Growing in the Flow: Modeling Circulation, Production, and Early Life History Ecology to Develop Recruitment Indices for Rockfishes

Recruitment variability to populations of winter-spawning rockfish derives primarily from highly variable survival through the larval stage, presumably as a consequence of environmental and ecological conditions affecting early life history stages.  We have developed a modeling framework in which (1) a coupled bio-physical model (CBPM) of the coastal ocean is forced with observed environmental conditions to simulate cross-shelf circulation and dynamics of the planktonic ecosystem during the winter-spring parturition season of rockfishes, and (2) an individual-based model (IBM) for larval and juvenile rockfish is used to simulate larval growth and potential survival as a function of conditions experienced by larvae entering the plankton over the course of the parturition season and across the continental shelf from near the coast to the shelf-break.  The CPBM is implemented in the Regional Ocean Modeling System (ROMS) as a 2-D cross-shelf slice of the coastal ocean forced with observed time series of environmental conditions for the period from 1983 to 2010.  Predictions of recruitment success are obtained by integrating the joint probability of (1) survival conditional on birth date, and (2) entering the plankton on a given date and at a given location, where the latter is based on the distribution of spawning over time and the distribution of adult habitat.   Simulated growth trajectories compare favorably to growth inferred from micro-increment analysis of otoliths from pelagic juvenile  rockfishes.  Moreover, time series of recruitment indices derived from the CBPM-IBM exhibit strong coherence with time series of recruitments estimated in stock assessments for several rockfish species.  Results from this work demonstrate the potential for IBMs to serve as useful tools for understanding recruitment dynamics in west coast rockfishes and motivate the incorporation of realistic IBMs for rockfish early life history stages into existing three-dimensional particle-tracking ocean circulation models currently used to explore dispersal and connectivity.