Thursday, July 05, 2007

Ohio shrimp

Long held beliefs that Ohio shrimp were extirpated from the Mississippi River in Missouri were scrapped in the early 1990s when a small population was found south of Cairo, Illinois. The largest of all freshwater shrimp in Missouri, Ohio shrimp are invertebrates of the embayment, living in big river systems from South Carolina to Texas. Their populations in Missouri and southern Illinois were almost knocked out in the 1940s by overfishing and, subsequently, by the dramatic channelization of the Mississippi River.

Ohio shrimp prefer warm, slow moving water that backs into sloughs and channels along big rivers. While the clear-bodied invertebrates live most of their lives in freshwater, they migrate some 1,000 miles to brackish waters to breed. They then return to backwater areas along the southern length of the Mississippi and other rivers to spend the rest of their lives. Alterations to their natural habitat have reduced and disturbed many of these backwater areas and changed the natural flow patterns required for reproduction and migration.

In 2006, biologists from the Cape Girardeau Nature Center (where the picture comes from)collected several shrimp for research and display purposes. Through trial and error, biologists have learned that the shrimp eat dead minnows, other invertebrates and decomposing vegetation. Changing the temperature and mimicking the salinity of south Louisiana brackish waters isn't enough to trigger breeding. But at least, one biologist told me, "we can keep them alive now."

Populations of Ohio shrimp are stable in South Carolina and they're found in small numbers in the Ohio River where they hadn't been seen for about 50 years until 2001. Listed as a state species of conservation concern (SCC), the Ohio shrimp's status is S1, Critically Imperiled in Missouri. It's doubtful that without massive changes in the Mississippi River's flow patterns these animals will ever become plentiful enough to harvest, but at least they're still around, hanging out with crayfish and spawning fish in the slackwaters where boats can't go.

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