Species Spotlight: Bryde's Whales vs Blue Whales
In our last species comparison we compared our resident Bryde’s whales with sei whales. This time, we are look at how our winter visitors, the pygmy blue whales size up to the Bryde’s whales.
Adult Bryde’s whales can weigh around 20-30 tonnes, the equivalent of about five African elephants. Adult pygmy blue whales can weigh around 90 tonnes – about the same as 15 African elephants!
Adult Bryde’s whales reach between 13-15 metres in length. Blue whales – the largest animal that has ever lived – can reach up to 33 metres. The type of blue whale we see here, the pygmy blue whale, reaches approximately 24 metres.
Want to know what a blue whale looks like? Pygmy blue whales look very similar to their larger relatives. However compared to Bryde’s whales, besides their length and weight, there are many subtle differences which help us tell the two apart.
- Head: The head of a pygmy blue whale is wide and flat compared to the Bryde’s whale, which is much narrower and features the three rostral ridges unique to their species.
- Dorsal fin: The dorsal fin of the Bryde’s whale is much taller and larger than the pygmy blue whales which is much smaller.
- Body colour: Pygmy blue whales, like other blue whales, have a light coloured skin which can appear blue-grey in certain lights. Bryde’s whales are much darker.
Bryde’s whales (also known as the ‘tropical whale’) are also found in both hemispheres but are thought to only inhabit warmer waters between 40° South to 40° North. In New Zealand, they are seldom seen further south than the North Island. Some populations of Bryde’s whales are known to migrate whereas others, like the ones in the Hauraki Gulf Marine Park, are resident.
Blue whales have a global presence. However, pygmy blue whales have only been seen in the Southern Hemisphere mainly in the Indian Ocean such as off the coast of Sri Lanka. Research has expanded the knowledge of that range in recent years to other areas including Indonesia, Philippines, Australia and of course, right here in New Zealand! The New Zealand pygmy blue whales have been seen all around the country with the majority of sightings off of the South Taranaki Bight.
5. Population Size
The global population of Bryde’s whales is unknown and their status is listed as ‘Least Concern’ on the IUCN Red List. However, in New Zealand Bryde’s whales are classed as ‘Nationally Critical’ under the New Zealand Threat Classification System due to their low population size of less than 200.
It is hard to know how many pygmy blue whales are left. The global population of pygmy blue whales is also unknown and their status is listed as ‘Data Deficient’ on the IUCN Red List. In New Zealand, the recently recognised population of pygmy blue whales is estimated to be approximately 700 but are classed as ‘Data Deficient’ due to only a small number of studies carried out on this subspecies so far.
Both Bryde’s and pygmy blue whales are rorqual whales. This means they have a series of long pleats under their mouth which extend to close to the belly button. These pleats help the mouth and throat expand when the animal is feeding.
Bryde’s whale have a varied diet, feeding on multiple different types of food including zooplankton (including krill) and fish. Blue whales are known for feeding on krill.
7. Dive Behaviour
Bryde’s whales typically surface 3-5 times over several minutes before undertaking a longer dive for approximately 5 minutes. They do not show their tail flukes when diving but do arch their back and tailstock.
Pygmy blue whales surface in a similar fashion to Bryde’s whales. When they go down for their longer dive, their dorsal fin and tail stock usually submerges at the same time. They will sometimes show their flukes (tail) as they dive.
8. Swim speed
Bryde’s whales are reported to have a fastest swim speed of about 13 knots (24km/h). New Zealand pygmy blue whales have been observed racing at speeds of 18 knots (33km/h) by Oregon State University researchers!
9. Sightings in Auckland
The Bryde’s whale population in Auckland is resident and therefore can be seen in the Hauraki Gulf Marine Park year-round. Historically, it has been uncommon for us to encounter pygmy blue whales in the Hauraki Gulf. However, since 2017 we have been seeing them more often, usually in the cooler Winter months – it is an interesting time for us and for blue whale research!