Testing the influence of asymmetrical competition on the survival and growth of age-0 largemouth bass

Timing of hatching has been linked to differences in ontogeny, growth, and survival in largemouth bass, generally attributed to density-independent processes. Differences in relative hatch date allow early-hatched cohorts to have an initial size advantage and longer growing season than later-hatched cohorts, causing greater survival of early-hatched cohorts. Asymmetrical competition may also explain the differences in mortality if early-hatched cohorts depress prey resources available to gape-limited later-hatched cohorts, but still have access to larger, unexploited prey. In the absence of the early-hatched cohort, later-hatched cohorts will either have decreased survival (relative hatch date) or compensate (asymmetrical competition). In 0.40 ha experimental ponds, we removed the early-hatched cohort in half of the ponds to test these predictions. Treatment ponds without the early cohort had greater recruitment than control ponds, suggesting density-dependent processes are regulating recruitment. Since the total number of eggs in each pond was not correlated with recruitment, density-dependent processes appear to only affect the later-hatched cohort, suggesting asymmetrical competition as the key mechanism. Although more plentiful, treatment fish were smaller than control fish and may be subject to greater size-selective mortality, especially overwinter.