Spatial and temporal distribution, haulout use and movement patterns of Steller sea lions (eumetopias jubatus) in northern California

I describe the spatial and temporal distribution, abundance and habitat use of Steller sea lions (Eumetopias jubatus) in northern California between 2006 and 2011 obtained through shore and at-sea surveys and by tracking branded individuals. Understanding Steller sea lion habitat use is critical in designing and implementing nearshore management initiatives such as the Marine Life Protection Act (MPLA) initiative. The MLPA initiative process began in northern California in 2009, affecting areas offshore of Mendocino, Humboldt and Del Norte counties. Between the Oregon border and Trinidad, California (Humboldt County) there is one rookery (Southwest Seal Rock) and eight non-breeding haulouts. Steller sea lions are more abundant on haulouts in northern California during the late spring and summer months than during the rest of the year. When Steller sea lions are numerous in the area, their distribution is influenced by age/sex class and breeding status. Adult males were seen more frequently on in-shore haulouts in both Trinidad and Crescent City, CA in late spring/early summer suggesting that these haulouts serve as staging areas for breeding or near-breeding aged bulls (Otter Rock mean = 7 ± 1, Sea Lion Rock mean = 4 ± 2, Castle Rock mean = 16 ± 5). Breeding Steller sea lion abundance peaked at Southwest Seal Rock during the June and July pupping and breeding season (mean = 574 ± 38). Presence of pups peaked at haulouts in Trinidad the late summer/early fall suggesting that these sites serve as "nurseries" for females and their dependent young (Otter Rock mean = 5 ± 2, Turtle Rocks mean = 6.3 ± 3). Steller sea lion pups were branded on Southwest Seal Rock in 2002 and 2004 by Oregon Department of Fish and Wildlife (ODFW) and National Marine Mammal Lab (NMML) as part of a larger population dynamics study. Females from these cohorts are now actively breeding in northern California, while fewer branded males have come back to the rookery during breeding season (49 females vs. 18 males). Resights of branded females were more common than males. Of the 62 branded animals that were seen in more than one year during the study period, 73% were female. Male Steller sea lions tended to be resighted farther from the natal site than females. Steller sea lions frequented many haulouts during a single year and females, in particular, showed fidelity to the northern California and southern Oregon near shore waters.