Crawfish Researcher Shares Thoughts On Mudbugs

By Roshaun Higgins

Baton Rouge Advocate

Christopher Bonvillain knows crawfish. An associate professor at Nicholls State University, he works in one of Louisiana's only aquatic ecology and astacology labs. Astacology is the study of crawfish - a big industry in Louisiana, with 110 million pounds harvested each year, according to the Department of Wildlife and Fisheries. In the U.S., there are 330 known species of crawfish; there are 39 species and subspecies in Louisiana.

Bonvillain earned his undergraduate degree in biology and his graduate degree in marine and environmental biology, both from Nicholls State. He then earned a doctorate in wildlife and fisheries science from LSU, focusing his studies on crawfish.

What kind of experiments do you do in the astacology lab?

A lot of our work is out in the Atchafalaya Basin, which is where the largest wild crawfish harvest is from in Louisiana though pond crawfish are the majority of crawfish in Louisiana.

So, a lot of what we do is we look at how environmental factors affect crawfish populations. We look at water quality or, more specifically, dissolved oxygen in the water because crawfish can survive low-oxygen waters, which is what we have in a lot of our swamps.

And we do a lot of stuff for the north shore of Lake Pontchartrain, in the Tangipahoa River basin. And we're looking at crawfish up there to maybe see what's the distribution of crawfish, if there are any species that have conservation concerns.

So, crawfish are getting smaller from having lower concentrations of oxygen in the water that they live in. Is that something that's been happening for a long time? Or is that a recent development?

Even before humans were here, swamp waters were low in oxygen. But human disturbances, oil and gas canals and logging canals, stop the natural flow of water. Then, the leaves and twigs, everything is inundated by water in the spring.

All that stuff starts decomposing, and that decomposition process uses up oxygen. When the water doesn't flow good, when it just sits there, that's when you can have really low-oxygen water for months at a time. So crawfish survive, but they're going to be stressed.

Crawfish can breathe atmospheric air, but that means they have to stay at the surface. Because they're not actively eating and foraging as much, they're stressed.

So that's why we're seeing smaller crawfish; they're maturing at smaller sizes. That's why we're looking into eggs. If a female matures at a small size, she's got a smaller body. She just won't be able to hold as many eggs because she's a smaller crawfish. That's why we're looking at the egg production.

With some aspects of climate change, such as warmer water, is that affecting crawfish populations?

Warm water holds less oxygen than cold water. So, one thing we're seeing is these hypoxic, or these extremely low-oxygen, conditions. So if we're getting warmer faster and warmer for longer, it's going to cause lower oxygen concentrations in the water.

But the biggest thing is, is the change in weather patterns. because wild crawfish need that flood pulse of the Mississippi River. When you get that spring flood pulse of water that comes up the river, that water comes up the Atchafalaya, and that water goes to the flood plain, and that's what makes it crawfish season.

Right now, the river is really low with drought conditions. If this continues into the spring, we're not going to have a good wild crawfish harvest. If we're not getting enough rain in the Midwest come down here to have a flood pulse, that's going to affect crawfish season. Or if the flood possibly comes up for one month, then we only have a monthlong wild crawfish season.

Could you describe how crawfish farms, or ponds, work versus the commercial fishers catching wild crawfish?

So, the commercial fishers are dependent on the water level. Crawfish, in general, for their life cycle, need water to inundate the flood plain and drain back down. In the ponds, they're controlling that. They flood their ponds, and they de-water ponds.

In a lot of Louisiana, ponds have crawfish and rice. Then typically in October, they've harvested the rice and there's stubble left behind. In November, they flood their ponds. That's the environmental cue for crawfish to come out of their burrows and that rice stubble that's left behind, that's what the crawfish feed on. You don't have to add food to the pond. That's when the crawfish get harvested.

They'll keep doing that probably until around April or May. If somebody's not doing rice, they can maybe still keep running their ponds until probably May or June. So we say it's crawfish season, right? But there's no regulated season in the Department of Wildlife and Fisheries.

But right now is when crawfish could start to be found. It'd be expensive right now because it's the pond crawfish. You can get the pond crawfish November through February, but the water's still cold and the crawfish aren't moving very much. When we get to March, April, May, the water warms up.

If it's a normal year, the water comes up the Mississippi River and you also start getting the wild crawfish harvest. Then you have the wild and the pond both on the market at the same time. That's when we see prices start to drop.

Do you have any any interesting crawfish fun facts?

There are some red swamp crawfish that you get at a crawfish boil. There's some genetic mutations where every now and then we see a blue red swamp crawfish.

And another thing, every now and then I hear some people think there's a poisonous or venomous crawfish. There are no crawfish anywhere in the world that are poisonous or venomous. I get asked that all the time.