Basking sharks form groups based on their genetics when returning to forage on spring plankton blooms such as those that occur on the west coast of Scotland, Ireland and the Isle of Man in the in the Northeast Atlantic.
According to a new study from the University of Aberdeen and published in the latest issue of the journal Scientific Reports, by analyzing DNA samples they were able to identify individual shark genetics when they returned to forage. The researchers were able to put together a database of of more than 400 DNA profiles, taken across five oceanic regions.
They found that the same fish repeatedly returned to the same feeding sites in successive years and were often joined by other sharks that shared a genetic link between them.
“Although developing genetic markers was challenging, the biggest obstacle to understanding how this endangered species uses the oceans was lack of DNA samples collected routinely from aggregations,” lead author Dr. Lilian Lieber said. “At the start of our study, the relatively few available samples were from stranded sharks taken years and hundreds of kilometres apart, making them useless for population analyses.
“A breakthrough came when we discovered our techniques worked on skin mucus. We routinely swabbed aggregations of sharks quickly and with minimal disturbance, to obtain genetic profiles of individuals traveling together.”
Even though basking sharks are highly migratory, capable of swimming hundreds of miles each year, the study found basking shark groups consist of individuals more related to each other than the rest of the population, indicating a tendency to travel as extended family parties following prescribed seasonal migration routes.
The study also revealed the first evidence of genetic differences between populations. Sharks sampled off Ireland in Spring, perhaps having overwintered near the US east coast, were genetically distinct from other Northeast Atlantic fish.
“Perhaps relatives hang out together, which could facilitate learning migration routes and encourage other cooperative behaviors,” University of Aberdeen’S Dr. Catherine Jones said. “This means there’s more going on in basking shark aggregations than first appears in that they don’t fit the shark stereotype of a lonesome independent predator.”