An evaluation of implementing long-term MSY in ecosystem-based fisheries management: Incorporating trophic interaction, bycatch and uncertainty

Maximum sustainable yield (MSY), often defined in relation to a single species considered in isolation, has long been considered a cornerstone in fisheries management. It is difficult to expand the concept of MSY for the purpose of ecosystem-based fisheries management (EBFM). Here we consider MSY for a fishery in a multispecies fish community by addressing issues of trophic interaction and bycatch, along with parameter uncertainty. A size-spectrum model, which fully considers trophic interactions within the fish community, was used for simulating various fisheries scenarios including a single species fishery, a multispecies stow-net fishery, and a multispecies trawl fishery. Population biomasses, yields, and ecological indicators were used to assess the dynamics of the fishery and fish community status. The single species fishery with no bycatch resulted in a low impact on non-target stocks, but led to the collapse of the target stock at low fishing mortality rates. The stow-net and trawl fisheries had broader ecosystem impacts, but allowed target stocks to be fished at much higher fishing mortality rates with higher yields. Ecological indicators were related non-linearly to fishing mortality, possibly diminishing their effectiveness as management tools. Background resource carrying capacity was found to be a greater source of uncertainty than reproductive efficiency. This study demonstrates that bycatch mortality can play an important role in trophic interactions likely via predation release and depensation, and thus influence the resilience of fisheries to fishing pressure. The study indicates that the combination of mixed fisheries and multispecies effects lead to complex fish community dynamics that may present additional challenges for fisheries management.