# Changes between Version 3 and Version 4 of EwEugProduction

Ignore:
Timestamp:
2010-01-28 14:52:18 (10 years ago)
Comment:

--

Unmodified
Added
Removed
Modified
• ## EwEugProduction

 v3 Production rate is the sum of natural mortality (''M = M0'' + ''M2'') and fishing mortality (''F''), i.e., ''Z'' = ''M'' + ''F''. In the absence of catch-at-age data from an unexploited population, natural mortality for finfish can be estimated from an empirical relationship (Pauly, 1980) linking ''M'', two parameters of the von Bertalanffy Growth Function (VBGF) and mean environmental temperature, i.e., [[Image(wiki:EwEugImages:08000016.png)]] Eq. 16''' '''[[Image(wiki:EwEugImages:08000016.png)]] Eq. 16''' where, ''M'' is the natural mortality (/year), ''K'' is the curvature parameter of the VBGF (/year), ''L'',,''∞'',, is the asymptotic length (total length, cm), and ''Tc'' is the mean habitat (water) temperature, in °C . Beverton and Holt (1957) showed that total mortality (Z = P/B), in fish population whose individuals grow according to the von Bertalanffy Growth Function (VBGF), can be expressed by: ../Resources/Images/08000017.png '''[[Image(wiki:EwEugImages:08000017.png)]] Eq. 17''' where ''L,,∞,,'' is the asymptotic length, i.e., the mean size the individuals in the population would reach if they were to live and grow indefinitely, K is the VBGF curvature parameter (expressing the rate at which ''L,,∞,,'' is approached), ../Resources/Images/08000018.png is the mean length in the population, computed from L’ upward. Here, L’ represents the mean length at entry into the fishery, assuming knife-edge selection. Note that ../Resources/Images/08000018.png must be > L’.