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Diving with Dwarf Minke Whales

Inquisitive 'Little' Acrobats of the Sea

As a recreational diver you don't often get the chance to dive with whales, but this little known small species ought to be on the top of every divers 'wish list'. Their inquisitive nature and gentle demeanour mean the possibility of incredible interactions that will live long in the memory of those who dive with them in the Great Barrier Reef. Once experienced, many scuba divers will return for a second or third opportunity to interact with beautiful dwarf minke whales and even to contribute to their conservation efforts.

So what is a dwarf minke whale? How does it differ from a regular minke whale? How big are they anyway? Where and when can I dive with them? Enough questions. Time for some answers ...

Diving with minke whales on Australia's Great Barrier Reef - photo courtesy of Mike Ball Expeditions

Fact Sheet

Family name: Balaenopteridae
Order name: Cetacea
Sub-order: Mysticeti (baleen whales)
Common name: Minke whale
Scientific name: Not yet assigned

Minke whales are baleen whales, (meaning that they do not bite their food, they filter it from the water). They are the smallest of the 'great whales', or rorquals, and are part of the Cetacea order; which includes whales, dolphins and porpoises. There are currently over 80 recognised species of this order.

There are current 2 subspecies: the northern (or common) minke whale (Balaenoptera acutorostrata) and the Antarctic minke whale (Balaenoptera bonaerensis). Those that you can dive with from Australia's Great Barrier Reef are dwarf minke whales, a possible 3rd subspecies yet to receive an official scientific name. They are smaller than the Antarctic, have a flipper stripe and live in tropical southern hemisphere waters.

Distinguishing Features

The minke whales family name, Balaenopteridae, can be loosely translated to – "baleen whale with a fin". Baleen refers to the horny keratinous substance found in two rows of transverse plates which hang down from the upper jaws of baleen whales, and the fin refers to the small dorsal or back fin.

Dwarf minke whales are more streamlined than other whales. Their pointed snout is distinctively triangular, narrow and pointed (which explains it's nick-name, 'little piked whale'). There are 55 to 75 grooves which run along the throat to the belly for approximately one-third of their body length; the grooves are obvious only if the whale turns to expose its belly. These grooves allow the its throat to expand considerably while they are filter feeding.

They have paired blowholes and have a characteristic white band on each flipper which contrasts its very dark grey top colour. Unlike other toothed whales and dolphins, which use fine scale echolocation for hunting purposes, it is thought that minke whales use echolocation for identifying large scale objects, such as reefs or vessels. Interestingly, our hands and the whale's flippers, or pectoral fins, contain the same bones. These are used to manoeuvre; for example, they are extended just before the whale surfaces and may act like the dive planes of submarines. As the animal rolls or spins, one flipper is extended while the other remains close to the body.

It is the second smallest baleen whale; the honour of smallest belongs to the pygmy right whale. The largest dwarf minke whale to be measured was 7.8m but they average 5m in length. As with other baleen whales, the female is generally larger than the male.

Behaviour

They are generally solitary mammals but may congregate in small pods of 2-3, however, they have been observed in large groups when food is abundant. Dwarf minke whales are acrobatic and in many ways behave more like dolphins than other baleen whales.

They are known to approach ships and to sometimes even keep up with moving vessels for up to half an hour. Like all rorquals, the minkes are fast swimmers and can reach speeds of 30-40 km/h.

Dwarf minke whales display some uncommon surface behaviours. They play 'peak-a-boo' above the water by rising vertically and either expose their snout (known as 'headrise'), or 'spy-hop' where the eyes are also above the waters surface. The most enthralling behaviour to witness is 'breaching'. This is where the whale comes out of the water completely. Some speculate that the purpose is to remove parasites, others suggest that it is to make a noise to alert other whales in the vicinity of the breacher's presence and size, and some think it is simply 'joie de vivre'.

A spectacular but rare behavior is when a minke whale exhales while still submerged. This may be a 'bubble trickle' when a small trickle of bubbles are released from its blowholes; a 'bubble trail' is when a trail of bubbles are released while the creature is moving forward (the bubbles may appear to be a screen or curtain when passing upwards through the water column); and when the whale abruptly releases a large amount of air forming a cloud of bubbles it is known as a 'bubble blast'.

The best chance of divers or snorkellers to interact at close distances (3m or less) with dwarf minke whales is to remain relatively still (by holding onto a rope) and to remain calm. This subspecies is inquisitive and often approach snorkelers and may remain in their vicinity for extended periods of time. Approaches of 1m or less are rare but have occurred. This is thought to happen when the whale gains confidence through the swimmers calm and predictable movements. Dwarf minke whales interactions occur mostly in Australia. Under Australian law, it is illegal to swim towards a whale closer than 30m as well as to touch one; fortunately being inquisitive they are known to approach swimmers of their own accord.

