Myocastor Coypus)
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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. <[email protected]>. Abstract Coastal marshes on Delmarva Peninsula, Chesapeake Bay, Maryland, USA, provide valuable ecosystem services including flood prevention, erosion control, filtration, and carbon sequestration, and support commercial and recreational fishing, trapping, hunting, and ecotourism that generate billions of dollars for the region. Nutria (Myocastor coypus) were introduced to Dorchester County on the eastern side of Delmarva peninsula in 1943. They spread rapidly and reached peak densities in the late 1990s when vegetation studies linked nutria herbivory to massive wetland loss throughout Maryland’s lower eastern shore. A coalition of state, federal and non-governmental organisations obtained congressional funding to eradicate nutria from the Delmarva Peninsula and, beginning in 2002, implemented a systematic eradication plan. The eradication team used integrated methods to complete the initial reduction of nutria populations on 60,000 ha of marsh in five counties across Maryland’s lower eastern shore. Population reductions to near-zero were accomplished using trapping and shooting applied systematically using GPS and GIS to apply removal efforts at the landscape level. Residual animals were removed using dogs and targeted trapping. New techniques for detecting nutria at low densities are currently being evaluated including dogs, lures and attractants, call surveys, judas nutria, and decoy cages. Recovery of nutria-damaged marsh has been significant and has halted further conversion of marsh to open water. The programme now aims to create a nutria-free coastal marsh ecosystem across the Delmarva Peninsula by 2014. Keywords: Coypu, impacts, eradication, Chesapeake Bay, Delmarva Peninsula, trapping 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