Illinois Natural History Survey Reports

              1
R e p o r t s
November/
December 1996
No. 342
I N S I D E
Acanthocephalans and
Rotifers Provide Clues
for Study of Evolution
of Animal Parasites
2
A Land Cover Map of
Illinois
3
IN MEMORIAM
Dr. Warren Ulrich
Brigham
4
Microbial Larvicides in
Mosquito Control
5
Species Spotlight:
Eastern Box Turtles
6
Dr. Lorin I. Nevling,
INHS Chief, to Retire
7
Continued on back page
I LLINOIS
NATURAL
HI STORY
S U R V E Y
Locations of 21 Illinois reser-voirs
that were sampled to encom-pass
range of limnological and
morphological characteristics.
Fish communities in Illinois reser-voirs
can be infl uenced by changes
in environmental conditions
throughout the year. Within these
fi sh communities, larval or young
fi shes are often the most suscep-tible
to these fl uctuations in abiotic
and biotic conditions. During
the critical early life stage of fi sh,
slight changes in the environment
can drastically affect the recruit-ment
of young fi sh into the adult
population. In fact, of the vast
number of larvae that hatch, only a
small percentage actually reaches
the juvenile or adult stage. Even
though biologists have recognized
the importance of identifying the
factors infl uencing recruitment,
most studies have only dealt with a
single lake or reservoir system. As
a result, environmental variation
is minimized due to restrictions of
space and time. Our study was de-signed
to examine several abiotic
and biotic factors thought to deter-mine
larval fi sh growth rates across
a series of Illinois reservoirs.
We sampled 21 reservoirs
(see map) every other week
from May through July 1995.
On each date, we collected
larval fi sh and zooplankton
samples and measured tem-perature,
dissolved oxygen,
and secchi disk depth. Lake
morphometrics and water
chemistry data were obtained
from previous lake surveys.
Principal Components Analy-sis
(PCA) was used to reduce
the large number of variables
to a smaller set of factors. The
PCA scores were then corre-lated
to larval fi sh growth rates
for each reservoir.
The most abundant larval
fi sh species across reservoirs
were gizzard shad (Dorosoma
cepedianum), sunfi sh (Lepomis
spp.), crappie (Pomoxis spp.), and
brook silversides (Labidesthes
sicculus). The peak densities of
these young fi sh varied greatly
across reservoirs and ranged from
1 to 250 fi sh per liter. Zooplank-ton
levels (the major food source
for young fi sh) showed similar
high variation across reservoirs
and through time.
The fi rst principal component
(PC 1) is composed of mean
depth, shoreline length, and the
surface area of the reservoir.
These variables accounted for the
most variation among the reser-
Critical Factors in the Early Life History of
Illinois Fishes
Otolith bone in larval fi sh used to determine age and growth.
Photo by Randall Claramunt, INHS Center for Aquatic Ecology