Minke whales, known for their relatively small size among baleen whales and their global distribution, play a crucial role in marine ecosystems. These fascinating creatures, whose common name originates from a case of mistaken identity by a Norwegian whaling spotter named Meincke, exhibit unique feeding behaviors and dietary preferences. This article delves into the diet of minke whales, exploring what they eat, how they feed, and the ecological factors influencing their feeding habits.
Minke Whale Overview
Minke whales are members of the baleen whale family, characterized by the presence of baleen plates in their mouths instead of teeth. These plates filter small prey from the water. The scientific name Balaenoptera acutorostrata translates to "winged whale, sharp snout," aptly describing their appearance. Compared to other whales, minke whales are known for their relatively small size as well as black/purple/dark gray slender bodies. Their dorsal fin is sickle-shaped and tall. They are one of the most abundant rorquals in the world, and their population status is considered stable throughout almost their entire range (especially when compared to other species of large whales).
There are two main species of minke whales: the common minke whale (Balaenoptera acutorostrata) and the Antarctic minke whale (Balaenoptera bonaerensis). Taxonomists further categorize the common minke whale into two or three subspecies; the North Atlantic minke whale, the North Pacific minke whale and dwarf minke whale.
Minke whales typically live between 30-50 years, but in some cases, they may live for up to 60 years.
Physical Characteristics
Minke whales are the smallest baleen whale in North American waters. Minke whales are relatively small, dark, and sleek, reaching lengths of up to 35 feet and weighing up to 20,000 pounds. Females may be slightly larger than males. They have a fairly tall, sickle-shaped dorsal fin located about two-thirds down their back. Their body is black to dark grayish/brownish, with a pale chevron on the back behind the head and above the flippers, as well as a white underside. Calves are usually darker in coloration than adults.
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Common minke whales vary in body size, patterns, coloration, and baleen based on geographical location. They may vary individually as well. Northern Hemisphere minke whales are distinguished from other rorquals by their relatively small size and a well-defined white band located in the middle of their dark flippers. They have 230 to 360 short, white/cream colored baleen plates on each side of their mouth and 50 to 70 abdominal pleats are located along their throat.
Dwarf minke whales are significantly smaller in size, growing up to lengths of about 26 feet and weighing up to 14,000 pounds. Their baleen plates have a thin black border. Dwarf minke whales can also be distinguished from other minke whales by a bright white patch on the upper part of their dark pectoral fin that extends up towards the shoulder and back area. They also have a dark half-collar that wraps around the head and reaches the throat grooves.
Antarctic minke whales have 200 to 300 baleen plates on each side of their mouths. Their pectoral flippers are usually solid gray with a white leading edge, and the noticeable band seen in the northern and dwarf form is generally absent. Unlike other minke whales, the color of their baleen is asymmetrical, with fewer white baleen plates on the left side than on the right side of the forward part of their mouth. The rest of their baleen plates are dark gray.
Distribution and Migration
Common minke whales prefer temperate to boreal waters but are also found in tropical and subtropical areas. They feed most often in cooler waters at higher latitudes and can be found in both coastal/inshore and oceanic/offshore areas. Their distribution is considered cosmopolitan because they can occur in polar, temperate, and tropical waters in most seas and areas worldwide. Minke whales, like some other species of cetaceans, migrate seasonally and can travel long distances. Some animals and stocks of this species have resident home ranges and are not highly migratory. The distribution of minke whales varies by age, reproductive status, and sex. Older mature males are commonly found in the polar regions in and near the ice edge-often in small social groups-during the summer feeding season. Mature females will also migrate farther into the higher latitudes, but generally remain in coastal waters. Immature animals are more solitary and usually stay in lower latitudes during the summer. Minke whales in Alaskan waters are migratory, but animals in the inland waters of California/Oregon/Washington are considered "residents" because they establish home ranges. Northern minke whales have a widespread distribution in the Northern Hemisphere and are found throughout the northern Atlantic and Pacific Oceans. Their range extends from the ice edge in the Arctic during the summer to near the equator during winter. Dwarf minke whales are distributed close to the polar region in the Southern Hemisphere, especially during the summer months, but are more common in temperate and warmer waters of middle and lower latitudes. They are frequently reported in areas off of Australia (such as the Great Barrier Reef), South America, and South Africa. The dwarf minke whales are usually found between 20° and 60° South, but immature individuals generally do not travel past 42° South. The difference between the timing of the seasons may prevent the two closely related species from mixing.
