American shad

American shad are the only anadromous shad on the west coast and have the ability to return to spawn for several years. They live most of their life in marine waters where little is known of their life history on the Pacific coast. At sea, shad are schooling fish and thousands are often seen at the surface in spring, summer, and autumn. They are hard to find in the winter, as they tend to go deeper before spawning season. They have been pulled up in nets at deep as 65 fathoms. Shad are river-specific and each has a discrete spawning stock and adults return to their natal river to spawn.

They are very sensitive to water temperature and any dramatic changes in the temperature of its habitat can have a very negative impact on the fish. They will not tolerate water temperatures below 41 °F. The ideal habitats for juvenile shad are large reservoirs. Fish ladders and dam bypasses are necessary to assist in the migration of the American shad past dams.

Shad are native to the Atlantic coast and were introduced to the Pacific coast in the early 1870s. Records document commercial landings in the Columbia River in 1885. Shad have become abundant and well established in the Columbia River and tributaries, including the Snake River and the Willamette Rivers. Shad are now found from southern California to Kodiak Island, Alaska.

Extensive biological and ecological information exists about American shad in its native Atlantic coast habitat. Similar information is lacking about American shad in the Columbia River system. Shad migrate upstream with adult salmon through fishways in the Columbia River dam system. Competition between salmonids and American shad for passage through fishways has resulted in some dams being modified to allow for better shad access to upstream habitat . American shad have migrated past Bonneville, The Dalles, John Day, McNary, and Priest Rapids Dams and as far as the Lower Granite Dam on the Snake River.

American shad flourished on the West Coast and in the Columbia River after their introduction in the late 1800s. The reasons for shad abundance vary, but it is strongly believed that the freshwater habitat created by dam reservoirs is ideal for spawning and rearing. The Dalles Dam was built in 1956, the adult shad count at Bonneville Dam (downstream) increased from a 22–year average of 15,475 fish (1938–59) to 329,850 fish in the period 1960–64.

The American shad introduced into the Sacramento River came from a hatchery on New York’s Hudson River. In 1885, shad were introduced into the Columbia River from the Susquehanna River in Pennsylvania. However, shad had been observed in the Columbia River earlier. It is believed they were transported northward by the Davidson Current that flows from San Francisco to Vancouver Island. Shad have become very abundant in the Columbia River system, with as many as 4 million shad estimated in 1990.