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Subject: Re: Fishing of large vs. small fish
From: Mark Tupper <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Thu, 11 Jul 2002 13:35:48 +1000

text/plain (111 lines)

Dear Fish-Sci,

Regarding the Conover and Munch study, there were some excellent discussions
posted on FishFolk over the last couple of days. If anyone not subscribing
to FishFolk would like to read this material, I will happily compile it and
send it to you.

Mark Tupper

Dr. Mark H. Tupper, Assistant Professor
University of Guam Marine Laboratory
UOG Station, Mangilao, GU 96915, USA
tel 671-735-2185; fax 671-734-6767

Coordinator, Marine Protected Areas Research Group

----- Original Message -----
From: "William Silvert" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, July 10, 2002 4:14 AM
Subject: Fishing of large vs. small fish

> The AFS mailing list recently reported the following item. I don't find it
> surprising, a number of my colleagues are concerned about
> 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 item got posted, but it is several years out of date.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
> at SEARN.
> 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
> 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
> 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
> 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.
> the remaining fish matured and spawned, the team repeated the process.
> Initially, the large fish-harvested tanks produced the highest yields.
> 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
> tanks. Additionally, since the reproductive capability of large fish is
> greater than that of small ones, small fish-harvesting resulted in more
> fertile animals. Juvenile survival rates were about the same for all
> 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,
> of the funders of this project. A successful industry is based on a
> 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
> The researchers thus propose both creating no-fish areas to prevent an
> irreversible loss of important genetic diversity, and setting a maximum
> limit in addition to the minimum. --Rachael Moeller
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