Direct and indirect community effects of rebuilding plans

Many fish communities are heavily exploited and rebuilding plans need to be implemented for depleted species. Within an ecosystem approach to management, development of rebuilding plans should include consideration of the expected consequences of the rebuilding of the target species on the rest of the marine community. Using size- and trait-based single-species and community models, a general assessment is made of the direct and indirect ecological consequences of a rebuilding plan based on a reduction in fishing mortality. If fishing mortality is sufficiently reduced, the time-scale of rebuilding is in the order of the time to reach maturation of an individual, and the expected trajectory can be reliably predicted by a single-species model. Indirect effects of increased abundance are a decrease in individuals in the trophic levels above and below the target species. The decrease in biomass of the neighbouring trophic levels is expected to be much smaller than the increase in the target species and to be largest in species on the trophic level above. We discuss which effects could be responsible when a rebuilding plan does not result in the expected increase and how our results could be applied in a practical management situation.