In 1954, Warder C. Allee and Joshua C. Dickinson conducted an experiment on the smooth dogfish aimed at establishing dominance-subordination hierarchies in Chondrichthyans. This pioneering study, which lacked subsequent testing and analysis, has laid the groundwork for a persistent belief in rigid social structures among sharks. The dominance-subordination hierarchy, which is modelled on the social structure of the chicken, was proposed without convincing evidence in the context of Chondrichthyan vertebrates. It has affected the study of shark behaviour ever since, and stood in the way of the search for the true understanding of their societies.

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The experiment and its flaws

Allee and Dickinson’s experiment involved placing sixteen smooth dogfish in confined tanks and observing their behaviour. In such a situation, no shark who wanted to escape the proximity of another could do so, and no shark who wanted to establish a region for him or herself, could be rid of the others. 

In a species with a dominance-subordination hierarchy, this would facilitate high levels of aggression, yet, in spite of active efforts by the researchers to provoke competition for food among the sharks, including starving them for up to six days, they were unable to do so. 

Not one clear incidence of aggression involving dominance-subordination was seen, though the stated purpose of the experiment was to establish just such behaviour. This absence of agonistic incidents challenged the establishment of dominance-subordination hierarchies, but with no explanation, the researchers used collision avoidance to claim that dominance and subordination was present. 

Though they did not identify the mechanism by which the presumed dominance was enforced, they concluded that their experiment had established that dominance-subordination hierarchies are present in Chondrichthyes.

Thus, the foundational study by Allee and Dickinson, which is still cited as having established dominance-subordination hierarchies in sharks, lacks robust scientific support.   

Subsequent studies: Challenging the status quo

Subsequent studies of elasmobranch behaviour, including blacktip reef sharks, bull sharks and lemon sharks, consistently contradicted the notion of dominance-subordination hierarchies. Observations revealed a lack of intra-specific aggression, with sharks displaying social behaviours contrary to the expected territoriality and conflict. Instead, the term “heterarchy,” emphasizing flexible responses based on individual variation, cognition, and circumstances, emerged as a more appropriate descriptor for shark social communities. 

Sharks develop relationships with conspecifics through interactions that begin in the nursery, and respond to each other as individuals. Individual and social differences have been found to explain the apparently complex organization of what is interpreted as social networks. The perceived absence of rigid hierarchies challenges the long-held belief that sharks operate within dominance-subordination structures.

The observed collision avoidance among confined sharks is attributed to the sharks’ natural instinct for self-protection rather than complex societal analyses. Given their lack of the protection of a bony skeleton and their much smaller mass, self-preservation is a more plausible explanation for the tendency of smaller sharks to avoid collisions.

Rethinking shark societies

As we continue to unravel the mysteries of marine life, it is essential to approach shark behaviour with an open mind and a willingness to explore alternative explanations, fostering a deeper understanding of the intricacies of elasmobranch societies beyond oversimplified narratives. Sharks, it appears, have unique and complex social relations that differ significantly from traditional models based on terrestrial species. The challenge now is to unravel the intricacies of shark societies and redefine our understanding of their social dynamics.

About the author

Ethologist Ila France Porcher, author of The Shark Sessions and The True Nature of Sharks, conducted a seven-year study of a four-species reef shark community in Tahiti and has studied sharks in Florida with shark-encounter pioneer Jim Abernethy. Her observations, which are the first of their kind, have yielded valuable details about sharks’ reproductive cycles, social biology, population structure, daily behaviour patterns, roaming tendencies and cognitive abilities. Please visit: ilafranceporcher.wixsite.com/author.

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