Observation of a Whale Shark Rhincodon typus (Orectolobiformes: Rhincodontidae) in the offshore waters of Rushikulya, Orissa, India
Wildlife Institute of India, PB#18, Chandrabani, Deharadun, Uttarakhand 248001, India
The Whale Shark Rhincodon typus Smith, 1828 grows to a length of approximately 12m and a weight of approximately 30 ton making it not only the largest fish but also one of the largest extant animals. Despite its size, wide-ranging distribution and the ease with which it is identified, Whale Shark sightings are infrequently reported. The rarity of Whale Shark sightings has thus resulted in global concern regarding the health of whale shark populations. This concern led to the species being assigned Vulnerable status by the IUCN Red List of Threatened Species (Norman 2005). Additionally, Whale Sharks are protected in India under Schedule-I of the Indian Wildlife (Protection) Act – 1972 (IWPA 2003).
On 22 February 2009, a Whale Shark, accompanied by two sucker fish (Remora sp.) was sighted at 1120hr (IST), 3km offshore and 12km north of the Rushikulya River mouth (85o10Õ18.26N & 19o26Õ28.45E). Bottom depths at the sighting location ranged from 18-20 m; however, the shark was primarily observed at the surface (Images 1 & 2). The atmospheric and sea surface temperatures at the sighting location were 310C and 290C respectively; salinity was 34%. The length of the whale shark was between 4.5-5 m based on its size relative to the 7m boat from which the observation was made. As the length at maturity for Whale Sharks is reported to be above 9m (Colman 1997), the shark we observed was likely a juvenile. Interestingly, most Whale Sharks reported globally range from 4-10 m in length (Colman 1997) and in Indian waters, 25% of the recorded whale sharks are between 5-6 m in length (Pravin 2000).
Sightings of Whale Sharks have been reported from almost all maritime states of India including Gujarat (Hanfee 2001), Maharashtra (Jadhav et al. 2005), Karnataka (Kemparaju et al. 2002), Kerala (Paul 2006), Tamil Nadu (Rajapackiam et al. 2006), Andhra Pradesh (Rao 1992), West Bengal and Goa (Pravin 2000; Choudhary 2008). Recently, there has been an increase in Whale Shark sightings off the Orissa coast, such as those documented by Bar (1998) and Rao (2004). Additionally, On March 2008, fishermen of Purnabandha Village (village near Rushikulya River mouth) reported a Whale Shark approximately 4km offshore near Rushikulya River mouth (Suresh Kumar, WII pers. comm. 27 February 2009). Furthermore, the Orissa Diary (Anonymous 2009a) reported the stranding of a dead, 5.5m Whale Shark at Gopalpur (a coastal town, 25km south of Rushikulya) in February 2009 and The Hindu (Anonymous 2009b) reported about beaching of another Whale Shark at Gopalpur on November 2008. Whether or not the increase in observations of Whale Sharks from the region reflects an increase in the abundance of the species or a result from increased public interest in the species is unknown. However, it is evident that Whale Sharks inhabit the Orissa coast with an unknown periodicity.
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