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Testing Tail-mounted Transmitters with Myocastor coypus (Nutria)
Sergio Merino, Jacoby Carter, and Garrett Thibodeaux

Southeastern Naturalist, Volume 6, Number 1 (2007): 159–164

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2007 SOUTHEASTERN NATURALIST 6(1):159–164 Testing Tail-mounted Transmitters with Myocastor coypus (Nutria) Sergio Merino1, Jacoby Carter1,*, and Garrett Thibodeaux1 Abstract - We developed a tail-mounted radio-transmitter for Myocastor coypus (nutria) that offers a practical and efficient alternative to collar or implant methods. The mean retention time was 96 d (range 57–147 d, n = 7), making this a practical method for short-term studies. The tail-mounts were less injurious to animals than collars and easier for field researchers to implement than either collars or surgically implanted transmitters. Introduction Myocastor coypus Molina (nutria) are large semiaquatic rodents endemic to southern South America that have been introduced around the world as a furbearer (Carter and Leonard 2002). Methods used to monitor nutria activity include visual observation, mark-recapture, and radio-telemetry (Evans et al. 1971, Guichon et al. 2003, Lohmeier 1981, Reggiani et al. 1995). Because of their amphibious nature and susceptibility to dermatitis, the use of radiocollars is not always practical and often results in morbidity or mortality (Coreil and Perry 1977, D. Birch, US Fish and Wildlife Service, Blackwater National Wildlife Refuge, Dorchester County MD, pers. comm.). During an enclosure study in 2002–03, we monitored nutria using both radio-collars and implantable transmitters, but found neither satisfactory. When collars were loose, the animal’s foot could be caught between the collar and the neck, hindering the animal’s ability to feed and resulting in death (n = 3). Collars that were too tight dug into the animal’s skin, causing dermatitis, morbidity, and subsequent death (n = 3; J. Carter, pers. observ.). Surgically implanted transmitters have been used successfully in Louisiana (Hammond et al. 2003), but we found this method to be cost prohibitive and logistically challenging. Considering the limitations of radio-collars and implants, we needed another short-term practical field method to track nutria movements. In winter and spring 2003–04, we conducted a study to determine if tailattached transmitters could be used for short-term studies (2 to 3 months) of nutria movements and home range. Methods Our study site was Salvador Wildlife Management Area, located 23 km southwest of New Orleans in St. Charles Parish, LA (90°20'W, 29°50'N). The habitat was composed of thin-mat floating marsh (locally called 1USGS National Wetlands Research Center, 700 Cajundome Boulevard, Lafayette, LA 70506. *Corresponding author - 160 Southeastern Naturalist Vol. 6, No. 1 “flotant”), primarily Type III (Sasser 1994), and open water with submerged and floating aquatic vegetation. The site was only accessible by airboat or mudboat. We modified collar transmitters (model M2030, Advanced Telemetry Systems,Isant; MN, USA) for use as tail-mounted units. Transmitters were attached onto the exterior of a 􀂧 5-cm length of 19-mm or 25.4-mm diameter schedule 40 PVC pipe using a 2-part epoxy (hereafter referred to as a “unit”). We captured nutria from an airboat using long-handled fishing nets. The nutria were restrained in a wire squeeze cage. We cleaned tails with water and disinfected with alcohol. We then slid a unit onto the tail to determine size and attachment site. The unit was removed and epoxy applied to the attachment area. We rotated the unit as we slid it over the attachment area to ensure even distribution of the adhesive inside the pipe. The unit was held in place for 3 min. We used a “quick set” epoxy glue which bonds in 60 sec. The animal remained in a holding cage for approximately 15 minutes to cure the epoxy. The nutria was then released within a kilometer of where it was captured. Transmitter status was checked weekly from October 2003 to mid-December 2003, and every 2–3 weeks from mid-December to March 2004. The transmitters were equipped with a movement-sensitive mortality signal that doubled the pulse rate after 8 h of inactivity, but were reactivated if the animal moved again. We determined the detectable ranges of our transmitters to be 0.5 km if placed at a depth of 15 cm underwater, and between 1–1.5 km if placed at or above the water surface. When recovering transmitters generating mortality signals, we attempted to determine the cause. When the unit remained attached to a carcass, we examined the attachment site for signs of injury. When only transmitters were recovered, we determined predation by the presence of teeth