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Subject: Re: Stock Assessment models
From: Shareef Siddeek <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Fri, 7 Apr 2000 12:29:46 -0800

text/plain (40 lines) , shareef_siddeek.vcf (14 lines)

> Shareef Siddeek wrote:
>  Are we correct in assuming these vital parameters length dependent?

> Steve Gutreuter wrote:

> This is an important question, I think.  In my opinion, the answer is
> 'sometimes (most of the time?), yes.'  There is a substantial literature
> on this issue.
> In general, we might expect body size to mediate life history parameters
> in organisms that have indeterminate growth, show a wide range in
> body size, show size-selective predation (e.g., via gape limitation
> of animals that swallow food whole), are affected by size-selective
> predators, and etc.  These features apply to many (most?) fishes.
> I think the inclusion of size-based assessments is entirely appropriate and
> natural.

In general what Steve has said is true mostly for finfish, young stages of
animals and small and edible (to predators) form of animals (not animals with
spines and other abnormal morphology and behavior). That is another story. My
specific question is that if we are to partition, for example, natural
mortality into two components: a constant part + a size specific part; then
the size specific part is a function of prey size and predator abundance in
the vicinity, etc. But how does the constant part behave? Is it size or age
specific. The constant part includes all other causes (diseases,
environmental stress, old age, etc.). My thinking is that this constant part
results from a cumulative effect over time; therefore should be age specific
not size specific. Is this correct?


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