Trends in the Abundance of American Shad, Alosa sapidissima, in the Delaware River Basin

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Abstract
The American shad,Alosa sapidissima, was very abundant in the Delaware River Basin until 1901. Annual commercial landings from 1890 to 1901 (about 11 to 17 million lb) were several times greater than in any other river system. Abundance declined rapidly after 1901, except for a resurgence in 1907 which may be interpreted as evidence that by 1903 pollution was affecting successful seaward movement of young produced in the Delaware River. Less than 0.5 million lb were landed in 1920. Abundance has remained low since 1920, although fluctuations have occurred. Extra-Delaware Basin fish mix with Delaware Basin fish at the mouth of Delaware Bay. It is not clear how far extra-Delaware Basin fish penetrate upbay, but they do not enter fresh water of the Delaware River. Records available for several years in the period 1890–1901 indicate that 39% of the total Delaware Basin landings came from fresh water of the Delaware River, suggesting that landings at that time were primarily dependent on Delaware Basin fish.

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