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Subject: Fishing of large vs. small fish
From: William Silvert <[log in to unmask]>
Reply-To:William Silvert <[log in to unmask]>
Date:Tue, 9 Jul 2002 19:14:29 +0100

text/plain (61 lines)

The AFS mailing list recently reported the following item. I don't find it
surprising, a number of my colleagues are concerned about over-exploitation
of large mature fish, but I thought that the item was worth reposting.

Some of you may have seen a posting on the newsgroup about
the FISH-ECOLOGY mailing list being located at SEARN. I don't know how the
item got posted, but it is several years out of date. FISH-ECOLOGY is
located in the Canary Islands, and FISH-SCI continues to be the list located

William Silvert, co-owner, FISH-SCI list

July 09, 2002
Study Questions Wisdom of Harvesting Only the Largest Fish


Fisheries managers frequently set minimum size limits for captured animals,
mandating that the smallest--and thus youngest--be freed to allow for full
maturation. But findings detailed in the current issue of the journal
Science suggest that these regulations may actually be shrinking the average
size of wild fish over time. Plucking the largest fish from the gene pool,
the authors report, leaves only hereditary information from the smallest
fish for the next generation.

To examine the potential evolutionary effects of selective extraction ,
David Conover and Stephan Munch of the State University of New York at Stony
Brook studied a common marine fish called Menidia menidia. Allowing groups
of the fish to grow in separate tanks, the scientists removed and weighed
the largest 90 percent of individuals from some tanks, the smallest 90
percent from others, and a random 90 percent assortment from the rest. After
the remaining fish matured and spawned, the team repeated the process.
Initially, the large fish-harvested tanks produced the highest yields. After
four generations of such "fishing," however, the total weight of all the
fish extracted from the small fish-harvested tanks, as well as the average
weight of each creature, amounted to twice that of the large fish-harvested
tanks. Additionally, since the reproductive capability of large fish is much
greater than that of small ones, small fish-harvesting resulted in more
fertile animals. Juvenile survival rates were about the same for all groups,
indicating that evolved changes in growth, not viability, caused these
results. The findings suggest that in the real world, taking only the
largest fish may in the long run result in a calamitous decrease in yield,
and thus income, for the entire industry.

Fishing is big business for many coastal communities. "In New York State
alone, the commercial fishing, recreational fishing, and the seafood
industries make a $11.5 billion contribution to the state's economy and
employ over 100,000 people," remarks Jack Mattice of New York Sea Grant, one
of the funders of this project. A successful industry is based on a healthy
fishery, however. "Our study illustrates how well-intentioned management
plans that appear to maximize yield on ecological time scales may have the
opposite effect after accounting for evolutionary dynamics," Conover notes.
The researchers thus propose both creating no-fish areas to prevent an
irreversible loss of important genetic diversity, and setting a maximum size
limit in addition to the minimum. --Rachael Moeller

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