Age-specific recruitment and natality of California sea lions at San Miguel Island, California
Article first published online: 29 NOV 2011
2011 by the Society for Marine Mammalogy Published 2011. This article is a US Government work and is in the public domain in the USA.
Marine Mammal Science
Volume 28, Issue 4, pages 751–776, October 2012
How to Cite
Melin, S. R., Laake, J. L., DeLong, R. L. and Siniff, D. B. (2012), Age-specific recruitment and natality of California sea lions at San Miguel Island, California. Marine Mammal Science, 28: 751–776. doi: 10.1111/j.1748-7692.2011.00538.x
- Issue published online: 5 OCT 2012
- Article first published online: 29 NOV 2011
- Received: 1 February 2011 Accepted: 21 August 2011
- birth rate;
- population dynamics;
- reproductive rate;
- sea lion;
- El Niño
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.