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Effective management and monitoring programs require confidence regarding basic biological sampling. Gear comparisons are often required to determine the most effective techniques. Such is the case for populations of invasive Asian carps Hypophthalmichthys spp., which have recently occurred in large numbers throughout sections of the Mississippi River basin. We tested five gears (mini-fyke nets, beach seine, purse seine, pulsed-DC electrofishing, and gill net) that targeted juvenile (age 0) Silver Carp H. molitrix at sites along the Illinois River during 2014 and 2015 to determine the most effective ones for age-0 Silver Carp. We considered the most cost-effective gear to be the one that provided the largest catch at a minimal expenditure of labor. Mini-fyke nets were the most effective at collecting large numbers of age-0 Silver Carp, followed in decreasing order by beach seines, pulsed-DC electrofishing, purse seines, and gill nets. The smallest Silver Carp were caught in beach seines and the largest were caught in gill nets, and there was considerable variation in size distributions among gears. However, when we considered cost-effectiveness in terms of labor hours for each gear, both beach seines and mini-fyke nets had similar and overlapping labor expenditures. Gill nets and purse seines were not cost-effective, as they required more labor and had lower overall catch rates. Received May 23, 2016; accepted September 19, 2016
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A Comparison of Sampling Gears for Capturing Juvenile
Silver Carp in RiverFloodplain Ecosystems
Scott F. Collins,*Matthew J. Diana, Steven E. Butler, and David H. Wahl
Illinois Natural History Survey, Kaskaskia Biological Station, 1235 County Road 1000N, Sullivan,
Illinois 61951, USA
Effective management and monitoring programs require con-
dence regarding basic biological sampling. Gear comparisons
are often required to determine the most effective techniques.
Such is the case for populations of invasive Asian carps
Hypophthalmichthys spp., which have recently occurred in large
numbers throughout sections of the Mississippi River basin. We
tested ve gears (mini-fyke nets, beach seine, purse seine,
pulsed-DC electroshing, and gill net) that targeted juvenile
(age 0) Silver Carp H. molitrix at sites along the Illinois River
during 2014 and 2015 to determine the most effective ones for
age-0 Silver Carp. We considered the most cost-effective gear to
be the one that provided the largest catch at a minimal expendi-
ture of labor. Mini-fyke nets were the most effective at collecting
large numbers of age-0 Silver Carp, followed in decreasing order
by beach seines, pulsed-DC electroshing, purse seines, and gill
nets. The smallest Silver Carp were caught in beach seines and
the largest were caught in gill nets, and there was considerable
variation in size distributions among gears. However, when we
considered cost-effectiveness in terms of labor hours for each
gear, both beach seines and mini-fyke nets had similar and over-
lapping labor expenditures. Gill nets and purse seines were not
cost-effective, as they required more labor and had lower overall
catch rates.
Effective management and monitoring programs require con-
dence in basic biological sampling. Fisheries scientists typically
rely on a range of differing active and passive gears to quantify
and describe sh assemblages. Because of biases inherent to the
design and deployment of sheries gears (e.g., species collection,
habitat limitations, gear evasion, and deployment durations),
some gear types may be ill-suited in specicapplications
(Lyons 1986; Weaver et al. 1993; Bayley and Austen 2002;
Breen and Ruetz 2006;Lapointeetal.2006; Hubert et al.
2012). Species traits, such as their mobility (sedentary versus
mobile), ontogenetic shifts in habitat associations, and patchy
distributions caused by schooling, can affect catches. Because of
these factors, evaluating the effectiveness of multiple gears is
often required to ensure condence that sampling reects the
numbers of organisms in nature and minimizes nondetections.
Detecting and monitoring populations of invasive Asian
carps, namely Silver Carp Hypophthalmichthys molitrix and
Bighead Carp H. nobilis, exemplify this basic knowledge gap.
Presently, sheries scientists are working to describe the abun-
dances, distributions, and movements of these shes at various
life stages throughout the Mississippi River basin (e.g.,
DeGrandchamp et al. 2008; Sass et al. 2010; Collins et al.
2015;Cooke2016; Norman and Whitledge 2015). Important
gains have been made for adults; however, progress for juveniles
has been slower, in part because of variable reproduction among
years (DeGrandchamp et al. 2007; Irons et al. 2011). Thus, there
have been few opportunities to test the effectiveness of gears
targeting these early life stages or to track cohorts through time
and space. Indeed, early detection of reproduction of these inva-
ders provides vital information for the management of these
species. Moreover, identifying effective gears allows scientists
to begin describing the dynamics of early life stages, including
building recruitment indices and identifying the factors that
inuence interannual variation. During 2014 and 2015, high
reproduction of Silver Carp in the Illinois River resulted in
these sh being vulnerable to sampling gears, allowing for com-
parisons of catch rates between gears (ACRCC 2016).
To address which sampling gears are most effective under
differing seasons and river stages, we compared sheries gears
at sites along the Illinois River to determine the most effective
sampling approach for collecting juvenile (age 0) Silver Carp.
We de ned effectiveness as the ability of the gear type to
capture greater numbers of sh. Our objectives were to
*Corresponding author:
Received May 23, 2016; accepted September 19, 2016
North American Journal of Fisheries Management 37:94100, 2017
© American Fisheries Society 2017
ISSN: 0275-5947 print / 1548-8675 online
DOI: 10.1080/02755947.2016.1240121
compare juvenile Silver Carp catches and the cost-effective-
ness of mini-fyke nets, beach seines, purse seines, pulsed-DC
electroshing, and gill nets at multiple main-stem and contig-
uous backwater lake habitats along the Illinois River.
Study design and sampling regime.Comparisons of
sampling gear for juvenile Silver Carp were conducted within
the LaGrange pool of the Illinois River, which is known to have
high abundances of Asian carps (Sass et al. 2010;Collinsetal.
2015; ACRCC 2016). Sampling gears were evaluated at two
main-stem sites along the Illinois River and two contiguous
backwater lakes. Sampling sites were located near Beardstown,
Illinois (river kilometer [rkm] 133.6), which was paired with Lily
Lake backwater (rkm 133.7), and near Havana, Illinois (rkm
192.1), which was paired with Matanzas Lake backwater (rkm
186.7). These locations along the Illinois River are frequently
used for monitoring Asian carp populations and testing
experimental gears (e.g., Collins et al. 2015; ACRCC 2016).
