[env-trinity] Mainstem Trinity River spawning survey update through Oct 2

[Chamberlain, Charles]

Hi all,
Our latest in-season report from the Trinity River Salmon Spawning Survey
is available from the Fisheries web page of the Arcata Fish and Wildlife
Office:
http://www.fws.gov/arcata/fisheries

We surveyed from Lewiston Dam to Pigeon Point and Big Bar to Cedar
Flat Monday-Thursday this week.  Our crews mapped the location of 294 redds
and 110 carcasses.  The figure below is clipped from our weekly report
available at the link above.  Activity is picking up and folks are
reporting seeing MANY fish throughout the surveyed reaches so I'm hopeful
of a rebound "into the blue" soon.

[image: Inline image 1]



*Fun fact for the week...  *

*Did you know*....  Redd dewatering can influence a salmon fry's success or
failure to hatch and emerge from a redd, but determining the influence
isn't as cut and dry as one might think - no pun intended :)   River levels
that recede through a spawning season can put redds at risk of dewatering.
We thankfully weren't able to locate any dry redds after this latest
emergency flow release.  Even if we had though, a redd with exposed gravels
doesn't necessarily indicate mortality of the eggs within.  The average
depth of Trinity River Chinook Salmon egg pockets is about 9 to 12 inches
below the original bed surface (Evanson 2001
<http://odp.trrp.net/Data/Documents/Details.aspx?document=278>).  Most or
all of a redd's mound can be exposed before the water drops below the egg
pockets within.  A number of studies and experiments have observed survival
of eggs, even when water level receded below that of the egg pocket!  In
those cases, capillary action alone was enough to keep eggs moist and
alive.  Early life stages within a redd are more tolerant of occasional
dewatering.  Eggs and embryos respire through diffusion across moist cell
membranes.  Tolerance decreases as a fish hatches and comes to depend on
its gills for respiratory needs (Reiser and White 1983
<http://scholarworks.umass.edu/fishpassage_journal_articles/294/>, Becker
and Neitzel 1985 <http://link.springer.com/article/10.1007%2FBF00007708>).


I'll check in with you again next week,
Charlie

Charles Chamberlain
Supervisory Fish Biologist
U.S. Fish and Wildlife Service
1655 Heindon Road, Arcata, CA 95521
http://www.fws.gov/arcata/fisheries
(707) 825-5110
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