TUCKAHOE STATE PARK -- Larry Leasner doesn't know why some kinds of fish swim hundreds of miles upstream to spawn in the spring. But he's helping them anyway, building "fish ladders" that help them scale dams and other blockages in Maryland's rivers.
"I guess it's one of nature's secrets," Mr. Leasner says with a bemused smile.
He and Carla Fleming, one of the three staff members of the state's Fish Passage Program that Mr. Leasner manages, can explain how fish ladders work:
They're a series of little walls built alongside dams that slow the water enough that fish can swim upstream against the flow. And they know what kinds of fish are using ladders: lots. Trout. Alewives. Perch, two kinds. Herring, two kinds. And on and on.
But the why of fish migration to spawn remains unclear. Water temperature, chemistry, instinct -- scientists aren't sure what makes a 4-year-old herring ready to reproduce leave the ocean ** where it has grown up and swim toward the place where it was born.
"Actually, it's amazing," Mr. Leasner says. "Herring are only 8 to 12 inches long and have a brain the size of a pea. When they're born, they go out to the ocean as juveniles. After swimming in the ocean for four years, most will return to the stream they were born in."
They are getting some help with the trip, thanks to the Fish Passage Program.
Funded by a mix of federal and state money and fees from developers, the program will spend about $1 million this year to unblock rivers and creeks in the state -- among them the Anacostia, Patuxent, Bird, Chester, Patapsco, Potomac, Susquehanna and Wicomico. At Tuckahoe Creek in Queen Anne's County, a completed fish ladder beside a dam has reopened 22 miles of spawning habitat upstream.
The program, under the aegis of the Department of Natural Resources, also received almost $500,000 in late December from the National Oceanic and Atmospheric Administration.
That money will be used on two sites on the Chester River in Kent County, and at Johnson's Pond dam on the Wicomico River near Salisbury.
The state's Fish Passage Program began in 1988 as a way to work toward the goal stated in the multistate 1987 Chesapeake Bay Agreement: to "provide for fish passage at dams and remove stream blockages wherever necessary to restore passage for migratory fishes."
At the end of last year, Maryland's Fish Passage Program had completed 38 projects that opened 158.6 miles of the state's marine habitat.
The long-term goal is to reopen 2,526 blockages to historic spawning areas in the Chesapeake Bay watershed, opening 1,356.75 miles of spawning habitat in Maryland, Virginia and Pennsylvania. All three states have fish passage programs, and work is being done in the District of Columbia.
Fish-ladder construction is one part of the complex, multistate and multiagency effort to restore the Chesapeake's aquatic life to its historically fertile levels, Mr. Leasner says. Reopening waterways to fish allows them to return to areas where they used to spawn until dams, ponds and other man-made alterations blocked them.
The most widely used way to give fish access past dams and other blockages is the "fish ladder" -- more properly called the Denil fish ladder. The ladders are widely used in the Pacific Northwest for spawning salmon, as well as on the East Coast.
Most of the program's cost is used to design and construct ladders, Mr. Leasner says. Once built, they require little maintenance -- mostly just clearing trash from them from time to time.
"We're allowing them to go back to historical spawning habitat. The theory is that if you restore and increase the habitat, the population will increase," Mr. Leasner says.
The passage program includes monitoring, he says, and it indicates the ladders are successfully increasing the fish population, although it's too soon to calculate numbers with scientific certainty.
What is certain, however, is how far the fish population has declined since the turn of the century.
Figures compiled by U.S. Fish and Wildlife show that by 1920, river herring were the second most valuable commercially harvested finfish in the Chesapeake. In 1908, for instance, 66 million pounds of river herring -- the common name for alewife and blueback herring -- were caught baywide. In 1968, that number had fallen to 36 million pounds.
And since then, it's fallen even more: In Maryland in 1994, the last year for which figures were available, only 96,112 pounds were harvested, according to Dale Weinrich of the state's Tidal Fisheries Division.
Like other fish, river herring have been hurt by overfishing, pollution and loss of habitat owing to construction of dams and other barriers. Barriers alone have eliminated nearly 1,000 miles of spawning habitat in bay tributaries, the agency's figures show.
But river by river, creek by creek, fish are getting more habitat.
"We have a list now of 28 species that are using at least one fish ladder in Maryland," Mr. Leasner says.
"We haven't done as much monitoring as we would like to, but I think the monitoring to date proves that these things work very well."