New Publication: 6 September 2017 (Mourier et al)


DIVING INTO THE SOCIAL LIVES OF SHARKS, A MATTER OF SCALE
6 September 2017 | Contact: JOHANN MOURIER | Royal Society Open Science

In research published this week in the Royal Society’s Open Science journal, Post-Doctoral Researcher Johann Mourier in collaboration with Macquarie University in Australia, used a social network analysis to examine the social interactions of Port Jackson sharks, arguably the most common sharks in southern Australia. “One of the most interesting elements about this research is that we show for the first time that these sharks show very strong preferences for particular individuals”, says Dr Johann Mourier, the lead author on the paper. “The large aggregations that these sharks form in the breeding season is not a random collection of individuals. These sharks prefer to hang out with other individuals of the same sex and size”.

Sharks are not well known for being social animals, but researchers have been studying their social behaviour in and around Sydney, Australia for several years now. Many animals form social groups to varying degrees, but studying the social lives of large aquatic animals is inherently difficult largely because it is hard to observe their behaviour. The Fish Lab at Macquarie University and Dr Mourier have circumvented this problem by using acoustic tags which identify individual animals when they are within range of the receiver (effectively a hydrophone with a memory card). By analysing the time-stamps, the researchers can tell who hangs out with who and for how long.

The paper also makes an important point in that the scale at which you record these social interactions is very important. “It is obvious from our analysis, that you cannot generate an accurate picture of social interactions if you collect data at a large spatial scale.” explains Mourier. “Meaningful social interactions are only detected if you look at relatively small spatial scales. You have to get up close and personal to really understand how these animals interact with one another”.

"Despite their small size and benthic lifestyle, Port Jackson sharks make impressive migrations”, explains Culum Brown, co-author and manager of the Fish Lab at Macquarie University. Sharks tagged during the breeding season (winter) in Jervis Bay in NSW, migrate all the way to Tasmania and back1. When they return to their breeding reefs, they do so with incredible accuracy. “Both males and females return to the same rocky reef to breed year after year” explains Jo Day from Taronga Zoo, a co-author of the paper. “This is pretty unusual for sharks, but it means that these guys establish long term relationships over many years”.

The team hope that their work will help understand the social behaviour and movement patterns of sharks generally and help dispel the “mindless killer” label these fascinating creatures are all too often lumped with.

1Additional information: Bass N, Mourier J, Day J, Knott N, Guttridge T, Brown C (2017) Long-term migration patterns and bisexual philopatry in a benthic shark species. Marine and Freshwater Research 68(8): 1414-1421.

REFERENCE
Mourier J, Bass NC, Guttridge TL, Day J, Brown C (2017). Does detection range matter for inferring social networks in a benthic shark using acoustic telemetry? R. Soc. Open Sci. 4: 170485. http://dx.doi.org/10.1098/rsos.170485

CONTACT
Johann Mourier (Perpignan, France)