Nutria Control Methods and Some Current Research Gary Witmer USDA/APHIS/WS National Wildlife Research Center Fort Collins, Colorado USA
Thanks to colleagues who did reviews of nutria control….. • Dwight LeBlanc WS State Director Louisiana And Jeff Mach Genesis Labs Wellington CO (and thanks to many for the photos used in this presentation!)
LDWF, 2003 Nutria are one of many invasive vertebrate species that have become established in the US (of some 20 mammal species)…. • Native to South America • Brought to the US for fur industry • Now established in 15+ states • Cause damage to marshes, crops, and compete with native species
Control versus eradication….. • Some places want to eradicate (e.g., Blackwater NWF, MD) • Some places want to manage as a natural resource (e.g., Louisiana)
Eradications are not easy to accomplish and the tenants of a successful eradication include (from Parkes and Murphy, NZ)…… • All individuals must be put at risk • Animals must be removed faster than they can reproduce • The risk of immigration must be zero Hence, a well-planned strategy with contingencies must be in place with adequate resources and a sustained effort to be successful Post-eradication monitoring is essential !
Methods available to manage nutria populations include….. • Trapping • Leg-hold traps • Conibear traps • Live traps • Capture with nets • Shooting • Use of dogs to locate • Baiting with zinc phosphide (rodenticide) • Incentive payment/bounty programs Note: IPM approaches usually employ multiple methods!
Other methods are not effective or do not reduce nutria populations (but may reduce some types of damage)…. • No repellents or fumigants effective nor registered • Frightening devices are ineffective • Barriers to protect trees, property, banks • Cultural methods (water level control; control plant food and cover) • Avoid certain land uses in high risk areas
Trapping nutria….. • Leg-hold and conibear traps effective, but labor intensive • Live traps for research or relocation (the latter not done much!) • Regs vary by state; usually required to check daily • Usually set in runs or “haul out” areas • Some trap-shy animal and sex-bias problems • Some injuries result • Can catch non-targets • Use of boats and airboats is very important
Can also catch nutria with dip nets…. • Need skilled individuals • Costs and labor rather high • Biases in sex and age animals captured? • Used mainly to get research animals
Shooting nutria….. • Small bore rifle or shotgun effective • Check state regs! • Nutria are mainly nocturnal so limited access to population? • Trained dogs can help locate nutria • Encourage other hunters (e.g., duck hunters) to harvest • Some concern about lead in carcasses (e.g., eagles might consume) so remove or deep bury
With trapping and shooting…. • Pelt prices low…so low effort and harvest • Need more markets for pelts and meat • Incentive program (as in Louisiana) can be effective • Can also use federal and state trappers and shooters
One rodenticide is available for use on nutria…. • Zinc phosphide (0.67%) on sweet potatoes or carrots • Restricted use pesticide • Must follow EPA label carefully! • Place baits on rafts or banks near burrows or runs • Limited use (localized scale), but can be effective • Some non-target risks (but we determined the risks to alligators are small)
Research underway and additional needs…. • “Enough is known about nutria biology, ecology, and the damage they cause… what is needed is to develop & implement effective & efficient control methods, especially trapping strategies….” (paraphrased from Bounds 2003 review) Despite those words…..
Some preliminary research done or underway includes…. • More effective lures for traps • Multiple capture traps • Alternative rodenticides • Unpalatable marsh plants for restoration • Fertility control in rodents • Methods to determine presence and densities
Lure/attractant research has found…. • Olfactory cues work best? • 284 nutria captured w/ leg-hold traps: 35 control, 50 synthetic gland secretion, 56 apple-based lure, 66 nutria urine, and 77 nutria fur extract • Lure-treated leg-hold traps increased trapping success by 42% to 120% over untreated traps • 15 non-target animals captured: • 6 wading birds • 5 swamp rabbits (Sylvilagus aquaticus) • 2 alligators (Alligator mississippensis) • 1 hawk (Buteo jamaicensis) • 1 raccoon (Procyon lotor)
A multiple-capture trap looks promising…. • 22 nutria captured: 10 in food-baited traps and 12 in marsh plant-baited traps • 1 triple capture in marsh plant-baited trap; 2 double captures in food-baited traps; nutria were observed on two occasions to escape from traps • No non-target captures in January 2007, but 3 small alligators (Alligator mississippensis) were caught in an earlier trial (April, 2006) • Suspected swamp rabbits (Sylvilagus aquaticus) were able to enter trap, eat the food bait and then exit trap • More effective lures still need to be developed because, many nutria were observed near traps by motion-activated cameras but were not captured
Additional research is finding…. • New toxicant may be registered? (Genesis Labs working on) • Unpalatable marsh plant (Justicia lanceolata) for restoration? • Fertility control research underway (PZP, GnRH, diazacon)
Still problematic: methods to monitor populations…. • Radiotelemetry and visual marking methods need improvement • Trap-mark-recapture has biases • Remote cameras may help • DNA ID of individuals may help (fecal DNA?)
Nutria management will continue to challenge managers, but improvements are needed to…. • Provide adequate funds for management • Reduce populations and damage to acceptable levels • Provide more cost-effective and less labor intensive methods of management • To allow balanced natural resource management that is acceptable to all stakeholders
Contact information Gary W. Witmer Research Wildlife Biologist USDA National Wildlife Research Center USDA/APHIS/WS NWRC 4101 Laporte Avenue Fort Collins, CO 80521-2154 Phone: (970) 266-6335 Fax: (970) 266-6089 Email: firstname.lastname@example.org