Sampling events occurred twice annually in summer (July
August) and fall (late SeptemberOctober) of 2014 and 2015
after the detection of larval and postlarval Silver Carp during
monitoring efforts by multiple agencies. Sampling of paired sites
(i.e., Illinois River main stem and a nearby contiguous backwater
lake) typically occurred over a 1-week period. All gear types
were deployed concurrently at each site and deployment of gears
were interspersed so that no particular gear type blocked or
inhibited another gear. Likewise, gears were deployed in their
intended environments following standard approaches. Because
hydrology varied, so did the location of the shoreline. Yet, gears
specic to shoreline sampling were conducted at the shoreline
and those specic to deeper waters were deployed in a similar
and consistent manner. Differences in river stage during our
2-year evaluation were assessed using data from a gauging
station located near Meredosia, Illinois (U.S. Geological
Survey gauging station 05585500; Figure 1).
Description of sampling gears.Five sampling gears were
selected for experimental evaluation. Gears sampled either
shoreline habitats (05mfromthebank)ordeeperwaters
(typically 1015 m from the shoreline) of channel margins at all
sampling sites. Littoral shorelineareasweresampledusingmini-
fyke nets and beach seines; gill nets and purse seines were used to
sample deeper water areas, and electroshing was used to sample
areas along the nearshoreoffshore continua (Gutreuter et al.
1995). Mini-fyke nets (4.5- ×0.6-m lead, 0.6- ×1.2-m trap,
3-mm mesh; eight net-nights per site habitat per sample event)
have smaller mesh sizes than traditional fyke nets and are
deployed by extending the lead from shore and deploying the
trap in 0.31mdepth.Beachseines(10mlength,3-mmmesh;
four hauls per site habitat per sample event) also sampled shoreline
habitats in areas free from rocks or woody habitat. Beach seines
were pulled parallel to the shoreline over a 10-m distance and
retrieved to shore. Sampling with pulsed-DC electroshing (250
V, 8 10 A, 60 Hz, varied pulse width) consisted of four 15-min
transects per site habitat per sample event (Gutreuter et al. 1995).
Each transect was parallel to and within 5 m of the shoreline
and followed an in-and-out pattern that integrated the nearshore-
FIGURE 1. Continuous measurement of stage height of the Illinois River from 2014 to 2015 at U.S. Geological Survey gauging station 05585500, Meredosia,
to-offshore continuum (Gutreuter et al. 1995). Small-mesh purse
seines (122 ×3.05 m, with 2.5-cm mesh; four hauls per site
habitat per sample event) were deployed in deeper water
habitats in order to encircle any sh in the open water. One
end of the purse was buoyed, then the boat was driven in a
large circle while releasing the seine, returning to the end. The
purse line was then cinched at the bottom and then pulled into
the boat (Hayes et al. 2012). Finally, oating experimental gill
nets (45.8 m long ×3.05 m deep, consisting of 1.9-, 2.5-, 3.2-,
3.8-, and 5.1-cm mesh panels; four 4-h sets per site habitat per
sample event) were deployed in open-water habitats. All
captured sh were enumerated, and subsamples of each
species in each gear (n=30persitevisit)weremeasured
(mm TL).
Analyses.For consistency, we limited analyses of juvenile
Silver Carp catches to age-0 individuals (<200 mm TL). No
age-1 Silver Carp were observed in 2014, and only small
numbers were captured in 2015. Previous analysis of Silver
Carp growth in the Illinois River (Stuck et al. 2015) as well as
examination of seasonal, size-frequency distributions from
multiple years of sampling (S. E. Butler, unpublished data)
indicated that age-1 Silver Carp in this system are
considerably larger than 200 mm by the summer sampling
period but that age-0 individuals do not surpass this size by
fall. We compared catches to evaluate the gears with the
highest total and mean numbers of age-0 Silver Carp
collected. Raw catch numbers were used due to difculty in
scaling catches into rates in similar units across gears. For
instance, catches of purse seines are measured on a per haul
basis, and sampling a single replicate can take minutes. In
contrast, mini-fyke net catches also represent numbers within
a net but collect over a 24-h period. The scaling from minutes
to a full day would be mathematically feasible; however, it
could introduce biases, and metrics would not be reective of
what is sampled in the eld by sheries scientists. Such
inherent differences are unique to each gear.
Mean catches were evaluated within a gear type to assess
the effect of sample period (i.e., summer and fall of each year)
and differences between the main-stem Illinois River and
connected backwater lake habitats using two-way ANOVA.
Differences in catch rates among habitats during sample per-
iods were assessed via the interaction of sample period and
habitat. Additionally, we tested for differences in lengths of
age-0 Silver Carp collected between gears using two-way
ANOVA. For this analysis, we compared lengths across
gears as well as evaluated the interaction of gear and habitat.
Data were log
transformed to meet the necessary distribu-
tional assumptions.
Because hydrology varied over time, we further compared
catches of age-0 Silver Carp over time to native shiners (Emerald
Shiner Notropis atherinoides,SpottailShinerN. hudsonius)and
centrarchids (Bluegill Lepomis macrochirus,Orangespotted
Sunsh L. humilis,BlackCrappiePomoxis nigromaculatus)in
sampling gears where these taxa are frequently collected. We
reasoned that if a reduced catch of age-0 Silver Carp corre-
sponded with a reduced catch of native shes, hydrologic con-
ditions rendered gears inefcient. However, if age-0 Silver Carp
catch changed but catch of native species remained similar, the
pattern suggests that gears are effective, but age-0 Silver Carp
were not present in these sampling locations.
Cost effectiveness of sampling gears.Accounting for
differences in both catch rates and effort (e.g., crew size, labor
hours) required to deploy (and recover when appropriate)
sampling gears provides a means of identifying the most
cost-effective monitoring strategy. Here, we considered the most
cost-effective gear to be the one that provided the largest catch at a
minimal expenditure of labor. Because Silver Carp catch rates
were low and inconsistent during 2015 (see Results), we used
2014 catch rates to determine effect sizes between gears. Crew
sizes (two or three individuals) and effort varied for each gear type.
The effort required to deploy or collect (i.e., remove sh) and
redeploy mini-fyke nets was estimated to be between 5 and 9 min.
Because mini-fyke nets were deployed overnight, requiring two
trips, effort was doubled to 10 and 18 min. Individual beach-seine
hauls varied between 5 and 7 min. Purse-seine hauls ranged from
10 to 15 min. Pulsed-DC electroshing sampled 15-min transects.
For electroshing, we added an additional 20 min to account for
preparing the boat (e.g., setup of electrical equipment, installation
of boom arms). Experimental effect sizes (i.e., differences in
overall catch rates between gears) were used to determine how
many replicates of a gear would be required to achieve similar
numbers relative to the gear with the greatest average catch rate.
Daily labor estimates in hours, LD
where G
is the number of gears of type ithat were deployed,
is the daily effort required to use the gear, recorded in
minutes and divided by 60 to convert to hours, and C
is the
eld crew size. Other factors such as travel times between
sites and handlingprocessing times of sh were not included,
as these vary by protocol, agency, and monitoring sites.
