My thought is that the greater impact to the fish will be from the
actual replacement activity (moving and replacing cables in the column),
with very little impact caused by two divers themselves. This is based
on the 6000+ man-dives conducted by my group in Puget Sound over the
past 20 years, many of which occur in popular salmon fishing areas and
migration corridors. In all those dives, we have seen adult salmon on
less than 20 occasions, and in most of those cases, the salmon actively
avoided our presence. Further, having done 20-30 dives in Lake
Washington, I cannot recall encountering salmon at the depths you
mention, although I have seen them at shallower depths.
Marine Fish Biologist
Wash. Dept. of Fish and Wildlife
From: Scientific forum on fish and fisheries
[mailto:[log in to unmask]] On Behalf Of Bigler, Brian S.
Sent: Wednesday, March 11, 2009 9:37 AM
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?
NW Region Biology Program Manager
Washington State Department of Transportation Seattle, WA