marks. If a detached unit was still intact with no chew marks, we presumed that it fell off the tail. Conical indentations were caused by an Alligator mississippiensis Dundin 1802 (alligator) attack, and linear marks were presumptive of chew marks by the incisors of nutria. Results and Discussion We determined project status 18 times between October 3, 2003 and March 11, 2004. All 12 deployed transmitters were recovered (Table 1). With few exceptions, we were able to check the transmitter status once a week for the first 2 months of deployment and thereafter an average of once every 2 weeks. We were prevented from checking the transmitters some weeks because of logistical problems, inclement weather, or access restrictions. Transmitter recovery All transmitters were recovered within 1.2 km of their initial nutria release site. Seven of the transmitters fell off, and 5 animals died with their units attached. We observed 2 animals soon after their units fell off and noted that their tails were red and raw where the skin sloughed off with the 2007 S. Merino, J. Carter, and G. Thibodeaux 161 unit: significant amounts of hair and skin remained glued to the inside of the PVC pipe (Fig. 1). Of the 5 mortalities, 3 were designated alligator attacks Figure 1. Photograph of a nutria tail where the transmitter unit was removed. Note the missing hair where the unit was attached and some remaining epoxy. Table 1. Deployment and recovery of radio transmitters. Date of Retention Last normal Mortality Transmitter time Release signal sensor recovered (days)A Cause of mortality signal 03 Oct 2003 27 Jan 2004 19 Feb 2004 19 Feb 2004 118 Mortality- unit still attached to nutria 08 Oct 2003 18 Dec 2003 14 Jan 2004 19 Feb 2004 71 Detached from tail 08 Oct 2003 19 Feb 2004 02 Mar 2004 02 Mar 2004 133 Detached from tail 08 Oct 2003 19 Feb 2004 22 Feb 2004 22 Feb 2004 136 Animal shot by trapper 22 Feb 08 Oct 2003 02 Mar 2004 11 Mar 2004 11 Mar 2004 147 Detached from tail 15 Oct 2003 13 Jan 2004 27 Jan 2004 27 Jan 2004 95 Detached from tail 15 Oct 2003 18 Dec 2003 14 Jan 2004 02 Mar 2004 71 Detached from tail 15 Oct 2003 13 Nov 2003 20 Nov 2003 14 Jan 2004 29 Mortality from alligator 15 Oct 2003 11 Dec 2003 15 Dec 2003 27 Jan 2004 57 Detached from tail 15 Oct 2003 27 Jan 2004 19 Feb 2004 19 Feb 2004 106 Mortality from alligator 21 Oct 2003 11 Dec 2003 15 Dec 2003 02 Mar 2004 57 Detached from tail 21 Oct 2003 28 Oct 2003 29 Oct 2003 29 Oct 2003 7 Mortality from alligator ARetention time was calculated from the date of release to the date of the last normal signal. 162 Southeastern Naturalist Vol. 6, No. 1 from teeth marks and separation of transmitter from PVC pipe, one died for unknown reasons, and one animal was taken by a trapper. We examined the nutria that died for unknown reasons, but found no signs of infection or tissue damage at the unit attachment site. We were unable to recover any of the other carcasses for examination. We calculated retention time for each transmitter by using the most recent date we found a normal signal (Table 1). Considering only those animals whose transmitters fell off, the average retention time was 95.9 (± 37.5) days with a range of 57–147 days. All of the whip antennas were intact, even though they were within reach of the animal (Fig. 2). To calculate survivorship for the animals used in the study, we treated the five animals that died as mortalities, and the 7 other animals that dropped their transmitters were presumed as having survived for the approximately 5 months of the study. The survivorship of 58.3% is within the range of values reported in the literature, where survivorships as low as 29% to 31% have been reported (Bounds et al. 2003). However, because we don’t know the fate of the animals that dropped their transmitters, 58.3% is probably an overestimate of survivorship. Several important questions remain unanswered by this study. First, do the tail-mounted transmitters affect the nutria’s ability to move about and forage? We think that transmitter units were unlikely to affect movement because (1) unlike the tails of muskrats or beavers which are flattened, nutria tails are round in cross section and apparently not adapted to assist in aquatic Figure 2. Picture of a nutria collected 5 weeks after the transmitter unit was attached. Note that the antenna is intact and there are no signs of irritation at the site of attachment. 