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Is it good-looking or does it smell good? Preliminary observations about great white shark's discriminatory patterns
The White Shark Carcharodon carcharias L. is a top predator worldwide distributed. Its high survival and adaptation capacity is related with high developed senses, used to efficiently interact with a target. During daily activities of cage diving in the Marine Reserve of Dyer Island (South Africa) the behavioural patterns of the white sharks in front of different targets were observed. Previous studies showed that in an unnatural situation, as the cage diving is, the white shark displays a curiosity approach and it long investigate the situation before an attack. The aim of the present study was to understand if a white shark, in front of a still floating decoy similar to the natural prey (Cape fur seal, Arctocephalus pusillus pusillus) and a bloody piece of tuna fish, makes a choice based upon the sigh or the smell. The preliminary data analysis showed that the choice of the target could be related to size (and consequently) age of sharks. We also analyzed the type of approach (vertical, horizontal or diagonal) and observed that in this case the choice could be related to light and weather conditions. A correlation between type of approach and type of target (decoy or bait) was also observed: usually vertical tactics were more often used in presence of sealshaped decoy, while horizontal tactics were showed in presence of tuna bait. Our observations suggest that these patterns appear to be adapted for exploiting a challenging suite of surface-dwelling prey species and may be the basis of a speculative hunting strategy wherein individual sacrifice much of the possibility of identifying a potential prey item in exchange for an increased chance of capture.