Basking Sharks Get Own Identity Parade!

A shame to be launching this record of SOSF’s basking shark project after the Basking Shark Season is over, but the entry serves to mark the start of the IT work required for the launch (or re-launch) of a key component, the European Basking Shark Photo-ID (identification) database. This is to be operated in association with Marine Conservation International, the Plymouth (UK) -based Shark Trust (www.sharktrust.org), and the software and website engineered by the Marine Biological Association Laboratory at Plymouth. After months of trialling we now have an agreed format for the catalogue needed to accompany the database of photographs, and today hopefully the IT work involved will begin in earnest.

So what’s it all about? Well the idea is that many Basking Sharks can be recognised as individuals by the shape and distinctive marks on either side of their fins. But in fact it is only a minority of individuals that have distinctive features, and until recently standard photographic equipment rarely produced photographs sharp enough for individual recognition. Now with a good digital SLR camera and modest telephoto lens, plus sunlight coming from the right direction, it’s possible to get sets of digital photos good enough to recognise perhaps a third of Basking Sharks individually. This means we can not only use the data to track the movements of some individuals – in support of our ongoing satellite tagging work, but, more importantly, we can use the developing ratio of new to previously recorded individuals to estimate the total size of the regional population.

From Mauvis’ and my work in Scotland over previous years we already have 30 or more matches between sets of photographs taken on different occasions. Most were re-sighted within a week of first recording, but some were encountered again a year or more later. The re-sightings rate is allowing us to make some first ball-park estimates of population size, which seem to fit with the observation that there were more sharks sighted around the central Inner Hebrides this summer than for many years. Meanwhile our dogged Cornwall-based research assistant Gabi Gilkes is ploughing through our sets of photographs from this summer to see if she can find matches with photographs from previous years, either our own, or from other research teams participating in the wider project. We are awaiting the results with baited breath!!