Surveys of white sharks (Carcharodon carcharias) off bathing beaches in Algoa Bay, South Africa

Abstract

The present study provides information on the existence of a possible inshore nursery area for white sharks (Carcharodon carcharias) in Algoa Bay, South Africa. In total, 43 flights were conducted, using a Robinson R22 helicopter, between October 2010 and March 2012. A total of 50 white sharks was sighted, with a maximum sighting rate of seven sharks per hour in October 2010. The majority (96.0%) of sharks observed were less than 2.5 m in length, immature and sighted between October and March (98.0%). A hurdle model, comprising a logistic regression to model presence–absence and a log-normal generalised linear model for abundance showed that water temperature and barometric pressure explained the sightings of sharks, peaking in mid-December. The sighting of sharks was best explained by barometric pressure, month and year. A total of 58 white shark catches was recorded from key informant interviews with shore anglers between July 2009 and December 2011. Sharks ranged in size from 1.5 to 2.5 m in total length, with young-of-the-year sharks (<1.75 m) accounting for 69.0% of the catch. Defining key habitats for young-of-the-year and juveniles is critical for the management and conservation of white sharks worldwide.