American Shad (Alosa sapidissima)

American shad are native to the East Coast of North America, from Newfoundland to central Florida. In the late 1800’s, they were introduced to the Sacramento River in California, and by 1885 mature adults were found in the Lower Columbia River, the Willamette River, and as far inland as the confluence of the Snake and Columbia rivers. The Shad population has grown since that time to a record high in the Lower Columbia River of 5.3 million adults migrating upriver past Bonneville Dam in 2004.

Like salmon, shad are anadromous, but in contrast to salmon, they are iteroparous – spawning up to four times in the west coast rivers. They migrate to the Columbia River between May and July, spend 3-8 days in egg incubation after spawning, and then return to the ocean. Juveniles grow rapidly and migrate to the sea in the fall.  The increase in shad populations in the Snake River is associated with water flow and increasing water temperatures, but there exist significant questions about the effect of non-native shad on general river ecology and interactions with Fall Chinook juveniles that use reservoirs for rearing habitat. FERL scientists are studying several aspects of the shad population as the initial steps to understanding the ecological role shad play in the Columbia and Snake rivers. Recent sampling has included collecting and PIT tagging adult shad at Bonneville and Lower Granite dam, documenting size , spawning history, and sex; archiving scales, otoliths, and  fin clips for genetic stock identification and DNA; monitoring shad migration past multiple dams on the Columbia and Snake river.  Data from shad research will be used to increase scientists’ general understanding of fish migration behavior as well as assist in the management of regional fish populations.

Life-history of American Shad on the West Coast.  (Figure: C. Caudill)

Watercolor of an American shad by S. F. Denton, 1904 (Wikipedia)

FERL conducts shad sampling, DNA testing, tagging and tracking through Bonneville, Lower Monumental, Ice Harbor, and Lower Granite dams in the Columbia and Snake rivers. (FERL)