Increased environmentally driven recruitment variability decreases resilience to fishing and increases uncertainty of recovery

Abstract

Independent of the effects of spawning-stock biomass (SSB), environmental variability in juvenile production, driven by factors such as temperature and food supply, have considerable potential to influence population resilience to fishing and depletion. Here, we analyse 18 time-series of Atlantic cod (Gadus morhua) stocks and empirically estimate this "environmental variability" in recruit-per-spawner (RPS) ratios. We then investigate the role of environmental recruitment variability on population resilience to fishing and ability to recover following depletion. To this end, cod population dynamics are simulated through a period of fishing, followed by a period of recovery, with alternative scenarios of recruitment variability and autocorrelation within it. The major effect of environmental recruitment variability is manifested through uncertainty. Firstly, the higher the recruitment variability, the shorter and less variable the time required for the population to decline below 15% of its carrying capacity, K. Secondly, higher variability leads to higher uncertainty in recovery time. Both these patterns are further strengthened by autocorrelation. Our findings suggest that increased environmental recruitment variability decreases resilience to fishing and increases uncertainty in recovery, thus challenging some traditional views that variability confers high productivity and rapid ability to recover from collapse.