The most characteristic sound made by the whales is a mechanical sounding call that has 3 rapid pulses and a longer trailing note. They also produce a series of pig-like grunts, moans and belches. When whales vocalise near swimmers, sounds such as these can be heard easily underwater, and if they occur in very close proximity, vibrations from the sound waves can sometimes be felt in one's chest.

At the surface, dwarf minke whales will spout (breathe) 5-6 times per minute, in preparation for a deep dive, they will spout 3-5 times in short intervals and may arch and expose much of their back. On average they submerge for 6-12 minutes, however they are capable of diving for up to 20 minutes.

Feeding Habits

Minke whales are seasonal feeders, carnivores, and there are regional differences in their diet. The dwarf minke whale's diet includes crustaceans (e.g. krill), squid, small crabs and small vertebrates such as sardines, anchovies, cod, herring, mackerel, sand lace, saury, wolfish and capelin (they compete for the same food source as blue whales). They use different feeding techniques, including trapping schools of fish at the surface of the water, as well as by side-lunging into schools of fish whilst gulping large amounts of water containing prey. Sea birds are associated with their feeding and foraging as they are attracted to the concentration of prey just below the surface.

Reproduction

They are sexually mature at 3-8 years of age; they breed every 2 years in late winter to early spring in warmer waters near the surface. It has been speculated that the congregation of dwarf minke whales in the Great Barrier Reef is for mating purposes.

Apparent courtship behaviour (e.g. synchronous and belly-to-belly swims) is observed here from June to August. After an approximately 10-month gestation period, a single calf is born in warm shallow waters measuring approximately 2m and weighing about 450 kg. The calf instinctively swims to the surface; if necessary it's aided by its mother using her pectoral fins, where it takes its first breath. Within the first 30 minutes the calf is able to swim unassisted.

It will nurse for 5-10 months and will stay with its mother for a year, or possibly longer. There are no known birthing grounds for dwarf minke whales, sightings of calves have occurred mostly in April til June from Victoria to southern Queensland.

Life Cycle

Minke whales reach puberty at about 2 years of age. It is estimated that females grow for about 18 years, and males for about 20 years. The common minke whale has an average life span of around 50 years.

Predation

Orcas are known to prey on minkes, especially in parts of the southern hemisphere. Of course there is also the top predator – man. Only in recent decades have minke whales been taken by whalers to any extent. Previously they were thought to be too small to be a worthwhile catch, however, as the larger whale species became depleted, the whalers began to hunt the minke as a replacement.

Since the late 1960s and 1970s, Japan, Russia (which has now ceased whaling), and (to some extent) Norway have focused their whaling efforts on minke whales. Fortunately the Japanese 'scientific' whaling program has not targeted the dwarf minke whale since 1993. Some minkes observed off Australia have scars which appear to be caused by traditional harpoons that indicate that they have travelled to the South Pacific nations who still practice traditional hunting.

Distribution & Habitat

The distribution of these whales is considered widespread because they can occur in polar, temperate, and tropical waters in most seas and areas worldwide. The common minke whale subspecies is generally found in the North Atlantic Ocean and the North Pacific Ocean, although it is not uncommon for it to be found in the waters of the Southern hemisphere. Conversely, the Antarctic and dwarf minke whales are rarely found too far north.

Ecological Considerations

The ever-present threats to rorqual whales are entanglements in fishing gear and ingestion of marine debris, especially the vast quantities of plastic that float in our oceans. This threat has been confirmed by examining the contents of stranded whale's stomachs.

Climate change and the resulting rise in sea surface temperatures and ocean acidification may also result in a change in the quantities of available food for whales as well as have an impact on their migratory patterns.

The diverse geographical locations of the different minke whale subspecies makes it problematic to get a clear picture of their numbers, migratory routes as well as threats to these gentle mammals. The IUCN Red labels the common minke whales as least concern, the COSEWIC places the minke whale species in the 'Not At Risk' category.

The scientific community of the International Whaling Commission agreed upon a population estimate of 515,000 for the Antartic minke stock. The dwarf minke whale is listed as a migratory species and is protected under the EPBC (Environment Protection and Biodiversity Conservation Act 1999) Act. Data collected from their population in Australian waters has resulted in very conservative estimates of the population and has shown that there are several hundred animals (not thousands). Unfortunately there is insufficient data available on the population for a conservation status to be assigned.

Dive Sites


More detailed information on dwarf minke whale diving destinations:

Australia


Dive The World Recommendations: Ribbon Reefs, Australia.


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