| Summary: | # Male southern elephant seals at Marion Island Elephant seals at subantarctic Marion Island in the south Indian Ocean (46°54'S 37°44'E) have been monitored at an individual (mark-recapture) and population (census counts) level since 1983 (Pistorius, de Bruyn, & Bester, 2011). Almost all pups born at the island were tagged with two livestock tags on the hind flippers every breeding season (austral September-November), with tags containing information about cohort and individual identity. Beaches were surveyed regularly inside (7-day intervals) and outside (10-day intervals) breeding seasons, during which both tagged and untagged individuals were recorded according to age group and breeding state (or social status). For each breeding season, all individuals at the island were tallied on 15 October – the peak haul-out date of this colony (Condy, 1979). The life-history traits of males from the Marion Island population are age- and breeding state-structured; dispersion from the natal colony is relatively low for both pre-breeders (ψ_(a 1-5)^E = 0.05) and breeders (ψ_(a ≥6)^E = 0.14) with approximately half of pre-breeders returning; breeding season detection probabilities are high across years (p = 0.95 ± SD 0.05); and tag loss probabilities are constant for all adult ages (see Lloyd et al., 2020 for details). There is a low level of individual heterogeneity in survival probability between individuals of the same age and breeding state (σ = 0.000017), but larger inter-individual differences in breeding success (i.e., the probability of being dominant; σ = 0.23; Lloyd et al., 2020). Therefore, individual heterogeneity in breeding success is likely prevalent and must be considered when making predictions (Vaupel & Yishiin, 1985; Cam et al., 2002). # Data analysis Only males that had recruited to the breeding population were considered. This provided a dataset of 291 individuals with complete life histories (i.e., birth to ‘apparent’ death [see below]) and 35 individuals with incomplete life histories (i.e., ...
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