Long-term mating tactics in an aquatic-mating pinniped, the bearded seal, Erignathus barbatus

Abstract

Studies of aquatic mating tactics in long-lived mammals are rare because of the difficulties involved in gaining repeated information on individuals over multiple years. We used acoustic array recordings as a tool for studying the mating tactics of bearded seals over 16 years off Point Barrow, Alaska. Males produce underwater vocalizations during the mating season that show clear individual differences. The most commonly used trill types, AL4 and AL1i, were analysed over 6 years (1985–1986, 1992–1993, 2000–2001). For each vocalization, we measured 17 parameters and determined an X , Y location through cross-correlation analysis. Classification trees showed that 100 individuals were present over the study period (22–40 males per year). Individuals showed clear site fidelity with 13–25 males returning over consecutive years. Six males were present over the entire 16-year period. Kernel home ranges were 0.32–3.2 km 2 for 34 territorial males and 5.3–16.3 km 2 for 66 roaming males. Throughout this study all but two males used the same mating tactic. When these males switched tactic (from territorial to roaming), the duration of their calls also changed, while all other acoustic variables remained constant. The vocal parameters for all the other males remained stable throughout their tenure. It appears therefore that although males can alter their mating tactics as circumstances change, only a few do so. Instead mating tactics tend to show long-term stability in vocal characteristics, strong site fidelity and periods of tenure that cover a significant proportion of the male's adult life span.