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Hi Dick,

My comments apply to any fishery. Because there is a 1-many RELATIONSHIP 
between abundance and fishing mortality (or exploitation rate) then, by 
definition, fishing mortality is not a FUNCTION of abundance ALONE. Therefore 
to define "depensatory exploitation" in terms of the shape of the function 
cannot be generally applicable - because, in general, no such FUNCTION exists.

I agree with you entirely, that understanding how fishermen respond to 
changes in abundance is critical (for a number of applications). 

Regards
Patrick

On Sunday 30 July 2006 15:32, you wrote:
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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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-- 
----------
Patrick Cordue
Director
Innovative Solutions Ltd
www.isl-solutions.co.nz

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