Darran,

> 1) Whether orientation of the fish in a gillnet can be used as a
> predictor of direction of fish movement, and
>
> 2) Whether the presence of young fish in the net can equate to fish
> moving through this area rather than fish just "hanging out" in this area?

        I think that you may have some important problems with the
assumption that the orientation of the fish is indicative of the
large-scale movements.  The orientation of the fish in the gill net is
really only an indication of the small-scale or local movements of the
fish.  It doesn't really tell you whether the fish is in the process of a
large-scale movement.  Especially if you're setting a net for only 15
min, then the orientation of the fish may be more indicative of the
direction that the fish fled when you set the net rather than the large
scale direction that he is moving.

        A better way to go about the sampling would be to conduct a survey
that gives you fish number per stream meter with a fairly high spatial and
temporal resolution.  For a small system, this might be done with a series
of seining and electrofishing samples.  For a large system that is at
least 5 m deep, hydroacoustic sampling may be best.  I've run
hydroacoustics from a 16' jon boat with good success.  If you want to go
the hydroacoustic route, you may contact Lars Rudstam, at Cornell
biological station, <[log in to unmask]>, or we may be able to
collaborate with you.  Unfortunately, our acoustic systems are in heavy
use this summer and we may not be able to do somthing when you need to
sample.  I suggest contacting Lars because he is a good fisheries
acousitcs person and is fairly close to you.

cheers,
Jeff Tyler



On Tue, 20 May 1997, Darran L. Crabtree wrote:

> To all,
>
>         Darran Crabtree here, grad student, investigating the roles of coastal
> wetlands to Great Lakes fishes.  I would like the opinion of anyone who
> cares to share it on the matter below.
>         I am interested in determining whether the Irondequoit
> wetland contributes young fish biomass (age 0+ and 1+) to the adjacent
> Irondequoit bay.  To do this I must quantify the movements through the
> mouth of the Irondequoit creek (the only connection between the wetland
> and the bay).  I envision (I realize envisioning can get me in trouble)
> setting a portion of a gillnet (small mesh) perpendicular to the flow of
> the creek.  I will set it for only a short duration of time, anywhere from
> 0.25-1.0 hr.  What are your opinions of my assumption that the orientation
> of the fish in the gillnet (head stuck in the net pointed downstream or
> upstream) is indicative of the direction that that young fish is going
> (out of the wetland or into the wetland).
>          We have gillnetted in this area before and have only caught
> large, predatory, adult fishes such as salmonids and channel catfish.  I
> believe that this habitat (right in the mouth of the creek) is a prime
> foraging area for fish predators, but that there are temporal pulses of
> young fish moving through the creek mouth.  So with out doing a tagging
> study (we tried this in another part of the wetland and found that the
> populations were too large to get adequate recaptures), can I simply say
> that in this hostile habitat (numerous predatory fishes around) small,
> young fish should minimize time spent there.  Thus, any fish caught
> should be using the creek mouth as a "highway" between the wetland and
> bay, not as a residence.
>
> I would like your opinions on:
>
> 1) Whether orientation of the fish in a gillnet can be used as a
> predictor of direction of fish movement, and
>
> 2) Whether the presence of young fish in the net can equate to fish
> moving through this area rather than fish just "hanging out" in this area?
>
> Respond to my address below.
> Thanks in advance,
>
> Darran
>
> Darran L. Crabtree
> State University of New York
> College of Environmental Science and Forestry
> 243 Illick Hall
> One Forestry Drive
> Syracuse, New York 13210
> (315)-470-6949
> [log in to unmask]
>
>
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========================================================
Jeffrey A. Tyler, Ph.D
Great Lakes Center                    ----------------
Buffalo State College                | G = mG+(1-m)g  |
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Buffalo, NY 14222                     _:______
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