River stage over the 2-year experiment differed between
sampling periods (July 1September 30) of each year
(Figure 1). River stage averaged 2.91 ±1.38 m (mean ± SD)
in 2014 and 4.02 ± 2.93 m in 2015 from July to September.
Flooding in July of 2015 resulted in river stages of 7.77 ±0.75
m, which delayed our sampling. River stage decreased to 2.56
± 0.94 m during the summer 2015 sample period (August
1019) and 2.06 ± 0.38 m during the fall 2015 sample period
(September 2030).
Age-0 Silver Carp comprised 37% of all shes sampled
(N= 40,390) across all gears, sites, and habitats. Total
numbers of Silver Carp varied substantially between years
and gear types. A total of 40,285 (99%) juvenile Silver
Carp were collected in 2014 and only 105 (<1 %) indivi-
duals in 2015 across all sites, habitats, and gears (Table 1).
Total catch of age-0 Silver Carp was greatest for mini-fyke
nets, followed in decreasing order by beach seining, purse
seining, DC boat electroshing, and gill netting (Tabl e 1 ).
Gears that collected the greatest mean numbers of age-0
Silver Carp (i.e., mini-fyke nets and beach seines) were asso-
ciated with shoreline sampling that occurred at shallower depths
(Tab le 2). Mini-fyke nets, which collected the most Silver Carp,
were deployed at an average depth of 0.7 ± 0.4 m (mean ± SD)
over the course of the study. Average catches of juvenile Silver
Carp in mini-fyke nets were lowest during summer 2015 (Time:
3, 15
river and backwater lake habitats (Habitat: F
1, 15
P= 0.15), nor were there any interactions between factors
(Time ×Habitat: F
3, 15
= 2.04, P= 0.18). Catch rates of Silver
Carp in 2014 averaged 1,012 ± 2,489 sh per night in the main-
stem Illinois River and 50.1 ± 146.2 sh per night in backwater
lakes (Table 2 ). However, during 2015, mean catch rates were
substantially lower. In contrast, catch rates in mini-fyke nets did
not differ through time for centrarchids (F
3, 15
= 2.12, P= 0.17)
and shiners (F
3, 15
= 3.40, P= 0.07).
Average catches in beach-seine hauls varied across sample
periods (Time: F
3, 15
= 3.77, P= 0.05), and the greatest
numbers of age-0 Silver Carp were collected in summer
TABLE 1. Total numbers of Silver Carp collected by gear in backwater lakes and main-stem river habitats of the Illinois River in 2014 and 2015. DC-EF = pulsed-DC
Habitat Site Mini-fyke net Beach seine Purse seine DC-EF Gill net
Backwater lake Lily Lake 330 2,210 261 43 0
Matanzas Lake 1,276 3 200 0 0
Illinois River Havana 29,330 253 5 8 0
Beardstown 3,061 2,935 13 357 0
Total 33,997 5,401 479 408 0
Backwater lake Lily Lake 0 0 0 0 8
Matanzas Lake 0 0 0 0 0
Illinois River Havana 53 1 1 38 0
Beardstown 4 0 0 0 0
Total 57 1 1 38 8
Grand total 34,054 5,402 480 446 8
TABLE 2. Catches (mean ± SD) in various gears of juvenile Silver Carp, centrarchids, and shiners in backwater lake (BW) and main-stem river (MS) habitats
of the Illinois River during 2014 and 2015. DC-EF = pulsed-DC electrofishing.
Year Habitat Mini-fyke net Beach seine Purse seine DC-EF Gill net
Silver Carp
2014 BW 50 ± 146 138 ± 538 28 ± 68 2.6 ± 4.1 0 ± 0
MS 1,012 ± 2,489 199 ± 491 1.12 ± 3.3 22 ± 83 0 ± 0
2015 BW 0±0 0±0 0±0 0 ± 0 0.5 ± 2
MS 1.7 ± 4.0 0.06 ± 0.2 0.06 ± 0.02 2 ± 4 0±0
2014 BW 24 ± 20 12 ± 12 0.18 ± 0.2 11 ± 16 0.3 ± 0.4
MS 92 ± 127 18 ± 20 0±0 0.8 ± 1.0 0.1 ± 0.1
2015 BW 71 ± 42 5.8 ± 5.8 5.8 ± 5.8 21 ± 14 0.6 ± 0.3
MS 88 ± 110 5.4 ± 8.1 5.4 ± 8.1 1.4 ± 1.1 0.3 ± 0.5
2014 BW 3.4 ± 5.9 13 ± 14 2.4 ± 4.1 1.1 ± 0.7 0 ± 0
MS 231 ± 420 44 ± 62 0.16 ± 0.1 4.1 ± 4.0 0 ± 0
2015 BW 41 ± 34 20 ± 13 20 ± 13 2.7 ± 3.3 0 ± 0
MS 569 ± 621 28 ± 24 28 ± 24 3.1 ± 2.1 0 ± 0
2014 and the fewest were captured in summer 2015. Beach-
seine hauls sampled mean depths of 0.79 ± 0.21 m and caught
199 ± 491 sh per haul in the main channel and 138 ± 538 sh
per haul in backwater lakes (Habitat: F
1, 15
= 0.12, P= 0.73),
and no interactions were detected (Time ×Habitat: F
3, 15
0.13, P= 0.93). Catch per haul of centrarchids (F
3, 15
= 5.82,
P= 0.03) and shiners (F
3, 15
= 5.80, P= 0.02) varied through
time, and lower catches occurred during fall sampling events
than during summer periods. For instance, centrarchid catch
per haul ranged from 9.1 to 18.2 during summers 2014 and
2015 and were 0.20.5 during fall. For shiners, catch per haul
averaged 2.0 in fall of 2014, which was greatly lower than in
all other sampling events (catch per haul range: 15.147.7).
Catch rates of age-0 Silver Carp were typically lower in
gears that targeted deeper water habitats farther from the
shoreline. In terms of catch rates, purse seines and DC elec-
troshing produced similar numbers (Table 2), but effective-
ness varied by habitat. Purse-seine hauls were conducted at
mean depths of 2.2 ± 1.02 m. Mean catch rates of purse seines
differed across sample periods (time: F
3, 15
= 161.04, P<
0.001) and between main-stem Illinois River and backwater
lakes (habitat: F
1, 15
= 76.43, P< 0.001), and had the highest
catches within backwater lakes during summer 2014 (time ×
habitat: F
3, 15
= 76.77, P< 0.001). Purse seines collected far
greater numbers of Silver Carp in backwater lakes than in
main-channel habitats, but only during summer 2014.
Because electroshing samples sh along the nearshoreoff-
shore continuum, depths ranged between 0.7 and 4.9 m.
