Nutria: Trouble for Waterways

by Adrian Lawler, Ph.D.
(retired) Aquarium Supervisor (l984-l998) J. L. Scott Aquarium Biloxi, Ms 39530
Original to Aquarticles

Introduction

Nutria are aquatic rodents that are mostly nocturnal. The scientific name, Myocastor coypus, comes from the Greek words for "mouse" (mys) and "beaver" (kastor). They were introduced to the United States from South America in the 1930s, and have also been introduced in Europe and Asia. Since they are mostly nocturnal, their presence in an area usually is indicated by their trails, feces, tracks, and tail drag marks, and by cut vegetation, disturbed algae along pond banks (1), and signs of bank undercutting (2) and digging.

Nutria may weigh 25 pounds or more, and live over 4 years in the wild and up to 12 years in captivity. Females usually have 6-7 litters during their reproductive life, with 2 litters (and pregnant with a third) per year, and 1-13 (average of 4.5) young per litter. At birth the young are fully furred, their eyes are open; and they can feed upon green vegetation within a few hours.

Nutria are vegetarians and have large appetites, consuming about 25 percent of their weight daily. Their natural food consists almost entirely of aquatic and semiaquatic vegetation, including roots, rhizomes, and tubers; in my area they feed extensively on plant (including grass) roots. Nutria often overharvest favored foods, causing the production of less favored food plants for themselves and other wildlife species. Nutria may construct burrows in levees, dikes and embankments.

Nutria may undermine stream banks (2), deplete wild vegetation, raid rice and other crops, and cause extensive erosion, land loss, and flood damage.

There are only a few predators to control them in the United States: alligators, cottonmouth moccasins, hawks, owls, and eagles. More enforcement of dog leash laws has enabled the nutria to spread further, especially into drainage ditches of southern cities, because harassment from dogs decreased.

I have been fighting nutria in my ponds and streams since 1973. I have incorporated some of my personal observations over the years in this report.

Problems (based on some of Lawler's observations in Mississippi)
Nutria in my area feed extensively on plant roots (including lawn grass roots along waterways). Their feeding activity increases with rising water (after rains or with an incoming tide). This rising water allows nutria to easier access plant roots higher on the bank (they are buoyed up higher along bank) and also to utilize the higher waters to help them wash dirt away from plant roots for them to easier eat (without ingesting a lot of dirt). So during high waters the erosion from higher waters plus increased nutria digging can lead to many tons of dirt being moved downstream, or to other parts of a pond, making both streams and ponds wider and shallower. Higher waters also mean nutria can gorge themselves faster. They can eat faster because higher waters and their pawing/digging actions make plant root food easier and quicker available.

Nutria turn wetlands into denuded areas, which are subject to erosion, and then turn into open water. Unless controlled, they keep on digging and eating on shoreline banks so land is constantly lost.

Many southern cities have enabled nutria to thrive and expand their habitats. Having open (rather than tiled) drainage ditches in many cities has opened up extensive water pathways for nutria to extend their habitat space into the back yards of the subdivisions. Nutria are no longer confined to shoreline marshes and natural waterways, and can be found in ditches along busy highways and in city neighborhoods.

Lawler's observations also indicate that the following effects are due to nutria, which:
.....make water body wider and more shallow and thus make aquatic residents (mostly fish) more available to wading bird predation.
…..make water body wider and more slow moving (if waterway is a stream); with less water agitation there will be less absorption of oxygen in the water.
…..make land lower in elevation, due to erosion, and thus more prone to flooding, especially in hurricanes.
…..make water more muddy due to their digging activity leading to a decrease in photosynthesis in the water and thus a decrease in oxygen in water.
…..release toxins formerly bound up in sediments.
…..increase transport of sediment downstream with outflow or outgoing tide (coastal marshes are going away, especially in Louisiana) leading to severe erosion problems. In tidal areas the sediment displaced can smother oyster beds.
…..burrow into earthen dams and levees, thereby causing increased seepage and possible eventual failure (nutria were a possible factor in levee failure and flooding in New Orleans due to levee seepage in hurricane Katrina).
…..decrease bank cover, and thus decrease habitat and hiding places for many animals around waterways.
…..change plant species number and distribution along waterways.
…..decrease habitat space available to species living on land by making the land turn into water.

