What Happened to the Minke Whales this year?

A report by HWDT Sightings Officer Laura Mandleberg

November 2005

This year, unusually low numbers of Minke whales were observed around the west coast of Scotland. This was certainly the case for our immediate area (Inner Hebrides), where local whale-watching boats and our own research vessel ‘Silurian’ observed a dramatic difference in the distribution of Minke whales compared to previous years.

Minke whales, which arrive in Scottish waters to feed every year, are usually seen frequently and regularly throughout the spring and summer months, with a general increase in recorded sightings in August and September. However, this year we observed a change to this pattern. After a fairly normal start to the season, with frequent and regular sightings of Minkes being recorded in the usual feeding grounds, we noticed a shift in the distribution of whales. From mid-June onwards, it became clear that the Minke whales had congregated to feed in a very small area, because for the next month or so, the majority of whale sightings were confined to just one sea loch, Loch na Keal. Loch na Keal is an open sea loch on the west side of Mull opposite the famous island of Staffa, where many seabirds arrive every year to breed, including the well-loved puffin. To observe such a high concentration of whales feeding in such a small area is fairly unusual compared with the distribution of Minke whale sightings in previous years. We normally record a more scattered distribution of whales feeding over a much larger area. In addition, the lack of Minke sightings reported from elsewhere in our area whilst the whales were feeding in Loch na Keal (mid-June until mid-July) was atypical. There are a few possible explanations for these differences: perhaps this year the feeding was exceptionally good in Loch na Keal - that is, good enough to attract high numbers of whales to the same area. Or, maybe feeding in other areas was especially poor this year, therefore forcing the whales to feed in a very small area.

We know that there was an exceptional amount of food in Loch na Keal this year because the whales were feeding just in this one sea loch for nearly a month! On average, there were between 5 and 10 whales feeding in the loch, but on some days, as many as 15-20 Minkes were counted! Spectacular feeding frenzies involving masses of hungry Manx shearwaters, razorbills and guillemots were observed, and lots of ‘lunge feeding’ activity - a feeding strategy used by minke whales to trap small, schooling fish at the surface. It was extremely exciting to see two obviously very young whales, or calves, feeding in Loch na Keal. These two youngsters were so small (approx 2.5-3 metres in length), that they were often mistaken by one whale-watching boat for dolphins! At such a small size, it is thought that these individuals may have only just been weaned from their mothers, whose milk they would have been suckling for the first six months of life. It is therefore possible that we were witnessing the whales during their first feeding season! It was also interesting to observe half–way through this month of feeding frenzies in the loch, the arrival of some very large adult Minke whales, including the possible arrival of two of our sponsored whales, Face and Nick! Up until this point, mostly juvenile whales had been recorded. This observation of the juveniles arriving before the larger adults, who arrived later in the season, matches patterns recorded in previous years.

With such a high concentration of whales feeding in a relatively enclosed area on a limited supply of fish – we knew that there would only be enough food in the loch to sustain the whales for a limited period. So, after a month of intense feeding in Loch na Keal, the whales eventually moved on as expected, and by the middle of July, there were no more whales left in the loch. Where the whales went to next and whether they travelled to the next feeding ground together as a group, or separately is not yet clear? However, their sudden disappearance from Loch na Keal certainly suggested that they left the area at the same time. It was certainly interesting to hear reports of groups of feeding Minke whales off Shetland, Orkney and in the Moray Firth around the same time that the Minkes disappeared from our area! Comparisons between dorsal fin Photo-ID shots of the Loch na Keal whales with the Moray Firth whales will help to establish whether the same individuals were seen in both locations and will provide important information on the movements of the North-East Atlantic population of Minke whales.

Sadly, from this point onwards very few Minke whales were reported feeding again on the west coast of Scotland. This is extremely unusual for August and September, which are often the months with the highest number of Minke whale sightings. So what caused this observed change in Minke whale distribution and should we be concerned? Well, firstly, it is important to remember that the marine environment is very dynamic with many factors influencing the production and eventual distribution of plankton and fish in the water column. This makes it very difficult to predict exactly where the whales are going to be feeding from year to year, or even from month to month, especially if they are feeding on a number of different prey species. However, one theory to the lack of whales feeding around the west coast of Scotland this year is poor sandeel stocks, forcing the whales into new feeding grounds. Sandeels make up a very important part of the Minke whale diet and are also a vital source of food for many of Scotland’s seabirds. Given that 2005 was reported as yet another poor breeding season for Scotland's seabirds, in particular on the west coast colonies (Tiree, St Kilda and Canna), the link between low numbers of Minke whales and a sandeel shortage seems obvious. It is not yet clear whether the apparent lack of sandeels on the west coast is a result of warming seas due to climate change but the early arrival of basking sharks and the unusually high number of sunfish (a species brought up with the Gulf Stream) sighted this year may serve as early indications to warmer sea temperatures. Finally, it is important to emphasise that, although this year has seen a decline in Minke whale sightings, it is too early to deduce whether this is part of a long-term shift in distribution, or just a ‘one-off’ year. Close monitoring of sightings in the following years will enable us to answer some of these questions and help us understand more about the factors involved in influencing the movements of these enigmatic creatures.