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Eye contact with a shark is a crucial element during an interaction with a diver. Different mask frames change the size of a diver’s available field of vision, and so make a person’s eyes unequally visible from different angles, particularly when comparing mirrored to regular glass. This study examined whether it matters to a shark if it can see a diver’s eyes when getting closer. The test-subjects changed masks in a random, timed routine, while the relative distance, the absolute distance between a shark and diver expressed in a fraction of the shark’s body length, between approaching shark and human was tallied. Sharks came significantly closer (p = 0.0139) when a diver’s eyes could not be detected, showing that they orient themselves and approach based on the human’s eyes. Given that human comprehension of sharks is rudimentary, every possible benefit, even a minimal one like choosing the most optimal mask, is recommended whenever approaching sharks are likely to be encountered. more...

It is unknown if resting sharks can sleep, which is also true for gliding ones. Here, a videotaped bull shark is presented that drifted in an uncontrolled manner for 120 seconds while sinking with 0.1 m/second. Several aspects are discussed to determine if the shown behavior reflects the commonly accepted definition of sleep. Additionally, the idea is also discussed if this state might reflect a “quiet waking state” instead of where the shark still maintained some vigilance despite its general appearance. more...

Sharks and sharksuckers maintain a mutualistic symbiotic relationship; thus, it is surprising to observe a lemon shark, Negaprion brevirostris, killing a sharksucker, Echeneis lucrates, which has been recorded during a dive with lemon sharks. Does this observation indicate that the symbiosis between the two species may shift occasionally? The awkwardness of the recorded kill, combined with its comparatively long duration, suggests this bout be a freak incident, rather than a common occurrence; thus, the mutualistic relationship needs not be questioned. What triggered the bout, however, can only be speculated. Although the caloric value of the killed sharksucker is not known, a feeding-oriented behavior can likely be rejected as the potential cause based on the teleost’s rather small size, and an irritation related issue is more likely to have triggered this bout. more...

Feeding is the likely cause for tooth shedding in sharks. Although the overall process of loosing teeth has been well studied, hardly any emphasis has been given to the actual separation mechanism between a shark’s tooth base and the surrounding jaw tissue. Attention is given to this very process, in connection to a never before videotaped tooth loss of a white shark, Carcharodon carcharias, that occurred within 0.3 seconds. Since the shark did not bite into anything prior to this observation, the cause for this tooth loss does not seem feeding but fatigue related, triggered through a combination of mechanical and potentially biochemical degradation processes. more...

This study examines the approach patterns of sharks in the vicinity of human divers, focusing on the diver’s body orientation and a shark’s distance from the sea bed when approaching the diver. A standardized video method was used to record the scenario of diver(s) kneeling in the sand while being approached by sharks. This showed that sharks had a preference to move in from outside a diver’s field of vision while larger sharks stayed closer to the sea floor. This may simultaneously enhance camouflage while reducing potential escape routes for the approaching animal. This stealth behavior raises the question of how sharks may interpret humans when moving towards them. more...

Five unprovoked shark attacks are reported from Sharm-El-Sheikh, Egypt, between 30 November and 5 December 2010. Three of the five attacks are attributed to an oceanic whitetip shark, Carcharinus longimanus with a distinctive crescent-shaped notch in the upper lobe of the caudal fin. The shark was observed during the first attack on a snorkeler and photographed underwater during the second shark attack on a swimmer. In a video taken several months prior to the attacks, the same shark is hand-fed underwater by a divemaster with additional fish in a pack over his buttock. The shark can be seen swimming behind the divemaster while he removed additional fish from this pack. In Victims 1, 2 and 5, the shark removed an extensive amount of tissue from the victims’ buttock. The three victims also lost a hand and/or a portion of their forearm, suggesting the injuries were inflicted by a shark conditioned to associating food with hand-feedings and the human form. The remaining two attacks, Cases 3 and 4, were attributable to the shortfin mako shark, Isurus oxyrinchus. This was determined from a unique dental pattern of the right side of the upper jaw due to a prior injury. This same “misalignment” dental pattern was observed in the injuries sustained by Victims 3 and 4. We conclude that the shortfin mako shark was responsible for the attacks on Victims 3 and 4, and the oceanic whitetip shark was the causal species of attacks on Victims 1, 2, and 5. more...