Site pages
Current course
Participants
General
Topic 1
Topic 2
Topic 3
Topic 4
Topic 5
Topic 6
Topic 7
Topic 8
Topic 9
Topic 10
Topic 11
Topic 12
Topic 13
Topic 14
Topic 15
Topic 16
Topic 17
Topic 18
Topic 19
Topic 20
Topic 21
Topic 22
Topic 23
Topic 24
Topic 25
Topic 26
Topic 27
Topic 28
Topic 29
4.2.3.1. Pauly’s empirical formula
4.2.3.1. Pauly’s empirical formula
Natural mortality in fishes can also be correlated to mean environment temperature. The interrelationships can be expressed for length growth data by the multiple regressions as below:
For length-growth data
log10M =$$ -0.0066 - 0.279$$ log10 L$$\infty$$+ 0.6543 log10K + 0.4634 log10T
For weight – growth data
log10M = - 0.2107 - 0.0824 log10 w$$\infty$$ + 0.6757 log10K+ 0.4687 log10T
‘M’ is the natural mortality in a given stock, ‘L$$\infty$$ ’ (total length in cm) and ‘W$$\infty$$ ’ (live weight in g) being the asymptotic size of the fishes of that stock and ‘K’ the growth co-efficient. The value of ‘T’, is the annual mean temperature in ºC of the water in which the stock is found.
The above two equations give reasonable estimate of ‘M’ for about any set of growth parameters and temperature value. However for certain schooling pelagic fishes particularly for clupeoid fishes, the ‘M’ is generally overestimated by the above two equations. In such cases, it might be appropriate to reduce the estimate of ‘M’ by multiplying K by 0.8 (Pauly, 1983).
The equation should be avoided for crustaceans and molluscs or any other invertebrates. Pauly’s formula does not cover these groups.