An alternative method to estimate the contribution of south coast spawning to west coast sardine recruitment

A small proportion of sardine eggs spawned on the south coast have been shown to be successfully transported in model simulations to a pre-defined west coast nursery area (Miller et al. 2006, Coetzee 2014). All analyses to date that consider this possible contribution of south coast spawning to west coast sardine recruitment, assume that the proportion informed by Miller et al. (2006) equates to the proportion of south coast spawner biomass (Bsp) that forms part of the west coast “effective spawner biomass”, where stock-recruitment relationships assume recruitment is related to the effective Bsp. In contrast, this document considers the proportion informed by Miller et al. (2006) to equate to the proportion of recruitment resulting from south coast spawning that subsequently moves to and forms part of the west coast recruitment as observed by the time of the May recruit surveys.