Slime samples taken from basking sharks have provided unprecedented insight into the movement and connectivity of basking sharks in the North East Atlantic. These were collected using the method that Irish Basking Shark Project (IBSP) developed with the University of Aberdeen.
Developing a method to identify individual sharks is important for tracking shark movements, estimating population sizes and linking populations. Shark research groups normally use photo ID and visual tag methods to identify individual sharks, but these techniques have limitations and there has been uncertainty regarding their efficacy for basking sharks over longer time periods. In 2010 members of the IBSP and researchers from the University of Aberdeen developed a new method for identifying individual sharks by extracting their genetic sequence from the slimy mucus that they secrete onto their abrasive skin. Since that date the simple method, which entails using a cotton pad to rub the skin, has been adopted by other active basking shark research groups in Scotland, England and the Isle of Man. The preliminary results from this collaborative and coordinated effort were recently published in Scientific Reports.
The findings confirm the findings from other visual tag, photo ID and satellite transmitter-based tracking studies that have shown basking sharks regularly moving between surface hotspots in the Northeast (NE) Atlantic throughout the summer season and inter-annually. The results also confirm the connectivity between various NE Atlantic hotspots and indicate that the Irish Sea is an important movement corridor for the species, with an estimated population of 380 sharks. This is one of the first population estimates for a discrete geographical area of the NE Atlantic and a big step in establishing the international importance of such areas for the species. More controversially, the paper also identifies genetic structuring in the NE Atlantic population, indicating that sharks encountered together in surface hotspots are more related than previously thought and that a distinct group of early season (April-May) migratory sharks may exist off the southwest coast of Ireland (Co. Kerry).
The IBSP and other research groups focused on the conservation of the basking shark continue to gather slime samples from sharks encountered on the surface. In time, we hope that this simple technique will provide further insight and knowledge on this elusive and endangered species. For more information you can read the published paper at https://www.nature.com/articles/s41598-020-58086-4 (or check out our project pages).