Re: NANFA-- How fish get from A to B

Shireen Gonzaga (
Tue, 14 Dec 1999 11:04:24 -0500

Dave Neely wrote:

> ALL available evidence supports the hypothesis that the ichthyofauna of
> North America is a product of many different types of events.

OK, that sounds reasonable.

> IF shorebirds were capable of spreading fish all over the place, then WHY do
> so many species of NANFs have very discrete ranges, tied strongly to river
> drainages?

First of all, I was not referring to shorebirds as the carriers--that's
unlikely for other reasons (tho' possible in the case of dowitchers,
avocets, and stilts). I was referring to large wading birds like herons
and egrets. Sorry if that was not clear.

To speculate on an answer to your question, I would suggest that
bird-carried eggs are only viable over short distances where flight
time is under 10 minutes or so. That would explain the discrete
ranges of some fish. And explain why only some species
"mysteriously" appear--perhaps these species have eggs that can
survive for short periods of time out of water.

> How come I can sit on the eastern Continental divide in MD and
> PA, and catch Etheostoma olmstedi from streams draining East and Etheostoma
> nigrum from streams draining West? How come Waccamaw killifish aren't spread
> all up and down the doggone Eastern Flyway? Why does the range of Lucania
> goodei stop in the Choctawhatchee when herons fly all they way up the
> goldang Mississippi?

As I said above, speculatively, these transfers from different
bodies of water have to occur over short periods of time before
the eggs dry out.

Regarding your migration argument, let's talk a minute about
avian movements. There are two general categories.

A) During migration, birds travel large distances at a stretch, in
the case of some shorebirds, non-stop over several days. In
such circumstances, the eggs would not survive.

B) During the breeding season, birds tend to congregate at
particular locations. During this time, their movements are
restricted to short movements to ponds within a local area.
Under those circumstances, local transfers of fish eggs
become more likely.

You may then ask, over long periods of time, why don't we see a
leap frog effect that increases the range of the fish? That's a
complicating question. Perhaps it does happen to some extent.
Perhaps this kills my argument... I'm not sure. But also remember
that many waterbirds often demonstrate site fidelity. They tend to
come back each year to a particular location to winter over or
breed. That may partly explain the low rate or non-existence of
range expansion for fish "transferred by bird-transportation."

One more thing... let's not over-generalize this for all fish. Some
fish eggs, like killies, may be more predisposed to surviving out
of water than others. That's why I'd like to know more about the
survivability of killie eggs in dry areas over timescales of several
weeks to months.

> There's been a very productive research program concerned with the
> zoogeography and evolution of the North American ichthyofauna, starting with
> a late 1800s paper by Cope, and continuing to the current day. Check out
> Mayden, RL 1992, 'Systematics, historical ecology, and North American
> freshwater fishes' for a really good review of the topic. Hocutt and Wiley's
> 1986 'Zoogeography of NA Freshwater fishes' is another good read.

Were any of the co-authors ornithologists? :-) One of the big problems in
scientific research is the compartmentalization of the various disciplies,
with no dialog between them. Nature does not exist in compartments. We

> In short, bird transfer seems very, very unlikely except in very restricted
> situations, and then only over very short distances.

So you're saying it's not impossible... I'm suggesting that it may be more
common than you think, within restricted areas

David, your post was extremely informative and interesting--I'm going to
file it in my email fish reference folder. But it still does not address my
question regarding this particular refuge in Delaware.

Again, I will ask, how else could the fish get there? From my knowledge
of the area, floods and artificial placement are not possible. The appearance
of the fish is an _annual_ event. The only other way the fish could get
there is if eggs were able to survive in dry conditions for several months.
Is _that_ possible?


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