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Re: Scripps Oceanography News Release: Fishing Throws Targeted Species Off Balance


Steven Atran <[log in to unmask]>


Scientific forum on fish and fisheries <[log in to unmask]>


Mon, 21 Apr 2008 10:37:11 -0400





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> Fishing typically extracts the older, larger members of a targeted species
> and fishing regulations often impose minimum size limits to protect the
> smaller, younger fishes.
> “That type of regulation, which we see in many sport fisheries, is exactly
> wrong,” said Sugihara. “It’s not the young ones that should be thrown
> back,
> but the larger, older fish that should be spared.

I basicly agree with most of what's been said, except for the above, which
infers that fishing should explicitely target the younger fish in order to
protect the older individuals. Even ignoring the complications of release
mortality, there is a fundamental problem with this approach. A fishing
mortality rate high enough to truncate a stock at or near the minimum size
limit is likely to be high enough to also decimate the younger age classes
if effort is shifted through the use of a maximum (or slot) size limit, or
by other means, without also taking action to reduce fishing mortality
overall. If that happens, where is the next generation of older fish going
to come from, once the current generation dies out? A better approach is to
allow fishing mortality across the full range of available age/size classes
so that no one age gets an excessive anount of fishing pressure. Rather
than set management targets in terms of Bmsy, Boy, or minimum stock size
thresholds, a better target would be to achieve an optimum age or size
distribution of the stock. This would assure that fishing mortality on the
younger fish is kept low enough to allow a reasonable number of fish to
escape to the older age classes, and that fishing mortality on the older age
classes is low enough to allow individuals to make a substantial
contribution to the reproductive success of the stock before being caught or
dying out. If the stock can be kept at a desired age/size distribution, the
biomass level should take care of itself. Unfortunately, this would require
a change to the Magnuson-Stevens Act, which requires management to be based
on maximum sustainable yield.

Steven Atran
Tampa, Florida

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