This study in the UK was the first one to demonstrate social personalities in individual sharks, namely small-spotted catsharks. A group from the Marine Biological Association in Plymouth, UK and the University of Exeter, including D. Jacoby, D. Sims, L. Fear & D. Croft has conducted the research.
Small-spotted catsharks hunt at night and during the day rest on the seabed in groups while camouflaging to avoid predators. The scientists used this lifestyle to research their aggregation habits and preferences. They designed the following experiment: 10 groups of 10 juvenile, aquarium-bred catsharks and studied them in 3 different aquarium based situations, simulating different habitats.
Aggregation Habits and Preferences
Situations created by the scientists where small-spotted catsharks might hide in:
- 1st Situation: Simple habitat with gravel and pebbles with little hiding opportunities.
- 2nd Situation: Complex habitat, filled with stones and places for the sharks to hide.
- 3rd Situation: Mix of the previous two, providing intermediate complexity and some hiding places.
Results: Individual sharks who tended to form groups continued to do so no matter the habitat, while sharks tending to prefer to hide on their own also did so in each situation, showing there is such a thing as social or antisocial sharks!
It has to be said, however, that there was a difference in the aggregation patterns in the different habitats: On the gravel, providing a less complex background and thus skin tone matching is more efficient to hide, less aggregation has been recorded. This is equally fascinating as it hints that small-spotted catsharks are able to assess the context of when to form groups and make decisions based on multiple complex factors. And this behavior has to be innate, as the individual sharks were born and bred in an aquarium. Also, interestingly, their social behavior in resting groups had no impact on potential swimming groups, as they go back to a solitary lifestyle when swimming and looking for prey.
Since its publication, shark social life has been investigated in many different species. Blacktip Reef Sharks have been shown to form communities by active choice rather than aggregating randomly when food is abundant. However, despite that burgeoning research, most shark aggregations remain a mystery. Whale Shark groupings in Mexico, Basking Sharks in Ireland, Silky Sharks off Malpelo Island, Hammerheads in the Galapagos…. have barely been studied and are still poorly understood!
Sources:
- Jacoby, D.M.P., Croft, D.P. and Sims, D.W. (2011). Social behaviour in sharks and rays: analysis, patterns and implications for conservation. Fish and Fisheries, 13(4), pp.399–417. doi:https://doi.org/10.1111/j.1467-2979.2011.00436.x.
- Jacoby, D.M.P., Fear, L.N., Sims, D.W. and Croft, D.P. (2014). Shark personalities? Repeatability of social network traits in a widely distributed predatory fish. Behavioral Ecology and Sociobiology, 68(12), pp.1995–2003. doi:https://doi.org/10.1007/s00265-014-1805-9.
- Mourier, J., Vercelloni, J. and Planes, S. (2012). Evidence of social communities in a spatially structured network of a free-ranging shark species. Animal Behaviour, 83(2), pp.389–401. doi:https://doi.org/10.1016/j.anbehav.2011.11.008.