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Whale sharks form seasonal feeding aggregations at particular coral reef locations (Colman 1997) that are critical to the life cycle of this vulnerable species. Our year-round observations at Christmas Island (10 30′ S, 105 40′ E) from 1996–2008 revealed that whale sharks aggregate in summer (> 90% observed between December and March). During the 2007–2008 summer aggregation (November 28–April 30), we used under-and above-water observations to estimate total length (TL; to nearest 0.25 m) and the presence of people or boats alongside the shark was used as a reference. Photographs also confirmed length estimates. All observed individuals were probably juveniles (mean TL= 4.60 m; range= 2.5–8 m; n= 82), given maturation occurs over 9 m (Colman 1997). Swimming under the sharks and searching for claspers indicated a sex ratio of 1: 3.3 male: female (n= 13), although male biased sex ratios …