Fine scale movements and activity areas of white sharks (Carcharodon carcharias) in Mossel Bay, South Africa

Abstract

Previous work on white sharks indicate the species show seasonally limited movement patters, at certain aggregation sites small areas may play vital roles in the life history of a large amount of the population. Acoustic telemetry was used to estimate habitat use of white sharks, Carcharodon carcharias, while aggregating at Mossel Bay, South Africa. Total range of all shark tracks combined accumulated 782 hrs and covered an area of 93.5 km 2 however, within this range, sharks were found to highly utilise a core habitat (50% Kernel, K50) of just 1.05 km 2 over a reef system adjacent to a river mouth. Individual tracks revealed additional core habitats, some of which were previously undocumented and one adjacent to a commercial harbor. Much was found to be dependent on the size of the shark, with larger sharks (>400cm) occupying smaller activity areas than sub-adult (300-399 cm) and juvenile (<300 cm) conspecifics, while Index of Reuse (IOR) and Index of Shared Space (IOSS) were both found to increase with shark size. Such results provide evidence that larger white sharks are more selective in habitat use, which indicates they have greater experience within aggregation sites. Furthermore, the focused nature of foraging means spatially restricted management strategies would offer a powerful tool to aid enforcement of current protective legislation for the white shark in similar environments of limited resources and capacity.

Sex‐specific and individual preferences for hunting strategies in white sharks

“…individuals (e.g. Jewell et al 2013). Chumming by ecotourism dive vessels generated a high probability of sharks either remaining in or switching to ARS behaviour.…”

The control of risk hypothesis: reactive vs. proactive antipredator responses and stress‐mediated vs. food‐mediated costs of response

“…White sharks are not present at all colonies, so seals on other islands experience very little risk of white shark predation at their breeding colony (Bonfil et al 2005;Dudley 2012). Risk also varies seasonally, because white sharks feed on seals only during the winter months (Hammerschlag et al 2006;Jewell et al 2013), and these patterns create strong spatial and temporal variation in predation risk between sites and seasons. At sites and times where predation risk is high, adult seals cannot leave the island to eat without passing through a band of high-risk, nearshore water where sharks concentrate their attacks.…”

“…; Jewell et al . ), and these patterns create strong spatial and temporal variation in predation risk between sites and seasons. At sites and times where predation risk is high, adult seals cannot leave the island to eat without passing through a band of high‐risk, nearshore water where sharks concentrate their attacks.…”

Nine decades of fish movement research in southern Africa: a synthesis of research and findings from 1928 to 2014

“…Movement within estuaries is constrained and particularly suited to fine-scale acoustic tracking, which has focused predominantly on spotted grunter Pomadasys commersonnii (Kerwath et al 2005;Naesje et al 2007;O'Connell 2008;Childs et al 2008a, b, c) and to a lesser degree on white steenbras Lithognathus lithognathus (Bennett et al 2011 and dusky kob Argyrosomus japonicus (Cowley et al 2008;Naesje et al 2012). Although logistically more difficult, fine-scale habitat usage has also been investigated to a lesser degree in the marine environment with both acoustic telemetry (Hissmann et al 2006;Kerwath et al 2007b;Jewell et al 2012;Kock et al 2013) and conventional mark-recapture (Attwood 2002;Kerwath et al 2007a;Maggs 2011;Maggs et al 2013b). Fine-scale habitat usage has most often been discussed in the context of residency and in association with estimations of home range with the objective of evaluating protected area sizing and spacing.…”