess, I.D.; Conner, W. and Visser, J. 1997. Nutria - another threat to Louisiana’s vanishing coastal wetlands. Aquatic Nuisance Species Conclusions Digest 2: 2. LeBlanc, D. 1994. Nutria. Animal and Plant Health Inspection Service. The Chesapeake Bay Nutria Eradication Program B71-B80. Animal Damage Control, Port Allen, LA., U.S.A. now aims to create a nutria-free coastal marsh ecosystem Tiner, R.W. and D.G. Burke. 1995. Wetlands of Maryland. U.S. Fish and across Delmarva Peninsula by 2014. Given the worldwide Wildlife Service, Hadley, MA., U.S.A. 193 pp. distribution of nutria and its status as an invasive pest (Carter and Leonard 2002), the lessons learned from our Weibe, J. and Mouton, E. 2009. Coastwide nutria control program 2008- 2009: nutria harvest and distribution 2008-2009 and a survey of nutria programme will help instruct those interested in controlling herbivory damage in coastal Louisiana in 2009. [On-line]. Available at: or eradicating nutria elsewhere. Ongoing control http://www.nutria.com/uploads/0809CNCPfinalreportforwebsite.pdf programmes in Italy and Louisiana, USA, show promise [Accessed 17 Jan 2010] for reducing damage to acceptable levels if eradication is Willner, G.R.; Chapman, J.A. and Pursley, D. 1979. Reproduction, deemed impossible (Bertolino and Viterbi 2009, Wiebe and physiological responses, food habits, and abundance of nutria on Mouton 2009). The Delmarva programme has important Maryland marshes. Wildlife Monographs 65: 43 pp. implications for enhancing the effectiveness of control efforts, identifying additional eradication opportunities, and preventing invasion through the early detection and removal of invaders.
ACKNOWLEDGEMENTS The Nutria Project is funded by the US Fish and Wildlife Service Partners for Fish and Wildlife programme and Blackwater National Wildlife Refuge. Other partner agencies and organisations include: USDA APHIS Wildlife Services, USGS Patuxent Wildlife Research Center, Maryland Department of Natural Resources, University of Maryland Eastern Shore, Tudor Farms, Inc. Additional funding for development of Judas nutria technique is provided by the National Fish and Wildlife Foundation and Tudor Farms, Inc. I am greatly appreciative to Mike Haramis for assistance in drafting this manuscript and Dan Murphy, Jonathan McKnight, Kevin Sullivan, Glenn Carowan and Leo Castro Miranda for reviewing this manuscript. Special thanks go to the field staff whose tireless efforts and sacrifices have made this possible.
REFERENCES Bertolino, S. and Viterbi, R. 2009. Long-term cost-effectiveness of coypu (Myocastor coypus) control in Piedmont (Italy). Biological invasions 12: 2549-2558. Campbell, K. and Donlan, C.J. 2005. Feral goat eradications on islands. Conservation Biology 9: 1362-1374. Carter, J. and Leonard, B.P. 2002. A review of the literature on the worldwide distribution, spread of, and efforts to eradicate the coypu (Myocastor coypus). Wildlife Society Bulletin 30: 162-175.
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