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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:Thu, 20 Apr 2000 08:49:46 -0800

text/plain (22 lines)

Campbell Davies wrote:

> This pattern has also been taken to imply that tropical fish are faster growing and shorter lived than their temperate counter parts. A growing body of work on demographics of tropical reef fish using validated age-based methods is showing that the relationship between average maximum size, longevity and M is very loose and varies considerably within and among taxonomic groups of reef fish.

> Specifically, that many species of small reef fish have substantially greater longevity than larger commercial species. Whether this is a natural pattern or an artifact of a history of selective fishing is yet to be demonstrated. Nevertheless, comparison of estimates of M derived from Pauly's equation and estimated obtained from age based catch curves suggest that the former are quite positively biased. This is the result of extremely "flat-topped" growth curves and considerable longevity beyond the inflection point.

My comment:
Yes, when fish stop growing at the maximum length and continues to live, natural mortality to growth parameter relation becomes blurred. That is why I queried about the validity of directly transferring continuous growth ideas to modeling of non-ageable animals, which either grow severely discontinuous way throughout their life span, stop growing at some stage of their life, or both.


Shareef Siddeek
Alaska Department of Fish and Game
Juneau, Alaska

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