Brian,

My thought is that there would be little impact.  Fish may be inclined to swim a short distance from the divers and temporarily displace the fish until the divers pass. The air expelled by the divers rising through the water column may have a similar effect.  However, no permanent impacts would be expected.  If noise producing equipment is used to attach the cables, or if pyles are required to be driven into the lake bottom, there may be impacts from those activities.  Two divers attaching a cable (I assume they would simply use some sort of manual wrench) would not be expected to have any more impact than recreational divers or divers collecting scientific data.   

Cheers,
Justin

-----Original Message-----
From: Scientific forum on fish and fisheries [mailto:[log in to unmask]] On Behalf Of Bigler, Brian S.
Sent: Wednesday, March 11, 2009 12:37 PM
To: [log in to unmask]
Subject: Impacts of divers

I am working on a project that will replace some anchor cables on the
two floating bridges that cross Lake Washington in Seattle, Washington.
The project will use a pair of divers to replace these cables in water
from 40 to 200 feet deep.  Lake Washington is the largest lake in
Western Washington, and supports a number of salmonid species, including
anadromous sockeye.  Adult sockeye are known to find thermal refuge at
50 to 90 feet deep during the warmest part of the summer, and this
season the population is expected to be 105,000.
 
A question has arisen on the potential impact that two divers would have
on these fish, and I am at a loss to find a source of information.  Does
anyone know, or can anyone provide best professional judgment, on the
potential impact of a pair of divers moving vertically through the
thermal refuge layers where sockeye would be dispersed?  

Brian Bigler 
NW Region Biology Program Manager
Washington State Department of Transportation 
Seattle, WA 
Direct: 206-440-4519 
Cell:    206-919-1610 
FAX:    206-440-4805