Nutria and other invasive aquatic species

The North Coast of Oregon is blessed with some beautiful rivers, lakes, wetlands and estuaries. And like anything beautiful, these places are coveted by many–including invasive plants and animals which have been introduced to our area in the century and a half since the first European settlers made their way through the Coast Range passes in the 19th century. Humans have intentionally and unintentionally introduced hundreds of plants and animals in their journeys across North America. Now we introduce new species on a global scale. The result is not always pretty. In most cases, the hitchhikers have failed to prosper because conditions were just not what they had adapted to over millennia in their home ranges. For example, the tomatoes in my garden are certainly not adapted to this climate, otherwise I wouldn’t need to baby them so much to produce a few fruit. But others have found the new environment just to their liking. Often lacking the natural checks and balances from the home territory, these critters and plants have often taken over where native species once dominated. The new upstarts are the basis for fundamentally altering whole ecosystems across our country. Like other forms of pollution, biological pollutants can be persistent and devastating! The U.S. government defines invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” I will profile a few over the next few entries and provide more information for those interested in exploring more.

Nutria in Smith Lake, OR

We start our tour of the invasion with a little understood animal that was introduced into Oregon 1937–the Nutria (Myocaster coypus). Native to South America, these 5-15 lb. amphibious rodents have spread across much of Western Oregon including many of the wetlands along the coast. Nutria were introduced as a replacement for declining fur bearers such as otter and beaver. When the farms went out of business, the animals were abandoned to the environment–if they had not already escaped. Nutria can be found along large rivers and small streams, as well as in lakes and wetlands. Recent research shows them in saltier estuarine ecosystems too, though it appears they favor freshwater. They have quickly spread by water throughout the west-side PNW, though these tropical rodents are limited by cold temperatures.

In most cases, Nutria compete with beaver and muskrat for the same types of habitat, slow moving waters with abundant vegetation. Unfortunately, they do much more harm (from a human perspective) than these other two native species. Nutria burrow into banks and construct extensive tunnel complexes 3-21 feet long for their family groups. In high densities, these tunnels can undercut banks and cause considerable amounts of sediment to enter the water. The rodents consume bank vegetation which can also lead to increased rates of erosion. The animals will consume upwards of 25% of their body weight a day! For people trying to restore riparian plant communities, Nutria herbivory on tree and shrub seedlings is constant problem. When combined with our non-native Himalayan blackberries, infested streams will receive large quantities of sediment. For our native salmonids, sediment is not a welcomed addition to the spawning streams. In other parts of the country, especially coastal Louisiana, Nutria have been responsible for damage to 40,500 hectares of wetlands. These wetlands are rapidly converting to open water, leaving the region more vulnerable to storm surges from future Katrina-strength hurricanes.

Nutria can be difficult to eradicate, though with persistence it is possible to control them. Organized trapping along watersheds is one method that has been successful in places like East Anglia in the UK. Methods include trapping, shooting, and poisoning, though the last method can lead to collateral damage of domestic animals and other wildlife so is not recommended. In areas where Nutria are causing severe damage, agencies and others have developed programs promoting the use of the animal’s fur and even meat. Check out Louisiana’s interesting website, for more on natural history, control and utilization. I actually found a recipe for Nutria here. It is after all, barbecue and potluck season on the North Coast. Pass the Nutria, please!

On a more serious note, Portland State University’s Center for Lakes and Reservoirs (CLR) recently held a regional Nutria workshop aimed at discussing the state of the science and management for the Pacific Northwest invasion. Scientific papers from this meeting can be found at CLR’s website.


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