Population size and structure of whale sharks Rhincodon typus at Ningaloo Reef, Western Australia

Abstract

We used photo-identification to produce estimates of population size and structure of whale sharks Rhincodon typus at Ningaloo Reef, Western Australia. We analysed photographs of whale sharks taken from 1992 to 2004. A combination of spot and stripe patterns behind the last gill slit and forward of the dorsal fin (lateral view), and distinctive scars and marks on the body and fins were useful for identifying individual sharks. These patterns appeared to be unique to individuals and distinctive markings could be recognized on some sharks for more than a decade. From 581 photographs, 159 individuals were identified. Of these, 74% were male, 16% were female and 10% were of indeterminate gender. Photographed sharks ranged in estimated size from 3 to 10 m total length (TL). The size distribution of sharks was bimodal with a large peak at 8 m and a smaller peak at 6 m TL. Sixty individuals were resighted during the study. Of these, 46 were resighted at different times during the same year (sometimes on multiple occasions) up to 4 mo after they were initially photographed, and 33 were resighted (4 on > 2 occasions) in different years. The interval between inter-annual resightings was typically 1 to 3 yr; however, 2 sharks were resighted after a period of 12 yr. We estimated the super population of whale sharks that visit Ningaloo Reef to consist of approximately 300 to 500 individuals (95% confidence interval) based on closed population models, or 320 to 440 based on Jolly-Seber open-population models. Our study shows that photo-identification offers a practical, non-invasive and non-destructive means to obtain data on the population size and demography of whale sharks.

Long-term membership of whale sharks (Rhincodon typus) in coastal aggregations in Seychelles and Djibouti

“…and sex ratios (82 male : 18 female) are similar to those reported in several other aggregations. Meekan et al (2006) reported 118 males (82.5%) to 25 females (17.5%), with male sharks averaging 6.8 m and females 6.3 m at Ningaloo. Graham and Roberts (2007) found a mean length of 6.3 m AE 1.7 m s.d.…”

“…Most information on these sharks comes from studies conducted in coastal areas where the sharks are known to aggregate on a regular basis and where the majority of sharks have been found to be juveniles or sub-adults (,8 m), such as at Ningaloo Reef, Western Australia (Meekan et al 2006), the Maldives (Anderson and Ahmed 1993;Riley et al 2010), northern Mexico (Eckert and Stewart 2001) and the Philippines (Alava et al 1997) (Fig. 1).…”

“…In several Indian Ocean aggregations, and in both of the latter, many of the individual animals have been photographically identified by the spot patterns on their sides, posterior to the gill slits. These markings on this species have been shown to be stable over time (Arzoumanian et al 2005;Speed et al 2007) and have enabled the estimation of population size using standard catch, mark and recapture analysis (Meekan et al 2006;Rowat et al 2009). Many individuals in these aggregations exhibit site fidelity, having been recorded at the same site over many years (Arzoumanian et al 2005;Meekan et al 2006;Graham and Roberts 2007;Rowat et al 2009).…”

“…These markings on this species have been shown to be stable over time (Arzoumanian et al 2005;Speed et al 2007) and have enabled the estimation of population size using standard catch, mark and recapture analysis (Meekan et al 2006;Rowat et al 2009). Many individuals in these aggregations exhibit site fidelity, having been recorded at the same site over many years (Arzoumanian et al 2005;Meekan et al 2006;Graham and Roberts 2007;Rowat et al 2009). However, while movements of individuals between adjacent mainland aggregation sites have been documented through photo identification (Holmberg et al 2009), they have not been found between any disparate sites to date.…”

Individual identification of Eurasian perch Perca fluviatilis by means of their stripe patterns

“…For example, individuals of whale sharks Rhincodon typus could be re-identified through decades based on their pigmentation patterns (Hueter et al, 2013;Meekan et al, 2006). Recently, Huntingford et al (2013) have shown that mirror carp Cyprinus carpio can be individually identified by their scale pattern.…”