Annual re-sightings of photographically identified white sharks (Carcharodon carcharias) at an eastern Pacific aggregation site (Guadalupe Island, Mexico)

摘要

A systematic, reliable method for identifying white sharks, Carcharodon carcharias Linnaeus, from underwater photographs was developed and applied to examine site fidelity at Guadalupe Island, Mexico (29°N, 118°W). The most reliable features for repeat identification in multiple years were the pigment patterns on the gill flaps, pelvic fins, and caudal fins. Pigment patterns in all three regions were asymmetrical on the right and left sides making it necessary to photograph both sides to catalog each individual. However, once cataloged, an individual could be re-identified using a partial body image. Using this method, 73 individuals were identified between 2001 and 2005. Site fidelity was indicated through repeated annual sightings of individuals with 78% of the identified sharks observed over at least 2 years. Males were found to arrive at Guadalupe Island as early as July and females in September. Peak abundances at the site occurred August-December. The sex ratio was not significantly different from unity in 2002, 2004, and 2005. This monitoring technique has shown Guadalupe Island to be an important white shark aggregation site in the eastern Pacific.