pump/filter for 8x8x2 pond?

Hi, I'm getting an 8'x8'x20-24" pond and am trying to decide if a
pump/filter is a must have. I checked the rec.ponds faq but am not sure
how much difference the volume/temperature makes.

I'd like the pond to have some amphibians (we see plenty of Pacific Tree
frogs in the garden) and possibly some small fish if I can find
compatible and preferrably native. With the right balance of
oxygenating/shade providing plants, beneficial molluscs etc would a pond
of that size maintain its own balance without the need for a pump/filter
or is the pond too small for that? The garden contractor says
pump/filter is vital. Location is Pacific Northwest if that is relevant
wrt seasons.

Also, is this something one can compromise on, ie run a pump some of the
time? Garden contractor says no, pump must run all the time..

Thanks
Guy

ps sorry if this is a vfaq