Gambian Giant Pouched Rats

The Gambian giant pouched rat (Cricetomys gambianus) in the Florida Keys is an example of how a severe invasive species threat can be managed in a logical, practical and efficient manner, once a threat has been identified. This largest of rat species (up to 2.8 kg; Rosevear 1969) is highly prolific and holds potential for extreme ecological and agricultural negative impacts (Perry et al. 2006, Engeman et al. 2006). Although the species escaped from a captive breeder on Grassy Key around 1999, it was not identified as established in the wild until residents brought it to the attention of the USFWS in 2004. Perry et al. (2006) established the existence of a breeding population and its dispersion potential was subsequently modeled (Peterson et al. 2006). Dispersal of the species to mainland Florida could have resulted in continued spread through much of North America where significant negative ecological and agricultural consequences could ensue (Peterson et al. 2006).

Following verification of the population's existence and confirmation of its invasive and destructive potential, information and methods essential for successful eradication were rapidly developed, including detection and monitoring technologies, population indexing methodologies, population distribution, habitat preferences, trapping methodology, acceptance of bait matrices, efficacy tests of toxicants, and bait stations that exclude native species (Engeman et al. 2006, 2007d). To test and fine-tune the methods prior to implementing full-scale eradication, a pilot eradication project was implemented on Crawl Key, a small key adjoining Grassy Key to which the species expanded its range. Afterwards, surveys found no evidence of Gambian giant pouched rats remaining on Crawl Key, although Hurricane Wilma undoubtedly also contributed to their mortality. The criteria (see Engeman et al. 2006, Parkes and Murphy 2003) were considered obtainable for a successful eradication to commence on larger Grassy Key, location of the much larger primary population. Surveys following the hurricane on Grassy Key verified the survival of the Gambian giant pouched rat population, and with a greater range than previously thought. Next and a little over two years after the initial report, the full-scale operation to eliminate this population occurred. At least two years of monitoring for Gambian giant pouched rats should be applied to both Grassy and Crawl Keys, as well as other potential sites of occupancy such as refuse transfer sites (including the mainland landfills) and locations of credible reports of sightings should also receive continued monitoring to help insure no propagules from Grassy Key are surviving elsewhere.

Thus, the rapid response eradication effort for Gambian giant pouched rats can be described as a progression of accomplishments:

1. Verify presence

2. Develop detection and population monitoring methods

3. Develop and test potential control tools

4. Test eradication approach (Crawl Key)

5. Apply eradication methods and strategies to Grassy Key

6. Surveillance for survivors or satellite populations

The eradication effort is currently in the surveillance phase. This phase appears to be working well, as the Gambian giant pouched rats that have occasionally been detected on Grassy Key have been successfully targeted for removal. No Gambian giant pouched rats have been detected outside of Grassy Key.

Whereas the logic and flow described here for this eradication effort makes it seem as though the path to Gambian giant pouched rat eradication was a smooth continuum once the problem was identified and verified, it was, in reality, a series of fits and starts (Engeman et al. 2007d). No single block of funding was available to develop the necessary information and implement an eradication effort. Funding and in-kind resources were provided from > 10 federal, state, and local government entities, as well as private concerns. Even Hurricane Wilma may have assisted the eradication effort to some degree, as it struck at a time lessened resources were available for the work. The storm surge overwhelmed a large part of many of the keys, possibly removing small propagule populations.

One potential pitfall that hopefully will not occur is complacency at the apparent success so far. That could undermine availability of necessary resources to see the follow-up monitoring through to its conclusion. Lack of continued vigilance could result in the hard work to date being undone, or worse if survivors or propagules go undetected, eventual Gambian giant pouched rat dispersal to the mainland. On the other hand, successful eradication of this species hopefully would help reduce the general reluctance of managers to attempt eradications of other invasive species in Florida (see, for example the comments by Donlan et al. 2003).

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  • valentin
    How gambian pouched rats are a threat to agricultural?
    8 years ago

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