Ocean distribution of the American shad (Alosa sapidissima) along the Pacific coast of North America

We examined the incidental catches of American shad (Alosasapidissima) taken during research cruises and in commercial and recreational landings along the Pacificcoast of North America during over 30 years of sampling. Shad, an introduced species, was mainly found over the shallow continental shelf, and largest catches and highest frequency of occurrences were found north of central Oregon, along the coasts of Washington and Vancouver Island,and in California around San Francisco Bay. Migrations to the north off Washington and Vancouver were seen during spring to fall, but we found no evidence for large-scale seasonal migrations to the south during the fall or winter. The average weight of shad increased in deeper water. Sizeswere also larger in early years of the study. Most were caught over a wide range of sea surface temperatures(11–17°C) and bottom temperatures (6.4–8.0°C). Abundance of shad on the continental shelf north of 44°N was highly correlated with counts of shad at Bonneville Dam on the Columbia River in the same year. Counts were negatively related to average weights and also negatively correlated with the survival of hatchery coho salmon (Oncorhynchus kisutch), indicating that survival of shad is favored bywarm ocean conditions. Examining the catch during research cruises and commercial and recreational landings, we concluded that American shad along the Pacific coast have adapted to the prevailing environmental conditions and undertake only moderate seasonal migrations compared withthe long seasonal migrations of shad along the Atlantic coast of North America. We suggest that the large spawning populations in the Columbia River and San Francisco Bay areas explain most of the distributional features along the Pacific coast.

Bibliographic Details

Main Authors:	Pearcy, William G., Fisher, Joseph P.
Format:	article biblioteca
Language:	English
Published:	2011
Subjects:	Biology, Ecology, Fisheries,
Online Access:	http://hdl.handle.net/1834/25353
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