Causes of mortality in young jack mackerel

Abstract

Field and laboratory experiments were conducted with the purpose of partitioning jack mackerel Trachurus symrnehicus larval mortality into portions due to starvation and to predation. Field collections were made to determine larval condition, growth, net retention and production; laboratory experiments were conducted to determine growth and body shrinkage due to preservation treatment. Age-specific starvation and total mortality rates were estimated and predation was inferred as the difference between the two. In the offshore oligotrophic part of the spawning habitat, larvae suffered a high rate of mortality which rapidly declined as they developed. Predation was the major source of mortality of yolk-sac larvae. As the yolks were absorbed and the larvae began to feed, starvation became a significant source of mortality. As the larvae further developed, starvation rapidly declined and predation again became the dominant source of mortality, although at a much lower rate.