#rorqual

[bogcreacher]

seawings Yeagh I augh. ough. .

[secularsasquatch]

[marinebiology1]

Bryde's whale

[ketu-orca]

Since rorquals are winning the poll, here's a common minke whale.

[neanderthalfakemon]

#130 - Falleen

[alphynix]

Once again it's a PBS Eons commission roundup day!

An unnamed Cerro Ballena rorqual whale and the long-necked seal Acrophoca, from "How the Andes Mountains Might Have Killed a Bunch of Whales" https://www.youtube.com/watch?v=iNk6r5WljGc

The poposauroid pseudosuchians Shuvosaurus (life restoration) and Effigia (skeletal) from "When Dinosaur Look-Alikes Ruled the Earth" https://www.youtube.com/watch?v=QsmV34Co32c

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Nix Illustration | Tumblr | Pillowfort | Twitter | Patreon

[moneyisnobject]

MUB Design, “Rorqual”

[orcinus-ocean]

Endangered Cetaceans, part 20

Sei whale, Balaenoptera borealis

The third entry in this series of the Balaenoptera genus, the sei whale is the fourth largest rorqual after the blue, fin and humpback whale (which, while not a Balaenoptera, is a rorqual as well)

Also known as the “lesser fin whale” due to its similarity to its larger cousin, it is extremely fast, but does not have great stamina.

They vary in size across the globe, so that males average from 13.7 - 18.6 meters and 15 - 20 tons, and females, which are considerably larger, from 15 - 19.5 meters and 18.5+ tons, across different parts of the world. The whales in the southern hemisphere are the largest, the ones in the North Pacific are the smallest.

A newborn calf measures 4.4 - 4.5 meters in length, roughly similar to a beluga whale, and they wean from their mother when they measure 8-9 meters, at only 6-9 months old.

An adult eats about 900 kg of food every day, in the shape of zooplankton, krill, and copepods.

Despite its scientific name (”borealis” meaning “northern”), the sei whale is found almost all over the world, except for the coldest arctic and antarctic waters, the northern Indian ocean, and a few smaller seas.

The entire species is classified as endangered, with no subpopulations listed separately. They were moved up to this listing in 1996, before which they were considered vulnerable.

Like with virtually all other baleen whales, old, large-scale industrial whaling is what nearly killed off the species, and is the reason for their threatened status even today.

Large-scale whaling ended decades ago and was decreasing before then, but it takes a very long time for such a slow-reproducing animal (11 month pregnancy, one calf every 2-3 years, 8-10 years for calf to reach sexual maturity) to return to its former abundance.

In the 19th and 20th century, about 255 000 sei whales were taken, and today, there are around 80 000 in the entire world. That’s eight times as many as there are blue whales, but it’s still barely a third of its original population estimate.

North Atlantic

14 000 were taken in the North Atlantic (on both the European and American side), as well as an unknown number of 30 000 unidentified rorquals.

Prior to WW2, not counting the unidentified whales, 7500 sei whales were taken off Norway and Britain, but fewer than 200 in the period following, due to depletion. They are now apparently extinct in the region - surveys in the area during a span of 13 years (1987, 1989, and every year from 1995-2005) found only a single sei whale.

In the central north Atlantic (Iceland) however, the species is still abundant, where a survey in 1989 estimated the species to be 10 300 strong.

There is no recent estimate for the western North Atlantic, by the northern United States and Canada’s east coast. The last estimate comes from the late 1960s, and put the population at just over 2000 whales. 1200 sei whales were taken off Nova Scotia in 1962-71.

North Pacific

This population as well is not well studied, the last assessment being from 1974. The “exploitable population” in that time (animals large enough to be caught legally) had declined from 42 000 in 1963 to only 8600 in 1974 (or in other words, that’s a decline of 80% in half of one generation for the species).

Over 40 000 sei whales were caught there during this period. It was so bad, the Californian whaling stations during the 1960s had a 75% reduction in their sei whale catches, and they stopped hunting them in 1975. It is unknown how well the North Pacific population has recovered since then.

In a small survey of 1996 and 2001, only 56 whales were found off the American west coast.

In the Eastern Tropical Pacific, all potential sei/Bryde’s whales that could be specifically identified were found to be Bryde’s, suggesting that Sei Whales are now rare.

In one area of the western North Pacific (Asia), they are estimated at 4100 animals, but no assessment for the entire region has been accepted.

Southern Hemisphere

Over 200 000 of the 255 000 sei whales killed in large-scale whaling operations, were taken here, between 1905-1979. The greatest catches took place in 1960-1972 when over 5000 sei whales were killed every year, nearly 20 000 in 1964 alone.

This huge increase in the take of sei whales was largely due to the fact that the blue, fin and humpback whales were already severely depleted by that time.

Largely caught in Antarctic water in summer, they were also taken off Brazil, Peru, South Africa and Chile in winter.

Here as well, the most recent estimate is very old, from 1979. The “exploitable population” (estimated to be about two thirds of the entire population) had declined from 64 000 in 1960, to only 11 000 in 1979.

This excludes one area of the Antarctic (”Area II”), where nearly 30 000 sei whales were taken in only two seasons, from 1964-1966.

Abundance off Brazil declined by 90% during 1966-1972, and no recovery in the region has been recorded since then. Abundance estimates off South Africa declined by over 95% in the same period.

They became protected in the north in 1975, and in the south in 1979.

Like with many other large whales (if not all), they were saved on the doorstep of extinction, and would not be here today if industrial whaling hadn’t stopped when it did.

Other threats seem to be small in this species. Two sei whales ever have been recorded as killed by vessel strikes.

It is unknown how much current human activity is affecting them, but in 2015, 337 sei whales were found dead in Chile at the same time. Other than the frequent mass strandings of pilot whales, this is the largest mass stranding event of whales ever recorded.

http://www.iucnredlist.org/details/2475/0

https://en.wikipedia.org/wiki/Sei_whale