Whale Shark (Rhincodon typus) Issues Paper

Department of the Environment and Heritage, May 2005
ISBN 0 6425 5082 4

Population

Size

Yearly numbers of Whale Sharks in Ningaloo Marine Park is estimated to vary between 200 and 400 individuals (Davis et al. 1997). These sharks appear to congregate on Ningaloo Reef between March and May, and reach peak densities roughly two weeks after the coral has undergone mass spawning (Taylor, 1996) although further analysis of records from the ecotourism industry will confirm this. Figures for the global population of Whale Sharks are not available, although an advanced monitoring program using photo-identification has been implemented with sighting information (and identification photographs) of Whale Sharks from 16 separate countries currently included in the ECOCEAN Whale Shark Photo-identification Library (see www.ecocean.org). The methodology used to enable the identification of individual Whale Sharks has been subjected to vigorous testing and established that natural markings on the skin of Whale Sharks (in particular the spot patterning behind the gill slits) does not change over time and can be used for population monitoring using mark-recapture studies (Brad Norman, pers. comm.).

Trends

Despite relatively limited information being available on population trends for the Whale Shark, the World Conservation Union's Red List (2003) classifies the species as "Vulnerable" (A1bd+2d).

'The life history of this relatively scarce but cosmopolitan tropical and warm temperate species is poorly understood, but it may be relatively fecund and migrates extremely large distances. Catches have declined and populations apparently been depleted by harpoon fisheries in several countries targeting localised concentrations of this huge, slow-moving and behaviourally-vulnerable species, and there is incidental capture in other fisheries. Directed fisheries, high value in international trade, a K-selected life history, highly migratory nature, and low abundance make this species vulnerable to exploitation. In recent years dive tourism involving this species has developed in a number of locations around the world.' (IUCN Red list 2003).

Fishery data for the Whale Shark, though quite scarce, points to a decline in seasonal catches, with the declines often occurring in the space of only a few years since the establishment of directed commercial fisheries, for example in the Philippines and in India (CITES Prop. 12.35). Catches from Taiwan's commercial fishery have declined by 30-90% from the 1960s - 1980s, 50-80% from the mid 1980s to the 1990s, and around 70% during the four years from 1997 to 2001 (CITES Prop. 12.35). The annual Whale Shark catch in Taiwan declined by 58% (from 272 to 113 Whale Sharks) in the period of January 2001 to March 2002, although Chen and Phipps (2002) indicate that this decline may also be attributed to confusion over the introduction of a new Whale Shark catch reporting system. Since 2002/03, officials in Taiwan have implemented a Total Allowable Catch (TAC) on the number of Whale Sharks permitted to be killed each year (80) (Chen and Phipps, 2002). This number has been taken each year, although it is believed that there is still a level of misreporting and that the catch maybe slightly higher (Brad Norman, pers. comm.).

Data from the Philippines and India, although over much shorter time scales, indicate similarly steep reductions in catches. In the Philippines, catches declined on average 27% per year during the 1990's before the Government closed the fishery. In Gujarat, India, Whale Shark catches appear to have declined by 40% in 1999-2000 before the Government closed the fishery (CITES Prop. 12.35).

Due to the whale shark's tendency to migrate from one region to another, apparent declines in numbers of seasonal sightings (for example in South Africa and Thailand) may be due to unsustainable fishing in other parts of the whale shark's range (CITES Prop 12.35), or to inter-annual variability (Stevens, pers. comm. 2004).

Of particular concern is the apparent reduction in the frequency of sightings of large individual Whale Shark in Taiwan. Until the late 1990's, the average size of Whale Sharks caught in northeastern Taiwan was significantly larger (e.g. 10-20m specimens). This is in contrast to records from 2000 to present, indicating that the mean total length of Whale Sharks captured in Taiwan has declined to approximately 4.6m (Chen & Phipps, 2002; S.J. Joung, pers. comm. to Brad Norman, 2004). It is likely that this reduction in mean length of Whale Sharks in Taiwan is a direct result of the larger (breeding) females being 'fished out' from the Whale Shark 'population' in the waters surrounding Taiwan (Brad Norman, pers. comm.).