The Influence of Maternal Age upon Fishery Harvest Reference Points

Maternal effects, defined here as the reduction of larval viability with reduced spawner age, have been proposed as a feature of marine populations that motivate the conservation of age and size structure, and have been observed in both Atlantic cod (Gadus morhua) and Pacific rockfish (Sebastes spp.) stocks.  In this study, we simulated “cod-like” and “rockfish-like” populations to explore how estimates of management reference points such as F_msy  (the F level associated with maximum sustained yield) and F_crash (the F level where equilibrium yield is reduced to zero) may be affected by life-history pattern, recruitment variability, exploitation, and environmental variability.  In these simulations, larval survival was dependent upon spawner age, and estimates of F_msy and F_crash were made using either total larvae (proportional to eggs and spawning stock biomass) or viable larvae (i.e., larvae remaining after mortality dependent upon spawner age is applied) as measures of reproductive output.  Over a range of harvest rates and levels of recruitment autocorrelation for each life-history type, estimates of F_msy obtained when using total larvae were similar to those obtained when using viable larvae.  However, estimates of F_crash obtained when using total larvae were larger than those obtained when using viable larvae because of the greater truncation of age structure and reduction in larval survival rates associated with the high fishing mortalities of F_crash.  These results suggest that the potential for biased estimates of stock productivity when maternal effects are not recognized is most pronounced at high fishing mortality rates, and further reinforces the desirability of maintaining harvest rates at or below F_msy.