ALTERNATIVE REPRODUCTIVE TACTICS IN ATLANTIC SALMON - FACTORS AFFECTING MATURE PARR SUCCESS

In Atlantic salmon, as in most salmonids, males can mature early in th e life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full-size adults. The alternative lif e histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affect s the individual's state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to un derstand not only the relative contribution of the different male type s to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the result s of a study designed to investigate the factors that affect the repro ductive success of mature parr. We used highly polymorphic minisatelli te DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40%, with individu al parr fertilizing up to 26% of the eggs. A strong positive correlati on was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reprod uctive success are discussed in relation to the evolution of male mati ng strategies and life history in salmonids.