Developing Techniques for Estimating Nutria (Myocastor coypus) Abundance

Science Center Objects

Nutrias (Myocastor coypus) are an aquatic rodent imported from South America to the United States in the 1920-40’s for the fur farms. Since their original importation they have become established in the wild in many regions of the United States.

PROJECT ON HOLD DUE TO FUNDING CONSTRAINTS

Nutria caught by camera trap at the Dugas Road Landfill, Lafayette LA
Nutria caught by camera trap at the Dugas Road Landfill, Lafayette, LA

The Science Issue and Relevance: Nutrias (Myocastor coypus) are an aquatic rodent imported from South America to the United States in the 1920-40’s for the fur farms. Since their original importation they have become established in the wild in many regions of the United States. In their introduced range they have few natural predators and their populations frequently increase to numbers where they create problems. These problems may include the degradation of marsh by overgrazing (also called ‘eat-outs’), and erosion of stream and pond banks and failure of water control structures due to their burrowing. At high population densities they have been shown to be vectors of parasites and diseases that affect people and livestock. While eradication is the preferred option, it is impractical in most regions because nutrias are widely distributed, prolific, and readily disperse. Therefore, good population estimates are needed to better understand the extent of the nutria problem locally and so control efforts can be assessed. Currently, there is no way to accurately estimate nutria population size short of complete removal. A variety of studies have shown that box traps have low recapture rates making estimation unreliable. Other methods that have been tried but none so far have proven effective.

Girard Park in the City of Lafayette, LA
Girard Park in the City of Lafayette, LA

Methodologies for Addressing the Issue: 

  1. Develop and compare techniques to live capture nutria for mark-recapture studies. These may include modified no-kill snare techniques, multi-catch traps, hair traps, and DNA-finger printing of feces. 

    Develop and test techniques for individual identification including the use of RFID tags, and DNA identification from hair samples of captured animals, hair traps, and feces, and use of marked PVC pipes for visual identification and mark/recapture using camera traps. 

    Develop and test telemetry techniques for nutria. 

The plan is for trail cameras to be used in various locations to determine the areas with nutria traffic, but presence of scat, evidence of feeding, and burrows are also used to assess the areas nutria frequent. A map of potential trapping locations is grouped by presence type, and a stratified random assignment of trap location to trap type will be performed. Traps will be set at various locations for a period of time (perhaps one to two weeks) and then be randomly assigned a new location. A subset of the traps will have trail cameras to assess the number of visits by nutria and non-target species to the traps and capture rates (number of capture divided by number of visits by species). Traps will be visited within 16-24 hours after being set depending on weather, and access issues.

For initial captures, regardless of method caught, the animals will be placed in a squeeze cage and have a RFID tag implanted; their weight, sex, and body condition will also be recorded. Guard hair and blood samples (and scat sample, if offered) will be collected and stored for DNA fingerprinting if funding allows. Recaptured animals (as determined by the presence of RFID tags) will have their ID, weight, sex, and body condition recorded. Non-target animals will be noted, weighed, and released. Unless otherwise directed by the Lafayette Parish Department of Environmental Quality, all animals captured, regardless of species will be released.

North Dugas Landfill, north Lafayette, LA
North Dugas Landfill, a former municipal landfill that is now a Cajun Prairie restoration site adjacent to Dugas Road, north Lafayette.

Future Steps: Funding was available to initiate the monitoring design and located study sites but was discontinued shortly thereafter. When funding is reestablished and a systematic method for detection and capture is initiated in the test areas, its effectiveness will be tested in marsh dominated systems in the area managed by the coastwide nutria control program.

Locations:

  • Girard Park -- 30.205824°, -92.020638°
  • Restoration Site - North Dugas Landfill -- 30.281208° -92.071123°