Updated: Apr 27
I love an aquarium! In my opinion, aquariums are a wonderful way for the general public to learn more about marine life in an exciting and interactive environment. If members of the public feel engaged by exhibits at an aquarium, they may learn about endangered species and become more passionate about conservation issues. Whatsmore, aquariums have the potential to contribute to the protection of threatened species through breeding programs. This becomes increasingly important, as more and more species of sharks are being classified as endangered in the wild. Yet, in order for an aquarium to be a place of value for both human beings and also the animals on display, it is of critical importance that the habitats are designed and maintained correctly.
You may be surprised to learn that you cannot just fling a shark into an aquarium and expect it to survive. In order to keep sharks healthy they must have ample space to swim, in water of the right temperature, acidity (pH) and salinity and be fed the correct, nutritious foods at a sensible rate (not too much, not too little).
Also, it has been known for different species of sharks to attack each other in aquaria and for individuals to injure other members of their group (as they do naturally in the wild!), so it is important to keep them in groups they will be safe amongst (Wyffels et al, 2020).
Sharks commonly assort themselves in the wild according to their sex and size. Newly born juveniles (known as "neonates") stay within a "nursery habitat", whilst older, larger sharks occupy a different habitat. Animals of different ages are rarely found together. This is known as "size segregation". Similarly, the ranges of males and females of a species often do not overlap. This is known as "sexual-segregation". So, when housing individuals in an exhibit together, it is important to choose their tank-mates carefully, to mirror their natural behaviours as much as possible.
Juvenile bonnethead sharks in a nursery tank at L'Oceanogràfic aquarium, Valencia
Also, not every species of shark is equally as easy to keep in an aquarium; there are certain species of sharks which adapt well to life in an aquarium and some that DO NOT. For example there have been several attempts to keep great white sharks (Carcharodon carcharias) in tanks and the results have always been tragic. In aquariums in the USA and Japan, white sharks have only survived a matter of days within aquaria; dying because they refused to eat anything. The only success stories with white sharks have come from keeping very young animals, which can be housed in a relatively small tank, for a relatively short period of time. The longest a great white has been housed was at the Monterey Bay Aquarium, when a very small juvenile (1.2m total length) was kept for 198 days, before being rereleased back into the wild. Larger, older individuals simply cannot be kept in an aquarium environment; they need a larger area to roam on a day-to-day basis and to migrate seasonally.
On the other hand, there are many species of sharks which do very well in an aquarium and can live long, healthy lives in tanks. For example, zebra sharks (Stegostoma tigrinum (formerly Stegostoma fasciatum)), many species of bamboo sharks (Chiloscyllium species) and many reef sharks (Carcharhinus species) do very well in aquariums.
One of the most robust large species that you can often see in an aquarium is the sandtiger shark (Carcharius taurus). These sharks have been popular in aquariums for a century because they are fantastically fearsome-looking, but actually have a very docile nature. In fact there are many aquariums where you can dive with these sharks in their tank! Sandtigers do well in aquariums because they are comfortable living in a relatively small range and are fairly tolerant to stress (if they are caught in the wild and moved into the tank) (Wyffels et al, 2020).
However, it has proved challenging to breed these sharks in aquariums. In the whole world there has only been 27 incidents in just 7 aquariums, where these sharks have successfully reproduced. Many of these only through artificial insemination and, sadly, many have ended in still-births. It is thought that the environment in the aquarium was not suitable and many teams have been working on figuring out how they need to house the sharks in order for them to reproduce...
And the Marineland Dolphin Adventure aquarium (MDA), in association with the Georgia Aquarium in the USA was successful! A female sandtiger shark gave birth to healthy offspring through aquarium breeding (rather than insemination) in 2018 (Wyffels et al, 2020).
The husbandry team described the environmental conditions they created in the aquarium, which brought them success. They housed their breeding group of sharks (2 males and 5 females) in an outside tank, which was supplied with through-flowing seawater from the neighbouring Atlantic Ocean. The team maintained water conditions at 31–34 ppt salinity and pH 7.9–8.1, with dissolved oxygen at 90%. As the tank was outside, there was natural light and the water temperature (between 17 - 26°C) and day-length (10.2 - 14.1 hours daylight) fluctuated seasonally, as they would under wild conditions (Wyffels et al, 2020).
This level of detail, maintaining so many environmental parameters, would be very challenging for many aquariums and the team suggested that conditions must be just-so in order to ensure healthy offspring. They stated that this would be especially challenging for aquaria which house their sharks in mixed species groups, as changing environmental conditions seasonally to benefit the sharks could be damaging to other species, which might normally be found under different condions when outside a closed system (Wyffels et al, 2020).
Sandtiger sharks have relatively low "fecundity" (how fertile they are over the course of their lives) because they mature at a late age, have a long reproductive cycle and only produce small litters with each pregnancy. Therefore, they are susceptible to population declines in the wild. The species is currently classified as 'vulnerable' by the IUCN, meaning they are threatened with extinction. However, this work could prove to be very important in the future, as successfully breeding these sharks in aquariums could mean more sharks could be introduced into the wild, to bolster the dwindling population. Hopefully, other aquariums will be able to follow suit, and successfully breed more of these and other species of sharks, to contribute to their conservation in the future.
IUCN (2020). International Union for the Conservation of Nature Red List of Threatened Species. Access online.
Wyffels J, Coco C, Schreiber C, Palmer D, Clauss T, Bulman F, George R, Pelton C, Feldheim K & Handsel T (2020). Natural environmental conditions and collaborative efforts provide the secret to success for sand tiger shark Carcharias taurus reproduction in aquaria. Zoo Biology.