The population of Taransay is given here for each census from 1841-1901:
1841 88 33m 39f + Rha 16 6m 10f (Raa was Cleared in 1840 for John Macdonald, Tacksman)
1851 55 25m 30f
1861 55 25m 30f
1871 68 36m 32f
1881 31 16m 15f
The 40% decline between 1841 and 1851 was followed by a period of stability but, interestingly, some 16 of the 68 people living on the island in 1871 were born elsewhere in Harris, Lewis and Ross-shire. Nine came from the the Bays, four from the West and one each from Bernera, Scarp and Ensay. Lochs, Lewis and Gairloch supplied the remaining two.
A decade later the population was down to 31 living in half-a-dozen households and a couple of years later the cottars were barred from raising livestock and growing oats or barley. Unsurprisingly, such conditions made life untenable and we can see the results in the final two censuses.
An excellent online source on Taransay is: http://www.paparproject.org.uk/hebrides7.html