The Extreme Morphological Effects Captivity Has On The Sand Tiger Shark
The Sand Tiger
The Sand Tiger Shark (Carcharias taurus) is a species of Carcharias shark usually found in South Africa, Australia, Japan, the east coasts of North and South America and the Mediterranean where temperate or subtropical waters are present. Usually found in coastal areas around submerged reefs they inhabit various depths up to 190m, they have been known to grow up to a maximum length of 3.3m and weight as much as 159Kg. Their mouth almost overflowing with protruding-spike like teeth and short pointed snout are the two most noticeable features that usually make it recognisable. Whilst commonly referred to as Sand Tigers this species has several different names depending from country to country, a few examples are The Grey Nurse Shark, Spotted Ragged-tooth and Blue Nurse Shark. They feed on a wide variety of prey from crustaceans, squid, skates and even other sharks with same species cannibalism being common. This cannibalism occurs regularly during gestation periods inside female sharks where the strongest most developed pup will often eat its weaker brothers and sisters for nutrition when all the yolk within its egg sac has been consumed, a reproductive strategy known as intrauterine cannibalism. The Sand Tiger possesses several unique biological adaptations like the previously mentioned reproductive strategy that other elasmobranch species don’t, unlike other species they are able to maintain neutral buoyancy by storing large gulps of air from the surface. They then hold these in their stomach and release them when they need to sink, this saves substantial energy that would be used from having to be constantly on the move to stay level in the water column.
The Effects of Captivity
The Sand Tiger Shark (Carcharias taurus) is one of the most common species of pelagic sharks found in public aquariums across the world due to their large size and “Ferocious” appearance. However, despite this appearance they are seen as quite gentle and placid animals with no recorded human fatalities. They are also widely used as it was originally thought that they were able to adapt quickly and well to being in captivity, but after several studies were conducted into the effects on this species body when exposed to prolonged captivity it was shown that this is not the case. The exact cause of these deformities has been difficult to pin point as several different hypotheses have been put forward, these range from pre-existing injuries obtained from capture and transport, poor diet in captivity and even the shape and size of the tank they’re kept in. In a study conducted by Daniel Huber looking at the possible reasons behind these spinal deformities he found that 35% of all Sand Tigers in public aquariums showed signs of spinal deformities (he does not state whether this figure is worldwide or only in North America). These deformities ranged from dislocated spines to compressed vertebrae. In the same paper it was found that these spinal defects correlated with vitamin C and zinc deficiency, aquarium size and size at capture. Vitamin C and other minerals such as zinc and potassium are crucial in the proper development and maintenance of cartilage-collagen, without these, spinal problems will begin to develop, this hypothesis was pursued further in paper by Anderson (All papers mentioned are available for further reading at the end of the article).
Video of a Sand Tiger in Captivity with clear signs of a compressed vertebrae. Original author: All Five Oceans
Another leading theory on the cause of these spinal defects is abnormal swimming behaviour due to restricted tank space in aquariums. A study conducted by Erin Tate looked into this possibility. Sand Tigers in a public aquarium were observed and the time the sharks would be swimming and gliding were recorded over a set period. Sharks who were afflicted with spinal problems had a higher swim to glide ratio than those who were healthy, these results suggested that more time swimming was placing unnatural pressure on the spines of Sand Tigers where in a natural environment spend a larger proportion of time gliding and only actively swimming when hunting or when having to traverse vertically through the water column, however, in a tank that is already constricted by its size and presence of other species and objects it means the time swimming will be much greater, to try and tackle this problem aquarium architects will design large complex tanks to discourage repetitive swimming behaviours and provide enough length for sharks to to complete natural swimming repertoires.
- Correlations of Swimming Patterns with Spinal Deformities in the Sand Tiger Shark, Carcharias taurus: https://pdfs.semanticscholar.org/f12c/7c0240033b93b8b8bc13e5cbd8481f331107.pdf
- Mechanical properties of sand tiger shark (Carcharias taurus) vertebrae in relation to spinal deformity: http://jeb.biologists.org/content/216/22/4256.long
- Correlations of capture, transport, and nutrition with spinal deformities in sandtiger sharks, Carcharias taurus, in public aquaria: http://www.bioone.org/doi/10.1638/2011-0066R1.1?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&
- The IUCN Red List of Threatened Species-Carcharias taurus: http://www.iucnredlist.org/details/3854/0