Abstract
Whale sharks Rhincodon typus migrate to Ningaloo Reef every year and are observed there between March and July. Encounter data in the form of digital images, many taken from DVD’s provided by tourism operators and lodged in the ECOCEAN Whale Shark Photo-identification Library (http://www.whaleshark.org/), and sightings data collected by the Department of Environment and Conservation (DEC) from logbooks and “black boxes” used by tourism operators, were obtained for the years from 2006 until 2010. Over these five years, 430 individuals were identified in the Library and of these, 267 were resighted at least once. Most of the resightings (76%) occurred in the same year as the previous sighting, with 20% occurring one year apart and 4% at least two years apart. Individual sharks were sighted on up to a maximum of 33 days over the five years, with a median of two sighting days per individual. The average annual residency of individual whale sharks, estimated using the encounter data and the program Socprog (Whitehead 2009), was 34.04 days over the five year period and the longest estimated residency time was 190 days. Data collected by the DEC from tourism operators showed that the highest density of sightings were in the northern part of Ningaloo, between 21°50’S and 22°05’S (offshore from Tantabiddi), with a peak density of 118.55 sightings per km2. The highest density of sightings in the southern part of Ningaloo occurred between 22°45’S and 23°10’S (offshore from Coral Bay), with a peak density of 11.44 sightings per km2. Significant inter-annual variation was found in the number and distribution of sightings, particularly in the strong La Nina year of 2010. This study highlights the value of the data provided by the tourism operators and the spatial information collected by the DEC for the conservation of whale sharks.