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Subject: Re: depensatory exploitation
From: Dick Allen <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Sat, 29 Jul 2006 23:32:24 -0400
Content-Type:text/plain
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Patrick,

You assumed a managed fishery.  There are no effective controls on either
fishery inputs or outputs in the U.S. fishery for American lobster, for
example.  The same may be true for the Chesapeake blue crab fishery that
prompted Rom's inquiry.  In those cases, knowledge of the functional
response of the fisherman to changes in abundance of the target species is
critical.  In southern New England we are now moving into a regulatory
framework that will have the theoretical ability to control lobster trap
numbers.  The functional response of the fishermen will be a big factor in
the effectiveness of the effort control program.

Dick Allen
Fisheries Dept. Graduate School
Univ. of Rhode Island
(401) 874-7153
[log in to unmask]

-----Original Message-----
From: Scientific forum on fish and fisheries
[mailto:[log in to unmask]]On Behalf Of Patrick Cordue
Sent: Saturday, July 29, 2006 6:19 PM
To: [log in to unmask]
Subject: Re: depensatory exploitation

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Hi Rom,

It was good to get the long definition, as the short definition was a bit
unclear. However, there appears to be a conceptual problem. You talk of
functional responses and fishing mortality as a function of abundance. In
some deterministic systems this will be true, but, in general, fishing
mortality is not a function of abundance (there is no 1-1, or many-1
relationship).  Consider a managed fishery. In year y1 biomass is B and the
catch is C1, in year y2 biomass is also B, but the TAC (for example) is set
at a different level (for whatever reason) and the catch is C2. There is a
1-many relationship (not a function, not a functional repsonse).

Regards
Patrick Cordue

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