REMEMBER. YOU CAN ORDER A FULL COPY OF THE REPORT

FOR ONLY £5 + P&P FROM MCS TODAY.

Overview

The most obvious trend in the basking shark reports coming in to MCS is that there is a 'channel' of sightings of sharks up the Irish sea between the Southwest (principally Cornwall, Devon and Dorset), up to the Isle of Man, and into Scottish waters in the area of the Clyde sea,  up into the seas off the Minch (Skye and Mull and other inner Hebridean Islands). and northwards into the waters of Shetland.

However, picking out trends in the data spread over time shows that there has been an increase in the number and geographic spread of sightings reported from Scottish waters (Figures 1-4. below).

Figure 1. Map of UK shark sightings between 1993 and 1998

Figure 2. Map of UK shark sightings between 1999 and 2004. Notice the increase in both the number (density of plots), and distribution (wider area) of sightings in Scottish waters, compared to the mid 1990s. This northern increase in sightings is nowhere more obvious than in Shetland waters, where before 1999, there were only 2 sightings.

Figure 3. Shows the number of sightings in three different periods from southwest regional waters.

Figure 4. Shows the number of sightings in three different periods from Scottish waters. Note the large increase (peak) in sightings (green line) for 1999-2004 years. principally in the month of August.

Summary and Conclusions

Clearly there is an increasing importance of basking shark hotspots in Scottish waters, still principally on the western side of the nation. However, the last 3 years has seen an even more marked shift in sightings from the southwest to Scotland. There has been a 65% increase in reports from Scottish waters since 2001 (when the last basking shark techincal report was published) up to 2004, with a concurrent decrease in southwest sightings of 66%.

The increase in sightings in Scotland isn't just as a result of increasing awareness and promotion of Basking Shark Watch in Scotland. Colin Speedie with the Wildlife Trust carries out effort-based surveys (surveys which follow set 'transects', and record observer effort to avoid repeat counts of the same sharks) from southwest England, up to Scotland on an annual basis. He has reported exactly the same shift in sightings. Even this year, he has mentioned that in terms of shark sightings it has been a poor year for the southwest for May and early June - the time when the sharks have historically been in southwest coastal waters in large numbers.

MCS is seeing this trend continue this year. We only received (thus far) 5 sightings of sharks in shallow southwest English waters for May 2005, whilst 11 sharks have already been reported in May for Scottish waters (I am writing this piece in mid-June 2005). The average number of sharks in Scottish waters in May over the last 17 years has been nearly 3, so numbers of sharks in Scotland in May are at least going to be 3 times the average for 2005. Before this year, large numbers of reports of basking sharks have only been recorded from Scotland during July and August, so this year we may be seeing an earlier as well as greater peak than average for Scotland than ever before.

The big political and biological question is: Is this shift a trend which is occuring due to climate change? Basking sharks feed at depth and the surface on zoo- (animal) plankton. principally coming to the surface during spring/summer months to feed on blooms of Calanus copepods (zooplankton). The timing of these blooms is usually related to the onset of phyto- (or plant) plankton blooms on which the Calanus feed. Blooms of phytoplankton are triggered by increased light, and increased availability of nutrients. Blooms for many phytoplankton species are also affected by temperature, and temperature-driven variables in oceanographic conditions.

Scientists based in Plymouth (Sir Alistair Hardy Foundation for Ocean Science) have already shown a northward shift in Calanus populations. both in timing, geographical ocurance, and involving different species of Calanus copepods in the North sea. It could be that the big latitudinal (north-south) shifts we are seeing in basking shark sightings over the 1000km or so of the UK could be correlated with changing sea temperatures, and distributions and densities of Calanus in surface waters. The blooms in Calanus copepods and sea surface temperatures are likely in turn to affect the number of basking sharks seen at the surface in any one geographical location. MCS is currently working on trying to quantify these effects.

So. carry on recording!

So. please keep us posted with your sightings - the long term nature of our dataset could be vital for establishing the reasons why we have recently seen large-scale changes in basking shark sightings. Click here to see a list of recent sightings or register a sighting of your own.