The initial facts about the migration are these: each year, close in time to the vernal equinox when the sun crosses the equator and day and night are of equal length, this member of the herring family begins to enter innumerable inlets and tidal estuaries down the length of the Atlantic coast, from Newfoundland to the Carolinas. Scientifically known as _Pomolobus pseudoharengus_ (also, under an older classification, _Alosa pseudoharengus_, along with species of shad), the alewife is an “anadromous” fish, meaning that like the salmon and shad, but unlike its relative the sea herring, it grows in salt water but leaves it as a three- or four-year-old adult, to spawn in fresh. A “catadromous” fish, like the eel, does just the opposite, growing up in fresh water and spawning in the sea. The alewives, I learned, were due to come in from the Bay when the temperature of the brackish water that flowed into it was warmer than that of the salt water. In fact, a local resident had already noticed a group of eight or ten alewives of apparently large size that had appeared in the brook a few days before. Their arrival was a token that the land, though still cold, was warming up more quickly than the sea--just about the time a few male red-winged blackbirds showed up too, in advance of housekeeping. But if some began their migration in March, the first big run was not likely to come until the middle of April or later, depending on how long and cold a winter it had been. During an exceptionally cold season the alewives might not appear in volume until the first days in May. Where were they now, and what were they doing? Schooling somewhere offshore, and waiting to move in? I stood on the beach and the sea still looked and felt and smelled as raw and cold as winter--iron-gray, massive, keeping its counsels--although, as I understood it in an incomplete way, the waters were undergoing seasonal adjustments at varying depths in the shallow coastal areas. Spring changes would begin to take effect. Perhaps I knew them, smelled them, on the sea wind. I was impatient. I wondered what specific combination of length of life, biological responses, currents, tides, the composition of the sea water, might impel one roving school of fish to leave the sea and start inland. March, that season of the whole air hesitating and blowing back and forth, the circuit of the compass, especially in low-wooded seaside lands, is a time of hesitation, preparation, and violence. It is waiting weather.