Length Based
Yield per Recruit (YPRLEN) is an implementation
of the
basic Thompson-Bell model for estimating the expected lifetime yield
and biomass from a cohort subjected to varying levels of fishing
mortality.
In the length-based model the user provides parameters of a
von Bertalanffy growth equation. Age is taken as relative
with the model starting at age zero. The user also provides
parameters for equations relating weight, selectivity and maturity to
length.
The user provides a small age step as an integration factor.
This is converted to length by the von Bertalanffy equation
and the other required data is derived from length.
This approach may in many cases provide a more accurate
lifetime yield and biomass curve than the traditional age-based YPR
model.
In the September 2004 update of YPRLEN, several alternative
selectivity models were introduced.
Users can export an age-based file that can be used as input
to the age-based YPR model.
Length
Based Yield Per Recruit