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i am not sure that i like the idea of allowing a large number of fish to
accumulate on a lower seine net until the entire site has been
electrofished - presumably many of these fish are disoriented and may
not recover, especially if 'pinned'to the net by the force of the
current. in eastern canadian salmonid streams where i work, we often
electrofish in a downstream direction using block nets but only in
riffles and runs where there is a moderate to strong current. in
addition, we use a 2-person 'lip-seine' immediately dowstream (<2m
away)of the person with the electrofisher to capture displaced fishes as
we progress thru the site. this seine is lifted and checked throughout
the sweep. the lower block net is also checked at the end of each sweep
within a site but captures very few fish relative to the lip-seine. i
should note that when mortalities do occur they are almost always for
those fish which have drifted down onto the lower block net - hence, my
concern.
the lip-seine technique that i have described (poorly, i'm afraid), is
very effective and was originally developed by dr. paul elson in the
50's. it is rarely used outside of maritime canada. i was skeptical of
its effectiveness when i first arrived here 10 years ago from ontario
(where upstream sampling with dip-netting was the norm) but am now
convinced that it is the best electrofishing technique for
shallow,swift, low conductivity streams.
hope this helps.
rick cunjak
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