I've been working on growth of sea cucumbers for a decade. Through empirical mark-recapture studies in the field lasting years, other authors (Uthicke et al. 2004) and I have found that large animals tend to shrink in length and weight. Possibly, a sign of senescence. The negative growth is problematic for standard fisheries growth models (e.g., von Bertalanffy, logistic, Gompertz).
Can anyone point me to some studies in which the older animals shrink, or lose weight/size? (this is actually well known for human height vs age). Any growth models that would produce a quadratic form to the age-vs-size curve?
Hi!
I do not know about any growth model that tackle shrinking. However, jellyfish are another type of organism that can exhibit shrinking. This is not necessarily linked to aging as ecological factors (most importantly food availability) play a big role.
See for instance:
Article Population dynamics and factors controlling somatic degrowth...
https://academic.oup.com/plankt/article/36/6/1585/1480566?login=true
I hope this helps!
Hi Steve !
In cephalopods there is also a shrinkage linked to senescence, but this is generally a very short phase followed by death immediately after reproduction. So I don't think anyone has introduced this phenomenon into growth models because this fraction of the population doesn't interest fishing.
Seasonal shrinkage is a phenomenon known even in vertebrates (birds, shrews) and can affect the whole body or only part of it. Is the phenomenon in holothurians irreversible or not?
Hi Steven Purcell,
There is always the fanfin anglerfish, Caulophryne jordani, in which the male hangs onto the female in a quasi parasitic maner and shrinks.
There are probably more, I'll think about it;
Regards, Greg
Any von Bertalanffy curve fit to a dataset that does not include some data on large/old individuals is apt to produce wildly wrong estimated asymptotic length. There are two reasons behind the data calculation error, Those are: 1) the growth is linear for the age interval which you have or 2) the sample is too small.
If you can provide me with some real data I can give it a shot!
I'm trying to improve my regression software with new models, according to the needs of researchers!
www.lerenisplezant.be/fitting.htm
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