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Researchers must wait to see how flood affects crawfish

Researchers must wait to see how flood affects crawfish Writer: Johnny Morgan at 225-578-8484 or jmorgan@agcenter.lsu.edu

(08/24/16) The impact of the recent widespread flooding on the upcoming season will depend on many factors according to LSU AgCenter and Louisiana Sea Grant aquaculture and coastal resources specialist Mark Shirley
“We really won’t know the extent of damage until we get into the harvest season later this winter,” said Shirley, in a recent newsletter to crawfish producers. Greg Lutz, a professor and specialist at the LSU AgCenter Aquaculture Research Station, explained that crawfish typically spend their summers sealed in burrows along the pond levees, while crawfish farmers plant rice or other vegetation to serve as the basis for a natural food chain once the ponds are flooded again in the fall. Female crawfish lay their eggs – which are carried under their tails– while sealed in their burrows. Egg laying begins in late August, peaks in late September or early October and continues all the way until November or even early December, Lutz said. “Normally, after a mama crawfish decides to lay her eggs, she waits until a good heavy rain before she comes up out of the burrow, and she’ll wait as long as it takes,” he explained. “On the other hand, when flood waters cover pond levees the ground is saturated and crawfish have no choice but to get out of their burrows.” Flooding crawfish ponds in August is discouraged because crawfish are forced from the protection of their burrows to face hot, stagnant water and predation by fish, birds and other predators, Lutz said. Few crawfish producers have the pumping capacity to maintain adequate oxygen levels under these conditions. Surviving crawfish that have been forced out of their burrows will eventually try to go back down in the ground. Ray McClain, a professor at the AgCenter Rice Research Station near Crowley, has shown that female crawfish can survive several episodes of being flushed from the ground by flooding and still go on to spawn in the fall if they can get back into a burrow. Shirley added that “if the floodwater recedes within a few days, many of the females will be able to re-burrow or find an existing burrow to move into.” What should a crawfish farmer do? Crawfish farmers can mitigate damage by draining ponds as soon as possible to eliminate predatory fish that entered with flood waters. If rice was planted in the last month for crawfish forage, once fish have been eliminated growers should put a couple of inches of water back to help the rice grow and control some of the weeds. In fields where rice was harvested, rice straw will be decomposing and water should be drained out as quickly as possible. The wet ground will help the stubble re-sprout, but producers are encouraged to wait until early October to flood up. For ponds where rice could not be planted as a forage crop or ponds with natural vegetation, producers should still drain as soon as possible to get rid of fish. In general, these ponds will have serious water quality problems in the fall, so waiting until temperatures have cooled off in mid- or late October to flood is recommended. “We shouldn’t assume that there is going to be a blanket net negative impact for the industry as a whole, McClain explained. “I really think there will be negative impacts for some producers, yet others probably will see little or no effect.” The fact that there shouldn’t be any drought-linked impacts this year is probably going to offset some of the negatives from the flooding. “Bottom line is – neither the farmers nor the consumers should give up on the upcoming crawfish season just yet,” said Lutz. Ray McClain can be reached at 337-788-7531 or rmcclain@agcenter.lsu.edu Mark Shirley can be reached at 337-898-4335 or mshirley@agcenter.lsu.edu Greg Lutz can be reached at 225-765-2848 or glutz@agcenter.lsu.edu