With this issue the Darby Creek Advocate begins a series highlighting Darby's fascinating aquatic creatures.

In early April, when Darby’s waters still run cold and strong, if you are very lucky and happen along the right spot—usually far upstream in some Darby tributary—you may be treated to an amazing sight: a group of small, eel-like fish digging a nest in the gravels of a riffle.

These "eels" are actually least brook lampreys, one of Darby’s least known but most interesting creatures. Usually when people think of lampreys--if they think of them at all--they think of the predacious sea lamprey. This ocean-going Atlantic Coast native is infamous for decimating gamefish populations after it was introduced into the Great Lakes early in the last century. A large species that can exceed two feet, the sea lamprey feeds by attaching itself to a fish with its suction-cup mouth and boring into its flesh with abrasive teeth.

The lampreys are a diverse and ancient line tracing back over 300 million years. Most people are surprised to learn that 18 species live in North America’s streams, seven of which are found in Ohio. Three species have been recorded in Darby: the silver lamprey, which is considered a stray; the northern brook lamprey, which has disappeared; and the least brook lamprey, which maintains a reproducing population in the upper reaches of Big Darby.

The six-inch-long least brook lamprey is actually a nonparasitic species (about half of America's lampreys do not feed on other fish). Nonparasitic lampreys have a very interesting life cycle with two distinct periods: a lengthy immature period (around 5 years) and a much shorter adult period. During each period they require a distinctive type of habitat.

Least brook lampreys begin their lives in small, higher gradient streams where adults lay their eggs. When eggs hatch lamprey larva begin migrating downstream to find calmer waters in the pools of lower gradient streams. There they must locate stable sand or mud bottoms where they can dig burrows. Here they will spend the bulk of their lives filter-feeding on food particles that drift by. During this stage lampreys do not have developed eyes or teeth.

After years of slow growth the larva will transform into adults, at which time they finish out their life cycle much as salmon do, by undertaking a return migration to spawning grounds in small tributaries. Here males and females meet on riffles for the first time and begin an exhausting mating ritual in which they use their mouths to excavate nesting pits and their writhing bodies to sweep these nests clean. Eggs are laid and fertilized and the adult lampreys die.

On the one occasion when I have succeeded in finding spawning brook lampreys it was after a lengthy hike up a Darby tributary that was so clogged with logjams I was certain no lampreys could have penetrated so far upstream. Yet there they were in a shaded trickle: four lampreys writhing together in their instinctual dance. One was tattered and bloody, clearly at the end of its life, but continued relentlessly digging its nest and shivering its body and rubbing against its fellow travelers. They rested only rarely, and then only for a moment. It was humbling to think that lampreys had been performing this dance for far longer than man has walked the earth.

Because least brook lampreys must reproduce in high gradient streams, the species has its population center in the hilly country of the Allegheny Plateau. In Ohio, it inhabits unglaciated areas to the south and east of the Darby watershed. Nevertheless, at some point after the last glacier retreated the least brook lamprey managed to establish a disjunct population in the glaciated upper reaches of Big Darby where a number of headwater tributaries flow out of hilly ground in Logan and Champaign counties, providing the necessary combination of high gradient spawning habitat and lower gradient pools downstream. Records of this species also exist for similar terrain in the headwaters of Little Darby Creek, but its status there is uncertain.

Today, a recent boom in housing, industrial expansion, and road-building in Darby’s headwaters threatens the creek’s isolated population, which is vulnerable to increasing levels of sedimentation and stormwater runoff, both of which destroy the pool habitat of the species’ larval stage. This is unfortunate, for Darby would lose an irreplaceable piece of its wildness if it ever lost the timeless spring migrations of lampreys.

by John Tetzloff