Common minke whales reach sexual maturity at an age of 5 to 7 years (NAMMCO 1999), and live as long as 42 years in the North Atlantic (Audunsson et al. 2013). They are essentially annual breeders, with most mature females becoming pregnant every year. Mating occurs in the late winter and gestation lasts about 10 months, with calves born in low latitudes during the winter (Martin et al. 1990). While the mating strategies of common minke whales are not well known, there is evidence of sexual segregation during the summer, with the larger females reaching higher latitudes than the smaller males. This has implications for management, as much of the catch in northern areas can be composed of females. For example, the proportion of females in the coastal West Greenland harvest ranges between 71% and 78% (Laidre et al. 2009).
Common minke whales feed on a wide variety of fish and invertebrates. In the North Atlantic, they consume mainly krill (Thysanoessa spp. and Meganychtiphanes spp.), herring (Clupea harengus), capelin (Mallotus villosus), sandeel (Ammodytidae), cod (Gadus morhua), polar cod (Boreogadus saida), haddock (Melanogrammus aeglefinus), as well as other species of fish and invertebrates (NAMMCO 1998). The diet varies both by location and over time. In the Northeast Atlantic, krill dominate the diet in far northern areas, whereas capelin, herring and haddock become more important further south in the Norwegian Sea and along coastal Norway. Sandeel and mackerel become more common in the diet in southern areas such as the North Sea (Winsland et al. 2007) In the Central Atlantic, capelin appears to make up a larger part of the diet, but herring, sandeel and cod are also important (Víkingsson et al. 2013). Interannual variations in diet composition, probably reflecting prey availability, have been noted in the Northeast Atlantic (Haug et al. 1999, Winsland et al. 2007) and around Iceland (Víkingsson et al. 2013).
These two photos show the stomach contents of two common minke whales off Iceland, with sandeels (left) and haddocks (right) Photo: Marine Research Institute, Iceland.
Like other baleen whales, common minke whales arrive in the summer feeding areas in a relatively lean condition but accumulate blubber rapidly over the summer. Christiansen et al. (2013), using data from whales taken in the Icelandic common minke whale harvest, determined that mature common minke whales accumulated about 0.5 cubic metres, or nearly half a tonne, of blubber over the summer feeding season. This blubber serves as an energy store for migration and reproduction in southern areas where less food is available for common minke whales.
Common minke whales are very important predators in the marine ecosystem, particularly in the Northeast and Central Atlantic stock areas. They are estimated to consume more than 1.8 million tonnes of prey annually in the northern Northeast Atlantic stock area (NAMMCO 1998), much of which is commercially important species of fish such as herring, cod and haddock. This consumption is similar in magnitude to the total commercial fishery for pelagic fish in the area (Toresen et al. 1998). The common minke whale is the most important marine mammal predator on fish in Icelandic shelf waters, consuming about 1 million tonnes of fish per year (Sigurjónsson and Vikingsson 1997). Multispecies modelling has indicated that these levels of consumption may have important implications for the yield of commercial fisheries in the northeast and central Atlantic (NAMMCO 1998; Stefánsson et al. 1997), however this modelling is still at an early stage. The effects of multi-species interactions may be counter-intuitive: for example, Lindstrøm et al. (2009), using a multi-species model for the Barents Sea including cod, capelin, herring and common minke whales, suggested that increased predation by common minke whales would actually have a positive effect on the capelin stock, even though capelin were a major food item for the whales. This occurred because common minke whales also consume cod, which are a major predator on capelin.
Common minke whales are themselves preyed upon by humans, killer whales (Orcinus orca), and perhaps by large sharks in southerly latitudes. Numerous instances of killer whale predation have been observed (e.g. Ford et al. 2005). Pods of killer whales begin the hunt by chasing the common minke whale at speeds of 15-30 km/hr. In most cases, the common minke whale can maintain this speed for a longer time than the killer whales and gradually outdistances them. However, if the common minke whale is confined in a bay or otherwise unable to escape, the killer whales kill it by repeatedly ramming it or holding it underwater (Ford et al. 2005). The magnitude of killer whale predation on common minke whales and its importance at the population level is not known.
|See killer whales attacking a common minke whale at Svalbard.|
Common minke whales are a host to a number of internal and external parasites, as well as commensals, and other epibiotic fauna. Off Iceland, indication of sea lamprey Petromyzon marinus attacks can be found of over half of the whales, while copepods such as Caligus elongatus and Pennella balaenopterae are also found on 10% of whales. The whale louse Cyamus balaenopterae, the pseudo-stalked barnacle Xenobalanus globicipitis and the goose barnacle Conchoderma auritum were also observed (Ólafsdóttir and Shinn 2013).
Epibiotics on common minke whale caught off Iceland- sea lamprey scars (left) and a fixed Penella (right) Photos: Marine Research Institute, Iceland.