Unlike purse seines, no differences were detected across sam-
ple periods (Time: F
3, 15
= 1.17, P= 0.37), between main-stem
river and oodplain lake habitats (Habitat: F
1, 15
= 1.56, P=
0.24), or in their interaction (Time ×Habitat: F
3, 15
= 0.98, P=
0.44). Gill nets were set at a mean depth of 2.3 ± 0.9 m.
Because so few Silver Carp, centrarchids, and shiners were
collected in gill nets statistical analysis for gill-net data was
not warranted.
Total lengths of age-0 Silver Carp varied across gear types
(Figure 2;F
4, 29
= 2.81, P= 0.04), but only between gill nets
and beach seines (Tukeys honestly signicantly different test:
P= 0.05), which collected the largest and smallest individuals,
respectively. In general, gill nets collected larger age-0 Silver
Carp. Lengths of Silver Carp did not differ between backwater
lake and main-stem river habitats (F
1, 29
= 0.23, P= 0.54).
Cost-effectiveness in terms of hours of labor varied widely
across gears (Table 3). Based on comparisons of overall mean
catch rates in 2014, mini-fyke nets collected the largest num-
bers of Silver Carp. A comparison of effect sizes relative to
mini-fyke-net catch rates indicated between three and four
hauls or transects would be required to achieve similar catches
with other gears (Table 3). Consequently, the labor required to
achieve these catches ranged from as low as 0.52 labor-hours
for beach seining to as high as 45 labor-hours for pulsed-DC
electroshing. In general, when accounting for the labor
invested, mini-fyke nets and beach seines were similar and
had overlapping daily labor estimates. In contrast, using gears
deployed in deeper waters to achieve similar catches would
require considerably greater levels of effort. Because gill nets
often produced no sh per set, cost-effectiveness could not be
estimated (i.e., multiplying effect sizes by zero).
Findings from our experimental gear evaluation indicated
that mini-fyke nets were the most effective at collecting large
numbers of age-0 Silver Carp, followed in decreasing order by
beach seines, pulsed-DC electroshing, purse seines, and gill
nets. However, when we considered effort for each gear type
to achieve similar catches, both beach seining and mini-fyke
nets had similar and overlapping labor expenditures. Our
inferences are limited to Silver Carp, as they comprised
more than 99% of the juvenile Asian carps collected during
the 2 years. Mini-fyke nets captured by far the highest num-
bers of age-0 Silver Carp. Beach seines also captured large
FIGURE 2. Total lengths (mm) of age-0 Silver Carp captured in each sam-
pling gear in main-stem river (MS) and backwater lake (BW) habitats in the
Illinois River during 2014 and 2015. The vertical line within each box
represents the mean. The ends of the box represent the 25th (left) and 75th
(right) quantiles. Whisker lines represent the upper and lower data point
values, but do not include outliers. Jitter points indicate outliers.
TABLE 3. Estimates of daily hours of labor required to collect similar catches
of juvenile Silver Carp between sampling gears, based on the crew size, effort
per gear, and effect sizes. Due to limited and often zero catches of Silver Carp
per set, data from gill nets were not analyzed.
Minutes of
Daily labor
Mini-fyke net 2 1018 1.0 0.30.6
Beach seine 2 57 3.1 0.50.7
Purse seine 2 1015 35.5 11.817.7
DC electroshing 3 35 41.7 45.1
numbers of age-0 Silver Carp and may be useful for rapid
monitoring purposes when overnight gear sets are not practi-
cal. In terms of catches of Silver Carp, mini-fyke nets out-
performed beach seines in a manner consistent with other
evaluations for different species and aquatic environments
(Lyons 1986; Clark et al. 2007). Both gears primarily target
shallow-water habitats (<1 m), but mini-fyke nets collected a
broader range of lengths of juvenile Silver Carp than did
beach seining. Other evaluations indicate mini-fyke nets col-
lect a greater range of species as well (Clark et al. 2007),
which is relevant if management objectives are to determine
differences in growth and size structure during monitoring
efforts or to avoid nondetections of uncommon species. Both
mini-fyke nets and beach seines are well suited for sampling
littoral locations of the Illinois River and backwater lakes,
shallow creeks, and ooded off-channel habitats.
Cost-effectiveness in terms of daily labor hours was similar
between beach seine hauls and mini-fyke net sets. When
controlling for catch rates but accounting for labor, both
gears were relatively similar. Greater numbers of sh were
caught in mini-fyke nets, but this method was more time
consuming to deploy and collect the gear in comparison with
beach seine hauls, which required greater numbers of hauls
but could be done relatively quickly. Instances where multiple
trips to the same site are required would result in either gear
being appropriate. However, if overnight gear sets are not
desirable, a more cost-effective use of time and labor would
be to sample a location via beach seining more frequently.
Neither purse seines nor gill nets were cost-effective because
of the higher labor cost relative to the number of sh captured.
Despite having similar, though slightly higher time require-
ments, the overall reduction in catch rates was the primary
driver of observed differences.
We ob s e r v e d diverg e n c e between c a t c h r ates of age - 0 S i l ver
Carp and native shes. Because catches of native shes were
consistent across sample periods, our ndings indicated that
mini-fyke nets were sampling other shes but not Silver Carp.
The reasons why catch rates of Silver Carp were low during
summer 2015 remain unclear, but catches may have been impacted
by multiple processes. For instance, Silver Carp may have been
occupying different habitats following high water conditions that
occurred in summer 2015, whereas shiners and juvenile centrarch-
ids were constrained to shoreline environments. However, this
assumes that processes such as recruitment, growth, maturation,
out-migration, and survival of Silver Carp were similar between
years, none of which did we evaluate in this study. Efforts to track
and monitor Silver Carp during or following higher river stages
might require alternate means of sampling. For instance, although
pulsed-DC electroshing was generally ineffective relative to
other gears during most sampling periods, it was slightly better
than mini-fyke nets in main-stem habitats during summer 2015.
Effective immobilization of sh via electroshing is closely
linked to body size (e.g., Dolan and Miranda 2003), as larger
sh are easier to immobilize than are small ones because less
power is required (e.g., Anderson 1995). Although large num-
bers of juvenile Silver Carp were visually observed by eld
personnel in close proximity to the operating electroshing
boat on some site visits, this was not reected in catches made
by this gear type. For perspective, pulsed-DC electroshing
accounted for only 1% of all age-0 Silver Carp collected
during our 2-year experiment. Electroshing settings followed
long-term resource monitoring program protocols (Gutreuter
et al. 1995), which may work well for large-bodied shes;
however, it is apparent that these same settings were ineffec-
tive at sampling small-bodied shes such as age-0 Asian carps
and that these settings for sampling juvenile Asian carps may
need further assessment.
