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We conducted a mark-recapture study of California sea lions ( Zalophus californianus) using pups branded on San Miguel Island, California, from 1987 to 2014, and annual resightings from 1990 to 2015. We used the Burnham model (Burnham 1993), an extension of the Cormack-Jolly-Seber mark-recapture model, which includes recoveries of dead animals, to analyze age, sex, and annual patterns in survival. Generally, females had higher survival than males. For female pups, the average annual survival was 0.600 and for male pups it was 0.574. Yearling survival was 0.758 and 0.757 for females and males, respectively. Peak annual survival was at age 5 and was 0.952 for females and 0.931 for males. Pups with larger mass at branding had higher survival as pups and yearlings, but the effect was relative within each cohort because of large between-cohort variability in survival. Annual variability in sea surface temperature ( SST) affected survival. For each 1°C increase in SST, the odds of survival decreased by nearly 50% for pups and yearlings; negative SST anomalies yielded higher survival. Annual variation in male survival was partly explained by leptospirosis outbreaks. Our study provides a unique view of one demographic parameter that contributed to the successful recovery of the California sea lion population. [ABSTRACT FROM AUTHOR]

We conducted a 15 yr mark-resight study of branded California sea lions ( Zalophus californianus) at San Miguel Island, California, to estimate age-specific recruitment and natality of the population. We used the Schwarz and Stobo model to estimate sighting, survival, recruitment, timing of births, abundance, and age-specific natality from sighting histories of 1,276 parous females. The advantage of this approach was that the reproductive status of females did not have to be known for all females of reproductive age. Probability of recruitment into the reproductive population began at age 3 or 4, peaked between ages 5 and 7, and slowly declined. Age-specific natality was similar for ages 4-16 but declined after age 17, suggesting that reproductive senescence occurs in older females. The average annual natality for parous females 4-16 yr of age was 0.77 (SE = 0.03); natality declined to 0.56 (SE = 0.10) for parous females 17-21 yr of age. Natality for both age classes was reduced during El Niño conditions by 24% and 34%, respectively. In addition to reducing natality, El Niño events may result in a delay of recruitment if females experience El Niño conditions before they turn 4 yr of age. [ABSTRACT FROM AUTHOR]