As Steller had not stated how numerous the Bering Island herds were, the Norwegian-American zoologist Dr. Leonard Stejneger tried to guess their probable number when first found, and wrote^*)1887:

"from what he [Steller] says in regard to their habits and the places they frequented, and from what I [Stejneger] know of the natural conditions of the island, I should regard fifteen hundred as rather above than below the probable number. It must be remembered that the sea-cow was an extremely bulky animal ... which lived chiefly near the mouths of the rivulets, feeding on ... the large Lamellarias. There are hardly more than fifteen places on the island which could afford them suitable grazing-grounds, and if each of these were regularly visited by an average of one hundred animals, one would easily be impressed by their number, especially if divided up into ten herds of from ten to twenty individuals."

So perhaps 2000 animals were alive (on both islands) in 1741^*)Domning 1978, P. 133.

It is recorded that at least 19 hunting expeditions, counting about 670 men, wintered on Bering Island between 1743 and 1763. Stejneger assumed that the actual numbers were substantially higher, and calculated that for supplying these groups, about 500 animals had to be harpooned. He estimated that further 1000 or more animals were killed in the senseless massacres described by Yakovlev^*)previous page.

After 1763 the seacows became rare, and it seems that the last animal was harpooned during the 1767/68 winter. Martin Sauer, diarist of the Billing expedition 1785-1794, wrote 1802 in his expedition report:

“Sea-cows were formerly frequent at the coast of Kamchatka and the Alëutian islands, but in the year 1768 the last animal of this species was killed, and since then none has been seen any more."

K. E. von Baer^*)1840 and J. F. Brandt^*)1846 maintained that most likely 1768 is the year of extinction.

The Swedish Baron Eric A. Nordenskiold believed that at least one seacow had survived the slaughter ansd had been seen alive as late as 1854. Near the end of his Vega expedition 1879, he spent 5 days on Bering where some inhabitants told him of respective sightings.

Three years later Stejneger questioned the same islanders in great detail. He came to the conclusion that the 1854-sighting most probably involved a female Narwal. Stejneger^*)1887:

“we have succeeded in materially strengthening Sauer's assertion, that the Rytina was exterminated in 1768!"

For most authors the wasteful hunting of seacows by the Russians was solely responsible for their extinction. Paul Anderson^*)1995 however suggested a more complex explanation, as hunting alone was insufficient to wipe out the Commander Island seacow population: The only food competitors of the seacows where the kelp-eating sea urchins. These were kept in check by the sea otter. However, the local sea otter population was nearly extirpated within 10 years after the Russians arrived. This may have resulted in an explosion of the urchins, and the last seacows may have starved due to the resulting shortage of kelp.

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