Revisiting Size Selective Mortality in Young Fish: Do Small Teleosts Really Pay a Cost?

Small juvenile and larval teleosts are typically more susceptible to starvation and predation, so the largest individuals tend to survive. However, most support for this ‘bigger is better’ hypothesis is experimental and struggles to account for natural variation. To assess how natural populations experience size-selective mortality, we reviewed the past 30 years of literature on the subject while compiling longitudinal survival data, which evaluates selection against size classes, to test for evidence that ‘bigger is better’. Our meta-analysis shows that the effect of body size on survival is consistently weak across species, populations, times, and locations. We discuss several reasons why larger young teleosts may not have a distinct survival advantage. We recommend that mortality not be treated as constant across young teleost size classes, as different ecological conditions may favour smaller, larger, or neither size class. We suggest several research areas are underexplored and could change how we think about the relationship between young teleost size and survival. Investigating these drivers will be important as temperatures rapidly rise, altering size attained in wild fish.