Long-distance Movement of a Pinniped Neonate

Understanding long-distance dispersal patterns for wide-ranging species is critical to developing effective conservation strategies (Lockwood et al. 2002, Shanks et al. 2003, Gerber et al. 2005, Figueira and Crowder 2006). California sea lions (Zalophus californianus) in the Gulf of California (GoC) are thought to include distinct populations based on limited dispersal and resulting genetic population structure (Schramm-Urrutia 2002). Comparisons of mitochondrial DNA collected from pups located on seven GoC rookeries suggest three distinct populations occur within the GoC (Schramm-Urrutia 2002). Although marked 1-yr-old juveniles have been identified on islands far from their natal site (>600 km), these occurrences are uncommon (Hernandez-Camacho 2001). Here, we report a neonate (i.e., a newborn <4 wk old) sea lion traveling >600 km during an 18-d period. Our observation represents the first published report of long-distance neonate movement among pinnipeds. As part of a large-scale study on sea lion behavior and demography on islands in the GoC, we marked newborns with unique codes shaved into their back pelage at three rookeries (Fig. 1). On 25 June 2006, a male pup with a fresh umbilical cord (pup weight: 8.5 kg, length: 79.8 cm) was marked at Los Islotes Island (Fig. 1). This pup was not observed at Los Islotes again for the duration of the field season (field dates: 17–25 June, 7–15 July, 5–13 August 2006) but was next observed on 14 July 2006 on Granito Island, >600 km north of Los Islotes (Fig. 1). It is unlikely the neonate swam this distance on its own. Although the female was unmarked, we believe the pup traveled with its mother because the pup was observed nursing at Granito Island and alloparental care is rare in otariids (Boness 1990, Georges et al. 1999).