Ron Macdonald looks at the evidence for humpback whale migration off Tiumpan Head in the Western Isles and if whales seen at this location are passing through on their way to warmer climes.
In a recent blog for Whale and Dolphin Conservation, The return of the giants: humpback whales in Scottish Seas, I speculated about the possible reasons why we are seeing more humpback whales in our seas.
This includes a recovery in the North Atlantic population after the ending of commercial whaling, a response to improving availability of their prey such as herring, sprat and sand eel, and migration from their feeding grounds in the Northeast Atlantic and Barent’s Sea to their breeding areas in the Caribbean, Cape Verde and the Azores.
In this blog I look more closely at the evidence for humpback whale migration at Tiumpan Head on the Isle of Lewis. Tiumpan Head is located at the tip of the Eye or Point peninsula, 11 miles north east of Stornoway.
I first turn to the Whale Track project, a research partnership involving the University of Tromsø, Akvaplan-niva, IMR, the Norwegian Institute for Nature Research and the University of Aarhus in Denmark.
The aim of this project is to gain a better knowledge about the migration of humpback whales, both during the winter period when they feed on herring outside Tromsø, and also after they leave the coastal areas and travel south. Since 2016 the project has satellite tagged 15 humpbacks. These whales have been tracked on their journey south to their breeding grounds in the Caribbean, and in one case back north.
What is striking is how close some come to the Northern and Western Isles before continuing the journeys to their southern breeding grounds. With the exception of one that visited Iceland before continuing its journey south, the whales chose a direct route. The image below of a spyhopping humpback whale was taken in January from a fishing boat off Sula Sgier, 40 miles to the north of the Butt of Lewis.2017
Some 20 miles south of the Butt of Lewis, at Tiumpan Head on the Point or Eye peninsula, 11 miles from Stornoway, the local Whale and Dolphin Conservation Shorewatch Team have been observing humpback whales.
The bar charts below from 2016 and 2017 show the monthly sightings.
Two things strike me; the first is the late autumn and winter peak in sightings and the shorter late spring/summer peak. Secondly, although the 2016 and 17 pattern is the same, the timing of sightings differ in that the winter peak in 2017 was later, extending well into late winter.
The Whale Track project is finding variation in the time humpbacks depart on their migration south, with some not departing until late January or February whereas others left much earlier in the autumn and early winter. The availability of shoaling and spawning herring in the Norwegian fjords and offshore are thought to important in how long the migrating humpbacks stay until the urge to breed drives them south and west.
If these are still available later in the winter then humpbacks will delay their departure. Could this be the reason why the histograms are different in 2016 and 17, with 2017 seeing a later departure from their feeding grounds in Northern Norway? The shorter spring and summer spike in the histograms, which are similar in both 2016 and 17 could be humpbacks returning north after the breeding season.
We also know that each of the breeding grounds have distinct and different peaks in abundance: Dominican Republic (February/March), Guadeloupe (April) and Cape Verde (May). Of course, Guadeloupe is the only known breeding area for a ‘British’ humpback following a match from Shetland in 2017. The image below shows a humpback whale off Shetland in 2017 on the left, and on the right in the foreground is the same whale off Guadeloupe.
Whales from all three breeding areas feed in Norwegian waters so we possibly have whales from both the Caribbean and North African breeding grounds passing close to the northern and western isles.
The more extended winter peak could be whales from different breeding areas passing by on their route south. Similarly, the shorter late spring and summer peak could be whales on their return journey north to their feeding grounds.
Of course until we carry out further research looking at humpbacks frequenting Tiumpan Head we have no actual evidence that what we are seeing are whales on migration from their northern feeding grounds to the Caribbean and possibly Cape Verde or only local movements around our coast.
Hopefully, the pointers to the area being important for migrating humpbacks will be looked at in the near future as part of the management of the proposed North-east Lewis Marine Protected Area.
Ron Macdonald is a member of the Trust’s Conservation Committee. He retired from SNH as Head of Policy & Advice in 2015 after 27 years of service. He wishes to thank Whale and Dolphin Conservation for access to their Shore Watch data and in particular Janet Marshall and Alice Walters, Konstantinos Sideris for help with producing the histograms, Audun Rikardsen and the Whale Track project for permission to reproduce their map and image, and finally, Brydon Thomason and Johnny Speedy for permission to use their images.