Scientific Research Papers

The spatiotemporal patterns of nearly 2 600 predatory interactions between white sharks and Cape fur seals at Seal Island, South Africa, were studied and compared with published patterns of white shark-pinniped interactions from other sites. Similarities between Seal Island and Californian sites included prey age class (juvenile), highest attack frequency versus distance from island (< 400 m), tidal state (high) and depth range (5—50 m). However, many differences were noted, including seasonal distribution (winter versus autumn), mean frequency of attacks (6.7 per day versus 0.7 per day), prey capture success rate (48% versus 64%), size of attacking sharks (2.1—4.5 m vs. 3.5—5.9 m), prey mass (low versus high), timing of attacks (frequency greatest early morning versus all day), wind direction (Northerly versus not significant), and light levels (low versus indiscriminate). The factors affecting white shark predatory success have been reported from Seal Island, but not from the California sites. These similarities and differences are discussed in terms of prey characteristics and environmental factors at each site. Our results suggest that factors affecting white shark predatory behavior and success rate are likely prey- and site-specific.

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Neil Hammerschlag, R. Aidan Martin, Chris Fallows

Effects of environmental conditions on predator–prey interactions between white sharks (Carcharodon carcharias) and Cape fur seals (Arctocephalus pusillus pusillus) at Seal Island, South Africa

Environ. Biol. Fish. 76, 341-350.

Abstract Effects of environmental factors on frequency and success rate of 2,546 natural predatory attacks by white sharks, Carcharodon carcharias , on Cape fur seals, Arctocephalus pusillus pusillus, were studied over an 8-year period at Seal Island, South Africa. Attacks occurred primarily during winter months (June–August). Attack frequency increased significantly during northerly winds, during high tides, and within 400 m of the island, but predatory success rate decreased with proximity to the island.

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Hammerschlag, N. and Fallows, C.

Galapagos sharks (Carcharhinus galapagensis) at the Bassas da India atoll:
first record from the Mozambique Channel and
possible significance as a nursery area.

South African Journal of Science, 101: 375-377.35-41 July/August 2005.

This paper reports the first record of Carcharhinus galapagensis in the Mozambique Channel from 54 individual sightings and describes their association with the oceanic atoll, Bassas da India. The geographic distribution of C. galapagensis is updated and the importance of the atoll to this species as a nursery area within the Mozambique Channel is discussed.

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Martin, R.A., N. Hammerschlag, R.S. Collier, and C. Fallows.

Predatory behaviour of white sharks (Carcharodon carcharias)
at Seal Island, South Africa.

Journal of the Marine Biological Association of the United Kingdom, 85: 1121-1135, 2005.

Between 1997 and 2003, there were 2088 natural predations by white sharks (Carcharodon carcharias) on Cape fur seals (Arctocephalus pusillus pusillus) and 121 strikes on towed seal-shaped decoys were documented from observation vessels at Seal Island, South Africa. White sharks at Seal Island appear to selectively target lone, incoming young of the year Cape fur seals at or near the surface. Most attacks lasted 51min and consisted of a single breach, with predatory success rate decreasing rapidly with increasing duration and number of subsequent breaches. A white shark predatory ethogram, composed of four phases and 20 behavioural units, is presented, including four varieties of initial strike and 11 subsequent behaviour units not previously de¢ned in the literature.

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Martin, R.A. 2004.

Journal of Fish Biology, 64: 1-6, 2004.

Natural mortality in the puffadder shyshark due to object play or kleptoparasitism by two species of marine tetrapod, the Cape fur seal Arctocephalus pusillus pusillus and the black-backed kelp gull Larus dominicanis vetula, was investigated in the present study. Range extension of the puffadder shyshark to False Bay, South Africa was also examined.

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