Fine-scale site fidelity in California sea lions, Zalophus californianus, in the colony at Los Islotes, La Paz Bay, Mexico

Abstract

Fine-scale site fidelity in polygynous pinnipeds influences individual interactions, social stability, and gene flow; over time, demographic processes may be altered, and local extinction of some colonies may occur. The goal of this study was to evaluate fine-scale site fidelity as it relates to reproductive success of California sea lion, Zalophus californianus, adult females at 3 different reproductive sites in the Los Islotes rookery in La Paz Bay, Baja California Sur, Mexico. Reproductive history data for 5 cohorts of California sea lions marked as pups between 1980 and 1984 were used to estimate the individual fine-scale site fidelity index and the return rate. A Pearson correlation was used to evaluate whether there was a relationship between site fidelity and reproductive success (number of pups that a female had during the stud period) during the 9-yr study period, and a chi-square test was used to compare reproductive success between sites. Adult female California sea lions showed high site fidelity to the colony, with the majority showing site fidelity values >40%; sites A and B had high return rates, whereas site C was the least preferred. There was no significant difference in the relationship between the fine-scale site fidelity index and reproductive success, or in reproductive success between sites. The high degree of fine-scale site fidelity apparently has not had negative effects on this colony, as evidenced by the significant increase in population size over the last 3 decades and the relatively high reproductive rates.