Bryde’s whales have been called the ‘tropical whale’ because of all the baleen whales they spend the entire year in tropical and subtropical waters that are warmer than 20ºc. They only make short migrations if at all and never venture into cold waters.
Their name is actually pronounced Broo-dess.
Common name: Bryde’s Whale
Other names: Eden’s Whale, small-type Bryde’s Whale
Scientific Name: Balaenoptera edeni
Conservation Status: No status listed for this species
Length: New-born calves 3+ metres, Adults up to 15.6 metres.
Weight: Birth weight is about 1 tonne, Adults up to 20 tonnes.
Field Identification
– Very streamlined body.
– Blow is a 3–4 metre tall cloud.
– V-shaped rostrum with three parallel ridges running longitudinally from two blow holes.
– Dark grey in colour graduating to white undersides.
– Extremely falcate (sickle-shaped) dorsal fin.
– Rarely shows its tail flukes.
Taxonomy
The Bryde’s whale complex comprises two species of rorqual and maybe three. There has been considerable confusion regarding the taxonomy of Bryde’s Whales, so they are described as a “complex” because the number of related species and their classification remains unclear because of a lack of definitive information and research.
The taxonomy is poorly characterised. The two genetically distinct, candidate species/subspecies/morphologies are Bryde’s whale B. brydei and the Sittang or Eden’s whale B. edeni. They are differentiate by geographic distribution, inshore/offshore preferences, and size. For both putative species, the scientific name B. edeni is commonly used or they are simply referred to B. cf brydei/edeni.
The Common Bryde’s whale (Balaenoptera brydei) is a larger form that occurs worldwide in warm temperate and tropical waters. The Eden’s or the Sittang whale (B. edeni) is a smaller form that may be restricted to the Indo-Pacific. There is also a smaller, coastal form of B. brydei is found off southern Africa, and perhaps another form in the Indo-Pacific which differs in skull morphology, tentatively referred to as the Indo-Pacific Bryde’s whale.
To add to this confusion, for many years the Sei Whale (B. borealis) was included with the Bryde’s Whales as well as the recently described Omura’s whale (B. omurai), which was formerly thought to be a pygmy form of Bryde’s, but is now recognised as a distinct species.
Bryde’s Whales gets its common name from Johan Bryde, the Norwegian consul to South Africa, who helped establish the first modern whaling station in the country. The first scientific description of Balaenoptera edeni was by zoologist John Anderson, first curator of the Indian Museum in Calcutta in 1878. He named it after the British High Commissioner in Burma, Sir Ashley Eden, who helped obtain the type specimen.
Description
Bryde’s Whales are the second smallest of the baleen whales and part of the rorquals which also include the Blue and Humpback whales. Like all baleen whales they have twin blowholes with a low splashguard to the front and two rows of baleen plates instead of teeth.
Bryde’s Whales closely resemble Sei Whales, but have a number of different characteristics.
Bryde’s Whales are a dark smoky grey on their tops and white below with the dark area extending down to include the throat grooves and peck fins. The boarder between the dark grey and white undersides is diffuse. Their rostrum is V-shaped with three parallel ridges running longitudinally between the blowhole and rostral tip. These three lateral ridges are the most characteristic feature of Bryde’s Whales as other rorquals have a single median ridge, as well as a slightly arched rostrum, which is accentuated at the tip.
The heads of Bryde’s Whales are about a quarter of their body length. They bodies are remarkably elongated, even more so than Fin Whales. The dorsal fin is extremely falcate (sickle-shaped) with a tapering tip and is located at about three-quarters of the way along the body. The throat grooves extend to beyond the navel, in contrast to the Sei Whale where they do not reach the navel. The broad, centrally notched tail flukes with rather straight posterior margins rarely break the surface.
Given the controversy surrounding in the taxonomic status of Bryde’s Whales there has been determining the characteristics of the smaller coastal forms compared to the offshore forms.
Female Bryde’s Whales are larger than the males throughout life with them being up to 60cm longer at full maturity. The “small form” Bryde’s Whale (B. edeni) are believed to reach physical maturity at nine metres and rarely growing longer than about 11.5 metres. In contrast the “ordinary” Bryde’s Whale (B. brydei) does not even reach sexual maturity until 11.2 metres (males) or 11.7 metres (females) and can grow up to 14.6 metres (males) or 15.6 metres (females). The average weight for the inshore form of Bryde’s Whale off South Africa was estimated as 10.77 tonnes.
Bryde’s Whales are quite solitary mostly seen swimming alone or in pairs. They may gather together more by coincidence when say feeding.
Distribution and Movement Patterns
Australia – Bryde’s Whales are seen in temperate to tropical waters, both inshore and offshore. They do not go below latitudes 40° N and 40° S and into waters cooler than 20 °C. They have been recorded in all Australian states except the Northern Territory.
Global – Bryde’s Whale is found in tropical and warm temperate waters over 16.3 °C, but generally in the 20 °C isotherm, between 40° N and 40° S. While no subspecies of Bryde’s Whale are currently recognised there are two distinct forms found off South Africa and Japan. In South Africa they are coastal forms that are considered relatively resident and undergoing northward migration to the equator during winter. It is possible that similar forms may exist in Australian waters.
