Improving Estimates of Recruitment Strength in Stock Assessments Via a Biophysical Modeling Framework

Fishery stock assessment is predicated on an understanding of the relationship between spawning stock and numbers of recruits to a population – a relationship which is poorly described for most species.  Advances in hydrodynamic modeling and larval ecology now give us new insights into how environmental processes drive recruitment strength.  A comprehensive biophysical modeling approach, the Connectivity Modeling System, was used to model recruitment events of red snapper Lutjanus campechanus and gag grouper Mycteroperca microlepis in the Gulf of Mexico.  This approach estimates expected annual recruitment strength due the interaction of physical oceanographic factors (GoM-HYCOM 1/25^o for years 2003 – 2013) with biological traits (spawning schedule, larval competency period and vertical swimming behavior).  These estimates were found to concur with predicted anomalies from the stock-recruitment relationship for the 2012 red snapper and 2013 gag grouper stock assessments.  Furthermore, stock assessment model fits were improved after the incorporation of these independent estimates of recruitment anomalies.   Because new cohorts are not observed in the fishery data until they are several years old, and thus the most recent years of recruitment are typically poorly estimated, incorporating these recruitment anomaly indices also has the effect of reducing stock management uncertainty in the near term.