Reproductive traits, gonad maturation and spawning of northwest Atlantic herring Clupea harengus harengus L

Analysis of the egg weight and fecundity (egg number) traits of nw Atlantic herring (Clupea harengus harengus L.) reveals that egg weight remains relatively constant among populations whereas the product of egg weight and fecundity (standardized to length) varies among populations. Spring (May-June)-spawning herring mature with less gonad material than do autumn (August-September)-spawning herring. Differences in reproductive effort among populations are shown to be linked to the relative allocation of storage energy to reproductive versus non-reproductive activities during gonad maturation. Spring-spawners, having a lengthy gonad maturation, divert proportionally more energy to non-reproductive activities than do autumn-spawners with a brief gonad maturation. Analysis of herring proximate composition reveals an elaborate system of storage energy accumulation and depletion, the timing of which are specific to spawning season. Storage lipids are the primary energy source for non-reproductive activities during gonad maturation. The amount of lipid depleted therefore determines susceptibility to diversion of storage proteins from gonad to active metabolism. A lipid utilization model developed from principles of fish metabolism predicts levels of lipid depletion during gonad maturation which are consistent with observed values for both spring- and autumn-spawning herring. The known winter distributions of nw Atlantic herring are predicted from the model, with the criterion of minimizing lipid depletion through migration to low temperature habitat. Similarly, the range in latitude of herring spawning, and differences in the latitudinal range of spring and autumn spawnings are shown to be consistent with temperature-dependent energetic constraints during gonad maturation. It is concluded that the population richness of Atlantic herring is linked to the utilization of storage energy during gonad maturation.