2.3.5. Reproduction

Mature individuals spawn during the breeding season, which occurs when successive time steps \(t\) have a spawning seasonality value \(sp(t)\) (expressed as a fraction of spawning activity per time step and summing to 1 over one year) above 0. At the first time step of the breeding season, all the energy contained in the gonadic compartment \(g(i, t)\) of individuals in school \(i\) is used to produce eggs. The sex-ratio is assumed to be 1 for 1 for all species and the number of eggs produced by school \(i\) for the whole breeding season is defined as follows:

\[N_{eggs} (i, t) = N(i, t) \dfrac{g(i,t)}{ 2 w_{egg}}\]

with \(w_{egg}\) the weight of an egg. The pool \(g(i,t)\) is then set to 0 and can start growing again (equation (2.3)) at the next time steps in view of the next spawning season. Then, the total number of eggs produced by the species \(s(i)\) for the breeding season is obtained as

\[N_{eggs_{tot}} = \sum_{j \lor s(j) = s(i)} N_{eggs}(j, t)\]

At each time step \(t\) of the breeding season, \(N_s\) new schools are produced by species \(s(i)\), with the number of eggs, and thus individuals, per new school \(i'\) calculated as follows:

\[N(i', t) = sp(t) \times \dfrac{N_{eggs_{tot}}}{N_{s}}\]

with age of offspring set to 0 (\(a(i', t) = 0\)), their somatic weight set to the weight of an egg (\(w(i', t) = w_{egg}\)) and their gonadic weight set to 0 (\(g(i,t) = 0\)). The new schools are released randomly depending on the specific larvae habitat map.