Risks and benefits of catching pretty good yield in multispecies mixed fisheries

Multispecies mixed fisheries catch ecologically interacting species with the same gears at the same time. We used an ensemble of size-based multispecies models to investigate the effects of different rates of fishing mortality (F) and fleet configurations on yield, biomass, risk of collapse and community structure. Maximum sustainable yield (MSY) and F-MSY for 21 modelled species' populations in the North Sea were defined at the Nash equilibrium, where any independent change in F for any species would not increase that species' MSY. Fishing mortality ranges leading to Pretty Good Yield (F-PGY), by species, were defined as ranges yielding >= 0.95 x MSY. Weight and value of yield from the entire fishery increased marginally when all species were fished at the upper end of F-PGY ranges rather than at FMSY, but risk of species' collapse and missing community targets also increased substantially. All risks fell markedly when fishing at the lower end of F-PGY ranges, but with small impacts on total fishery yield or value. While fishing anywhere within F-PGY ranges gives managers flexibility to manage trade-offs in multispecies mixed fisheries, our results suggest high long-term yields and disproportionately lower risks of stock collapse are achieved when F <= FMSY for all component stocks.