Norwegian whalers harvest only one whale species; the minke whale. Like all other species, minke whales can be divided into several (sub)populations. It is long determined that there is a northern (common) and a southern (Antarctic) variant of this whale species. It is has also been assumed that there were several subpopulations of the common minke whale.
Therefore the International Whaling Commission (IWC) divided the Norwegian whaling into five geographic areas: the North Sea, the Jan Mayen area, an area covering the eastern Norwegian Sea/western part of the Barents Sea and the Svalbard area (fig. 1).
However, based upon extensive DNA analysis, we have demonstrated that there is no scientific evidence to suggest that the common minke whale in the North east Atlantic is divided into several subpopulations, and therefore, the multiple catch areas are redundant.
All catch in one register
The Institute of Marine Research (IMR) manages a register containing information about genetics (DNA) of each minke whale taken by Norwegian whalers.
The registry was created to prevent illegal whaling. The control system involves taking a meat sample from all individual whales that is later used to create an individual DNA profile stored in the register alongside other information such as catch date and location. The register is open. Anyone buying whale meat can control it against the data in the register.
The collection started in 1997, and the register now contains DNA profiles from around 9,000 minke whales.
Practical challenges with five areas
If populations are separated for a sufficiently long time, geographical or otherwise, they can grow to be genetically distinct. Now we have enough genetic samples in the register to determine if there really are several populations of minke whale where Norwegians harvest.
In the absence of sufficient knowledge of the minke whale population structure in Norwegian waters, IWC in the 1990s shared minke whaling into five geographic sub-areas. Areas were created out of a desire to spread the catch geographically by the precautionary principle.
Should there exist different populations, the division would distribute hunting pressure and largely neutralize any negative effects that may arise if stocks are harvested without otherwise taking the population structure into consideration. However, it is no secret that this division into subregions presents practical challenges for the Norwegian whalers.
Recently we presented results from the analysis of approximately 3,000 minke whales, captured in the five management areas in 2004 and in the years 2007 to 2011 – from the North Sea in the south to Svalbard in the north. All data are sourced from the DNA register, and it is the first time that such an analysis has included so many individuals.
Nobody knows where they mate
There are still many unknown details concerning the minke whale migration. During winter it stays in unknown areas at low latitudes, possibly even down to the equator, where we have assumed that they calve and mate. From there they migrate to higher latitudes where it is present in spring, summer and autumn. There the minke whale finds plenty of food and builds up fat deposits.
We have reasonably good knowledge of the minke whale distribution, behavior and biology when it is present on the whaling grounds, but we know very little about where it is and what it is doing during the winter "holiday in the sun".
We have for example never succeeded in identifying some well-defined mating and/or calving areas. The fact that sexually mature females are caught by Norwegian whalers may indicate that mating and birth occurs over a fairly long period of time through an annual cycle. Thus, is it possible that there are no well-defined breeding grounds, and that males and females meeting at the "right time" just let go right then and there?
Amorous encounters between north and south
Genetic studies of whales have also provided some sensational observations. In 2007, a minke whale with a DNA pattern that differed significantly from what we regard as normal was captured and entered into the register.
Our Japanese research colleagues have for many years collected samples of minke whales in the Antarctic. This enabled us to compare the DNA profiles of whales from the north and the south, and the conclusion was that the whale from 2007 really was a hybrid that has an Antarctic minke whale mother, while her father is a common minke whale.
Some years earlier, in 1996, a female minke whale was also captured in the Norwegian catch with pectoral fins that lacked the typical white bands. The whale had gray colored pectoral fins and thus resembled more of its Antarctic relative. The whale's DNA profile could be established because it was taken a tissue sample, and this left no doubt: this was a pure Antarctic minke whale. First observation of Antarctic minke whales in the northern hemisphere was thus a fact.
In 2010 another minke whale displaying a deviat DNA pattern to the common minke whale was also captured by Norwegian whalers . This time it was a pregnant female whale. The genetic analysis showed that this whale was the result of a pairing between an Antarctic minke male and a female common minke whale from the North Atlantic. Analyses of the fetus, a female, showed that the hybrid mother had become pregnant after mating with a male common minke whale from the North Atlantic.
Drawn to food
The results of the DNA registry shows that there is a potential for hybridization between common and Antarctic minke whales that are thought to have diverged genetically for several millions years ago. Unless the frequency of meetings between the two species should change significantly, there is little reason to believe that the dividing lines between the two species will be challenged. It is known that the whales can swim long distances, but all previous observations have indicated that they have not wandered much longer than to the equator, usually during winter, before they head back to feeding grounds in high latitudes.
We do not know anything for sure about the reasons for these findings, but it is tempting to speculate that changes in nutritional conditions can be the driving force behind such extreme migrations. Perhaps we had southern guests visiting the north even before the creation of the DNA register in 1997?