Social Learning in the Lemon Shark, Negaprion brevirostris
Sander van Dijk, Tristan Guttridge & Dr. Samuel H. Gruber
Despite numerous studies on their learning capabilities, social learning capabilities have never been shown in elasmobranchs. However, several anecdotal accounts from divers, zoo keepers and also Dr. Gruber have given strong indications that elasmobranchs are in fact capable of this type of learning. For example, new recruits to the wild group of caribbean reef sharks (Carcharhinus perezi) that are used for the "sharkdives" at the Bimini Biological Field Station will be hesitant to take the bait and approach the wall of divers, but after a view observations they will join the more experienced sharks.
The lemon shark (Negaprion brevirostis) is a shark species that is known to engage into social interactions with con-specifics in various ways. Adult lemon sharks for example form winter aggregations at Cape Canaveral and Jupiter Inlet, Florida. Juvenile lemon sharks will form small groups and socially interact in a way that is similar to juvenile fish species. These facts and the long running research on the lemon sharks around Bimini done by Dr. Gruber and his colleagues at the BBFS make them an excellent subject for research on the social learning capabilities of sharks.
The research will focus on neonate, or one year old, lemon sharks caught by gillnets as part of the PIT tag program. The sharks are kept in large community holding pens at the BBFS until they are ready for training and they are move to one of the two experimental pens. To approach their natural way of social learning as close as possible we have chosen to teach sharks a novel feeding task. In essence this task requires the sharks to touch a target before they receive food. Then we compare the learning rates of sharks that have been able to observe a trained shark versus the rate of a shark that has been exposed to an untrained shark according to the "good-demonstrator versus bad-demonstrator" principle. In addition, the fact that we will be training the sharks individually this research will allow us to look into individual learning variation within sharks.
Social learning is the acquirement of information or behaviour by individuals through observation or interaction with individuals or their products. Hereby are the individuals that acquire the information referred to as "observers" and the suppliers of the information referred to as "demonstrators". A well-known example of social learning is the spread of sweet potato washing in Japanese macaques, Macaca fuscata , where a novel behaviour of one macaque (washing a potato before consumption) was copied by almost the entire population after several months. Recently it has become clear that even animals initially not perceived to be capable of complex social behaviour, like fish, are capable of social learning. Even more so, research on the low survival rate of released hatchery fish has suggested that social learning plays an important role in especially the early life stage of shoaling fish species (as reviewed by Brown&Laland 2003). Shoaling juveniles will for example learn about foraging grounds and predator avoidance behaviour from more experienced individuals.
1. To investigate whether juvenile lemon sharks will learn a novel feeding task sooner when they have observed a con-specific performing the task.
2. To investigate the individual learning variations in juvenile lemon sharks.
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