Research and Eradication Methods
A nutria is sterilized and fitted with a tracking device for the Judas project. USDA photo
During the earliest research efforts, nutria were trapped and fitted with radio collars so biologists could track their movements. Unfortunately, the Chesapeake Bay Nutria Eradication Project (CBNEP) found it difficult to accurately estimate nutria populations because of variations in fecundity (fertility) and mortality. However, this early research did help the CBNEP establish a grid size of 40 acres across the marsh to test trapping strategies (40 acres was found to be the average movement of nutria per day). The results of this study also helped the CBNEP understand that nutria move more in spring and fall and less in winter and summer.
Sterilized nutria were live captured and outfitted with tracking devices with the idea that they would be released back into the wetlands to lead CBNEP staff to other nutria that escaped detection. This concept has been used successfully in other eradication projects with various species including goats. Between August 2009 and December 2010 more than a dozen Judas nutria were radio collared and released in Blackwater National Wildlife Refuge and Fishing Bay Wildlife Management Area. Although tracking radio-tagged nutria was very labor intensive (some nutria moved more than 10 miles from their release location), the method led to the capture of several animals that had previously escaped detection. The concept had potential. The CBNEP believes that adding new GPS technology with real-time tracking capabilities would reduce the effort and increase the efficiency of using nutria to find nutria.
Detecting nutria is a fundamental component of the CBNEP’s eradication campaign. Whether for defining the population extent on Delmarva, or for detecting new invaders in previously trapped areas, efficient and reliable detection methods are critical to the success of the eradication effort. No single method is perfect, thus using a variety of techniques multiple times helps safeguard against missing animals.
Shorline survey. USDA photo
All detection methods are subject to some level of error and can lead to the failure to find nutria that are present. Weather and tides can destroy sign, habitat conditions can conceal sign and impede searches, nutria behavior can be unpredictable, and observers can simply get fatigued searching for the proverbial needle in a haystack. CBNEP staff continually search for new ideas and methods to combat these problems.
Platform Survey. USDA photo
Monitoring platforms are placed along waterways and offer a convenient resting place for passing nutria. Scents are applied to platforms to further entice nutria to climb aboard, where they often defecate and leave evidence of their visit. Hair snares are added to the platform to increase the chance of detecting a nutria. Project staff inspect each platform every 2 to 3 weeks for evidence of visitation. Once sign is detected, traps are set on the platform and the vicinity is thoroughly examined to locate, capture, and remove the invaders. This method allows large areas to be monitored with relatively little effort. The CBNEP has deployed up to 450 monitoring platforms at any given time during the project.
CBNEP staff boat along waterways at slow speeds during moderate to low water levels searching for sign on exposed mudflats, muskrat houses, haul-out areas, etc. Under the right conditions, shoreline surveys are a very effective means of determining the presence of nutria. Shoreline surveys are repeated several times to ensure the results are conclusive.
Hair snare device designed to snag hair from a nutria when it boards a monitoring platform. USDA Photo.
Landowner permission is obtained by project staff prior to accessing private lands. Staff on foot visually search for sign (tracks, feeding, scat, beds, etc.) in habitat that is not readily accessible by boat. Wildlife Specialists are trained to identify all wildlife sign in order to increase their effectiveness at detecting nutria. Reliability is highly dependent on weather and seasonal conditions.
Hunting Dogs and Detector Dog Searches
To learn how dogs help with the eradication effort see the Detector Dog page.
Hair snares are modified pieces of cable designed to snag hair from the back of a nutria. CBNEP staff can take hair samples collected in the field back to the lab and identify the hairs using structural characteristics. In 2013, CBNEP staff tested the snares and found they increased the chances of a nutria being detected on a monitoring platform by 80%! The results of their work can be found in the Wildlife Professional Fall 2013 (page 35).
March 4, 2016