The Bio-economic Model:

We consider a fishery in which two fishing fleets (a fleet of trawlers and a fleet of gill-netters) exploit a stock of soles (Solea solea). The simplified multi-fleet bio-economic model is described in discrete time with an annual step.

Biological Parameters: 

Economical Parameters: 

The Spawning Biomass Function (SSB):

The Stock Dynamic Function aims  to return the abundances by age at time t+1 based on abundance at time t and according to a vector of fishing effort multiplier: u.

The Production Function that calculates the annual catches per fleet

Function Income that calculates the annual income per fleet

Function Profit which calculates the annual profit per fleet, the effort multiplier u is applied to the number of vessels

Using the function Trajectories , you can plot the trajectories of the spawning stock biomass and profits for a period of 10 years, with a status quo scenario 


Here we add stochasticity to the recruitment. We create a recruitment matrix  to compare different management strategies.

Random Dynamic stock function and Random trajectories function.

Function Plot_traj_random, which plots the different SSB and profits trajectories with stochastic recruitment

Viability approach

Biological constraint: SSB(t) is maintained above a threshold value B


Economic constraint:  maintaining positive profits for each fleet over time ∏f(t)>0

The co-viability probability  of the fishery under a statu quo scenario with random recruitment:

Modified "plot trajecotries random" function to display the viability thresholds.

Updated on 24/08/2016