As divers, we often imagine diving with dolphins and few of us can even begin to consider the reality of a whale coming into view when we are underwater on scuba. However, there is a place you can be confident you will be visited by whales. That place is on Australia's Great Barrier Reef and those whales are dwarf minke whales.
What type of whales are they? Read on and find out all you need to know about these fascinating creatures ...
Family name: Balaenopteridae
Order name: Cetacea
Common name: Minke whale
Scientific name: Balaenoptera acutorostrata
Minkes are the smallest of the great whales and are part of the order of cetacea which includes whales, dolphins and porpoises. They are baleen whales meaning they filter food from the water rather than by biting prey. The minke whales that visit Australia are a possible 3rd subspecies, in addition to common minkes and Antarctic minkes.
The family name Balaenopteridae can be loosely translated to baleen whale with a fin. Dwarf minkes are streamlined with a triangular pointed snout. They have dozens of grooves from throat to belly which allow for the expansion necessary when filter-feeding.
They have 2 blowholes and they have a white band on each flipper which contain the same bones as the human hand! The flippers are used for manoeuvering, not propulsion. The female is generally larger than the male with the largest specimen of the species measured at 7.8m in length, while the average is about 5m.
These acrobatic little whales are sometimes seen in pods but tend to be solitary. When there is a large food source they can aggregate in numbers. As fast swimmers they can reach speeds of 30 to 40 km/h and have been seen swimming to keep up with boats for up to 30 minutes.
They are known to bubble-blast, spy-hop at the surface and to breach spectacularly. The jury is out whether breaching is for the removal of parasites, for communication, or simply for fun. At the surface they will breathe 5 or 6 times a minute before a deep dive, where they remain submerged for 6-12 minutes on average and 20 minutes maximum.
When sharing the water with minke whales it is advised to remain still and allow the whales to approach you. They sometimes come within just a few metres. Under Australian law it is illegal to swim to a whale closer than 30m or to touch them, but the law does not apply to the whale swimming up to you! The sounds you will experience can range from 3 pulses and a longer note, to sounds like grunting, moaning and belching. 'Experience' is the relevant word here since you may not only hear them but feel the vibrations in your bones.
The dwarf minke whale's diet includes krill, small crabs, squid, anchovies and sardines. Techniques include trapping the schools at the surface, or side-lunging into schools as sea birds circle in the air above.
Maturing sexually between 3 and 8 years of age, dwarf minkes breed every 2 years in between the southern hemisphere's late winter and early spring. It is believed that mating is the reason they gather on the Great Barrier Reef in such numbers. Between June and August you can see them swimming belly-to-belly. 10 months after conception, a single calf emerges weighing 450 kg and measuring 2m in length. Instinctively it swims to the surface to take its first breath and after 30 minutes it can swim without any maternal assistance.
Nursing for 5-10 months, the calf may stay with its mother for over a year. It is believed they grow for about the first 20 years and have an average life span of around 50 years.
Killer whales are known to prey on minkes, particularly in the southern hemisphere. In recent years minkes have begun to be taken by human whalers to a more significant extent, having depleted larger species. Since the 1970s Japan, Russia and Norway have focussed their efforts on minke whales. Some whales have been seen in Australia with scars seemingly from the traditional harpoons used in South Pacific island nations.
Threats they face include ingestion of marine debris, as evidenced by studying stomach contents, and entanglement in fishing gear. Sea temperature rises and acidification could impact on their food sources as well as their migratory patterns. The diverse spread of minkes makes estimating numbers a challenge although they are not currently considered to be an 'at risk' species.
The dwarf minke is a protected species under the Australia Environment Protection and Biodiversity Conservation Act 1999, and studies in Australian waters have counted several hundred dwarf minke individuals.
Minke whales in general occur worldwide in polar, temperate and tropical waters. The common minke whale is generally found in the North Atlantic and North Pacific oceans, seldom in the southern hemisphere which is the domain of the Antarctic and dwarf minke whales.
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