Thursday, February 28, 2008

Niangua Darter

As February draws to a close, we enter the spawning season for the Niangua darter, a federally threatened, state endangered fish. Actually, most of the year the Niangua darter looks like other darters, skittering around riffles in rather non-descript, drab colors. But when breeding season begins in mid-March, their bellies turn a brilliant orange and blue-green stripes appear on their sides.

Niangua darters were widespread in the Ozark Highlands before the construction of lakes and reservoirs interrupted their breeding phenology. Now, their disjunct populations are restricted to the Osage River drainage, which includes the Niangua and Little Niangua Rivers. They live in small, shallow pools created by eddies along the edges of fast-moving streams. Niangua darters prefer streams with cherty gravels with little to no sediment. The 8 existing populations of them live in small streams next to steeply dissected woodlands based in dolomite and chert gravels.

Niangua darters tend to stay around the same area for days at a time. In one survey, the same fish were found in the exact spot for 4 days in a row, venturing out only to feed periodically in the riffles. Their long, snout-like nose allows them to probe the gravel looking for stonefly and mayfly larvae. Occasionally, they'll feed on small crustaceans and mollusks. Relatively small fish (3-4 inches long), they certainly don't qualify for game fish, but federal agencies and non-profit organizations have stepped up to protect their habitat, nonetheless.

The list of direct threats to their continued existence is long. In Missouri, there's this downright awful practice of gravel mining: backhoes move into the rivers and dig out bucket loads of gravel to sell to developers (while they also remove mussel beds, crayfish and a whole host of insect larvae). Obviously, dredging streams removes shallow water habitat for darters and increases the sediment load in which they can't survive. Land clearing and cattle production in adjacent woodlands sends sediment and high levels of nitrogen into the water. One threat, however, is being actively managed. Culverts and low water bridges that isolate populations are being replaced with fish passages, allowing the populations to travel the length of the rivers.

As spawning season approaches, a short description of their breeding habits: males follow females into the shallow waters of riffles. Males will compete for females and spawning sites, often engaging in combat with other males. As the male approaches a female, she will bob her head rapidly. She'll then plunge, head first, into the gravel, leaving only her head and tailfin exposed. After spawning takes place, she emerges from the gravel, burying the eggs, leaving them behind, protected from predators in the chert.

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