Abstract: Globally, decision makers are seeking management levers that can mitigate the effects of climate change on ecosystem that have already been transformed from their natural state by the effects of fishing. There is particular interest in whether marine reserves can provide buffering (i.e., population-level resilience) against climate disturbances to fished populations. Here we examined one aspect of this question, by asking whether marine reserves could reduce the variability in either overall recruitment or in fishery yield, in the face of environmental variability. This could happen because greater reproduction of longer-lived, larger fish inside reserves could supplement recruitment to the fished portion of the population. We addressed this question using age-structured population models, assuming a system where some proportion of the coastline is protected in marine reserves (0-30%), and the remainder is fished. We simulated population dynamics with variability in the survival of the first age class, because recent extreme climate events (e.g., marine heatwaves) have reduced juvenile survival for some fish species. We examined buffering in terms of population variability, measured as the proportion of time a simulated population spent below a target reference point, with the idea that marine reserves could buffer the fishery against such disturbances. We found that populations with more area in marine reserves always had less variability in recruitment. However, adding marine reserves only reduced variability in fisheries yield when the fished part of the population was being harvested at a rate exceeding the maximum sustainable yield. This new result regarding buffering variability is line with previous findings that the 'spillover' effects of marine reserve benefits to fishery yields only accrue when the fishery outside reserve boundaries is being overharvested.