Based on total and mean catches, we recommend the
deployment of mini-fyke nets for sampling age-0 Silver
Carp. However, this requires two trips: rst to deploy the
net, then to collect the net and samples. Despite the added
effort, mini-fyke nets deployed overnight in shallow (<1 m)
littoral margins of the Illinois River provide the best chance to
collect large numbers of age-0 Silver Carp. Characteristics of
sampling locations such as slope and vegetation can affect
their ability to capture sh. Beach seines are also an inexpen-
sive sampling tool but have limited effectiveness where wood
structure, vegetation, or steep slope limit usage. Yet, beach
seines can be used to rapidly determine habitat use by sh and
to sample diets. Purse seines can be a useful tool for poten-
tially estimating sh densities; however, this gear is primarily
effective when deployed in off-channel and backwater lake
habitats where ows are limited. In contrast, pulsed-DC elec-
troshing collected more age-0 Silver Carp in main-stem
environments, but additional work to determine optimal set-
tings for collecting juvenile Asian carps is required.
This study was supported by the Great Lakes Restoration
Initiative, with funding administered through the Illinois
Department of Natural Resources (CAFWS-93). We thank K.
Irons and M. OHara of the Illinois Department of Natural
Resources for their assistance in coordinating this project. We
are grateful to the numerous individuals who have provided
eld assistance to make this project possible, including the
graduate students and staff of the Kaskaskia and Sam Parr
Biological Stations, Illinois Natural History Survey, and the
University of Illinois.
ACRCC (Asian Carp Regional Coordinating Committee). 2016. 2015 Asian carp
monitoring and response plan interim summary report. Available: http:// (June 2016).
Anderson, C. S. 1995. Measuring and correcting for size selection in electro-
shing markrecapture experiments. Transactions of the American
Fisheries Society 124:663676.
Bayley, P. B., and D. J. Austen. 2002. Capture efciency of a boat electro-
sher. Transactions of the American Fisheries Society 131:435451.
Breen, M. J., and C. R. Ruetz. 2006. Gear bias in fyke netting: evaluating soak
time, sh density, and predators. North American Journal of Fisheries
Management 26:3241.
Clark, S. J., J. R. Jackson, and S. E. Lochmann. 2007. A comparison of shoreline
seines with fyke nets for sampling littoral sh communities in oodplain
lakes. North American Journal of Fisheries Management 27:676680.
Collins, S. F., S. E. Butler, M. J. Diana, and D. H. Wahl. 2015. Catch rates and
cost effectiveness of entrapment gears for Asian carp: a comparison of
pound nets, hoop nets, and fyke nets in backwater lakes of the Illinois
River. North American Journal of Fisheries Management 35:12191225.
Cooke, S. L. 2016. Anticipating the spread and ecological effects of invasive
bigheaded carps (Hypophthalmichthys spp.) in North America: a review of
modeling and other predictive studies. Biological Invasions 18:315344.
DeGrandchamp, K. L., J. E. Garvey, and R. E. Colombo. 2008. Movement
and habitat selection by invasive Asian carps in a large river. Transactions
of the American Fisheries Society 137:4556.
DeGrandchamp, K. L., J. E. Garvey, and L. A. Csoboth. 2007. Linking adult
reproduction and larval density of invasive carp in a large river.
Transactions of the American Fisheries Society 136:13271334.
Dolan, C. R., and L. E. Miranda. 2003. Immobilization thresholds of electro-
shing relative to sh size. Transactions of the American Fisheries Society
Gutreuter, S., R. Burkhardt, and K. S. Lubinski. 1995. Long term resource
monitoring program procedures: sh monitoring. National Biological
Service, Environmental Management Technical Center, Technical Report
95-P002-1, Onalaska, Wisconsin.
Hayes, D. B., C. P. Ferreri, and W. W. Taylor. 2012. Active sh capture
methods. Pages 267300 in A. V. Zale, D. L. Parrish, and T. M. Sutton,
editors. Fisheries techniques, 3rd edition. American Fisheries Society,
Bethesda, Maryland.
Hubert, W. A., K. L. Pope, and J. M. Dettmers. 2012. Passive capture
techniques. Pages 223253 in A. V. Zale, D. L. Parrish, and T. M.
Sutton, editors. Fisheries techniques, 3rd edition. American Fisheries
Society, Bethesda, Maryland.
Irons, K. S., G. G. Sass, M. A. McClelland, and T. M. OHara. 2011.
Bigheaded carp invasion of the LaGrange reach of the Illinois River:
insights from the long term resource monitoring program. Pages 3150
in D. C. Chapman and M. H. Hoff, editors. Invasive Asian carps in North
America. American Fisheries Society, Symposium 74, Bethesda,
Lapointe, N. W. R., L. D. Corkum, and N. E. Mandrak. 2006. A comparison
of methods for sampling sh diversity in shallow offshore waters of large
rivers. North American Journal of Fisheries Management 26:503513.
Lyons, J. 1986. Capture efciency of a beach seine for seven freshwater shes
in a north-temperate lake. North American Journal of Fisheries
Management 6:288298.
Norman, J. D., and G. W. Whitledge. 2015. Recruitment sources of invasive
Bighead Carp (Hypophthalmichthys nobilis) and Silver Carp (H. molitrix)
inhabiting the Illinois River. Biological Invasions 17:29993014.
Sass, G. G., T. R. Cook, K. S. Irons, M. A. McClelland, N. N. Michaels, T. M.
OHara, and M. R. Stroub. 2010. A markrecapture population estimate
for invasive Silver Carp (Hypophthalmichthys molitrix) in the La Grange
Reach, Illinois River. Biological Invasions 12:433436.
Stuck J. G., A. P. Porreca, D. H. Wahl, and R. E. Colombo. 2015. Contrasting
population demographic of invasive Silver Carp between an impounded
and free-owing river. North American Journal of Fisheries Management
Weaver, M. J., J. J. Magnuson, and M. D. Clayton. 1993. Analysis for
differentiating littoral sh assemblages with catch data from multiple
sampling gears. Transactions of the American Fisheries Society
... Native (golden shiners) and invasive (bighead carp) planktivore treatments consisted of either high (six individuals per mesocosm) or low (three individuals per mesocosm) densities. Densities of all fish were within the natural ranges observed in lakes and rivers in this region (Collins, Diana, Butler, & Wahl, 2017). Treatments were randomly assigned to each mesocosm and housed under an overhead structure to reduce the direct input of sunlight which can increase water temperatures. ...
... After the experiment, only fish that were not fin-clipped were used for growth analysis. (Collins, Diana, et al., 2017), to which golden shiner densities were then matched. ...
