# 4.15. Reproduction¶

At the end of each time step, the numbers of eggs spawned by a species is calculated as follow:

$N_{Egg} = sexRatio \times \alpha \times season \times (SSB \times 10^6)$

with $$sexRatio$$ defined by the parameter species.sexratio.sp#, $$\alpha$$ is the annual number of eggs per gram of mature female defined by the parameter species.relativefecundity.sp#, $$season$$ defined by the parameter reproduction.season.file.sp# and $$SSB$$ the Spawning Stock Biomass. $$SSB$$ is calculated as the sum of the biomass of the schools that reached sexual maturity (defined by the parameter species.maturity.size.sp#). As $$SSB$$ is expressed in tons and alpha in grams of mature female, SSB is multiplied by $$10^6$$.

reproduction.season.file.sp# is the path of a CSV file that contains a time series of the season factor:

Table 4.9 Example of seasonal fishing distribution
Time step seasonality
0 0.03
1 0.03
2 0.025
3 0.025
4 0.03

One line per time step. The first column defines time, expressed in year. The second column define the fraction of eggs to be spawned by at each time step. OSMOSE will also be able to read an interannual CSV file with as many season factors as the number of time steps of the simulation.

Warning

The sum of the season factors over a year should sum to one (even though OSMOSE will not check, which somehow allows you to mimic interannual variability when CSV file is interannual).

If Osmose does not find any seasonality file, uniform spawning throughout the year is assumed.