With funding from Oregon Sea Grant, Berkeley, based at the Hatfield Marine Science Center in Newport, began studying the fish on an intuition-based hunch that their long life cycles served some evolutionary purpose. Black rockfish spawn hundreds of thousands of tiny, translucent live young that spend their first weeks in the plankton layer near the surface of the ocean, later settling out into bays, estuaries and nearshore reefs. It takes a Black rockfish five years or more to become a sexually mature adult. Surveying the survival rates of offspring from different age groups of an undersea population isn't like taking a census. Luckily for marine researchers, many fish lay down daily growth rings in their ear bones, or otoliths, that allow unusually precise aging.
Researchers can even determine the fish's date of birth, or spawn date.
They used the otoliths to find their ages, and examined their ovaries to determine when they would have spawned that spring. They found that the older fish spawned early and over a longer period of time. The younger adults spawned late. Throughout the late spring and summer the researchers collected juveniles that were by then residing in the bays and estuaries. They compared the spawn date of the adults with the birthdates of the juveniles.