Knowing fishes' ages is crucial for managing a fishery
Long-lived animals that mature and reproduce slowly produce fewer offspring than fast-growing, fast-reproducing animals like rabbits. Some deep-water fish grow slowly. If scientists find that the Pacific grenadier matures slowly and reproduces infrequently, increases in the Pacific grenadier catch off the central California coast could damage the fish population.
Traditional methods of determining a fish's age require scientists to capture live fish and collect years' worth of growth records: either the detainees are kept in aquaria for years to observe growth rates or the fish are measured, tagged, released, and recaptured years later and re-measured.
Such methods do not work with the Pacific grenadier. One reason is that dragging the fishes topside from their 600-meter-deep (2,000 feet) homes gives them "big, big pressure problems," says Allen Andrews, a researcher at Moss Landing Marine Laboratories. Gases in the fishes' bladders expand rapidly, popping their stomachs out their mouths and making their eyes bug out. The result: a lot of dead, ugly fish of indeterminate age.
The 1996 Pacific grenadier catch landed at Monterey Bay harbors was nearly 400 times more than the 1993 catch, going from fewer than 2,300 kilos (about 5 thousand pounds) in 1993 to almost 900,000 kilos (about 2 million pounds) last year.