Maternal effects and egg size in fishes: general patterns and the influence of system size
The need to protect size and age structures from selective harvest in order to maintain sustainable fish stocks has been emphasized in recent literature. The Big Old Fat Fecund Female Fish (BOFFFF) hypothesis has been influential in discussions of changing stock management strategies, and postulates that larger, older females have a disproportionate input into stock recruitment due to physiological advantages. In this study, we utilize a meta-analysis approach to test the assumption of the BOFFFF hypothesis, that larger female fish produce larger eggs and more viable offspring, at a broad scale. Following the meta-analyses, we assess whether larger females from a subset of studies use their gonadal investment more efficiently than small females. From our meta-analyses, we found positive, significant intraspecific relationships between female size and egg size. Moreover, we found positive associations between egg size and offspring viability (offspring size and survival). However, we found in a subset of studies that although proportional survival of offspring often increases with egg size, females that produced larger eggs yielded fewer surviving offspring per unit gonadal investment. This reduced efficiency in reproductive investment is a product of the trade-off between egg size and fecundity. We conclude that although larger females may appear to produce more viable individual offspring, their input to stock recruitment, according to total stock gonadal biomass, may not be disproportionate, as stated by the BOFFFF hypothesis. However, we did not account for whether the benefits of maternal effects extend beyond the larval stage.
The theory of optimal egg size implies that fish trade off between fecundity and individual gonad investment according to their environment. Past interspecific studies suggest that in general, fishes in large, marine systems produce smaller eggs than those in small, freshwater systems. This study aims to compare egg size intraspecifically among small and large systems. In particular, we focus on populations from the Laurentian Great Lakes, which exhibit similar broadscale physical processes as marine systems, and smaller inland lakes (<1,000 ha), whose ecosystems contain many of the same species. In 2018 and 2019, we collected egg samples from spawning walleye (Sander vitreus) and yellow perch (Perca flavescens) in both inland lake and Great Lake populations. From each female, we recorded total lengths, and measured average diameters of ten eggs. Using ANCOVA models, we compared mean length-adjusted egg diameters intraspecifically among populations of both species. For both walleye and yellow perch, we found that females from inland lakes produced larger mean length-adjusted egg diameters than those of the Great Lakes. This pattern was particularly evident for yellow perch, whereas for walleye the pattern was relatively weak, potentially due to stocking eroding population-specific selection for egg size. These intraspecific patterns are consistent with cross-system interspecific variation in fish egg size.