(D.11)
and if a gamma selectivity curve is used for the gear then
(D.12)
where is the selectivity constant for the fishery on the ith age class of vertebrate group FX, is the selectivity coefficient (spread of the curve) for the fishery on the ith age class of vertebrate group FX, is the selectivity coefficient (length at which 50% of the population is selected) for the fishery on the ith age class of vertebrate group FX and the length (lj,FX) of a vertebrate from cohort i in vertebrate group FX is given by:
(D.13)
with XCN the redfield ratio of carbon to nitrogen, wet is the conversion coefficient from weight to dry weight, w,FX is a scaling coefficient in the length-weight relationship for FX and w,FX is the exponent in the length-weight relationship. In practice the logistic or normal selectivity curves are used (unless otherwise specified for that scenario). The parameters used to specify the selectivity curve may be adjusted in response to “management decisions” made under some of the alternative management scenarios (i.e. gear restrictions can translate into changes in selectivity).
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