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

摘要

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 2.5m 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 2.5m in total length, with young-of-the-year sharks (<1.75m) 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.