Although the whale shark Rhincodon typus is the largest extant fish, it was not described until 1828 and by 1986 there were only 320 records of this species. Since then, growth in tourism and marine recreation globally has lead to a significant increase in the number of sightings and several areas with annual occurrences have been identified, spurring a surge of research on the species. Simultaneously, there was a great expansion in targeted R. typus fisheries to supply the Asian restaurant trade, as well as a largely un-quantified by-catch of the species in purse-seine tuna fisheries. Currently R. typus is listed by the IUCN as vulnerable, due mainly to the effects of targeted fishing in two areas. Photo-identification has shown that R. typus form seasonal size and sex segregated feeding aggregations and that a large proportion of fish in these aggregations are philopatric in the broadest sense, tending to return to, or remain near, a particular site. Somewhat conversely, satellite tracking studies have shown that fish from these aggregations can migrate at ocean-basin scales and genetic studies have, to date, found little graphic differentiation globally. Conservation approaches are now informed by observational and environmental studies that have provided insight into the feeding habits of the species and its preferred habitats. Notwithstanding these advances, there remain notable gaps in the knowledge of this species particularly with respect to the life history of neonates and adults who are not found in the feeding aggregations.

Abstract. In coastal waters of several locations globally, whale sharks (Rhincodon typus) form seasonal aggregations, most of which largely comprise juvenile males of 4-8 m length. Evaluation of the period that individuals stay within these size-and age-specific groupings will clarify our understanding of the transition between life-stages in this species and how this might affect their long-term conservation. Long-term photo-identification studies in Seychelles and Djibouti provided data to evaluate this.

To enable the study of population dynamics of wild animals the determination of the age, growth rate and maturity status of a sample of the individuals present is required; consequently, obtaining repeated accurate and precise total length (TL) measurements for individuals over time can be especially valuable. However, there are limited easily applied methods to ascertain the TL of large free-swimming fish, especially the largest extant species of fish, the whale shark (Rhincodon typus). This study expands on previous work and presents the results of a robust laser photogrammetry system developed to achieve accurate TL, pre-caudal length (PCL) and further morphometric measurements of whale sharks observed between 2009 and 2011 in seasonal feeding aggregations located in the Seychelles and Djibouti. Calculations for repeatability (r) indicated a high level of precision for the system with r approaching 1 for both TL and PCL, increasing further with the use of morphometric measurements. TL measurements of 'straight sample sharks' also provided geometric mean linear regression equations to enable the prediction of TL from defined morphological indices. Continuous validation of the system against objects of a fixed length also indicated a high level of accuracy for the method of measurement. We concluded that the laser photogrammetry system can be confidently employed to obtain accurate in-water TL, PCL and morphometric measurements for R. typus, with wide ranging implications and applications for the study of R. typus, and other large marine fauna.