Recruitment Variability of Largemouth Bass Along Environmental Gradients in the Sacramento – San Joaquin Delta

Largemouth bass is the dominant nearshore piscivore in Sacramento-San Joaquin Delta and supports a world-renowned recreational fishery.  It is abundant in a variety of habitats ranging from upstream freshwater regions of the system to downstream brackish marshes.  In heterogeneous systems such as this which support isolated populations of largemouth bass, distinct factors can affect recruitment across environmental gradients.  We recently started a project designed to determine the factors affecting largemouth bass recruitment by studying isolated populations of age-0 fish in flooded island habitats along the freshwater-estuarine gradient.  In our first year of study in 2010, we intensively sampled from summer through the onset of winter.  We are in the process of examining variability in abundances, hatch dates, growth rates, diets, and a variety of health and condition metrics in age-0 largemouth bass across the populations.  Results to date indicate that there is indeed variability in several traits among the isolated populations, and that recruitment success is probably context-dependent and affected by multiple unique factors.