Dietary Habits
Minke whales are opportunistic feeders with a diet that varies depending on their location and the season. They feed by side-lunging into schools of prey and gulping large amounts of water. Sea birds, attracted to the concentrated prey just below the surface, are sometimes associated with minke whale feeding and foraging. Minke whales opportunistically feed on crustaceans, plankton, and small schooling fish (e.g., anchovies, dogfish, capelin, coal fish, cod, eels, herring, mackerel, salmon, sand lance, saury, and wolfish). Unlike other whales, northern minkes do not feed exclusively on krill, instead taking whatever they can get of small fish, crustaceans, and plankton. Minke whales have a digestive system composed of four compartments with a high density of anaerobic bacteria throughout.
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Seasonal variations in diet exist. J-stock whales' primary prey type is Japanese anchovy during May and June, Pacific saury in July and August, and krill in September.
Primary Food Sources
- Krill: These tiny crustaceans are a staple in the diet of Antarctic minke whales, especially in the Southern Ocean.
- Small Fish: Various species of small schooling fish, such as herring, capelin, sand lance, and saury, form a significant part of the minke whale diet in the Northern Hemisphere.
- Plankton: As filter feeders, minke whales consume plankton, which includes a variety of microscopic organisms.
- Crustaceans: Apart from krill, other crustaceans like copepods also contribute to their diet.
Feeding Techniques
Minke whales employ a feeding technique known as "gulp feeding." They swim towards dense patches of prey and engulf large volumes of water containing the prey. The whale then uses its baleen plates to filter out the water, trapping the prey inside its mouth. This method allows them to efficiently consume large quantities of small organisms. In a captivating display, minke whales turn their bodies sideways and lunge into schools of prey while gulping large amounts of water, and their throats expand like a blue whale’s.
Ecological Role
Minke whales play an essential role in marine ecosystems. By consuming large quantities of krill and small fish, they help regulate the populations of these species. Additionally, their feeding activities can influence the distribution and abundance of other marine organisms, including seabirds that are attracted to the same prey concentrations.
Threats and Conservation
Despite their relatively stable population status compared to other large whale species, minke whales face several threats.
- Whaling: Historically, minke whales were not the primary target of whalers due to their smaller size. However, as populations of larger whale species declined, minke whales became a more attractive target. Today, whaling countries such as Greenland, Japan, and Norway still take common minke whales for food and for scientific research.
- Entanglement in Fishing Gear: Minke whales can become entangled in fishing gear, including groundfish trawls and gillnets. Entanglement can lead to injury or death.
- Ocean Noise: Underwater noise from human activities, such as shipping and seismic surveys, can disrupt the communication and behavior of minke whales.
- Vessel Strikes: Collisions with vessels can cause injury or death to minke whales.
- Climate Change: Changes in oceanographic conditions and sea ice coverage due to climate change can affect the distribution and abundance of minke whale prey, potentially leading to nutritional stress and reduced reproduction.
NOAA Fisheries is committed to the protection and recovery of minke whales. Minke whales in the United States are not endangered or threatened, but they are protected under the Marine Mammal Protection Act.
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Conservation Efforts
Numerous efforts are underway to protect minke whales and mitigate the threats they face.
- Regulations on Whaling: International agreements and regulations aim to manage and limit whaling activities. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) prohibits international trade of minke whale products, despite the efforts of some whaling nations.
- Fishing Gear Modifications: Efforts are being made to develop and implement fishing gear modifications that reduce the risk of entanglement.
- Noise Reduction: Measures to reduce underwater noise pollution are being explored, such as quieter ship designs and restrictions on certain activities in sensitive areas.
- Vessel Speed Restrictions: In areas with high whale densities, vessel speed restrictions can help reduce the risk of vessel strikes.
- Monitoring and Research: Ongoing research and monitoring efforts provide valuable information about minke whale populations, behavior, and the threats they face.
- WhaleSENSE program: Atlantic and Alaska regions developed by NOAA Fisheries and partners in collaboration with the whale watching industry to recognize whale watching companies committed to responsible practices.
Minke Whales and Whale Watching
Due to their relative abundance, minke whales are often the focus of whale-watching cruises setting sail from, for instance, the Isle of Mull in Scotland, County Cork in Ireland, and Húsavík in Iceland, and tours taken on the east coast of Canada. They are also one of the most commonly sighted whales seen on whale-watches from New England and eastern Canada. In the northern Great Barrier Reef (Australia), a swim-with-whales tourism industry has developed based on the June and July migration of dwarf minke whales.