Abstracts Biological Sciences

Aspects of the biology and ecotourism industry of the whale shark Rhincodon typus in North-Western Australia

by Bradley Michael Norman

The conservation status of the widely-distributed whale shark Rhincodon typus is presently listed as 'Indeterminate - Data Deficient'. One of the main hindrances to obtaining biological data on whale sharks that is relevant to determining its 'conservation status' is that this species has rarely been recorded as occurring in sufficient numbers to obtain quantitative data. However, R. typus does form aggregations at Ningaloo Marine Park (NMP), Western Australia, annually between March and June. This has enabled studies to be made of aspects of the biology of R. typus and of the possible impacts of the ecotourism industry on this species. Using a position provided on vessels involved with the whale shark ecotourism industry at NMP, R. typus was observed on 360 separate occasions in 1995, 1996 and 1997, and it was possible to sex 90.3% of these sharks. The majority of the sexed sharks (84.6%) were male and ranged in length from 4 to 12 m, with a mean of 7.4 m, while the females ranged in length from 4.5 to 8.5 m, with a mean of 6.2 m. The size and degree of abrasion of the claspers was used as an indicator of whether or not a male shark had mated. Using such criteria, it was estimated that male whale sharks start to mature at ca 8 m and that ca 50% are mature by the time they reach 8.6m. Observations suggested that R. typus feeds by using both suction and flow-through mechanisms. The prey that were observed being ingested included coral spawn, tropical krill, mysids and small jellyfish. The contents of a faecal sample contained parts of the exoskeleton of copepods and the scales of small fishes. The degree of mouth distension, which is assumed to be related to feeding activity, was low during most observation periods. Photographs of the scars and natural patterning on the skin of individual sharks were used to construct a photographic library for subsequent identification of these sharks. The features used for identifying individual sharks were chosen because they were considered likely to remain for a protracted period. The Whale Shark Photo -identification Library that was produced provides details on the characteristic features of 52 R. typus that were present at NMP. Six individuals were recorded at NMP in both 1995 and 1996, four in both 1996 and 1997, and one in both 1995 and 1997. No identified whale sharks were recorded in all three years. Rhincodon typus was distributed widely throughout NMP, with most boat and aerial sightings lying within 1 - 2 Ism of the reef crest between Tantabiddi and Turquoise Bay. Rhincodon typus was typically sighted in water depths of 10 to 30 m. The sharks were predominantly travelling parallel to Ningaloo Reef, with significantly more moving in a northward than southward direction. Acoustic tracking of R. typus in 1997 suggested that this species remains within NMP for extended periods and is at the surface for ca 17% of daylight hours. The number and species of fauna observed to be associated with R. typus were recorded, and a new species of copepod, Pandarus sp.…