Jaws: the revenge. A great white shark kills the son of a grieving widow Ellen Brody. In mourning, the family goes to the Bahamas to visit her other son. Unbeknownst to them, however, the shark has learnt who they are and follows the family…
But can sharks actually learn? The short answer: yes they can!
Above: great white shark (Carcharodoncarcharias). IUCN red list: vulnerable
Broadly, learning by animals (including humans) can be categorised into two groups (Lieberman 1990):
1. Associative learning. This is when an animal learns of association between two events. For example, when they are born human babies may learn that if they cry they get food or attention.
2. Non-associative learning: This when an organism learns in response to a single stimulus. For example, sheep that are placed in a field next to a road may at first be scared by the sound of cars passing by, after some time, however, they will get used to the sound and will no longer be scared by it. This is what’s know as habituation.
Sharks’ capacity for associative learning was first demonstrated in the late 1950s. In this experiment, adult lemon sharks (Negaprion brevirostris) were trained for 6 weeks to press a target upon hearing the sound of a bell, in order to receive a food reward. The sharks learnt so well that even after a 10‐week absence from exposure to the bell, they still exhibited this learnt behaviour. Furthermore, lemon sharks were shown to learn quicker than bull sharks in a separate experiment using the same design (Wright and Jackson 1964).
Sharks have also been shown to learn quicker than teleost fish and even mice in certain associative learning experiments. For example, in an experiment where these animals had to choose the white from a pair of black and white targets, results suggested that sharks learn discrimination tasks more rapidly (Aronson et al. 1967).
Sharks have also been shown to exhibit non-associative learning behaviours. For example, when exposed to underwater playback of low-frequency sounds, grey reef shark habituated and became less responsive minutes or even seconds after exposure to the underwater speaker (Nelson and Johnson 1972). This habituation behaviour has also been shown to occur in whitetip and blacktip reef sharks, silk sharks, Bonnethead sharks, silvertip sharks, Atlantic sharpnose sharks and lemon sharks.
Above: Juvenile Blacktip reef shark (Carcharhinus melanopterus). IUCN red list: Near Threatened.
The above examples demonstrate shark learning in experimental environments, but what about in the wild?
Marine animals exhibit many forms of learning in nature; learning navigation and migration routes, how to hunt for prey and avoid predators and orientation. For example, salmon learn the ‘smell’ of habitats to help them navigate to spawning grounds in rivers from the open ocean (Dittman and Quinn 1996).
This type of ‘homing’ behaviour has also been demonstrated in sharks. For example, juvenile lemon sharks have been able to return after being displaced 16 km from their home in Bimini, Bahamas (Edren and Gruber 2005). In another study, port Jackson horn sharks (Heterodontus portusjacksoni) displaced 3 km from their particular resting sites in Sydney Harbour, Australia, were located in the same locations just two days later (O’Gower 1995). The mechanisms of homing behaviour in sharks are currently unknown. However, work on scalloped hammerheads (Spyhrna lewini) suggests that sharks might use a geomagnetic navigational system.
Successfully locating and capturing of prey is essential for animal survival, and requires learning about prey behaviour and distribution. Recent work on basking sharks suggests that sharks are capable of improving their foraging by learning. The relative performance of basking shark movements were compared to computer-simulated sharks randomly ‘walking’ through a changing zooplankton biomass landscape. Sharks performed better than computer simulations, as they altered their behaviour in order to utilize the richest prey areas. Furthermore, adult sharks performed better than juveniles, leading researchers to believe that sharks learn about prey distributions and structure as they age (Sims et al. 2006).
Above: basking shark (Centorhinus maximus). IUCN red list: vulnerable
Why do we care if sharks learn or not?
Tourism across the globe encourages human-shark interactions. From a conservation perspective, it is interesting to understand how these interactions may alter shark feeding, mating or social behaviour. For example, studies on stingrays fed by humans (Cocoran 2006; Semeniuk and Rothley 2008) have revealed some very concerning damaging effects both behaviourally and physiologically to tourist‐fed animals compared to non‐tourist fed individuals. Additionally, if sharks are capable of learning to avoid fishing nets owing to negative experience or a particular stimuli, developing effective repellents could become an important way to reduce bycatch (Guttridge et al., 2009).
Aronson et al. (1967) Instrumental conditioning and light–dark discrimination in young nurse sharks. Bulletin of Marine Science 17, 249–256.
Cocoran, M. (2006) The effects of supplemental feeding on the activity space and movement patterns of the southern stingray, Dasyatis americana, at Grand Cayman, Cayman Islands, Masters, Nova Southeastern University, Fort Lauderdale.
Dittman, A.H. and Quinn, T.P. (1996) Homing in Pacific salmon: mechanisms and ecological basis. Journal of Experimental Biology 199, 83–91.
Edren, S.M.C. and Gruber, S.H. (2005) Homing ability of young lemon sharks, Negaprion brevirostris. Environmental Biology of Fishes 72, 267–281
Guttridge et al. (2009). The role of learning in shark behaviour. Fish and fisheries. 10(4)
Lieberman, D.A. (1990) Learning: Behaviour and Cognition. Wadsworth, Belmont, California, 500 pp.
Nelson, D.R. and Johnson, R.H. (1972) Acoustic attraction of pacific reef sharks: effect of pulse intermittency and variability. Comparative Biochemistry and Physiology 42A, 85–95.
O’Gower, A.K. (1995) Speculations on a spatial memory for the Port‐Jackson shark (Heterodontus‐Portusjacksoni) (Meyer) (Heterodontidae). Marine and Freshwater Research 46, 861–871.
Semeniuk, C.A.D. and Rothley, K.D. (2008) Costs of group‐living for a normally solitary forager: effects of provisioning tourism on southern stingrays Dasyatis americana. Marine Ecology-Progress Series 357, 271–282
Sims et al. (2006) Encounter success of free‐ranging marine predator movements across a dynamic prey landscape. Proceedings of the Royal Society B-Biological Sciences 273, 1195–1201.
Wright, T. and Jackson, R. (1964) Instrumental conditioning of young sharks. Copeia 2, 409–412.