Analysis of sightings of white sharks in Gansbaai (South Africa)

In Gansbaai (South Africa), at Dyer Island Nature Reserve, a large White shark population is present and can be observed due to the support of local ecotourism operators authorised reach field observation sites. Between 2009 2019, it was possible create database including information about each individual observed. total, 423 white sharks were sighted during 462 direct hours from boat, that included 220 diving “cage”. The mean sighting rate 0.91 (range 0.18–1.53) per hour rates dramatically declined in last three years study period. Ninety-nine unique Photo-Ids dorsal fin collected only five re-sightings occurred, which indicate transient behaviour for population. sex ratio showed females always prevalent over males throughout duration observations: ratios 1:2.2:0.8 males, females, unsexed sharks, respectively, prevalence immature female individuals (immature: 51 201 40 unsexed; adults: 49 14 1 undefined maturity: 5 19 43 sharks). predominance immatures applies females; there as many (51) mature (49). total length all between 150 cm 500 (mean 308 cm, n = 423) with few young-of-the-year adults recorded, indicating Area not nursery area nor an adult aggregation site, but seasonal feeding ground. interannual trend consistent long-term increasing peak (ca. 4–5 years) this could confirm that, Gansbaai, frequency affected by but, since 2017, loss sightings also recorded killer whales’ unusual fatal attacks.