RE: NANFA-L-- Releasing fish?

Peter Unmack (peter.lists at)
Wed, 13 Apr 2005 09:36:32 -0500 (CDT)

On Wed, 13 Apr 2005, Crail, Todd wrote:

> From what I understand, the point of the article was that _most_ exotics
> have little or no effect on overall systems. They have to compete like
> everyone else, deal with predation, etc. Which I can agree with.

So much of that depends upon the state of the recieving population, if it
is just after a major disturbance, or right before, what time of year.
Also, what species are present, how a given species makes a living (eg,
scavenger versus predator), how it is related to other critters present,
etc. There are millions of factors. But you only need one exotic to take
off and really make a mess of things. In the lower Colorado Basin there
have been about 90-100 recorded introductions of which only half have
established breeding populations. Some of these have incredibly small
ranges, like rock bass have never really spread beyond where they were
introduced. It isn't hard to go find one in one or two creeks, but they
have never really dispersed anywhere else (actually, in that creek you can
catch 5 species of centrarcid and none are native!). Goldfish is another
example, they don't seem to ever form big wild populations here, but in
Australia they did in some places.

> However, I guess they used San Francisco Bay as an example? My initial
> thought was "Yeah that's nice... That's pretty darn wide open, with
> species used to dealing with invasions, compared to an area of high
> endemism such as, oh, the Cumberland River."

Actually, the Bay is totally screwed up with all kinds of crazy exotics.
>From what Peter Moyle tells me one new exotic species replaces an old one
every like 3-5 years. That is how many new introductions are still
occuring (mostly from ballast water I think).

Peter Unmack
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