"In a study in the Bahamas, lionfish abundance was found to have increased rapidly between 2004 and 2010, by which time lionfish accounted for nearly 40% of the total predator biomass in the system."
I'm quite confused with the exact year or years that 'by which time' refers to.
Does 'by which time' mean 'by 2010' or 'the period of 7 years from 2004 to 2010'?
Based on the connotation that the context shows, I guess it means the former but I'm not quite sure. If the sentence was written "from 2004 to 2010, by which time …", I could have better understood. But what about "between 2004 and 2010, by which time…"?
Best Answer
by which time refers to a specific time that has previously been mentioned. It's typically the end of a process or event, so in your example 2010 would be the likely referent.
Had they intended to refer to the entire time period, they would more properly have used during which time.
Furthermore, the context makes it unlikely that lionfish accounted for the same percentage during the entire period. The sentence emphasizes an increase. While it's conceivable that the lionfish population increased proportionately with all the rest of the predators, so that the percentage stayed the same, it doesn't seem to fit with the sense of the sentence.