Food Availability Shapes Recruitment and Survival in a Population of Marine Fish

Many marine fish populations exhibit dramatic fluctuations in rates of recruitment and survival of young over time.  As a result, the fit of basic stock-recruit models are notoriously poor for most marine fish populations.  While substantial variation in these rates can potentially be explained using ecological or environmental indices, many such environment-recruitment relationships fail under reexamination.  To avoid spurious correlations that can lead to both erroneous understanding of population dynamics and poor management decisions, it is essential to incorporate variables that directly drive variation in recruitment and survival of marine fish.  We used data from long-term surveys on Santa Cruz Island, CA of black surfperch (Embiotoca jacksoni), their foraging habitat and their food availability to test whether food (known from experiments to influence adult densities) drives variation in recruitment and survival of young.  Surfperch provide a model system for studying the influence of extrinsic factors on demographic rates and populations of fish.  Surfperch are largely unexploited, well studied, have extremely low emigration and immigration rates, produce live young that are locally re­tained, and are known to be dependent upon a local food supply of small benthic invertebrates that occupy specific macroalgal habitats.  By incorporating in models the amount of food available (a) to mature adults (age 2+) when becoming pregnant and (b) to young-of-the-year (age 0), we substantially improved both Ricker and Beverton-Holt model fits.  Survival of young-of-the-year to subadults (age 1) also showed dramatic dependence upon food available to young-of-the-year fish.  These results show that the availability of food to fish in previous years can explain substantial variation in the abundance of subadults.  Thus, in a system where both the density of food within foraging habitat patches and the availability of foraging habitat fluctuate, the dependence of recruitment and survival upon this resource appears to drive the observed high frequency of low young-of-the-year and subadult densities. We conclude that patterns of food availability in previous years can provide an excellent metric for predicting years of poor recruitment and survival and help explain why extended periods of low population abundances persist.