Factors limiting the distribution of larval and juvenile fishes


Dewey, M. R., and C. A. Jennings.  1994.  Factors limiting the
distribution of larval and juvenile fishes in vegetated habitats
of the Upper Mississippi River.  Report by the National Biological
Survey, National Fisheries Research Center, La Crosse, Wisconsin,
for the National Biological Survey, Environmental Management
Technical Center, Onalaska, Wisconsin, April 1994.  EMTC 94-S005. 
Part I, 61 pp.; Part II, 19 pp.  (NTIS # PB94-177342)


ABSTRACT

We studied the use that young fishes make of vegetated and
nonvegetated habitats in Lawrence Lake (Pool 8, Upper Mississippi
River).  Habitat use was both extensive and variable.  Fish were
found in all portions of the macrophyte beds.  Backwater
macrophyte beds both near to and distant from the main channel of
the Mississippi River displayed similar patterns of habitat use. 
The open water site was used principally by gizzard shad and
unidentified Cyprinidae.  Habitat use in macrophyte beds with
differing vegetation densities in Lawrence Lake was probably
influenced by  multiple factors.  Physical and chemical
microhabitat data explained little of the variation in catch in
light traps.  Two-stage sampling analyses indicated that when fish
density is highly variable, sampling at many stations (one sample
per station) is needed to assess habitat use in relation to
vegetation density and species complexity.    We evaluated several
gears for both quantitative and nonquantitative sampling of
juvenile fishes in vegetated habitats.   From July through
September, we conducted field tests to compare catches from light
traps, fyke nets, hoop nets, gill nets, and minnow traps.  Three
quantitative sampling gears, an electrofishing frame, a drop net,
and a pop net, were used.  The electrofishing frame was modified
with a drop-net mechanism to assess the capture efficiency of the
electrofishing device and to serve as a drop net.  Light traps,
which principally sampled larval fishes, were effective in
vegetated habitats.  Catches with all three quantitative gears
were dominated by juvenile bluegills.  The electrofishing frame
caught significantly fewer fish in turbid vegetated areas than the
drop and pop nets, due to difficulty in observing and netting
stunned fish.  Capture efficiencies with the electrofishing frame
were higher in clear nonvegetated areas (mean 80%) than in turbid
vegetated areas (mean 5%).  The drop net and pop net yielded
similar catches in number and species composition.  With the drop
net, extensive seining (8-10 hauls) was required to collect all
fish within the net enclosure.  However, use of a removal method
to estimate absolute catch decreased seining effort to three or
four hauls, more comparable to that of the pop net.  We recommend
either drop nets or pop nets for quantitative sampling.    
Replicated tests with nonquantitative sampling gears were
conducted to evaluate the effectiveness of fyke nets, hoop nets,
small-mesh gill nets, and minnow traps in submergent vegetation
and the effectiveness of small-mesh gill nets and hoop nets in an
open water habitat.  Of the nonquantitative gears tested, fyke
nets produced the greatest numbers and species of fish.  In open
water, replicated sets of small-mesh gill nets and hoop nets
showed that the gill nets were effective for capturing gizzard
shad and golden shiners.


KEYWORDS


larval fish, backwaters, sampling gear, microhabitat, Upper
Mississippi River, aerial videography