Mary Tutwiler

Nutria, the coast, and the numbers

by Mary Tutwiler

Yesterday, a story about nutria in Louisiana hit the AP wire, and has been reprinted all over the country, from KATC TV-3 to the Chicago Tribune. The story says that the state’s latest survey of wetlands damage by nutria is down by about 3,000 acres, and credits the good news to the success of the state's Coastwide Nutria Control Program.
A report by the Louisiana Department of Wildlife and Fisheries says nutria damaged an estimated 20,333 acres of wetlands between the spring of 2008 and this spring, or about 3,000 fewer acres than the previous annual survey.
Hunters are paid $5 a piece by LDWLF for nutria tails.

Saving 3,000 acres of wetlands is a remarkable number, especially when you look at the coastal land loss figures. According to the numbers in the joint federal and state wetlands Web site,, Louisiana has lost up to 40 square miles of marsh a year for several decades. There are 640 acres in a square mile. So if you do the math, two years ago, nutria damaged 32 square miles of coastal marsh. This year they only ate 27 square miles.

Those numbers seem to point the big stick at nutria for causing more coastal land loss than any other item, such as oil field canals and salt water intrusion, lack of siltation, subsidence or ocean rise. It leads us to believe we can trap our way out of coastal erosion.

However there are a lot of caveats when you take a closer look at the complexity of the big picture. First of all, nutria graze, move on, and vegetation regenerates in many cases. So the damage is not permanent. Second, hurricanes are big killers of nutria. If you had travelled the coast roads right after Katrina, Rita, Ike or Gustav, you would have seen thousands of drowned swamp rats (along with other wildlife) because they can’t survive in the salt surge that covered the wetlands. More hurricanes last year, fewer nutria. Third, the state’s land loss figures come from satellite images, a snapshot based on tides and winds at any given moment.

Now I’m not saying that the nutria news isn’t good, or that coastal land loss isn’t as enormous as stated. I’m just questioning putting out numbers into a vacuum, with no context. Coastal restoration is a giant problem; it helps no one when you only get a little nibble of the picture without understanding what the numbers mean.