Why is mortality so high among young clupeiform fishes?

Young clupeiform fishes experience high mortality rates—often exceeding 99 percent—due to a combination of biological and environmental factors during their early life stages.1

The primary causes of this high mortality include:

• Predation: Larvae and juveniles are frequently consumed by larger fish, birds, comb jellies (ctenophores), and arrowworms (chaetognathans).1
• Environmental Displacement: Young fish are often carried by currents out of sheltered bays and into areas that lack the proper food sources required for their survival.1
• Habitat Requirements: For certain species, such as the Tanganyika sardine, failure to maintain vertical positioning within oxygenated water layers can be fatal.1

To compensate for these significant losses, clupeiforms have evolved high fecundity, early sexual maturity, and "repeated portion" spawning, which ensure that enough individuals survive to maintain the population.12