The Humpback whale around the British Isles

The Humpback whale (Megaptera novaeangliae)

                The humpback whale is a baleen whale that can reach 15m (51ft) in length. It is black or dark grey with long white pectoral flippers. It is found in the North Atlantic and is rarely seen on Atlantic coasts in Spring and Summer. It can be found in small groups and feeds on krill and shoaling fish (British Divers Marine Life Rescue, 2004-2012).

Humpback whales migrate nearly 10,000km in a year between their summer feeding grounds in near-polar waters and their winter breeding grounds in shallow, tropical waters. Observations of individuals suggest that oceanic populations are divided into a number of seasonal subpopulations which are not separated by geographical barriers (Baker et al. 1990). There are two populations of humpback whale, Southern hemisphere and Northern hemisphere. Their breeding cycles are unsynchronised and they do not interbreed (Johnson & Wolman, 1984). This was confirmed by Bakers et al. (1990) study of haplotypes which showed there was no overlap between the northern and southern populations, which was suggested to be due to strong maternal traditions regarding migratory destinations.

Humpbacks spend the summer on high latitude feeding grounds and migrate to low latitude winter breeding grounds, which is shown in figure 1. During the winter they are confined to shallow waters along coastlines and around oceanic islands which makes them vulnerable to modern whaling techniques. During the winter they fast and only eat during the summer (Johnson & Wolman, 1990).

In the eastern North Atlantic, during the summer humpbacks can be found from Iceland, Scotland and Norway to the Barents Sea, north of the Netherlands. In winter they can be found as far south as the Cape Verde Islands off the coast of Western Africa. In the western Atlantic they summer around the Denmark Strait off the east coast of Greenland, Labrador, Newfoundland and Nova Scotia and spend winter in the shallow waters around the Antillean chain of the West Indies. Each year humpbacks return to the same summer grounds (Johnson & Wolman, 1990).

Figure 1 – Geographical distribution of humpbacks whales (from Johnson & Wolman, 1984). Hatching = summer feeding grounds, stippling = winter grounds.

In the Northern hemisphere the diet of the humpback whale consists of krill, zooplankton, herring, Arctic cod and Pollock. Humpbacks distributions are heavily clumped in areas where food is abundant i.e. around the Newfoundland coast the humpbacks return coincides with the spawning of capelin and they feed at or below the surface (Johnson & Wolman, 1990).

The detection of humpbacks has been done in Britain using bottom-mounted hydrophones to detect whale song. Charif et al. (2001) did this from October 1996 to September 1998 and during this period, humpbacks were consistently detected between October and March from the Shetland-Faroe Islands to the southern waters west of the English Channel. This shows a south-westerly trend in their movements but there was no corresponding northern movement detected between April and September. This suggests that the offshore waters of the British Isles are used as a migratory corridor for humpback whales as they do between their feeding and breeding grounds (Charif et al. 2001).

References

Baker, C.S., Palumbi, S,R., Lambertsen, R.H., Weinrich, M.T., Calambokidis, J. & O’Brien, S.J. (1990). Influence of seasonal migration on geographic distribution of mitochondrial DNA haplotypes in humpback whales. Letters to Nature, 344:238-240.

British Divers Marine Life Rescue (2004-2012) Whales. Source: www.bdmlr.org.uk/index.php?page=whales-dolphins-amp-porpoises. Accessed: 28/02/2012.

Charif, R.A., Clapham, P.J. & Clark, C.W. (2001). Acoustic detections of singing humpback whales in deep waters off the British Isles. Marine Mammal Science, 17(4):751-768.

Johnson, J.H. & Wolman, A.A. (1984) The humpback whale Megaptera novaeangliae. Marine Fisheries Review, 45(40):30-37.