Chapter 4 Maturity
For the capelin assessment, maturity is length based. A simple rule of thumb is that fish larger or equal to 14 cm is mature. The model described here allows for a more delicate modelling of maturity. Let \(m\) be the maturity depending on length \(\ell\) of capelin and the two parameters \(p_1\) and \(p_2\), i.e. \[\begin{equation*} m(\ell) = \frac{1}{1+\exp\{4p_1(p_2 - \ell)\}} \end{equation*}\] Let \(N_{\ell, a}\) be the number at age \(a\) in length group \(\ell\) and \(\bar N_a\) is the number of immature capelin at age \(a\). That is \[\begin{equation*} \bar N_a = \sum_{\ell} (1-m(\ell))N_{\ell,a}. \end{equation*}\]
The maturity parameters are estimated using Template Model Builder (TMB).