Longitudinal changes and consistency in male physical and behavioural traits have implications for mating success in the grey seal (Halichoerus grypus)

We examined age-related changes and consistency in physical and behavioural traits of 20 male grey seals (Halichoerus grypus (Fabricius, 1791)) and implications for a proxy of mating success (number of oestrous females attended) over four successive breeding seasons on Sable Island, Canada. Across the study, young males (10-15 years) gained body mass, while old males (23-31 years) lost body mass. Body length was an important determinant of tenure (time spent at a site among females) and males of all ages exhibited a high level of consistency in duration of tenure (r = 0.40-0.50). In young males, our proxy of success showed a strong relationship with arrival body mass and also exhibited a high level of consistency (r = 0.50). None of the physical traits measured explained variation in success by exhibiting mating tactics that did not involve tenure, which is likely due to the opportunistic nature of those tactics. Whereas young male grey seals exhibited age-dependent improvements in success owing to changes in their physical state, later in life physical traits were less influential and suggest that nonphysical traits may compensate for a deteriorating physical state and its impact on male success.