In which a perfectly good idea goes down in flames.
J.R.R. Tolkien was careful to choose proper names that would avoid ridiculous resonances with his audience, in English at least. But he missed one.
Even among the radiant flowers of the Tree-lit gardens of Valinor, [the Vanyar & the Noldor] longed still at times to see the stars; and therefore a gap was made in the great walls of the Pelóri, and there in a deep valley that ran down the the sea the Eldar raised a high green hill: Túna it was called.
Silmarillion, Chapter 5
There’s a diacritical mark above the “u” in “tuna”, but it doesn’t help much. How did this slip by? That’s when I had an (what’s the opposite of “brilliant”?) idea: Maybe people didn’t eat tuna in 1920s England! After all, the idea of a tuna steak didn’t exist in the US until about 30 years ago.
So off I go to the Marine Management Organization of the UK. Their statistical report for 2015 confirms that tuna isn’t really a thing, as far as the domestic fishing industry is concerned. “Virtually all tuna available for use in the UK is from abroad.” That means I can use worldwide production statistics from the UN Food and Agricultural Organization. Unfortunately, their data only go back to 1950.  Fortunately, the statistics fit an exponential curve fairly well up to 2000,  so we can extrapolate backwards in time.
Extrapolation outside one’s data is generally risky, but in this case we have an endpoint to keep us in line: Tuna wasn’t a big consumer item until they figured out how to can it about 1900. The variation of the actual harvests around the regression line is about 100,000 tonnes per year. Between 1900 and 1914, the extrapolated curve is less than the error term, so the estimated tuna harvest is indistinguishable from zero. So far, so good: Canning tuna began in Oregon and California, so it could easily have taken a few decades for tuna to catch  on in England.
But then this whole thesis falls apart. “Demand soared with the onset of the First World War. Canned tuna provided a high-protein, portable, and convenient food for soldiers in the field.” That is suspiciously close to the 1914 breakpoint I just computed. Tolkien was a soldier in the field; there is no way he was ignorant of canned tuna. Confusticate and bebother these facts! In the words of Emily Litella, “never mind.”
One marvelous thing about the World-Wide Web is that it decreases the cost of following an idea into a dead end. I spent less than an hour on research, data acquisition, and analysis for this post, and it’s snowing outside so I had nothing better to do anyway. If I had tried to do this exercise when I was in college in the 1980s, it would have taken a week.
Update: Shawn, of Prancing Pony Podcast fame, points out that the fish in question was called “tunny-fish” in olden times. According to Google Ngrams, he’s right. You can clearly see the change-over when the American fisheries got into the act.
By the 1920’s the American word might just barely have been visibly more frequent (though the relative frequencies when spoken might have been different), but it would have been a moderately-impressive prophecy to anticipate that huge run-up in the second half of the century.
 Something bad must have happened in the 1940s to disrupt data collection.
 For once the pun is not intentional.