Case Study: Sharks in aquariums

Case Study: Sharks in aquariums

Until recently, only a few benthic species of shark, such as horn sharks, leopard sharks and cat sharks, had survived in aquarium conditions for over a year. Nowadays aquariums desire larger, open ocean (pelagic) sharks which brings further challenges in terms of providing adequate and appropriate space for the sharks to travel around in. There also arises the issue of electromagnetic signals. However, no aquarium tank can provide these animals an optimal environment and, in many cases, large shark species are dumped into unsuitable, restrictive and inappropriate tanks, where they do not survive or thrive for very long.

There are at least 24 species of shark displayed at Sea Life, including blacktip reef shark, grey reef shark, brown shark, bonnet shark, scalloped hammerhead shark, nurse shark and white tip reef shark. Each Sea Life centre has at least one species of shark, and most have more than five species. The most commonly-displayed sharks are blacktip reef sharks and nurse sharks.

In 2010, Birmingham Sea Life acquired two scalloped hammerhead sharks named ‘Thora’ and ‘Freda’. Both were estimated to be around three years old. They are the first to be displayed in a British public aquarium.

Shark3Hammerhead sharks, in the family Sphyrnidae, represent a small group of eight distinct species. They are a wide-ranging, coastal marine shark, with family representatives occurring in warm-temperate and tropical oceans throughout the world. They typically feed on teleost fishes, cephalopods, and crustaceans. Scalloped hammerhead sharks are highly mobile and partly migratory, inhabiting depths of up to 450-512 metres, with occasional dives to even deeper waters. In Hawaii, it has been discovered that the sharks travel as far as 5.1 kilometres in the same day.

The uniqueness, notoriety, and sheer visual presence of the scalloped hammerhead makes them an interesting candidate for public display. Unfortunately the very morphological feature which makes the scalloped hammerhead so popular, the cephalofoil (a term used for the unique shape of the animal’s head shape), also presents a challenge to workers with regards to the successful capture, transport, and maintenance of this shark. The capture and transport of scalloped hammerhead sharks historically has represented a difficult, expensive, and uncertain undertaking for the public aquarium community. During these processes, animals are often observed damaging their head and eyes by impacting the physical boundaries of the transport vessel or the holding facility. In addition, experience has demonstrated that scalloped hammerheads appear to be highly susceptible to the same physiological changes observed in other Carcharhiniformes during capture and transport, confounding an already difficult recovery process.

Scalloped hammerhead sharks can grow to over six foot in length (depending on the sex – female scalloped hammerhead sharks mature at a size larger than males), as is the case for many elasmobranch species. They are highly intelligent, and use the earth’s magnetic field during their migrations. Like other sharks, hammerheads are nocturnal, solitary predators during the night, yet in the day they naturally form large groups and frequently swim in deep water to forage and survive. This shark species tends to form huge schools whose function is presumed to be manifold and may, among other things, concern feeding habits and reproduction. All of these behaviours make them highly unsuitable for living in Birmingham Sea Life’s ‘Underwater Tropical Tank’.

IMG_3590Another species of shark clearly not suited for tank life include the bowmouth guitar fish – a species housed at 25% of Sea Life aquariums. Bowmouth guitar fish would naturally inhabit waters with a depth of 90 metres. They are primarily bottom-dwelling animals, preferring sandy or muddy substrates. Again, they are more active at night time.

The short-tailed nurse shark, housed in the ‘Ocean Tank’ at Scarborough Sea Life, is also a bottom-dwelling species, and a nocturnal predator who would roam widely, foraging for ground-dwelling crustaceans, urchins, squid and octopuses. At day, the Short-tailed nurse shark would sit on the open bottom or hide in holes or crevices. It is well adapted to life on the ocean floor, in common with other nurse sharks and has unique feeding apparatus, with a small mouth and enlarged pharynx that allows the shark to feed with a suction method. This adaption is redundant in a Sea Life tank.

