Adult American shad returning to the
Schuylkill River in the spring of 2003 most likely originated as
juvenile shad stocked there three and four years earlier as part of
a restoration program, biologists with the Pennsylvania Fish and
Boat Commission have confirmed.
The PFBC recently completed an analysis
of adult shad collected from the river earlier this spring by
fishery workers from the Philadelphia Water Department and a private
consultant, Normandeau Associates. Of the 24 American shad analyzed
at the PFBC's Benner Spring Fish Research Station, all were found to
have chemical tags indicating that they had been stocked by the
Commission in the Schuylkill in either 1999 or 2000.
The PFBC began stocking
the Schuylkill River with young American shad, called fry, in 1999.
Since then, an average of 500,000 fry have been stocked each year.
Eggs for the program were obtained from adults collected in the
Delaware River and transported to the Van Dyke Hatchery in Juniata
County, where the fry were reared for 10 to 30 days. All of the
stocked fry were tagged with a chemical tag to distinguish them from
shad naturally produced in the wild. Shad
fry, as young as three days of age, are immersed in a tetracycline
solution that is absorbed into growing bone tissue. At this early
age, the otolith, or earstone, is the only true bone present in the
fish. All other bones, still in their early stages of development,
are comprised of cartilage. The otoliths grow by adding rings,
similar to the rings in tree trunks, except that one ring is laid
down each day.
Using specially equipped microscopes,
researchers are later able to detect the chemical tag in the otolith
of adults and determine if the fish entering the river as part of
their spawning migration originated from a hatchery or in the wild.
Biologists are also able to confirm the age of the fish because
unique tag sequences are applied from year to year. Fifteen of the
fish collected from the Schuylkill River this spring were age four,
including 14 males and one female. The other nine fish were age 3
males, a surprising result since few male shad were previously
thought to mature as early as three years of age.
American shad is the largest member of the herring family. Adults
commonly reach four to eight pounds. Shad spend most of their life
in the ocean and return to freshwater to spawn. Each spring, adult
shad migrate into coastal rivers from Florida to Newfoundland.
Spawning takes place around dusk at water temperatures from 60 to 65
degrees. A single female shad can produce up to 600,000 eggs, but
most average 250,000 eggs.
American shad played an important part in the history of the United
States. It is said that General George Washington's troops subsisted
on salted shad from the Delaware River during that long, cold Valley
Forge winter in 1776. However, by the late 19th century,
pollution and man-made obstacles - primarily dams - blocked American
shad from many of their historic spawning grounds.
The Pennsylvania Fish and Boat
Commission is a national leader in restoring American shad to their
natal waters. The restoration effort on the Susquehanna River and
its tributaries is the largest such project of its kind. Recently,
increased efforts are being focused on tributaries to the Delaware
River, such as the Lehigh and Schuylkill rivers.
Fairmount Dam is the
first of 10 dams blocking migration on the Schuylkill River.
Fairmount Dam has a fish ladder in place, but it is old and somewhat
ineffective at passing shad. The Philadelphia
Water Department is replacing the old ladder with a more
modern design that should be completed by spring of 2005.