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Dear Bruce Watson,
I have read some literature that has found that coho are less likely to be
observed/collected when temperatures are cold. One study was done in
Icicle Creek, Washington, USA. In that study they used cyanide as well as
other methods. The cyanide resulted in the largest numbers of fish (I am
not suggesting this as a method). Some people have observed that like
steelhead, coho hang out in the gravel at cold temperatures.
Gary Sprague
Fish Biologist
Washington Dept. of Fish and Wildlife
Olympia, WA, USA
On Thu, 29 May 1997, Bruce Watson wrote:
> Dear colleagues:
>
> I am involved in a study of predation by outmigrating hatchery coho
> smolts on wild fall chinook smolts and pre-smolts. One of the things
> we're investigating is the proportion of coho that have recognizable
> fall chinook or diagnostic fall chinook bones in their stomachs.
> Unfortunately, the river we're working on has been above or near flood
> stage all spring, and we're having a terrible time collecting coho
> smolts. Neither back-back shocking nor boat shocking nor beach seining
> have been at all effective. Does anyone have an idea how we might more
> effectively sample outmigrating coho smolts in a raging river? Also,
> has anyone ever heard of a coho outmigration "stalled" by abnormally
> cool water temperatures occurring late in the spring? Previously,
> virtually all coho smolts released in our system had entered the
> Columbia by the second or third week in May. This release, however,
> seems to be "hanging up" somewhere, even though it's late in the season
> and flows are very high. Does the fact mean daily water temperatures
> are 10-12 deg F cooler this year than they typically are explain this
> lack of movement?
>
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