NEW ORLEANS (AP) — (9/21/19) For more than two sweltering August weeks, state and federal biologists worked to rescue endangered fish swept out of the Mississippi River during a flood fight that lasted for months. They waded or leaned out of boats with dip nets and went neck-deep into canals with seins to net endangered pallid sturgeon.
The endangered sturgeon and flat-billed, open-mouthed cousins called paddlefish were among untold numbers of fish carried out of the Mississippi River by water rushing through the Bonnet Carré Spillway while it was open for a record 123 days to protect New Orleans levees from high water. Both are ancient species , closely resembling fish known only from fossils, with hard plates armoring scale-less skin and cartilage rather than bones.
Now crews were working to return those found alive to the river. The Army Corps of Engineers, the U.S. Fish and Wildlife Service and Louisiana Department of Wildlife and Fisheries worked together on the project.
They measured and tagged 17 pallid sturgeon and 208 closely related shovelnose sturgeon before releasing them, said K. Jack Killgore, a research fisheries biologist with the Corps’ Engineer Research and Development Center Environmental Laboratory in Vicksburg, Mississippi.
He said about 10 paddlefish, “ram ventilators” which swim open-mouthed to force water past their gills while straining out the plankton they eat, also were rescued. The International Union for Conservation of Nature considers paddlefish vulnerable to extinction.
The excursion from Aug. 5-21 was both an assessment of the spillway’s effects on endangered and threatened species and a more general look at the spillway’s species diversity.
“We’ve probably documented about 70 species of fish in that spillway,” Killgore said. “Most are probably from the Mississippi River, but some are probably from Lake Pontchartrain,” into which the spillway empties.
One Gulf sturgeon was caught, tagged and released into the brackish lake. One dead pallid sturgeon and 43 dead shovelnose sturgeon were found.
The assessments began in 2008, after state Wildlife and fisheries workers caught a pallid sturgeon in flooded willows on the riverbank near the spillway days before it was opened.
Until then, scientists had thought the fish hunkered down in the river’s deepest part and weren’t affected by the spillway. And since the Endangered Species Act requires agencies to minimize number of endangered animals killed or removed from their habitat, they get returned to the river.
“It’s a positive thing to do. It’s not a huge expense … and it minimizes take,” said Paul Hartfield, an endangered species biologist for the Fish and Wildlife Service in Jackson, Mississippi. “The main reason we do it is to help us understand a bit more about population size and dynamics of the pallid sturgeon in the lower Mississippi River.”
Scientists have learned almost everything they know about the species in this area over the past 20 years, he said.
“Even as late as 2000 in the lower Mississippi River, we had fewer than 2,000 historical records of the species. We knew absolutely nothing about it,” Hartfield said.
One thing scientists have learned since then is that pallid and shovelnose sturgeon often interbreed. Although shovelnose sturgeon are much more plentiful than pallid sturgeon, they’re listed as threatened because the two species look so much alike that pallid sturgeon might be caught by mistake if shovelnose were legal catches.
The hybrids look like and act like pallid sturgeons, and without genetic testing there was no way to tell them apart, Hartfield said.
“It’s a natural experiment that’s going on down here,” he said.
Although 17 fish may not make much difference to a species estimated at 3,400 to 20,000 adults in the lower Mississippi, numbers swept into the spillway could run into the hundreds over a number of years, Killgore said.
“Tagging the shovelnose helps, too,” he said. The two species tend to live in the same general areas, letting biologists work out ratios that can be used to estimate pallid sturgeon numbers. “In the lower lower Mississippi River, it’s usually five to six shovelnose per one pallid. Up to Saint Louis (Missouri) it’s more like 100 shovelnose to one pallid,” Killgore said.