Abstract.—We
evaluated the habitat use and movements of 50 adult
bighead carp Hypophthalmichthys
nobilis and 50
silver carp H.
molitrix by means of ultrasonic telemetry
during spring–summer 2004 and 2005
to gain insight into the conditions that facilitate
their establishment, persistence, and dispersal in the
lower
Illinois River (river kilometer 0–130). Movement and
habitat use were monitored with stationary receivers
and boat-mounted tracking. The relative availability of
four macrohabitat categories (main channel, island side
channel, channel border, and connected backwater) was
quantified to determine selection; discriminant
function analysis was used to evaluate changes in
physical characteristics within each category. A flood
pulse
occurred in spring through early summer of 2004 but not
2005. Movement rates (km/week) of both species
were positively correlated with flow but not with
temperature. Including data from stationary receivers
greatly
increased estimates of daily movement. During low summer
flow, both species typically selected channel
borders and avoided the main channel and backwaters.
Both species rarely occupied depths over 4 m,
regardless of abiotic conditions. Flood pulses appear to
trigger dispersal, while habitat use is only specific
during low summer flow. Thus, movement prevention
efforts (e.g., dispersal barriers) will require
particular
vigilance during late-winter or spring flooding, and
controlled removal (e.g., harvest) should be directed
toward selected habitats during summer.
Summary: Harvest of the
shovelnose sturgeon, Scaphirhynchus
platorynchus, for caviar has increased. To
determine whether populations can withstand increased
harvest, detailed information regarding sexual
demographics is needed. We describe gender and
reproductive development of 306 shovelnose sturgeon from
the Middle Mississippi River (River km 0–322) during
September 2001 through December 2003. Using dissection
and histology, we identified three of the four gonadal
stages described previously for male lake sturgeon and
all seven stages for females. Males reached maturity at
a smaller size than did females. Gonads can be rapidly
inspected for sex and stage of development for the
shovelnose sturgeon. The sex ratio was not different
from 1 : 1. Seven intersexual fish occurred. Female
fecundity was positively related to body weight (number
of eggs =30.24 · body weight ) 8392; P=0.013; r2 = 0.45)
and weakly related to fork length (number of eggs
=146.37 · fork length ) 66 176, P =0.053, r2 =0.23).
Summary: Within harvested
populations, relationships between harvest intensity and
reproductive responses are typically unclear, rendering
regulatory decisions difficult. Harvest of the
commercially important shovelnose sturgeon (Scaphirhynchus
platorynchus) is increasing in the upper
Mississippi River; standardized seasonal sampling
revealed that adult abundance is declining. Relative
density of annual cohorts varied negatively
with historical harvest intensity (r2= 0.84), suggesting
that removal of mature adults is reducing the
contribution of
cohorts to population density. The results of simulation
modeling suggest that this currently unregulated fishery
is
experiencing both growth and recruitment overfishing.
Further, the current proposed multi-state minimum length
regulation was insufficient to maintain a sustainable
stock. Only a more conservative minimum length limit
(685 mm) produced yields that were sustainable at the
current level of mortality and provided room for the
fishery to grow. The annual mortality rate of the
sympatric, federally endangered pallid sturgeon (S. albus) was
similar to that of the shovelnose sturgeon population,
raising concerns that harvest-induced mortality is
affecting this congener’s vital rates.
Abstract.—Various gear
types have been used to sample populations of channel
catfish Ictalurus
punctatus in lotic
systems. However, these gears produce different
population characteristics (i.e., recruitment, growth,
and mortality). We compared the population demographics
of channel catfish in the Wabash River, Indiana, sampled
with baited 25- and 32- mm-bar mesh hoop nets and
three-phase alternating current (AC) electrofishing.
Based on catch per unit effort, the relative abundance
of channel catfish sampled with 32-mm hoop nets was
lower than that of fish sampled with 25-mm hoop nets and
AC electrofishing. Each gear type also resulted in a
different
length frequency, mean length increasing progressively
in sampling with 25-mm hoop nets, 32-mm hoop nets, and
AC electrofishing. Similarly, age-frequency
distributions differed among gears. The 25-mm hoop nets
biased the age structure toward younger individuals
(mean age= 2.5), whereas both 32-mm hoop nets (mean
age=4.0) and AC electrofishing (mean age=5.8) included
older fish. Catch-curve analysis generated different
mortality rates for the three gear types, the mortality
rate being highest (50%) in fish sampled with 25- mm
hoop nets. Gear-specific size and age structures led to
differences in von Bertalanffy statistics among the
25-mm
hoop nets and AC electrofishing, while the results for
32-mm hoop nets were uninterpretable. Because the
different gears led to conflicting parameter estimates,
management practices based on sampling with single gears
may be contradictory. Given the differences in gear
selectivity, biologists need to approach management
cautiously until calibration to the true size and age
structure is conducted.
Abstract.—Sagittal
otoliths and the articulating process of the pectoral
spine have both been validated as accurate
techniques for estimating the age of channel catfish Ictalurus punctatus
(<-age 4). However, there is limited information
onthe relative precision of estimates from these two
structures. Thus, we analyzed the precision of age
estimates derived from otoliths and the articulating
process of the pectoral spine and compared the dynamic
processes (recruitment, growth, and mortality) resulting
from those estimates. Aging structures were removed from
110 channel catfish captured from the Wabash River
(river kilometers 550–9.6) via day–timeelectrofishing.
The age estimation methodologies were similar to those
described in previous studies. Agreement between the
ages derived from the two structures was high; the
average percent error was 8.4%, the coefficient of
variation was 11.4, and the slope of the age bias plots
did not differ from 1, indicating similar age
assignments between structures. The corresponding
recruitment patterns, von Bertalanffy growth models, and
mortality rates did not differ between the aging
structures. We conclude that the articulating process of
the pectoral spine provides age assignments similar to
those of otoliths and that the dynamic processes do not
differ between structures. Further, based on the results
of this study, the articulating process of the pectoral
spine provides a suitable alternative to otoliths and
has the advantage that channel catfish do not have to be
sacrificed.
