Depends on the species and locale, I would guess.
Many desert stream minnows (e.g., spikedace, speckled dace, longfin dace) are
adapted to the flash floods that seasonally rip through their habitat.
The effects of flash floods, which are caused when local runoff concentrates
into narrow channels, can be sudden and dramatic. Conditions in creeks and small
rivers may change from clear to turbid water within seconds. Water temperatures
can drop more than 59F. And stable bottoms can be picked up and moved around.
Despite their violence, flash floods seldom destroy fish populations, as desert
fishes seek refuge behind boulders or along the banks when the floods occur.
In fact, these fishes actually *depend* on floods for having suitable places to
spawn. Flooding causes the resorting, loosening and cleaning of substrate
materials. Biologists call this "disturbance," and in this case, disturbance is
a good thing, for it shakes loose compacted or embedded areas of silt-free
gravel, making it ideal for spawning and the development of eggs.
Desert fish biologist John N. Rinne reports two instances in which desert
minnows have been attracted to areas disturbed by less-than-natural means. In
spring 1998, spikedace in a small tributary of the Gila River were seen
congregating in a road-crossing. Apparently the fish were attracted to how the
cars stirred the water and reshuffled the substrate. Likewise, hundreds of
speckled dace on the upper Gila River, after a flood-free winter, were seen in a
spawning aggregation in an area where earth-moving equipment were pushing up an
irrigation diversion in the channel. No spawning was occurring either above or
below this specific area. (For the record, Rinne does not suggest that more cars
and bulldozers should drive through streams to help desert fishes. He's merely
illustrating the degree to which spikedace and other native fishes are attuned
to disturbance events.)
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