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Introduction

Focusing on another local species here in the Pacific Northwest, the minke whale actually consists of two separate species: the common (or northern) minke, which is what we find in our waters, as well as the Antarctic (or southern) minke whale, found in the southern hemisphere. Being the smallest of the rorqual whales, the two species (and 2nd and 3rd smallest baleen whales behind the pygmy right whale) are incredibly similar, differing in geographical ranges and specific coloration and size.

Common/Northern Minke

The common/northern minke is found in our waters and in both the Pacific and Atlantic Oceans as far south as the equator, though the species is commonly found further south in the Pacific than the Atlantic in general. For example, minkes have been seen as far south in Baja, California in Pacific, but generally only as vagrants further south than New Jersey in the Atlantic. Like it’s southern counterpart, this whale is generally dark grey with a white underside and hints of white on the pectoral fins and flank. Growing to around 30 feet and 20,000 pounds, the common minke has 50-70 abdominal pleats outside its 230-360 baleen plates. These baleen plates are used for filtering food (krill, small forage fish, etc.) and are colored a cream or white hue.

Common or northern minke.

Dwarf Minke

The northern minke actually has a subspecies as well known as the dwarf minke! This subspecies appears similar, but only grows to a maximum of 26 feet and 14,000 pounds. This subspecies is distinguishable by a more pronounced white ring around the pectoral fins, as well as a thin black border on its baleen plates. Curiously, this subspecies of the northern minke is only found in the southern hemisphere! Little is known about it, as it is difficult to distinguish it between the southern minke whale within the same geographical range during initial sightings.

Dwarf minke. Photo: Matt Curnock.

Southern Minke

The southern minke is very similar to the northern, but can grow a bit larger to an average 35 feet and 22,000 pounds. Though dark grey like the northern species, the southern minke tends to have more white on the body, as well as clear white streaks extending from the blowhole that are more pronounced than the northern. An easy identifier between the two species are its baleen plates as well! Under their 22-38 abdominal pleats (fewer than the northern), the 200-300 baleen plates consist of two colors: black towards the throat and changing to white towards the rostrum. There is also a degree of asymmetry in this coloration as well, with less white coloration on the left baleen sets than the right.

There have been two confirmed accounts of hybridization between the northern and southern minke species. Both caught by in the Northern Atlantic, the two animals’ parents were clearly separate species, with one having a northern minke father and southern minke mother and the other having a southern minke father and northern minke mother, indicating both species are capable of raising a hybrid.

Diet & Behavior

We like to say that minkes are the harbor porpoises of the baleen whales. They share the attributes of being small, shy, inconspicuous and not flashy at the surface, so it is no wonder there is still a lot we don’t know about both of these species, but let’s discuss what we do know about minke diet and behavior.

Minke whales are generally loners, found by themselves or in small groups of 2 to 3 individuals. However, in the Arctic (when/where the food is plentiful) there can be loose aggregations up to 400 individuals! Researchers can use color patterns and scarring on the dorsal surface and flank to identify individuals.

Their seasonal distribution and migration patterns for nearly all populations are poorly understood (their size, behavior and distribution in remote pelagic habitats contributes greatly to this), and are less predictable and well defined as other baleen whale species. There also seems to be a large variation within and between locations/populations. For example, in the Pacific Northwest research has shown that some migrate (up to 400 km), but in Puget Sound they may have exclusive, adjoining home ranges (which is unknown in other baleen whales) and some may remain ‘resident’ (individuals are loyal to summer feeding grounds). In some areas they migrate, and others they remain in more restricted areas. Some research indicates that there are sex differences in migration routes/locations, and that females may be more likely found close to shore, and males found farther offshore. It is thought that minkes segregate more by age and sex than other baleen whale species, thus they seem to have a complex social and population structure that is poorly understood. 

Minke whales are sexually mature at 7-8 years. Pregnancy lasts 10 months and females calve on average every 2 years, but may be able to calve every year. Mating has never been observed, and breeding/calving grounds are unknown (again they don’t have those distinct migration routes that other baleen whales do). It is thought that mothers nurse their calves for only 4-6 months.

When it comes to food, they are opportunistic and feed on crustaceans, plankton, krill, and small schooling fish (e.g. anchovies, dogfish (which are small sharks!), capelin, coal fish (remember this from the Sei whale blog?), cod, eels, herring, mackerel, salmon, sand lance, saury, wolfish, and pilchard). Minke whales may have actually benefited from past whaling. As the larger whales were targeted (in the past minkes were too small to be worth it), that decreased their competition and increased availability of prey. Their food is not very deep, so they don’t need to dive long, normally around 6-12 minutes, but may be up to 15. As other rorquals (those baleen whales with throat grooves) do, they gulp feed, taking in all the water and prey and straining out the good stuff, but they like to do it on their side, known as a side-lunge. Birds circling or diving can often indicate marine mammals feeding below (so the marine mammals are working the prey and the birds join in after), but what is interesting is that minke whales may target areas where diving birds have previously schooled prey – making the birds do the work instead!

At the surface they are sleek and quick – they sometimes create a spray at high speeds that is described as a rooster tail (you may remember this term from the Dall’s porpoise blog). They are very active at the surface, but will occasionally breach, and are relatively shy around boats. They do not fluke up when they dive (like other rorquals), but may arch and expose a lot of their back and body in a high roll. They also are a little unique in that when they surface they come up snout first, in many other species the head does not come up like that. With larger whales you can use the shape of their blow to help identify species in the field. Minkes have a bushy, small/weak blow of 6.5-10ft, one that is easily missed in the field. However, if you are upwind you might not miss it due to the smell! All cetacean breath smells bad, but minkes take the cake – sometimes you can smell them before you see them.  Hence their loving nickname, “stinky minke”!

Status & Threats

Minkes are actually the most abundant rorqual in the world, and their population status is therefore considered pretty stable throughout their range. There are two stocks that the International Whaling Commission (IWC) currently recognizes as stocks of “concern”, and both are found in the Eastern North Pacific near Japan, China, and Russia. Commercial and/or scientific whaling still occurs in these regions which may be influencing these particular stocks more than others.

Threats include:

  • Whaling (as mentioned above)
  • Entanglement in Fishing Gear: really any gear that uses lines such as groundfish trawls, gillnets, herring weirs, lobster traps, purse seine nets, etc.
  • Vessel Strikes
  • Ocean Noise: the increase in shipping traffic may have detrimental effects on the minke’s ability to communicate, especially as they regularly use lower frequency calls which would be masked by larger ship noise.

Fun Facts

  • The scientific name for the minke is Balaenoptera acutorostrata. The two components of their name mean “winged whale” and “sharp snout” respectively, in reference to their fairly pointed rostrum.
  • The common name “minke” originates from Norway, where a rookie whale spotter apparently mistook a minke whale for a blue whale! The unfortunate whale spotter’s name was Meincke, which has transformed into minke.
  • Minkes can live up to about 50 years of age.
  • Their vocalizations are incredibly varied, including sounds such as clicks, grunts, pulses, ratchets, thumps, and boings. Yes, boings! These strange calls almost sound like they were made for a sci-fi or cartoon movie, but they’re actually a recently discovered minke call! Check out this YouTube video to hear the boing call.

cindy.elliser@pacmam.org

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