All NAMMCO member countries as well as Canada have participated in the NASS and T-NASS surveys, and the common minke whale has been a target species in all areas. These surveys are coordinated through the Scientific Committee of NAMMCO. In addition each country conducts other important research on the biology and ecology of common minke whales.
Summer distribution of common minke whales in the North Atlantic, showing sightings and effort from all North Atlantic Sightings surveys, 1987 - 2007, as well as 2007 CODA and SNESSA surveys.
Norway, along with other NAMMCO member countries, has a long-term goal of implementing ecosystem-based management for its fisheries and marine mammal hunts. A big part of this involves food web modelling to determine what effects the harvesting (or not harvesting) of one species might have on others in the ecosystem. Norway has concentrated its efforts in this area on modelling the Barents Sea ecosystem, which is relatively simple and has just a few very abundant species. Modelling requires extensive data on diet and energy requirements by age and size for all major species in the ecosystem, as well as information on the seasonal distribution and abundance of these species. These data become input into complex mathematical ecosystem models with acronyms such as SeaStar, Bifrost and GADGET. Output from these modelling efforts confirm that common minke whales are an important predator in the Barents Sea ecosystem, inflicting major mortality on adult and juvenile herring, cod and capelin (NAMMCO 2010).
The DNA registry, for which DNA profiles are taken from every common minke whale taken, has found uses outside the monitoring of legal catch in Norway. Skaug and Øien (2005) analyzed the profiles of 288 mother-fetus pairs in the registry to determine the partial DNA profile of the father in each case. They then searched the registry to determine if the father had also been caught. They were able to identify three likely cases of paternity in the dataset. These data can be informative about stock relationships in the area, as the time and location of every kill is known. They can also be used to roughly estimate the number of minke whales in the area through genetic “mark-recapture” analysis; this produces an estimate similar to that from sightings surveys, but with greater uncertainty because of the low number of recaptures. In addition to this, the registry has also been used to identify occasional instances of Antarctic minke whales, a species thought to occur only in the southern hemisphere, in the catch (Glover et al. 2010).
Norway has conducted extensive research to improve methods to quickly and humanely kill whales, the only country to do so in modern times. A major focus of this research has been the development and refinement of the explosive penthrite grenades used in the hunt, which replaced the “cold” non-explosive harpoon heads used earlier. The initial development and deployment of the penthrite grenade was completed in 1986 but refinement of the weaponry is ongoing. The use of the explosive grenades greatly increased the instantaneous death rate to over 80% today as opposed to only 17% for the cold harpoon, as well as greatly reducing the average time to death. In addition, post-mortem studies of killed whales have been used to determine the actual cause of death and to provide information to hunters to refine their abilities.
Common minke whales are widely dispersed in the northeastern Atlantic during the summer but virtually nothing is known about their movements, site fidelity and dispersal patterns in this area, especially in winter. Satellite telemetry is a powerful tool for collecting data on migration, winter distribution and key behavioural and physiological parameters of cetacean species. Norway started satellite tagging minke whales in September 1994 (Heide-Jørgensen et al. 2001) in the attempt of identifying their seasonal movement patterns along the coast of Norway.
Satellite tagging of a common minke whale in summer 2014 off Norway. The carrier for the satellite tag, that can be seen on the back of the whale, will fall of quite soon after the tag is implanted into the whale and leave the tag inside. Photo: K.A. Fagerheim, Institute of Marine Research, Norway.
After rejoining the IWC in 2003, Iceland began initiated work on a whale research program which was initially planned to include lethal sampling of common minke, fin and sei whales. Takes of the latter two species were later dropped from the program, and it became the Minke Whale Research Program. Such whaling is permitted under Article VIII of the International Convention on the Regulation of whaling, which allows contracting governments to grant special permits for scientific research. The main objective of the Program was to collect information on the feeding ecology of minke whales for incorporation into multi-species ecosystem models, with the overall goal of including these models in management programs for fish and marine mammals. Other objectives include investigations on stock structure, distribution and migration, growth and life history, parasites, diseases, biological parameters and pollutants (NAMMCO 2003, Pampoulie et al. 2013).
While initially envisaged to last for two years, the program was extended until 2007. Over this period a total of 190 minke whales were taken, with catches distributed around Iceland in proportion to the relative abundance observed from sightings surveys. More than 70 measurements and 80 samples were taken from each whale captured. The results, summarize by Pampoulie et al. (2013), were presented at a special IWC meeting in February 2013.
The results from the diet and feeding studies demonstrate that minke whales are opportunistic feeders that feed predominantly on fish. There is also some indication that the diet of minke whales in the area is changing in response to changes in the marine ecosystem. While sandeel dominated the diet in southern areas, it became less important after a decline in the sandeel stock. Over the same period herring became much more important in the diet. There have also been shifts in minke whale distribution that may be related to these changes in fish populations in the area. These in turn might be related to a recent increases in sea temperature in the area.
Length, age, abundance and catch data from the Research Program and previous work using commercial catches were included in a stock assessment model called Gadget, which can be expanded into a multi-species model. In this implementation, minke whale abundance was modelled to respond to the relative abundance of sandeel, a favoured prey in this area which has declined in recent years. The modelling outcomes show good fit to the available data and confirm that whaling mortality is very low for this stock. In the future the model will be expanded to include other species in order to further determine the role of the common minke whale in the marine ecosystem around Iceland.
Other key results of the Program include:
· Determining common minke whale age using earplugs or tympanic bullae was found to be unreliable. Aging using aspartic acid racemisation in the eye lens was found to be more accurate and reliable, revealing ages up to 42 years.
· Common minke whales accumulate blubber rapidly over the spring, summer and fall, with a mature whale adding as much as 500 kg of blubber on the feeding grounds. This energy reserve can then be used for growth, reproduction and migration to and from the breeding grounds.
· Satellite tagging was attempted on 12 common minke whales, and tags were successfully deployed on six whales (Víkingsson and Heide-Jørgensen 2013, 2014). Of these three endured into the whale’s fall southward migration. These whales migrated southwards in the mid-Atlantic, one of them reaching 28° S when transmissions ceased in early December. Migrating whales moved much faster than those on the Icelandic shelf, well over 100 km per day on average.
The Icelandic Minke Whale Research Program. Sampling of blubber thickness (left) and stomach content (right). Photos: Marine Research Institute, Iceland.
Aerial surveys primarily directed at common minke whales are carried out periodically in Greenlandic waters, most recently in 2005 and 2007 (Heide-Jørgensen et al. 2008, 2010). The 2007 survey included still and video camera systems as well as human observers. The data analysis was innovative in using data obtained from aerial photography and satellite tags to correct the survey for whales that were submerged during the passage of the plane.
Greenlandic researcher M.P. Heide-Jørgensen is a leader in the development of equipment and techniques for tagging whales with satellite-linked transmitters. Tags developed by Dr. Heide-Jørgensen have been used on several species in Greenland, Iceland, Norway and other areas. Common minke whales have proven to be one of the most difficult whales to tag successfully, as they are difficult to approach, offer a relatively small target and seem to shed tags effectively. The longest tag duration so far achieved is 101 days; less than 30 days is more typical and some tags never transmit at all (Víkingsson and Heide-Jørgensen 2013). Nevertheless the technique is still under active development and will likely provide further valuable information on minke whales in the future.
Minke whales are not taken or frequently sighted in the Faroes, and therefore are not a subject of priority research there.