The nurse shark is the second most commonly exhibited shark at Sea Life, and one of the largest shark species, growing over 16 foot in length. Another nocturnal species, the nurse shark would naturally spend the day hidden under submerged ledges or in crevices within reefs in large inactive groups of up to 40 individuals at around 75 metres depth. At Sea Life, not more than two individuals are housed together and hiding places in the Ocean Tanks are sparse.

The leopard shark, housed in 25% of Sea Life aquariums, is an active, strong swimmer, known to form large schools in the wild which appear to be somewhat nomadic.

The blacktip reef shark, housed in 90% of Sea Life aquariums, is amongst the ten most commonly species exhibited at Sea Life. The species is migratory and naturally wary of humans, yet these animals are frequently forced into close contact with both Sea Life staff and visitors during ‘close encounter’ experiences. In the wild, a typical foraging area for the blacktip reef shark is one square mile.

A member of staff at Great Yarmouth Sea Life stated that the aquarium houses five blacktip reef sharks “because they are a pack animal … like a wolf, or a family of dolphins”, however whilst blacktip reef sharks have been observed cooperatively hunting in the wild, they are generally solitary eaters. The staff member went on to say they also house a zebra shark alone, even though this species often forms loose aggregations of 20 to 50 in the wild.

Most sharks are either facultative or obligate ram ventilators, requiring constant forward motion to maintain respiration. This presents husbandry challenges to public aquaria maintaining sharks, as tanks should accommodate constant swimming motion by large animals. Klay (1977) described the swimming repertoire of sharks to include cruising, rest or glide, recovery, and turning stages, and calculated that shark species commonly housed in captivity need to conduct a normal swimming repertoire composed of all of the above stages. It is extremely difficult to house sharks in tanks large enough to provide sufficient distance to enable sharks to carry out full swimming cycles and necessitated excessive turning.

Sea Trek with sharksAside from size, tank design is important – small, cylindrical shark tanks affect the animals’ physical and psychological well-being and the constant swimming in circles, as observed at Sea Life aquariums (e.g. Manchester Sea Life), or rather, an excessive proportion of active, asymmetrical swimming, has been demonstrated to place undue lateral stress on the vertebral column, potentially contributing to scoliosis. A number of captive sand tiger sharks in public aquaria have developed spinal deformities over the past decade, ranging in severity from mild curvature to spinal fracture and severe subluxation, due to constrained aquarium space.

Additionally, because of their constant swimming, signs of depression in sharks due to their environment not being optimal are difficult to spot, as they are so different to ours. The study on sand tiger sharks revealed that these animals did not (or could not) glide, and they instead swam constantly. Overall, gliding was a rare phenomenon throughout the entire behavioural data set and the authors hypothesised that the repetitive circular swimming behaviour observed by the sand tiger shark, as observed in London Sea Life, is an example of an indirectly self-injurious, locomotory stereotypical behaviour. This constant swimming in one circular direction with no gliding behaviour to break the swimming cycle appears to be a repetitive and unvarying behaviour and as such, resembles stereotypic behaviour. It is reminiscent of locomotor stereotypies documented in terrestrial mammals, birds, and aquatic mammals.

Stereotypic behaviour often signals an elevated stress state. Alternatively, it may develop as a coping mechanism to help the animal manage in a stressful environment. In either case, it is often considered a behavioural symptom of sub-optimal animal welfare. The practical implications of their mode of transport is that sharks need lots of room, are unable to change direction or level easily, and dislike square corners. All sharks are also talented jumpers. Though selachian brains are small, sharks are amazingly well hard-wired to do what they do, and capable of substantial learning. The difficulties in captive care of sharks are multitude, including the need for large, highly filtered systems, poor adaptability in terms of behaviour for most open-water species, keeping cold to cool water species in warm to tropical temperatures, and not maintaining a high, stable salinity.

Of the few species which have been studied thoroughly, they are known to have low birth rates, relatively long generation times and modest population densities in the wild.

This case study is an excerpt from the 2014 report An Investigation into the UK’s Largest Public Aquarium Chain.Please click HERE to access the full text (including references)

Leave a Reply

Your email address will not be published. Required fields are marked *