>When I was sampling the Illinois River (Oklahoma), I took diurnal and
>nocturnal drift samples concurrently with my seining. Despite large
>populations of darters in the river, I rarely saw darters in the drift >and
>got the impression that those taxa (E. spectabile, E. zonale, E.
>punctulatum, E. blennioides) did not drift much. Similar observations >are
>made in at least two other upland stream studies:
Thanks for the info on the Floyd et al.(1984) and Brown and Armstrong
(1985)papers. I'll get them this evening.
I found a minor revelation in Paine, M.D. and E.K. Balon. 1984. Early
development of the rainbow darter, Etheostoma caeruleum, according to the
theory of saltatory ontogeny. Environmental Biology of Fishes 11:277-299.
Rainbow darters have benthic larvae, at least by 8-12h post-fertilization.
I'm somewhat perplexed by this. When the Tennessee Valley gang was
snorkelling in the Paint Rock and Flint the other weekend, I noticed lots of
individual larval darters, which I believed were E. simoterum and E. duryi.
I made this guess based on the saddle pattern (which was evident even at
12-15mm TL) and head shape. They were associating with clouds of larval
cyprinids, 0.3 - 0.6m off of the substrate. I watched several hang like
this, obviously holding station and feeding in the drift, for a period of
10-15 min.
Also, for those interested, some Percina (P. caprodes) seem to have pelagic
larvae- they float downstream for some period before settling out.
My original reason for asking is this- I'm working on a manuscript on
invaseness of introduced populations of darters, and examining rates of
dispersal. The focus is on introduced populations of rainbow darter in the
Potomac and Genesee rivers. So far, I'm coming up with dispersal rates on
the order of about 25 km/yr in a downstream direction, and 15 km/yr
upstream. Given the widespread perception that darters are relatively
sedentary, this is pretty amazing, even if you assume that they are
occupying an "open niche" in these darter-poor faunas.
I was hoping to be able to ascribe dispersal to larval drift, but I don't
think that will be the case, unless flood events played a role. Matthews
(1998) mentions some studies in which flood events kill almost all larval
fishes present, even before the peak of the hydrograph, but I'd be willing
to bet that the observed mortality was caused by impingement into the drift
nets at high velocity.
I've always sort of shied away from working with larval fishes, but have
just recently come to appreciate how little we know about this period in
their development. Wow! Maybe Bruce <is> on the right track, after all! ;)
anyway, thanks all...
cheers,
dave
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