# Co-viability Diagnostic

Description of the co-viability framework.

Two sets of constraints define the viability of the fishery:

• the first set of constraints relates to the population viability of the three species
• the second set of constraints relates to the economic viability of each individual sub-fleet.

Population Viability  is defined as the requirement that the Spawning Stock Biomass of each individual species is maintained above a threshold value. . The constraint is specified as:

${\mathsf{SSB}}_{s}\left(t\right)\ge {B}_{s}^{\mathsf{pa}},\phantom{\rule{1em}{0ex}}s=1,2,3.$The Economic Viability constraint consists in maintaining positive profits for the sub-fleets over time :${\pi }_{f}\left(t\right)>0,\phantom{\rule{1em}{0ex}}f=1,\dots ,16.$

Co-Viability Analysis (CVA) of the fishery seeks to assess whether a management strategy allows for both sets of constraints to be observed simultaneously. The ecological and economic viability constraints characterize an acceptable sub-region of the phase space within which the fishery evolves. A particular trajectory followed by the fishery will be called viable if it remains in this region during the prescribed period of time, with a sufficiently high probability.
Management strategies rely on different combinations of effort multipliers uf. Projections are computed over twenty years (T = 2028) starting from the initial stock abundances Ns,a(t0) at year t0 = 2008.

Updated on 23/08/2016