Three Yield-Per-Recruit/stock-recruitment approaches (deterministic, stochastic with plotMSY and stochastic with HCS) were used to explore reference points
for the management
of the Iberian sardine. The sensitivity of reference points was
evaluated in relation to alternative scenarios of productivity, growth and selectivity.
Growth and selectivity scenarios had a small impact on stock projections whereas productivity scenarios
were very influential. The three approaches gave coherent results, but the approach using HCS, assuming uncertainty in stock biology and recruitment dynamics, was preferred to derive reference points for sardine. In this
approach, the risks of the stock fa
lling below some low biomass level can also be taken into account. This possibility was considered to be useful in the case of the sardine
for which exploitation at maximum YPR or F0.1 resulted in values above historical
exploitation and higher than Floss,
therefore unsuitable as precautionary management targets.
Bloss (306 thousand t) is proposed as a proxy for Blim but given no indication that
recruitment is impaired below this biomass level, the group considers that the level of
risk of falling below this candidate for Blim acceptable in the evaluation of a management plan should be higher than the standard ICES value (5%).The stock productivity has declined over time; therefore a scenario of low productivity was assumed
(recruitment in the period 1993-2010). Under this productivity scenario, the Fmsy
value for the sardine stock is 0.34, a value associated with a high probability (45%) of
the biomass falling below the proposed Blim and therefore, incompatible with precautionary considerations. The WG proposes an F= 0.27, corresponding to a
Prob(B<Blim)<15% under equilibrium, as the best available candidate for an F management target (proxy for Fmsy) assuming the low productivity scenario (since 1993)
will continue in the future. This F provides high yield
conditional to a low probability
that the biomass falls below Blim=Bloss in equilibrium, thus incorporating precautionary considerations