2007 S. Merino, J. Carter, and G. Thibodeaux 163 locomotion, and (2) the nutria’s body form is such that these would not add significant drag. Second, are there problems associated with skin irritation? We found 2 animals with skin irritations from the tail-mounted units. The tails were red and raw where skin sloughed off with the units. However, the use of tail-mounted transmitters was relatively less stressful to apply for both the animals and animal handlers. The handling time to apply tail-mounts is greatly reduced compared to both collars and the implantation of units and does not require anesthesia. Epoxying of transmitters has been used on a variety of different animals including birds, fish, marine mammals, and crocodilians (e.g., Spears et al. 2002). No animals showed any signs of morbidity associated with the transmitters. We were unable to ascertain why one animal died, but there were no external indications that it was the transmitter unit. Conclusions For movement studies of short duration, we suggest that tail-mounted transmitters offer a viable alternative to collars or implants. Tail-mounts are easier and safer to place on the animals and, in our experience, animals are less likely to be injured by extended wear of the transmitter. Squeeze cages are less stressful for the nutria than restraint using a catchpole around the animal’s neck and shoulder. Benefits to the researchers are reduced handling time and less risk of being bitten by the animal when working with its tail. Because sloughing of skin causes detachment of the unit, we do not believe that a different adhesive would improve retention. Acknowledgments We would like to thank L. Nolfo (Ph.D. Candidate Tulane University, New Orleans, LA), for her assistance and animal-handling skills. The idea of attaching a transmitter to a tail was originally suggested to us by Dr. R. Aguilar, Senior Veterinarian at the Audubon Nature Institute, New Orleans, LA. We would also like to give special thanks to G. Linscombe (Louisiana Department of Wildlife and Fisheries) for his continuing support of nutria research and his openness to helping us try new things. Thanks also to B. Hulslander and W. Adams at the Barataria Unit of Jean Lafitte National Historical Park and Preserve for their assistance. This project was supported by funding from the Louisiana Department of Wildlife and Fisheries, the US Geological Survey (USGS) Invasive Species Program-Nutria Project, and the USGS/National Park Service National Resources Preservation Program (NRPP). Thanks again, Greg. This research is covered under the Louisiana Department of Wildlife and Fisheries Scientific Collecting Permit #LNHP-03-061 and was approved by the Institutional Animal Care and Use Committee (IACUC) of the USGS National Wetlands Research Center. Literature Cited Bounds, D., and G.A. J. Carowan. 2000. Nutria: A nonnative nemesis. Transactions of the North American Wildlife and Natural Resources Conference 65:405–413. 164 Southeastern Naturalist Vol. 6, No. 1 Bounds, D.L., M.H. Sherfy, and T.A. Mollet. 2003. Nutria. Pp.1119–1147, In G.C. Thompson and J.A. Chapman (Eds.). Wild Mammals of North America: Biology, Management, and Conservation. Second edition. John Hopkins University Press, Baltimore, MD. Carter, J., and B.P. Leonard. 2002. A review of the literature on the worldwide distribution, spread of, and efforts to eradicate the coypu (Myocastor coypus). Wildlife Society Bulletin 30:162–175. Coreil, P.D., and H.R.J. Perry. 1977. A collar for attaching radio transmitter to nutria. Proceedings of the Annual Conference, Southeastern Association of Fish and Wildlife Agencies 31:254–258. Evans, J., J.O. Ellis, R.D. Nass, and A.L. Ward. 1971. Techniques for capturing, handling, and marking nutria. Proceedings of the Annual Conference, Southeastern Association of Game and Fish Commissioners 25:295–315. Guichon, M.L., M. Borgnia, C.F. Righi, G.H. Cassini, and M.H. Cassini. 2003. Social behavior and group formation in the coypu (Myocastor coypus) in the Argentinean Pampas. Journal of Mammalogy 84:254–262. Hammond, E.E., L.E. Nolfo, J. Carter, S. Merino, and R.F. Aguilar. 2003. Surgical implantation of abdominal radio transmitters in wild nutria (Myocastor coypus) in southern Louisiana. Society of Wetland Scientist annual meeting, 8–13 June 2003, New Orleans, LA. Lohmeier, L. 1981. Home range, movements, and population density of nutria on a Mississippi pond. Journal of the Mississippi Academy of Sciences 26:50–54. Reggiani, G., L. Boitani, and R. De Stefano. 1995. Population dynamics and regulation in the coypu Myocastor coypus in central Italy. Ecography 18:138–146. Sasser, C.E. 1994. Vegetation Dynamics in Relation to Nutrients in Floating Marshes in Louisiana, USA. Coastal Ecology Institute, Center for Coastal, Energy, and Environmental Resources, Louisiana State University, Baton Rouge, LA. Spears, B.L., W.B. Ballard, M.C. Wallace, R.S. Phillips, D.H. Holdstock, J.H. Brunjes, R. Applegate, P.S. Gipson, M.S. Miller, and T. Barnett. 2002. Retention times of miniature radio-transmitters glued to wild turkey poults. Wildlife Society Bulletin 30:861–867.