SCUBA JUNE 2024 issue 146 | Page 49

The Hail-Mary Pass

Shark Trust MD Paul Cox looks behind some bewildering theories of inter-species romance in the elasmobranch world

Shark bites not ‘ mistaken identity ’

Shark advocates have long espoused the ‘ mistaken identity ’ theory for attacks on humans , but a new study claims there is no proof for the hypothesis . The mistaken identity theory originates from a 1974 paper by HD Baldridge , who proposed that some shark attacks may have resulted from mistaken identity , such as a black suited diver appearing as a seal . However a new study by behavioural scientists Eric Glua and Carl Meyer argues against the theory , highlighting the absence of hard evidence and pointing out that predatory sharks have excellent senses for identifying prey , particularly eyesight .

Their paper contends : “ In our opinion , sharks are very well adapted to exploring an environment where they sometimes encounter , and depending on the animal ’ s personality and hunger levels , investigate novel objects such as humans by biting them ... Sharks don ’ t make ‘ mistakes ’ but instead explore novel objects such as potential prey , which may either be abandoned or consumed .”

Sometime in the 14th Century , a Franciscan monk and philosopher called William of Ockham had an idea . It turned out to be quite a big idea , one that guides us all as we try to make sense of the world . Or at least it should . His idea , now known as Occam ’ s razor , states ( near enough ) that when searching for answers and weighing up two competing theories , it ’ s best to start with the simplest one . So , if your car doesn ’ t start in the morning , it ’ s best to check the battery rather than assume that an alien craft has visited overnight and deactivated your vehicle as part of a plan to capture your family .

Occam ’ s razor has been argued to be the very basis of the scientific method , upon which our understanding of the universe , our development of technology and our advances in medicine are based . You can also see its influence in the way that detectives solve crimes and doctors analyse your symptoms . And it ’ s a useful philosophy when picking apart conspiracy theories . Basically , it ’ s not a bad way to help make sense of the world . So , what has this got to do with Sharks ?

‘ Shark-Ray Hybrid ? Aquarium Suggests Shark May Have Impregnated Its Lone Stingray ’. This headline in the IFL Science online magazine is one of many that did the rounds last month after an aquarium director in North Carolina suggested that a stingray in its collection could have been impregnated by its tank mate , a bamboo shark . That would be truly extraordinary . As one contributor remarked , that would be akin to a snake knocking up a human ! It seems somewhat unlikely . So , call in the fun police , what ’ s the more rational explanation here ? It ’ s probably a case of parthenogenesis : asexual reproduction where a female can produce an embryo without fertilising an egg with sperm .

This is fairly remarkable in itself , particularly in large vertebrates , but it ’ s been seen in over 15 species in aquariums , where sharks and rays are often kept in single sex groups . Once thought of as a ‘ hail-Mary pass ’, a last-ditch effort when there are too few males to go around , recent studies in aquariums have shown that it can even happen when males are present .

So , maybe it ’ s a tactic that sharks and rays have at their disposal . Do they use it in the wild ? And could it be a valuable trait to overcome challenges faced by species with fractured populations ? How common is it ? It ’ s not clear , although there is some evidence of parthenogenesis in a wild population of Critically Endangered sawfish . When we look at parthenogenesis in sharks , we ’ re left with more questions than answers . But what ’ s for sure is that science , rather than speculation , will get us closer to the truth . And , for that , we owe a debt to William of Ockham .

www . sharktrust . org

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