The most comprehensive analysis ever undertaken of basking shark sightings in UK waters, by the University of Exeter, MCS, Cornwall Wildlife Trust (CWT) and Wave Action, is published in the journal Marine Ecology Progress Series.

Historically hunted
The northeast Atlantic hosted an extensive commercial fishery for basking sharks, mainly in Norway, Ireland and Scotland, where more than 81,000 were killed between 1952 and 2004, hunted largely for their liver oil. Large-scale hunting ended in the UK in the middle of the twentieth century, though it continued at low levels in Norway until 2000.

Little know lifespan
Protected under UK legislation since 1998 and more recently under international conservation agreements, basking sharks are regularly seen off the coast of the UK during the summer, but very little is known about where and how they live for the rest of the year. The research team set about understanding patterns in summer basking shark sightings in UK waters. They analysed 20-years-worth of data from public sightings - a total of 11,781 records - from databases generated by MCS and Cornwall Wildlife Trust. They combined these data with records from dedicated boat-based basking shark surveys to complete the largest study of its kind.

Rising numbers
Their analysis showed a rise in the number of sightings from the 1980s through to the 2000’s. It also suggests an increase in the proportion of medium and large-sized animals, suggesting an increase in the number of older sharks. Basking shark populations are believed to recover slowly from over-exploitation due to their slow growth to maturity and the relatively few offspring they produce in comparison to other fish species. These new results show that long-term protection may well be paying off, with UK basking shark populations showing increasing body size: a classic sign of recovery for over-exploited fish stocks.

Hotspots
The researchers identified three hotspots for sightings off the coasts of South West England, Western Scotland and the Isle of Man. Each year, the earliest records were of sharks off South West England’s coastline in April, with the latest being in Scottish waters in August. This could mean that sharks are moving northwards during the summer, possibly following the arrival of the plankton which they feed on, or may suggest the existence of different groups of sharks in each location.

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