Population structure of a whale shark Rhincodon typus aggregation in the Red Sea

Abstract

The presence of whale sharks Rhincodon typus were recorded around Shib Habil, a small, coastal reef off the Red Sea coast of Saudi Arabia, from 2010 to 2015. A total of 267 suitable photographs resulting in the identification of 136 individuals, were documented from 305 encounters. Sharks were divided evenly between the sexes with no evidence of temporal or spatial segregation. All individuals were immature based on size estimates and, for males, juvenile clasper morphology. Scars were reported for 57% of R. typus with 15% showing evidence of propeller trauma. Estimates of population size and patterns of residency were calculated by modelling the lagged identification rate. Multiple models were run simultaneously and compared using the Akaike information criterion. An open population model was found to best represent the data and estimates a daily abundance between 15 and 34 R. typus during the aggregation season, with local residence times ranging from 4 to 44 days. Residence times away from Shib Habil range from 15 to 156 days with a permanent emigration-death rate between 0·07 and 0·58 individuals year(-1) . These results are broadly similar to those from other aggregations of R. typus, although the observed sexual parity and integration found at this site is unique for the species and needs further study.

Long-Term Photo-Identification Reveals the Population Dynamics and Strong Site Fidelity of Adult Whale Sharks to the Coastal Waters of Donsol, Philippines

“…In Ningaloo Reef, Western Australia, Holmberg et al (2009) estimated whale sharks spent 33 days in the area using different methods. Contrastingly, at Utila Bay, Honduras and at an aggregation in Saudi Arabia's Red Sea, whale sharks spent c. 12 days in these areas, suggesting whale sharks are likely more transient there (Fox et al, 2013;Cochran et al, 2016). Residency patterns estimated through conventional mark-recapture techniques are a useful, noninvasive method for determining how whale sharks use certain sites.…”

Oceanic adults, coastal juveniles: tracking the habitat use of whale sharks off the Pacific coast of Mexico

“…Globally, it is one of the only areas from which immature whale sharks, of both sexes, and large mature females have been routinely recorded (Clark & Nelson, 1997; Eckert & Stewart, 2001; Ramírez-Macías et al, 2007; Ramírez-Macías, Vázquez-Haikin & Vázquez-Juárez, 2012; Ketchum, Galván-Magaña & Klimley, 2013; Cochran et al, 2016). Some of the few reported neonatal whale sharks have also been found in this region (Wolfson, 1983).…”

Long-term assessment of whale shark population demography and connectivity using photo-identification in the Western Atlantic Ocean

“…The results of this study demonstrate that whale sharks within the WCA represent an open population with significant emigration and re-immigration (incorporating permanent emigration), which is not surprising considering their large size and movement capabilities of this species [ 28 , 32 , 33 , 40 ]. Previous studies have shown open population models are the most appropriate for population estimates of whale sharks from photo-identification data [ 41 , 53 ] and the lack of asymptote in the discovery curve, as we observed, indicates that new animals are entering the region [ 28 , 29 ]. Given the vast available habitat for whale sharks in the WCA, it is entirely plausible that additional aggregation sites occur within the area that have not been identified by researchers or tourism.…”

“…The vast majority of whale shark data available is derived from juvenile male-dominated aggregation sites, with few exceptions [ 1 ]. Even the sexually integrated population in the Red Sea does not represent a reproductive population because the animals are immature [ 28 ]. This is also true for the entire WCA, which is dominated by males and 89% of the sampled individuals were smaller than size of maturity estimates (7.0–8.0 m) [ 5 , 40 ].…”

“…The applicability of photo-identification in studying the movements of marine organisms was first demonstrated by Würsig and Würsig [ 30 ] using individual-specific markings and/or fin shapes to identify and monitor cetaceans. More recently, photo-based analytical techniques, originally developed for investigating social structure in marine mammals [ 31 ], have been successfully applied to whale shark sighting data and used to calculate various population parameters [ 28 , 29 , 32 , 33 ].…”