Abstract
Donsol in the Philippines is the longest running community-based whale shark (Rhincodon typus) ecotourism site in Southeast Asia, with peak visitation in 2012 of over 27,000 tourists. In order to understand this aggregation and the importance of the area to whale sharks, dedicated photographic identification (photo-ID) research began in 2007. In-water photo-ID surveys were conducted from tourism boats, weather and operator permitting, from December to June between 2007 and 2016. Visual matches of the unique spot patterns of each individual shark were validated by the pattern-recognition software Interactive Individual Identification System (I3S), and on the online database Wildbook for Whale Sharks (www.whaleshark.org). A total of 1,985 photo-ID trips over 895 survey days resulted in 6,786 encounters with R. typus. Combined with encounters from both dedicated research and citizen science dating back to 1998, 479 individual whale sharks were identified, making up 44% of the known whale shark population in the Philippines (n = 1,095). Of these, photographs of the pelvic region confirmed the sex for 158 males and 22 females. Visual size estimates ranged from 2 to 10 m (mean ± S.D = 6.5 ±1.6 m). Maturity in males (LT50) was estimated at 6.8 ± 0.2 m total length, with 53% of males considered mature. Annually, the total number of individuals sighted varied between 15 and 185 ( mean ± S.D = 104 ± 55.53), with a recruitment of 3-90 new individuals yearly (mean ± S.D = 46.8 ± 36.29). Modelled residency using maximum likelihood methods suggested whale sharks spent 49.8 ± S.E. 14.5 (95% CI [32.3 – 78.6]) days in Donsol each season, with 47.1 – 60.8 whale sharks at any one time during the season. Twenty individuals were recorded through photo-ID at other sites across the Philippines. The extended residency of whale sharks at Donsol, paired with the presence of sexually mature animals and the economic value of the tourism industry, highlights the importance of Donsol for this endangered species.
Highlights
The whale shark, Rhincodon typus Smith 1828, a large planktivorous elasmobranch, is found in tropical and warmtemperate waters worldwide (Rowat and Brooks, 2012)
Some whale sharks display a degree of site fidelity on an annual and inter-annual basis (Graham and Roberts, 2007; Holmberg et al, 2008; Fox et al, 2013; Araujo et al, 2017), and this predictability makes the whale shark an ideal target species for wildlife tourism (Catlin and Jones, 2010; Rowat and Brooks, 2012)
The Philippines was home to targeted whale shark fisheries with two major landing sites in the Bohol Sea, though more sites were reported extending through the Sulu Sea and southern Mindanao (Alava et al, 1997)
Summary
The whale shark, Rhincodon typus Smith 1828, a large planktivorous elasmobranch, is found in tropical and warmtemperate waters worldwide (Rowat and Brooks, 2012). Some whale sharks display a degree of site fidelity on an annual and inter-annual basis (Graham and Roberts, 2007; Holmberg et al, 2008; Fox et al, 2013; Araujo et al, 2017), and this predictability makes the whale shark an ideal target species for wildlife tourism (Catlin and Jones, 2010; Rowat and Brooks, 2012). The municipal waters of Donsol were declared a whale shark sanctuary, and this was soon followed by a national ban on whale shark hunting, imposed in 1998 (FAO, 193, Department of Agriculture-Bureau of Fisheries and Aquatic Resources). Despite regulations and bans on direct hunting in several countries, the late onset of sexual maturity (Bradshaw et al, 2007) hinders population recovery and leaves whale sharks susceptible to overexploitation and anthropological impacts (Bradshaw et al, 2008)
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