Abstract

The nutria (Myocastor coypus) is a large aquatic rodent endemic to the Patagonian subregion of South America. It has been widely introduced around the world for the fur industry.² In most places, this invasive species has been very successful, even to the extent that population control measures have been instituted.^1,6.8

The nutria has a voracious appetite, eating 25% of its body weight per day.⁵ additionally, it is a destructive forager often uprooting plants and consumes preferred parts while the rest of the vegetative biomass is discarded.³ This kills the plants, resulting in habitat loss.⁹

In coastal Louisiana, this rodent is considered a nuisance in part due to its detrimental ecological impact on the unique flotant marsh habitat found in southern Louisiana. This type of freshwater tidal floating marsh is only found in delta systems of the Mississippi and Danube rivers.¹¹ the overall ecological impact of nutria on coastal wetlands is so severe that the state of Louisiana initiated a bounty on nutria in the fall of 2002 (D. Bounds, personal communication, 2003).

No study to date has ever investigated the habitat selection of nutria on the Louisiana flotant marsh. This investigative study explores how this rodent utilizes and impacts its nonnative plant community over the course of 1 yr at the Barataria unit of Jean Lafitte National Historical Park and Preserve (Jean Lafitte Park), Jefferson Parish, Louisiana USA.

Radiotelemetry is invaluable in this study because it allows the tracking of individual animals not only during the winter, but also during the summer when the dense vegetation does not normally allow for direct observation. This will facilitate the evaluation of the nutria's seasonal impact.

Implantable transmitters were chosen primarily due to the high morbidity and mortality associated with using radio tracking collars on nutria.⁴ Abdominal radio transmitters have been used successfully for tracking nutria in Maryland (D. Bounds, personal communication, 2003) and other aquatic mammals.^7,10

As part of a pilot study, 13 nutria were implanted with transmitters. Animals were captured in Salvadore Wildlife Management Area about 6–7 aquatic miles from Jean Lafitte Park due to the ease of capture at this locale. These nutria were immobilized once with tiletamine-zolazepam (Telazol®, Ft. Dodge Animal Health, Ft. Dodge, IA 50501 USA, i.m., 100 mg/ml, 10.0 mg/kg, range of 7.8–11.7 mg/kg) by hand-injection with the aid of a 3-ft animal control pole (Tomahawk®, Ben Meadows Company, PO Box 5277, Janesville, WI 53547-5277 USA). Surgeries were performed in the wet lab of the education building. Radiotransmitters were placed into the abdomen of nutria using a standard ventral midline approach. Mean duration for the surgical implantation was 38 min, and no surgery exceeded 60 min. No mortalities were associated with the surgical procedure. The animals were left in pens to recover overnight and were subsequently released into the marsh of Jean Lafitte Park.

None of the pilot animals suffered weight loss or observable behavioral changes due to the presence of the implants when the transmitters were retrieved up to 3 mo later. Preliminary results show that female nutria can conceive a pregnancy and sustain a pregnancy to full term if implanted during mid-gestation.

Although in its nascent stage, it is hoped this study will elucidate the feeding habits and preferences of nutria in the flotant marsh in southern Louisiana. This in tum will help direct more focused control efforts of the nutria population over all seasons. Preliminary results demonstrate that tiletamine-zolazepam anesthesia is an excellent method for the handling and surgical implantation of radiotransmitters into the abdomen of nutria. It also shows that this method of implantation has low morbidity and mortality and has a minimal effect on nutria behavior.

Acknowledgments

This work is supported in part by the Coypu and JSF Foundations. Many thanks to the staff at the Barataria Unit of Jean Lafitte National Historical Park and Preserve, Jefferson Parish, Louisiana, USA and to the hospital staff at the Audubon Zoo, New Orleans, Louisiana, USA. Special thanks to Dr. Dixie Bounds of Maryland Cooperative Fisheries and Wildlife Research Unit, University of Maryland Eastern Shore for both the use of equipment and as a consult. Without her help, this project would not be possible.

Literature Cited

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