2.7.6. Reproduction

The system starts from a pristine state, with no schools in the domain. For a few years (user-defined), Osmose will release some eggs for every species. The eggs enter the different steps of the life cycle, and once the fish reach sexual maturity, the reproduction process takes over. Osmose stops the seeding, unless the spawning stock biomass gets depleted. In that case Osmose resumes the seeding by releasing some eggs until there are again mature individuals in the system for carrying on the reproduction process. Osmose completely ceases the seeding when the simulation reaches the maximal number of years for seeding (user-defined).

For a given species:

\[ \begin{align}\begin{aligned}B_{mat} = \sum_{mature sch.}B\\N_{eggs} = FRAC_{fem} * \alpha * season * B_{mat}\ if\ SSB > 0\\N_{eggs} = FRAC_{fem} * \alpha * season * B_{seeding}\ if\ SSB=0\end{aligned}\end{align} \]

By following this approach:

  • No assumption is made about the structure of the populations but it emerges from individual interactions

  • it reduces computing requirements for the spin-up as the first years are the fastest to run

  • it reduces the number of time steps for the spin-up

  • it minimizes the amplitude of population oscillations

Finally, the seeding biomass is then used to add new schools to the system, depending on the value of \(N_{eggs}\).

If \(N_{eggs} < N_s\):

\[ \begin{align}\begin{aligned}N_{sch} = 1\\A_{sch} = N_{eggs}\end{aligned}\end{align} \]


\[ \begin{align}\begin{aligned}N_{sch} = N_s\\A_{sch} = \frac{N_{eggs}}{N_s}\end{aligned}\end{align} \]
Table 2.24 Reproduction paramters


Number of schools of species # to create during reproduction (\(N_s\))


Number of schools to create during reproduction (\(N_s\)). Used if no species specific value provided


Seeding biomass (\(B_{seeding}\), tons)


File providing the seeding distribution within a year


Fraction of females (\(FRAC_{fem}\))


Number of eggs per gram of mature female (relative fecundity)


Number of years when the artificial seeding is activated