Sagitta elegans arctica of the Canadian eastern Arctic waters has a life span of two years. Its breeding cycle is two-phase, or alternating, and the population consists of two distinct groups breeding in different years. The spawning period is long, extending from July into the winter, probably up to February. Winter spawning is taken to imply that the breeding behaviour is not timed to coincide with the maximum abundance of food, but that the cycle is determined by the growth limitations imposed by the low temperature....