Balancing Variations in Growth and Mortality in Understanding S/R Dynamics

First order approximations reveal that slight (10%) variations in average growth or mortality rates have the potential to result in the levels of recruitment variability that are commonly reported for commercial fish stocks.  Growth rates can be reliably measured based on otolith microstructure but findings links with variations in food availability have been variable.  Measurements of mortality rates have been a greater challenge and determining what ecosystem elements may be the primary drivers has proven difficult.  To fully understand the role of variations in each vital rate on the ability to forecast changes in stock recruitment relations, a sensitivity assessment needs to be based on what we know from previous observations about their level of variability, the inherent uncertainty in their estimation, and knowledge about the inherent variability of key elements (prey and predator, temperature) that regulate them.  Here, I will present a synthesis of the current knowledge of these three features of vital rates and the environmental variables that may act as primary drivers in order to gain a greater appreciation for their potential importance in driving variability in stock-recruitment relationships around a “stable state” and in shifting them from one state to the next.