Amazing news as a large basking shark was spotted in Crotia. The shark was feeding along the Ližnjan peninsula yesterday! This area is situated in the Adriatic sea and a loooong way from the Atlantic. You can see some video above that was uploaded to youtube by the guys who spotted from their boat.
We have written a blog post about shark migrations in the Mediterranean previously when there was a juvenile shark caught off Sicily (click here). Those sightings aren't too far away from Croatia (compared to the Hebrides) however it's still crazy to think about how far these geographical areas are apart.
Other research has shown that the genetic diversity is very low with the north Atlantic population of basking sharks and as such the opinion is that there is one large population closely related and that the Hebrides could be a mass get together to (try) and expand the gene pool! The government sponsored tagging efforts (and by other organisations such as MCI) have shown large migrations of sharks from the Hebrides and Isle of Man, to as far as the Canary Islands or Newfoundland, but not yet the Mediterranean. We also have received reports of shark sightings in Norway and Iceland, however these seem to be a northerly extension of the UK migration pattern.
These north Atlantic sightings are vastly spread out so it's interesting to come up with theories on seasonal or reproductive based migration patterns. The high incidence of juv sharks seen in the Med had led to speculation of this being a nursery area for sharks and given the long gestation period (>18m) then a breeding event in the Hebrides in July/August and 18 months would mean February pupping time, which fits in nicely with time period! Coincidence or not!? A number of juvenile sharks have also been spotted around the Isle of Man in previous year, with some reports of that area being a pupping ground. If there was a yearly migratory pattern (which has been demonstrated in satellite tags) then the 18 months would be a little out in terms of the juv sighting time around the IoM.
Perhaps there are different hierarchies of sharks, with large females (which have the liver size and energy store to cover big distances) being the main breeding population and then travelling the greatest distances to these grounds. Or perhaps there is a distinct and discreet Mediterranean population which doesn't travel as far and is separate from the Atlantic sharks. For all the tagging that has happened from the Hebrides (or Iom/Ireland) then no link has been made with the Mediterranean sharks so this is still a mystery and we can but made guesses and assumption based on the current available data, study and information!