Achieving fishery MEY may result in a reduction in net economic returns in a broader sense if the loss to consumers exceeds the gain to the industry. Such a loss may occur if supplies to the local market are reduced and prices paid by consumers increase. This results in a transfer of benefits from consumers to producers, which is considered undesirable in itself. However, if the loss to consumers is greater than the gain to producers then overall there is a loss of net economic returns. Similarly, the disutility associated
with bycatch in fisheries may also affect our interpretation of “optimal” yields if non‐monetary values are assigned. The “generic” multispecies bioeconomic model was used to estimate the impact on target fishing mortality rates of broadening the consideration of net economic returns to include also changes in consumer surplus and inclusion of non‐market values associated with bycatch. The model is run stochastically while maximising profit but varying the number of species caught, their biological characteristics and prices, fishing costs, price flexibilities, bycatch rates and values.

The results of the analysis were largely as expect, namely that including consumer benefits into the definition of MEY resulted in a higher optimal level of fishing effort and yield, while including non‐market costs associated with discards resulted in a lower optimal level of fishing effort and yield. The degree to which these factors affected the definition of MEY was, unsurprisingly, related to their overall magnitude relative to the benefits to the fishery.

Implementing MEY, once identified, also has several challenges. The study considered a range of harvest control rules, as well as other potential management options. The results of the model analysis suggest that “hockey‐stick” harvest control rules in multispecies fisheries may overly restrict the catch of species that are currently above their target biomass. Given the higher abundance, catch of these species is likely to result in increased discarding and lower economic returns than might otherwise be achieved. An alternative harvest control rule that allowed higher than “optimal” fishing mortality rates for species that were above their target biomass resulted in less discarding and higher economic returns.

Having quota on too many species may be counterproductive, as the fishery is largely constrained by the quota for the main species. Imposing quotas also on secondary species can result in a situation where a minor species becomes a “choke” species, restricting the total fishery for little benefit. Reducing the number of species subject to quota constraints to only those that were most important (in terms of revenue) resulted in improved economic performance of the fishery as well as lower levels of discarding. However, in the model changes in targeting ability of the fleet was not considered, so monitoring of fisher behaviour in response to proposed management regimes that only have a few species under quota would
be essential.