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• Early life stages of fishes are sensitive to ecological and environmental disturbances and experience very high mortality rates. During early ontogeny, the growth and survival of larval fish often depends on food availability. Because habitat and diet shifts are strongly tied to individual body size, factors that influence the growth rates of individuals (e.g. resource limitation, competition) also affect other aspects of ontogeny including the timing of habitat or diet shifts. In the context of biological invasions, non‐native species can potentially disrupt the interaction of larval fish with their food via competition for shared prey, reducing growth and survival during a vulnerable period of an organism's life history. • We hypothesised that invasive planktivores negatively affect native species through the vulnerable larval life stage via competition for zooplankton resources. To test this hypothesis, we conducted a series of experiments to assess and contrast the effects of invasive (bighead carp, Hypophthalmichthys nobilis) and native (golden shiners, Notemigonus crysoleucas) planktivores on zooplankton densities, and their effects on the growth, survival, abundance, and habitat use of larval bluegill (Lepomis macrochirus). • Overall, the effects of the invasive planktivore were consistently greater than the native planktivore in terms of reduced prey densities, reduced bluegill growth rates, and delays to the timing of ontogenetic habitat shifts. Growth rates of bluegill larvae were reduced by 58–87% in the presence of bighead carp and 37% in the presence of golden shiners (relative to controls), but such reductions did not consistently lead to reduced survival (in mesocosm experiment) or relative abundance (in pond experiment). However, we estimated that bighead carp and golden shiners delayed ontogenetic habitat shifts in bluegill by 9–24 and 1–3 days, respectively. • Although we did not detect an effect of planktivores on the numbers of larval bluegill, our findings suggest that bighead carp may still affect bluegill ontogeny and freshwater food webs by disrupting the timing of ontogenetic habitat shifts. By affecting the coupling of habitats via organism movements during early ontogeny, bighead carp may indirectly disrupt predator–prey interactions of native taxa.
... Larvae grow quickly and juveniles reach large sizes by their first fall (Williamson and Garvey 2005), escaping predation risk and minimizing overwinter mortality due to starvation and depletion of energy reserves (Coulter et al. 2018b). Juveniles are commonly captured in large numbers in the Illinois River (e.g., Collins et al. 2017) but are rarely encountered in other areas of invasion. For instance, juvenile Bigheaded Carp (50-150 mm) have only been captured above LD19 three times in separate years despite extensive sampling efforts by many agencies (K. ...
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Bighead Carp Hypothalmichthys nobilis and Silver Carp Hypothalmichthys moltrix (hereafter collectively referred to as Bigheaded Carp) have spread throughout the majority of the Mississippi River since the 1970s. The current northern invasion edge of Bigheaded Carp in the Upper Mississippi River (UMR) spans between Pools 14 and 20 because of limited passage at Lock and Dam (LD) 19. Mechanisms limiting adult Bigheaded Carp abundance above LD19 are unknown but may be due in part to lack of reproductive success influenced by adult abundance and environmental factors. Our objective was to investigate how relative adult biomass and river temperature and discharge affect maximum annual Bigheaded Carp larval production in the UMR using a Ricker stock-recruitment model. Adult Bigheaded Carp relative biomass (kg/h) was estimated annually with boat electrofishing and larvae were collected every 10 d between May and August 2014–2017 in Pools 14–20 in the UMR. Adult relative biomass ranged from 0.0 to 880.9 kg/h, whereas maximum annual larval densities ranged from 0.0 to 2,869.4 larvae/m3. After accounting for variability among pools and years, the most supported linear Ricker stock-recruitment model indicated the number of recruits per spawner decreased with increasing adult relative biomass and increased with mean discharge. Our results highlight the importance of adult biomass and river discharge conditions for reproduction of Bigheaded Carp along leading edges of invasion. Management strategies that aim to maintain low adult abundance where reproduction is not yet occurring could help limit population increases via reproduction, whereas reducing high adult biomass (e.g., commercial harvest, barriers) may result in greater Bigheaded Carp reproductive output in the UMR.
... Future research focused on comparison with other offshore techniques for sampling deeper in the water column (> 3 m; e.g. benthic trawls, gill nets), cost-effectiveness, including staffing time, operation cost, and data analysis may further inform Platform value to fisheries research (Collins et al., 2017). ...
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We performed a preliminary evaluation of a mobile sampling platform with adjustable push net and live box (Platform) against two common methods for sampling small-bodied fish (i.e., 10–100 mm) in two distinct lentic habitats. Nearshore (NS) littoral habitat was sampled by Platform and beach seine, and open water (OW) pelagic habitat by Platform and Kodiak trawl. Our goal was to evaluate the Platform’s ability to describe fish assemblage structure across habitat types in contrast to common techniques restricted to single habitat types that are less comparable due to gear-specific bias. Platform sample speed had a significant positive effect on recapture efficiency of both nearly neutrally buoyant objects and marked fish. Marked fish recapture efficiencies were similar for Platform in NS and OW, indicating similar efficiency across habitat types. Platform capture efficiency was similar to beach seine and greater than Kodiak trawl. With similar sampling time, the Platform collected more individuals and taxa in NS relative to beach seine and in OW relative to Kodiak trawl. Greater taxa detection by the Platform suggests that it may be effective at detecting species that are numerically rare in specific habitats when compared to these methods. Fish CPUE was significantly greater NS regardless of technique. However, by using the Platform, there is greater confidence that this difference was reliable and not a gear selectivity artifact. Overall, this preliminary study demonstrates the Platform's potential to collect standardized data across NS and OW habitats, track ontogenetic habitat shifts, and detect differences in small-bodied fish taxa richness, relative abundance, and density between NS and OW habitats. Continued experimentation beyond a single reservoir and fish size range is required before consensus can be established regarding the utility of this new push net design.
... • Beach seines are more effective at catching juvenile silver carp in river-floodplain systems and beach seines better able to capture smaller individuals. Beach seines also more cost-effective in terms of output per unit effort of labour (Collins, Diana, Butler, & Wahl, 2017). • Espino, González, Haroun, and Tuya (2015) demonstrated seine nets were effective at assessing juvenile parrotfish in seagrass habitats and best for accurate size measurements • Baltz, Rakocinski, and Fleeger (1993) utilized drop samplers to assess microhabitat use by fish in an extensive saltmarsh in Louisiana. ...
The limitations imposed by traditional sampling methods have restricted the acquisition of data on key fisheries parameters. This is particularly the case for juveniles because most traditional gear explicitly avoids the capture of juveniles, and the juveniles of many species use habitats in which traditional gear is ineffective. The increasing availability and sophistication of Remote Underwater Video Techniques (RUVs) such as Baited Remote Underwater Video, Unbaited Remote Underwater Video and Remotely Operated Underwater Vehicles offer the opportunity of overcoming some of the key limitations of more traditional approaches. However, RUV techniques come with their own set of limitations that need to be addressed before they can fully realize their potential to shed new light on the early life history of fish. We evaluate key strengths and limitations of RUV techniques, and how these can be overcome, in particular by employing bespoke computer vision Artificial Intelligence approaches, such as Deep Learning in its Convolutional Neural Networks instantiation. In addition, we investigate residual issues that remain to be solved despite the advances made possible by new technology, and the role of explicitly identifying and evaluating key residual assumptions.
