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To all,
My apologies for the tardiness of my summaries. My only excuse is
that I have been in the field testing some of the assumptions I put
forward previously. Below is a copy of my original posting and then a
condensed list of the responses. Additionally, I include some preliminary
results using gillnets as I have described.
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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,
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- Others have used orientation of fish in gillnet to infer
direction of movement (Hall, D.J., et al. 1979. Diel foraging behavior
... in golden shiner. JFRBC. 36: 1029- 1039.), however the lower water
clarity and the fact that my system is running water throws a couple of
snags into the situation.
- From orientation of fish in the gillnet one can only infer local
movements (over short distances) rather than large movement patterns (such
as from the wetland to the bay).
- But if I can show a "strong" statistical difference between
catches on either side of the net movements can be inferred.
- Gillnets may belly out in running water creating a more
effective trap for the downstream travelling fish. Also the tautness of
the net may cause fish to "bounce off" rather than become entangled.
- Large fish may tangle the net making it difficult to determine
orientation.
- In lakes gillnetting reveals no unidirectional movement even
with sets as short as 10 minutes.
- Other ways to get at fish movements include:
- pit tagging (always difficult to tag small fishes).
- sonic or radio tagging (again difficult with small
fishes).
- use a weir or inclined scoop trap (the mouth of the
Irondequoit Creek is too deep for both or
they would only sample a portion of the water column).
- underwater video (too turbid)
- hydroacoustics, hydroacoustics, hydroacoustics!!! (quite
a few people recommended this, and so I will try it). I
recently attended the International Association for
Great Lakes Research conference in Buffalo, NY where
they held a hydroacoustic workshop. Overall the experts
thought it would be difficult but accomplishable.
- another interesting reference on fish movements is
Gowan and Fausch. 1996. Mobile brook trout in two high
elevation Colorado streams: re-evaluating the concept
of restricted movement. Can. J. Fish. Aquat. Sci. 53:
1370-1381.
Well, I actually fished gillnets perpendicular to the flow of the
Irondequoit Creek (6-9-97 through 6-13-97) and found that:
1) Large fish would tangle the net making determining orientation
a troublesome task.
2) So I cut the net (then I had to reinforce the cut sides) so
that I only fished the smallest mesh size (7mm). Recall that I am
interested in the movements of young fishes. this has worked well
although I believe that orientation is more a result of local movements
rather than large scale.
3) A series of these small nets set progressively farther from the
wetland through the mouth into the bay might yield some patterns of fish
distribution which may allow us to infer previous movements.
This is project is constantly evolving and I believe that between the
gillnet work and some hydroacoustic observations we might be able to learn
more about this dynamic interface zone.
Thanks to all who responded and please send more info if applicable.
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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