Spawning Time and Egg Size of Atlantic Mackerel, Scomber scombrus, in Relation to the Plankton

Abstract

The mean date of peak spawning of Atlantic mackerel (Scomber scombrus) in the southwestern Gulf of St. Lawrence is July 1 ± 1 wk. This coincides with the maximum abundance of the summer plankton. Mackerel eggs average 1.3 mm in diameter at the beginning of the spawning season in June and decrease steadily to 1.1 mm by mid-August. There is a corresponding trend in the mean size of the plankton, which reach a minimum length in midsummer, and a maximum in winter. This recurring size cycle is as important as the seasonal change in plankton biomass in determining the abundance of suitable food organisms for newly hatched larvae. In an evolutionary sense, the observed reproductive characteristics of mackerel ought to be adaptive since the accurate timing of spawning and the progressive decline in egg size will tend to ensure that the parent stock produces larvae of a suitable size and at the correct time, so they encounter an abundant supply of appropriately sized food organisms. Key words: reproduction biology, plankton size composition, larval feeding, adaptive behavior, recruitment