... Certain gears may have unique advantages in smaller tributary rivers compared to gears traditionally used in open water mainstem habitats where structural elements and shallow depths do not impede gear operation. Detection and catch rates of juvenile BHC in large rivers varies among sample gears and may have significant implications in implementing population controls like barriers and deterrents upstream of reproduction fronts (Collins et al. 2017). Additionally, contracted commercial harvest of BHC is most effective when implemented in areas where reproduction is occurring (i.e., reduce propagule pressure) ...
Silver (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis), collectively bigheaded carps (BHC), are invasive fishes in the Mississippi River and surrounding basins. Increasing evidence suggests harmful impacts of BHC on native fisheries (e.g. competition). Monitoring abundance of BHC is difficult with traditional fisheries gears, and few studies have evaluated early life stage sampling. Identifying spawning locations of BHC through early life stage sampling has the ability to enhance management efforts to areas that have potential to serve as population sources. We evaluated the performance of three gears in sampling larval BHC and native taxa in large‐river tributaries in terms of abundance, community assemblage, and size structure. We sampled ichthyoplankton in tributaries with active (push net) and passive gears (drift net, light trap) from March through September of 2016. Relative abundance of BHC was greatest in push nets, followed by drift nets, and lowest in light traps. Native cyprinids and catostomids, and BHC comprised a large portion of total catch. Environmental and habitat characteristics (stream velocity, dissolved oxygen, and temperature) related to BHC reproduction influenced each gear’s ability to capture larval BHC, although relationships in final models were not significant. Taxonomic size selectivity existed among gears, particularly larger BHC collected in push nets. Push nets were the most effective in sampling BHC and remaining gears exhibited unique strengths. Although less effective than active push nets, drift nets proved useful for monitoring BHC in tributaries and may be advantageous in shallow systems with adequate flow. Light traps were ineffective at capturing BHC larvae in tributaries, but may offer utility in lentic habitats or for native cyprinids. Our comparison serves as a guide for monitoring larval BHC in their invaded range and for detection in new areas, such as tributaries of the Great Lakes.
... Presently, the Mississippi River and many of its larger tributaries harbor extremely high densities of bighead carps. These mobile fishes utilize both mainstem river and floodplain lake ecosystems (e.g., Sass et al. 2010;MacNamara et al. 2016) and are often the dominant fish encountered by fisheries scientists (Irons et al. 2007;Sass et al. 2010;Collins et al. 2015bCollins et al. , 2017a. As planktivores, bighead carps do not occupy a high trophic position within riverine ecosystems. ...
Pervasive environmental degradation has altered biodiversity at a global scale. At smaller scales, species extirpations, invasions, and replacements have greatly influenced how ecosystems function and interact by affecting the exchanges of energy, materials, and organisms. In this chapter, we examine how a variety of environmental stressors, and associated species losses and gains, change the exchange of resources (materials or organisms) within and among ecosystems. We specifically consider how changes that occur within an ecosystem may trigger effects that reverberate (e.g., directly, indirectly, and via feedbacks) back and forth across ecological boundaries and propagate to other ecosystems connected via exchanges of materials and organisms. Our synthesis provides cursory overviews of ecosystem “openness” as it has been addressed by community ecologists and the conceptual development of ecological frameworks used to examine resource exchanges between ecosystems. We then describe four case studies and examine how species losses and gains affect food web structure via resource exchanges between ecosystems, with particular emphasis on effects spanning land-water boundaries. Finally, we discuss the need for more complex conceptual treatment of the interconnectedness of food webs among ecosystems.
... Additionally, the decreased effort in labor for cloverleaf traps (<30 s; Mangan et al. 2005;Carl et al. 2016) relative to the other gears used herein (> 300 s for deployment and retrieval; Collins et al. 2017), the ability to be deployed in areas hard to sample with other gears (e.g., complex habitats), as well as the minimal investment cost per trap (≈ $150/trap) suggests that cloverleaf traps provide a cost-and time-efficient gear for sampling sub-stock length ...
Many Bluegill Lepomis macrochirus populations are dominated by fish ≤ 125 mm total length (TL) that may be underrepresented when using standard sampling gears. To identify efficient sampling methods for these populations, we compared catch per unit effort (CPUE) and TL-frequency distributions of Bluegill captured in cloverleaf traps, boat electrofishing, mini-fyke nets, and beach seine hauls from two northern Wisconsin lakes supporting populations dominated by fish ≤ 125 mm TL. Mean Bluegill CPUE ranged from 41 fish per cloverleaf trap lift (SE = 11) to 16 fish per beach seine haul (SE = 8). Cloverleaf traps generally captured small Bluegill relative to other gears and were the only gear to consistently capture Bluegill < 80 mm TL. Conversely, boat electrofishing captured the widest TL range of Bluegill and fish ≥ 80 mm TL composed a greater proportion of catch (37%) relative to other gears. With few exceptions, effort required to detect 10 or 25% changes in Bluegill CPUE was > 100 units of effort regardless of lake, sampling gear, or month. Furthermore, there was no consistency between lakes or months in terms of which sampling gear required the fewest number of samples to detect a 50% change in CPUE. Estimated units of effort needed to detect 10 or 25% changes in mean Bluegill TL were ≤ 16 for all sampling gears on the lake with consistently higher CPUE (i.e., more fish to measure per unit). In the lake with lower CPUE, cloverleaf traps consistently required less effort to detect changes in mean TL. We note that comparing sample size requirements among gears is not straightforward because gears are sampling differing segments of the Bluegill population. Our study emphasizes the importance of evaluating gear biases and sampling efficiency so that fisheries managers can develop suitable sampling protocols.
... We conducted a field experiment to assess whether herding fish using percussive sound or electrical stimuli can enhance catch rates and detection of bigheaded carp and other large river fishes in surfaceto-bottom gill nets. Our experiment was conducted at multiple locations along the Illinois River (Mississippi River drainage) as part of a larger study examining the most effective means of collecting and removing bigheaded carp and other invasive fishes (Collins et al. 2015(Collins et al. , 2017. Our primary objective was to identify whether catch rates in an entanglement gear could be enhanced through the use of sound or electricity and if there were differences between the two approaches. ...
