Chesapeake Bay - Migrating Fish and Spawning

Fish passages: If you build them, they'll come back
Bay Naturalist / By Kathy Reshetiloff - Bay Journal

Although March is named after the planet Mars, I picture a more literal translation of the word. Warmer temperatures lure wildlife to migrate or "march" from wintering areas to the Chesapeake Bay and its watershed.

Actually, the Chesapeake Bay is a highway for migrating fish. Some are beginning a journey from the ocean to fresh water to reproduce. These are known as anadromous, a word with Greek origins that means "running uphill." These fish literally swim upriver against the flow of water. But recently, the word anadromous more accurately depicts the uphill battle these fish must fight against such conditions as river blockages, pollution and overfishing.

The fish most famous for their spring runs in the Chesapeake are members of the herring family: blueback herring, alewife, hickory shad and American shad. As adults, these fish inhabit offshore Atlantic waters. During the spring, they swim up the Chesapeake Bay to fresh water to spawn, usually returning to the same river in which they were born.

How they do this is a mystery. Many scientists believe that this homing instinct may be due to an uncanny sense of smell and sensitivity to magnetic signals, polarized light and unique characteristics of the natal stream.

The alewife is silver with a bronze-green back, while the blueback herring, also silver, has a bluish back. Their silvery scales scatter light to reduce the herring's visibility to predators. Both species share a single dark shoulder spot and vary in length from 12 to 15 inches when fully grown.

The onset of spawning is related to water temperature and length of daylight. The spawning season for alewife generally runs from March through April. Blueback spawn from mid-April through late May. Alewife favor slow-moving sections of streams while blueback herring prefer to spawn in swift water.

Upon reaching the spawning ground, the males circle a lone female. As this mass of fish swirls around, the female releases her eggs and the males release their sperm. After spawning, the adults swim downstream and return to the ocean.

A female herring can lay several hundred thousand eggs. The eggs, about 1 millimeter in diameter, are sticky and adhere to rocks, gravel and debris. They hatch in three to seven days. Flowing water carry the larvae downstream toward saltier water. Juvenile alewife and blueback herring migrate from the Bay to coastal waters in the early fall and remain there until reaching sexual maturity in three to six years.

Larger than these river herring are the shad. Prompted by rising temperatures they, too, leave the ocean and return to the waters where they were born. Both species generally spawn from March to June.

Males arrive on the spawning grounds first, followed by egg-laden females. A female releases 100,000 to 600,000 eggs into the water to be fertilized by several males. Adult shad return to the ocean soon after spawning.

The transparent fertilized eggs are carried along by the current. The larvae hatch in four to 12 days. Juvenile shad spend their first summer in fresh water. By autumn, the young shad gather in schools and swim to the ocean. They will live in the ocean from three to six years, until they are sexually mature, then return to fresh water to complete their life cycle.

Overharvesting and degradation of habitat have made these once abundant fish dwindle in number. Although Maryland, Pennsylvania, Virginia and the District of Columbia allow herring fishing, there is a moratorium on taking hickory shad and American shad. Monitoring herring harvests and banning shad harvests alone, though, won't restore them.

Fish are cut off from historical spawning areas by culverts, pipes, dams and other obstacles. To help migratory fish reach their spawning grounds, Maryland, Pennsylvania, Virginia and the District of Columbia agreed to provide fish passages. A 10-year goal of reopening approximately 1,356 miles in the watershed by the year 2003 was established. Since 1989, 272 miles have been reopened to anadromous fish in the Chesapeake Bay watershed, with another 300 miles expected to be reopened by the end of 1998.

Fish passages may be as simple as notching, breaching or removing a blockage or may involve creating a fishway at the obstruction. There are five basic fishway designs: Denil, steeppass, pool and weir, vertical slot, and fish lift or fish elevator.

A Denil fishway is a series of sloped channels that allow fish to swim over the dam. Baffles in these channels slow the water down and pools between each section allow fish to rest. A steeppass fishway is similar to the Denil but usually has only one sloping channel with baffles. There is no need for resting pools as the steeppass is designed for smaller blockages.

A series of pools forming steps ascending a dam is a pool and weir fishway. The vertical slot fishway is similar to the pool and weir except each pool has baffles creating a narrow slot through which the fish swim.

A fish lift or fish elevator is used to pass fish over large obstructions. The directed flow of water guides fish to a hopper that raises the fish over the dam. Fish may be immediately released to an exit channel or transported to other areas for release.

Below is a partial list of fish passage sites in the Chesapeake Bay watershed.

Manchester/Browns Island Dams: Henrico County, Va. - Notch
Walkers Dam: New Kent County, Va. - Double Denil Fishway
Conowingo Dam: Harford/Cecil counties, Md. - Fish Lift
Tuckahoe Creek Dam: Caroline/Queen Anne's counties, Md. - Denil Fishway
Union Dam: Howard/Baltimore counties, Md. - Breach
Lake Waterford Dam: Anne Arundel County, Md. - Pool and Weir
Standing Stone Creek: Huntingdon County, Pa. - Denil Fishway
Safe Harbor Dam: York/Lancaster counties, Pa. - Fish Lift (to be completed in 1997)
Holtwood Dam: York/Lancaster counties, Pa. - Fish Lift (to be completed in 1997)
For information about fish passages, contact each state's coordinator:

Maryland: Larry Leasner, Maryland Department of Natural Resources,(410) 974-3365
Pennsylvania: R. Scott Carney, Pennsylvania Fish and Boat Commission,(814) 355-4837
Virginia: L. Alan Weaver, Virginia Department of Game and Inland Fisheries (804) 752-5504

Kathryn Reshetiloff is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.

Fish passages: If you build them, they'll come back
Article from Bay Journal March 1997

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