Once nutria get established in an area, their high reproductive rate soon results in overpopulation. If left unchecked, nutria can reproduce so much that waterway bank destruction is severe, and dams and levees are riddled with burrows.

Nutria are probably one of the most destructive erosion-causing animals around waterways.

Disease
In addition to direct waterway damage, nutria are the host for a nematode parasite (Strongyloides myopotami) that can infect the skin of humans, causing a condition called "nutria itch."

These rodents can serve as hosts for several human pathogens, including tuberculosis and septicemia, which are transmissible to people, pets, and livestock. Nutria can also carry parasites, as: nematodes, blood flukes, tapeworms, and liver flukes. Some of these parasites are found in nutria wastes; both the parasites and the wastes can contaminate drinking water and swimming areas.

Solutions
To effectively control nutria, one must know their habits so one knows how to attack them, including: times most active, when young leave burrows, favorite paths and slides, etc. Animals that have experienced little harassment, and are secure in their surroundings, can be seen feeding during the day.

Since nutria appear to like to burrow under concrete or metal (3), place such slabs in areas where you want the nutria to be so you can easier handle them.

The best deterrent I've found is fencing laid down along the banks of waterways (4) so nutria cannot dig into the bank for plant roots.

I use 2 x 3 welded wire at least 2 feet wide (tall) held tight to sides of bank with bamboo stakes. Place one foot below water level to deter nutria from digging under the wire, and one foot above water level to deter them from digging into the bank over top of the wire while they are in the water. The best wire to use would be used chain link fencing (about 2¼ inch mesh); for ponds use wire that has the galvanized coating oxidized or gone. Beware of using galvanized fencing in small ponds as heavy metal (zinc) poisoning of fish and other pond species can occur.

Small mesh fencing can be used to surround one's property and across any streams to stream bottom (so nutria cannot swim under fence). Such fencing will also assist in keeping nutria out of an area.

Some other possible means of control are as follows:

….birth control: Using sterilization or birth control chemicals in sweet potatoes or carrots may keep a nutria population under control. Such programs would have to be continuous because those nutria that die without reproducing are quickly replaced by others moving into the vacant habitat.
….bulkheading: Using wood, metal, concrete, etc. bulkheading along waterway denies nutria access to plant roots.
….dogs: Have dogs that chase and harass nutria away from your area.
….poison: Poisons are not recommended because other animals may get poisoned.
….predation: One can introduce alligators to the waterway to help control nutria.
….shoot: Spotlight at night and shoot. This option is not feasible in areas (most cities) where shooting is not allowed. Nutria are elusive and difficult to find where and when they are feeding at night.
….trap/snare: Where legal, one can use foot traps or snares along their paths or slides into the water. I have not been able to get them into a commercial live trap. I have succeeded in trapping them by putting a fence across, and to the bottom of, the bayou so they cannot swim under the fence. Then have a funnel trap connected to a 10-14 inch hole in the fence half above water and half below. Nutria swim along fence, through hole in fence, and through funnel, into large wire holding trap enclosed on all sides and resting on bottom of bayou.

Keep ditches open and water flowing; backed up water encourages nutria to live and eat where they can easily swim.

Since nutria will frequent areas where food is easy to obtain, fencing your waterways and ponds will eventually cause the nutria to stay with your neighbors, if their place is unfenced.

Summary

Nutria cause extensive plant damage, erosion, land loss, and flooding. They utilize higher waters to access higher food and to help wash dirt away from plant roots. One can fence the banks of waterways to keep them from digging along waterways, and also put fencing across streams to deter their movements.

Copyright 2006 by Dr. Adrian Lawler, Author Copyright 2006 by Aquarticles.com, Internet Sponsor

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