Date of Award

Fall 2002

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

Michelle P Scott


Quantitative information is lacking about how fur seals use habitat and how this use influences fitness. Such information is important for understanding the prospects for recovery of declining populations like those of South American fur seals (Arctocephalus australis) in Peru. In this study I examined the influences of habitat features and human disturbance on selection of breeding habitat by female fur seals in Peru; and I examined how mortality of pups was influenced by habitat features, female behavior, and the social environment on the beach.

Arctocephalus australis in Peru have declined gradually over the past decade, and declined dramatically (72%) due to low food availability during the severe El Nino in 1997--98. Pup mortality has been greater for fur seals in Peru than in other populations of fur seals due to pups becoming injured or separated from their mother when high densities of aggressive females move to limited water-access sites to avoid overheating. In 1999, the seals abandoned some historically important breeding beaches, and did not colonize new beaches.

I found that currently used breeding beaches were less likely to have human disturbance and more likely to have offshore islands, stacked rocks, tide pools, and abundant shade than abandoned or unused beaches. At low population numbers, females seemed to select habitat that maximized thermoregulation and minimized disturbance, but was detrimental to survival of pups.

Pup mortality remained high (20--46%) following the population decline, despite population densities one third those prior to the decline. Pup mortality was greater at rugged, rocky beaches exposed to heavy surf than at flat, open beaches with abundant tide pools. Females whose pups survived for ≥20 days spent less time exposed to heavy surf and suckling a yearling, and more time suckling their pup than females whose pups died. High percentages (23--52%) of females continued to suckle yearlings, possibly stemming from low food availability.

Birth sites and thermoregulatory sites were farther apart at the rugged beach than at the flat beach. This separation was associated with higher rates of movement and pup mortality. Population density did not differ between the two beaches (∼0.3--0.4 females/m2).