Biologists speaking at a symposium in Washington, D.C., last week warned that fundamental assumptions underlying current fisheries management practices may be wrong, resulting in management decisions that threaten the future supply of fish and the long-term survival of some fish populations. The symposium, organized by Steven Berkeley of the University of California, Santa Cruz, and Larry Crowder of Duke University Marine Laboratory, was part of the 2005 Annual Meeting of the American Association for the Advancement of Science (AAAS).
"Much of what we now know about fish populations is not being accounted for in current fisheries management," said Berkeley, a research biologist at UCSC's Long Marine Laboratory.
Berkeley's research on West Coast rockfish, for example, shows that large, old females are far more important than younger fish in maintaining productive fisheries. The larvae produced by these "big, old, fat females" grow faster, resist starvation better, and are much more likely to survive than the offspring of younger fish. Unfortunately, older fish tend to disappear under current fisheries management practices--the old fish get caught and the younger fish never have a chance to grow old.
"Our research shows that you need to maintain older fish in the population because those are the most successful at reproducing. But normal fishing at what we now think of as safe levels will not maintain old fish in the population," Berkeley said.
The effects of fishing on the age structure of a population is particularly striking in the various species of rockfish, which are very long-lived fish. Many rockfish can live for 50 years or more, and some species can live well over 100 years.
Current fisheries management actually aims to reduce the number of old, slow-growing fish in the population, leaving more room and resources for younger, faster-growing fish. Most marine fish produce huge numbers of eggs and larvae, so the assumption has been that the spawners that remain after harvesting will produce plenty of larvae to replenish the population. According to Berkeley, however, elimination of older generations drastically reduces the ability of the population to replenish itself.
Failure to account for the role of older fish in maintaining healthy populations may help explain the recent collapse of some major West Coast fisheries. The Pacific Fishery Management Council has declared several stocks of groundfish--a group that includes numerous species of rockfish and other bottom-dwelling fish--to be overfished. Tight restrictions were imposed to allow the overfished populations to recover, causing economic hardship for many in the West Coast fishing industry. Recovery of some stocks is expected to take decades.
One way to prevent such problems may be to establish marine reserves--areas where fishing is not allowed and fish populations are able to age naturally.
"Marine reserves are the only good way of protecting the full age structure of a population of fish, so that at least some of the population ages naturally," Berkeley said. "There may be other approaches, but no matter how you manage the fishery, you can't have a full complement of age classes unless some part of the population is off limits."
Other research presented at the symposium includes new findings about genetically distinct populations within the geographic ranges of some marine fish species, as well as evidence that successful breeders may be few and far between in some populations. These and other findings further undermine fundamental assumptions of current fisheries management, Berkeley said. "These are all things that should make us stop and think about how we manage fisheries," he said.
Berkeley and his collaborators have published recent papers on their research and its implications for fisheries management. Findings on the influence of maternal age on larval growth and survival appeared in the May 2004 issue of Ecology. Management implications of these and other findings were discussed in a paper in the August 2004 issue of Fisheries.
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