AMERICAN SHAD
DID YOU KNOW? American shad was introduced in the Pacific Northwest
in the late 1800's, and in 1990 the population of shad entering the Columbia
River was over 4 million fish.
SCIENTIFIC NAME: Alosa sapidissima, alosa
is an old name for European shad and sapidissima meaning most delicious.
COMMON NAMES: Atlantic shad, Potomac shad, white shad, common
shad, North river shad, and Connecticut river shad.
DESCRIPTION: A compressed silvery fish with a row of dark spots
(3-23) along its side. It can be easily distinguished by its sharp saw-like
scales or "scutes" along its belly. Average sized shad are 12-25
inches in length and 2.5 to 5 pounds.
LIFECYCLE: The American shad is a highly migratory anadromous
species that returns to its freshwater natal (birth) areas to spawn. Shad
spawn in estuaries, streams, and rivers in the spring and early summer
months. Spawning usually takes place over gently sloping areas with fine
gravels or sandy bottoms. In small groups; males and females disperse eggs
and sperm together and fertilization takes place in the water column. Males
and females may return to spawn more than once, and female shad can produce
30,000 to 600,000 eggs. The fertilized eggs float downstream and hatch
in 3 to 10 days. Juvenile shad tend to survive best in the slow waters
of reservoirs. They migrate downstream towards the ocean during late summer
and fall, with most migrating to the open ocean before winter. Some shad
will reside in rivers and estuaries up to one year before entering the
ocean. Shad normally spend 3-4 years at sea before returning to spawn.
RANGE: Along the Pacific coast from California to Alaska.
HABITAT AND ECOLOGY: The construction of dams on the Columbia
river basin has contributed to the decline of almost all species of anadromous
fish except the shad. Since the completion of the lower Columbia river
dams, shad populations have been on the rise. The slow moving waters of
reservoirs apparently provide ideal conditions for juvenile shad.
The shad is a plankton feeder who's diet varies depending upon the geographical
region. Throughout its life a shad consume copepods, amiphipods, shrimp,
zooplankton, and other small fishes. In freshwater the shad itself falls
prey to white sturgeon, juvenile salmonids, harbor seals, and other predators,
while in the ocean phase of life a shad is preyed upon by sharks, tuna,
sea lions, and others.
The American shad is very temperature sensitive and any changes in the
temperature of its habitat may result in negative impacts. Reservoirs often
act as ideal rearing habitat for juveniles; however, fish ladders, and
dam bypass systems are necessary to assist in migration past dams. Water
irrigation projects may also negatively impact shad populations.
ECONOMIC VALUE: Sport fisheries for shad have been building for
years in the Pacific Northwest. Shad are used as bait for other fisheries
and it is considered a good fighting sportfish that is rich in flavor and
is known for its excellent roe. Commercial fisheries have existed in the
Columbia River since the 1930's. Due to poor market demand and incidental
catches of protected salmon runs, significant commercial fisheries do not
exist in the Pacific Northwest.
Revised 12/16/96
