A question for linguists and mathematicians

Yesterday I concluded my blogging day with a report I entitled "The decimation of Atlantic food fish."  The scientific study described a decline in biomass of the fish "by a factor of nine over the [twentiety] century."

Sue Dunham quite correctly pointed out that by definition, decimation is a reduction by 1/10th, not a reduction to one-tenth, based on the Roman military discipline:

A unit selected for punishment by decimation was divided into groups of ten; each group drew lots (Sortition), and the soldier on whom the lot fell was executed by his nine comrades, often by stoning or clubbing. The remaining soldiers were given rations of barley instead of wheat and forced to sleep outside the Roman encampment...

The Italian General Luigi Cadorna applied decimation to under-performing units during the First World War. In his book Stalingrad, Antony Beevor recounts how, during the Second World War, a Soviet Corps commander of a division practised decimation on retreating soldiers by walking down the line of soldiers at attention, and shooting every tenth soldier in the face until his TT-33 pistol ran out of ammunition...

She and Wikipedia both note that by modern convention, the term can be used in a less precise way to indicate massive reduction -

In Wonderful Life: The Burgess Shale and the Nature of History, Stephen Jay Gould uses "decimate" to indicate the taking of nine in ten, noting that the Oxford English Dictionary supports the "pedigree" of this "rare" meaning.

So, this morning I wondered - is there a better term I could have used?  The Latin equivalent of a 90% reduction would apparently require a neologism like ? nonagintication.

But an even more interesting question is mathematical.  How many times must humans (and nature) have decimated the Atlantic food fishes (at 10% per decimation) to reduce the population to 10% of its original level?  Probably about twenty true decimations.  That makes the results of the study even more impressive.