>I was reading the latest AC yesterday, and on page 15 there's a box talking
>about the relative rarity of various fishes in MD. Rainbow darters are
>mentioned as having an estimated population of only about 600. My question
>is, aren't rainbows apparently an introduced species in MD? As exotics go
>they seem innocuous, but still...
Rainbows first turned up in the Potomac in 1976 or 1977, in the upper South
Branch in WV. After the 1985 flood, rainbows started appearing everywhere-
the first MD record was from Harpers Ferry the summer following the flood.
By 1992, rainbows were the dominant darter in lower Sideling Hill Creek and
several other tribs in the Ridge and Valley. There is preliminary evidence
that they are displacing native greenside and tesselated darters, at the
very least causing habitat and diet shifts. They now range from the lowhead
dam at Cumberland downstream to the Fall Line.
I haven't seen the new AC yet, but I assume the estimates are from the early
MBSS data- which while generally good, excluded 4th order streams and larger
(which they have since corrected). Most of the streams occupied by rainbows
in MD are 4th + order. The estimates of 600 darters are way off- I'd venture
we have 600 Maryland specimens in the Frostburg fish collection... but hey,
the MBSS is good, but isn't perfect. Their checkered sculpin estimates
(published in Transactions of the Am. Fish. Soc. last year) had a standard
error a magnitude larger than the estimate... an artifact of a localized
fish that is hard to survey by electrofishing.
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