You'll know that 'fish' takes an -es plural in certain circumstances. So there are many fish in the sea refers to there being a lot of fish-individuals, but there are many fishes in the sea would probably be used to mean that there are a lot of different kinds of fish (tuna, mackerel, etc.). But it seems weird to do this with moose:
there are a lot of moose in CanadaThen someone pointed out the different way we do plurals for game animals:
?? There are two mooses: the European and North American species
They're hunting quailIf you keep trying that sentence with different animal terms at different levels of generality (mallard-duck-bird, etc.), it gets even more confusing. In the 'hunting' example, the issue is whether or not the animal is treated as a mass noun (as we do when we talk about meat--you might eat a lot of chicken, but probably wouldn't say you eat a lot of chickens).
? They're hunting duck
* They're hunting bird
At any rate, something interesting is going on with respect to when we add -s to animal names. A corpus study of this would be an excellent way to investigate it--possibly also with native speaker judgement tests. If you're interested in exploring these things, I'd recommend reading up a bit on mass and count noun morphology/semantics. Chapter 8 of my in-press textbook (people who took Semantics should have it--or ask me for it) covers the basics of countability, and Anna Wierzbicka's chapter on 'Oats and Wheat' in her book The Semantics of Grammar (1988) helps one to think about all the different categories of countability there are. (There's more recent work in this vein, but check out that one first to see if the subject interests you.)
There's also a lot to think about in terms of different dialects and countability (not necessarily about animals)--are there patterns to the differences? See this blog post for some examples.