They were first seen off the British Columbia coast in the 1800s but are rarely caught in the Fraser River or any other river on the Canadian west coast. Migrants from U.S.A. rivers to the south are caught occasionally in the sea along the British Columbia coast. A closely-related shad, Alosa alabamae, occurs on the northern coast of the Gulf of Mexico and two other closely related species, Alosa alosa and Alosa fallax, occur in Europe, from the Baltic to Spain. Life History American shad, like the salmons, is a classic anadromous fish-that is, one which is born in freshwater, goes to sea to grow to maturity and returns to freshwater to spawn. In eastern Canada spawning runs enter rivers between late April and late June, depending on spring weather and geographic location.
Males arrive on the spawning grounds first, followed closely by the females.
Spawning usually takes place in deep areas of a river where there are moderate to strong currents. During the spawning act, which occurs at night, a single female is accompanied by several males and they swim close to the surface, splashing and rolling. The eggs are released in open water where they are fertilized by the males. A single female may release up to 400,000 eggs, but the average is about 130,00 per female. The eggs are 2.5 to 3.5 mm in diameter, transparent and slightly heavier than water.