| Summary: | Mating systems have received insufficient attention for their relationship with population dynamics and conservation biology. This is particularly true for marine fishes, many of which have recently experienced unprecedented declines. My research explored causes and consequences of variation in the mating system of Atlantic cod (Gadus morhua), a species that has been severely over-exploited and is currently at historic population lows. Using captive groups of Atlantic cod, I examined male reproductive success in relation to morphology, condition, and spawning behaviour. I found that number of offspring sired was highly variable among males and there was a positive association between reproductive success and male body size, as well as aggression. I also investigated the function of Atlantic cod sound production by quantifying individual variation in mass of the sound-producing musculature and temporal patterns and behavioural contexts of sound production. Males had drumming muscles larger than females and that increased in mass before spawning and declined thereafter. Drumming muscle mass of spawning males showed positive associations with body size, condition, and fertilisation potential, indicating that sound production may reveal information about male quality. Sound production occurred most frequently during the peak of the spawning season and was associated with agonistic interactions and courtship. These findings suggest that male sound production relates to mate competition. Slow recovery rates and continuing declines of Atlantic cod populations may be attributable to depensation. Using egg fertilisation and male abundance data from captive groups, I explored the basis of reduced mating success as a potential cause of depensation and found that as population size declines, fertilisation rate also declines and variance in fertilisation rate may increase. The former identifies a potential mechanism for depensation in cod and the latter has negative consequences for effective population size. My results have important implications for conservation of marine fishes, particularly those with mating systems similar to Atlantic cod. There is a need to incorporate knowledge of mating systems in population assessments, to undertake research on spatial and temporal scales of reproduction, and to initiate experiments to test hypotheses about marine fish mating systems, depensation, and correlates of individual reproductive success. Thesis (Ph.D.)--Dalhousie University (Canada), 2004.
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