Generally, Bryde’s Whales are considered to move in close association with their prey. There is no evidence of large-scale movements of the inshore form of Bryde’s Whales, with sightings occurring throughout the year. Offshore Bryde’s Whales may migrate seasonally, heading towards warmer tropical waters during the winter months. This may suggest that the migration is to allow breeding and calving to happen in the warmer waters.
Population
Bryde’s Whales have not been well surveyed within Australian waters. Their distribution and numbers are primarily assumed from incidental sightings, beached animals, and whaling data for all areas.
There are no estimates of the global population size of Bryde’s Whales due to a lack of data. It is considered likely that Australian inshore stocks of Bryde’s Whales will be small, possibly of similar size to those off South Africa with a total number of mature Bryde’s Whales within Australian waters considerably less than 10 000.
Habitat
Bryde’s Whales are found year-round in tropical and sub tropical waters waters between 40° S and 40° N that do not go below 16.3 °C. It is believed that the inshore forms travel the coast in search of prey in water less than 200 metres. Offshore forms are found in deeper waters up to 1000 metres in depth. Their dive times are relatively short suggesting they only use the upper layers of the ocean.
Specific feeding or breeding have not yet been discovered in Australian waters. The inshore form appear to be resident in areas with suitable stocks of pelagic shoaling fishes. Whilst the the offshore form appears to undergo extensive migrations between subtropical and tropical waters during the winter months.
Behaviours
Bryde’s Whales are generally seen alone or in pairs only coming together in larger numbers when feeding. They also appears to be livelier than most other rorquals and frequently breach clear of the water. Similar to Minke Whales, Bryde’s Whales will often approach boats.
Diving behaviour is quite variable depending on the whales activity. Dive duration is usually short at 1 to 2 minutes, but can last as long as 10 minutes. Dive depths varys from shallow to perhaps 300 metres. On resurfacing the whale will take several breaths, more following deep dives. When feeding Bryde’s Whales swim between 2 and 7 km per hour, but they can swim as fast as 20 to 25 km per hour.
Bryde’s Whales produce short powerful low frequency moaning sounds averaging 0.4 seconds in duration with most of the call energy at 124 to 250 Hz and a frequency modulation of up to 15 Hz.
Feeding
The Bryde’s Whale is considered to be a fairly opportunistic feeder, eating whatever shoaling prey is available. The smaller coastal Bryde’s Whales feed on schooling fishes, such as pilchard, anchovy, sardine, mackerel, herring and others. Where as the larger offshore form appears to feed on small crustaceans such as euphausids, copepods and pelagic red crabs (Pleuroncodes). As there is no differences in the number of baleen plates or the thickness of the bristles between inshore and offshore Bryde’s Whales their feeding habits may be one way to distinguished the coastal and offshore forms from one another.
Bryde’s Whales are often seen taking advantage of ‘fish balls’ herded together by other predators. So they can be often seen in company of other whales, seals, sharks and sea birds in areas of high fish numbers. To feed the whales will lunge through the fish balls taking large ’gulps’ whilst in their sides. They have been described as voracious feeders when compared to other baleen whales apparently feeding several times a day to consume the estimated requirement of 4% of body weight daily (about 600+ kg per day). Feeding occurs year round and the whales will follow the local movements of their prey.
Life Cycle
Given the confusion and controversy surrounding in the taxonomic status of Bryde’s Whales it has been difficult to come to an agreed life cycle for the various forms. Due to the lack of data for Bryde’s Whale off Australia assumptions are made from the information gathered South African and western North Pacific.
It is thought that Bryde’s Whales may reach over 50 years in age. The offshore form of Bryde’s Whale reach sexual maturity at between 11.0–11.4 m for males and 11.6–11.8 m for females, while the smaller inshore form reaches sexual maturity at about 11.3–11.5 m in females and 10 to 10.4 m in males. The age at sexual maturity is thought to be between seven and nine years.
Inshore coastal forms appear to breed and give birth throughout the year as this is consistent with an absence of migratory behaviour and year-round feeding observed. The offshore form appears to have a protracted breeding and calving season over several months during winter. Bryde’s whales have a 2-year reproductive cycle composed of 11–12 months gestation, followed by 6 months lactation and then a 6 month resting period. At birth Bryde’s Whale calves are about 3.4 metres.
Threats
Like all marine mammals Bryde’s Whales have a number of natural and man made threats. Fortunately Bryde’s Whales were not targeted species for whaling as other species so their not considered to be in danger or at depleted levels.
Natural – predation by Killer Whales and sharks. Disease and old age.
Man Made – Pollution, climate change, acoustic disturbance, ship strikes, entanglement and bycatch, over-harvesting of food sources such as fish stocks.
References/Sources
Australian Department of the Environment, Canberra
Whales, Dolphins and Porpoises by Mark Carwardine
Whales, Dolphins & Seals: A Field Guide to the Marine Mammals of the World by Hadoram Shirihai and Brett Jarrett
Copyright 2020 David Jenkins – Whale Spotter