Amid the hum of the Bay Area’s cities, it is easy to forget that to live here is to live alongside a vast ecosystem. The biggest and most vital is the Pacific Ocean. And once a year, the ocean reveals its abundance to herring fishers. “‘The water will be white, that’s when you know,” said Keith Nguyen, a kayak fisher from San Jose. Nguyen is describing the herring spawn, an annual event from November to February, when adult herring migrate…