Please note - you never say "population" when related to animal husbandry.

less

(nonstandard in some uses but often idiomatic with measure phrases; `we
had less apples' is not acceptable) fewer; "less than three weeks"; "no
less than 50 people attended"; "in 25 words or less"

less is similar to:

* fewer — (comparative of `few' used with count nouns) quantifier
meaning a smaller number of

http://www.answers.com/main/ntquery?method=4&dsid=502&deid=748337833&curtab=502_1&linktext=Meaning+#4

Did you read the article carefully? Or did you just see "nonstandard"? "We had less apples" is not acceptable, for sure. But "no less than 50 people attended" absolutely is.

"Standard English still usually requires this basic pattern: use less with mass nouns and fewer with plural count nouns, as in less employment, fewer jobs. But Common English—and even some Standard—increasingly uses less with plurals, especially after than. Edited English still follows the basic pattern rigorously , however, except in a few idiomatic locutions, as in in ten words or less; in certain phrases involving money, such as less than a thousand dollars; and in some phrases involving plural measures of time and distance or other measures, also with than (less than four days, less than ten miles, less than five cups of coffee). Even in these, Edited English prefers fewer, and for many conservatives, the use of less where fewer is expected remains a strong shibboleth.