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Fish herding (driving fish into nets) is used by commercial fishers to increase harvest of invasive bigheaded carp (Hypophthalmichthys spp.), yet has not been widely adopted for fisheries monitoring purposes. We conducted an experiment to assess whether fish herding using percussive sound or electrical stimuli can enhance catch rates and detection of bigheaded carp and other fishes in surface-to-bottom gill nets. Catch rates (fish net set⁻¹) from traditional gill net sets where no herding method was applied were compared to sets combined with either sound stimuli (physical impacts to the boat hull and water surface to produce percussive sound) or electricity produced from a pulsed-DC electrofisher to manipulate fish movements. For most species, herding increased catch rates and detection probability compared to control sets. Sound stimuli increased catch rates of Silver Carp (Hypophthalmichthys molitrix) by over three times, whereas electrical stimuli increased catch rates by over six times. Catch of Bighead Carp (Hypophthalmichthys nobilis) was highest in nets paired with sound stimuli. Herding methods also reduced the number of samples required to attain target detection probabilities for bigheaded carp. Herding techniques combined with gill netting may be a valuable option for targeted bigheaded carp sampling, especially when electrofishing or netting alone is ineffective for these evasive fishes. Synergistic methods may provide a cost effective means of improving detection probabilities for bigheaded carp at their invasion front or other locations where densities are low and uncertainty of capture is high.
Silver Carp Hypophthalmichthys molitrix have expanded their range to encompass most of the Mississippi River basin, including much of the Missouri River. However, there is a paucity of information concerning Silver Carp in the Missouri River basin, especially in tributaries. Little is known about how Silver Carp function in these tributaries or how connectivity with a main‐stem river can influence population demographics within either system. The Kansas River is a tributary to the Missouri River and has multiple physical anthropogenic barriers creating varying levels of connectivity within the system, as well as with the Missouri River. These varying levels of connectivity, or lack thereof, provide a unique opportunity to examine population demographics in river segments separated by barriers. We collected Silver Carp from upstream and downstream of the first two barriers on the Kansas River in the summers of 2018 and 2019. No Silver Carp were captured upstream of a hydropower dam at river kilometer 84 but were found upstream of a water diversion weir at river kilometer 24. Catch rates of adult Silver Carp were lower in the reach above the weir, but Silver Carp caught in this reach exhibited greater growth rates than Silver Carp captured below the weir. Catch rates of juveniles were also lower in the reach above the weir. Limited connectivity within the Kansas River via the water diversion weir could influence size structure and catch rates of Silver Carp captured above and below the weir. Lack of juveniles above the weir indicates that reproduction may be limited in this reach, and river conditions below the weir may be more suitable for rearing juvenile Silver Carp. This information is important for understanding Silver Carp population demographics across a range of river environments, providing critical information for the development and implementation of broadscale control plans.
Fish recruitment is complex, regulated by environmental factors that induce high mortality early in life. Additionally, age-0 fish can be difficult to sample, making recruitment difficult to detect. We used a robust design occupancy model to evaluate the effects of biotic (age-0 and adult common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), walleye (Sander vitreus), and northern pike (Esox lucius) relative abundance, prey availability, age-0 carp length) and abiotic (water level, temperature) factors on age-0 carp occupancy, detection, and extinction in 13 lakes in South Dakota, USA, for July–April 2008–2010. Age-0 carp occupancy decreased with increasing adult carp abundance and increased with increasing water levels. Age-0 carp detection probability was high during summer (>0.75) but decreased in fall and spring (0.34). Most lakes were occupied in July but overwinter extinction probability was high (59%), resulting in 51% occupancy probability by April. Other environmental factors were not supported, suggesting they had little effect on reproduction and survival. Our results indicate reproduction was universally successful but difficult to detect and that overwinter mortality often resulted in recruitment failure.
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Models for fish capture efficiency (catchability) using a boat-mounted AC electrofishing sampling protocol were estimated for warmwater fishes in Illinois lakes through a calibration process. Catchabilities were determined for 37 inshore zones in blocked enclosures or ponds and 5 large water bodies during fall or spring. The abundances of vulnerable fish populations were determined by census following draining or by treatment using rotenone or primacord of known catchability. Inshore catchabilities, based on a zone 0-13 m from shore, were strongly dependent on fish length (as a unimodal function), fish taxa, mean depth, and surface macrophyte cover. Under average environmental conditions, maximum catchabilities by taxon ranged from 0.0018 to 0.14 and ranked (highest to lowest) as follows: largemouth bass ? Micropterus salmoides, common carp Cyprinus carpio, crappies Pomoxis spp. in spring, shad Dorosoma spp., bluegill Lepomis macrochirus, green sunfish L. cyanellus, crappies in fall, freshwater drum Aplodinotus grunniens, suckers (Catostomidae), and catfish (Ictaluridae). Catchabilities for common carp and shad were significantly lower in large water bodies, indicating that significant numbers were outside the inshore zone. However, the results for other species, including large samples of largemouth bass and bluegills, indicated that populations in similar whole lakes could be estimated from the predicted inshore electrofishing catchabilities in fall or spring. Strong biases in relative population density when inferred by catch per unit effort were demonstrated under differing environmental conditions. Also, estimates of ratios related to fish size, such as mortality rates, were seriously biased when based on the size structure of uncorrected catches. Therefore, catchability models are considered essential for assessing the absolute and relative attributes of fish populations across water bodies.
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Bighead carp (Hypophthalmichthys nobilis Valenciennes 1844) and silver carp (H. molitrix Richardson 1845), collectively called bigheaded carps, have invaded the Mississippi River Basin and may have already entered the Laurentian Great Lakes where they could affect fishing and other industries. Developing models to predict potential spread and effects is difficult because local adaptation may have occurred among populations, parameter values for biological characteristics vary widely for these opportunistic generalists, and methodological differences complicate comparison and synthesis of studies. I review bigheaded carp biological parameters across a wide range of literature, including studies of native and introduced populations. I then evaluate how predictive models are parameterized, noting inconsistencies and highlighting data gaps. My analysis finds that although parameter values tend to vary substantially among and within systems, models are generally parameterized using the best information available, although bioenergetics and trophic models particularly need improvement. Some predictive tools can be updated using existing data (e.g., velocity requirements for spawning), but in other cases further research is needed. Research priorities include (1) better understanding bigheaded carp phenotypic plasticity among and within systems, (2) determining key biological traits of bigheaded carp populations at risk of seeding further invasions (e.g., Illinois River populations that may spread to Lake Michigan), and (3) monitoring bigheaded carp ecological effects on native fishes and plankton communities. A more complete awareness of strengths and limitations of predictive tools will lead to their improvement, thereby aiding managers in anticipating and counteracting bigheaded carp spread and effects.
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We compared three entrapment gears to determine which method was the most effective for capturing invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in terms of numbers of fish captured and labor invested. Gears were deployed concurrently in two backwater lakes of the Illinois River during the summers of 2012–2014. Overall, the nightly catch rates of all fishes, Bighead Carp, and Silver Carp were one to three orders of magnitude greater in pound nets than in either fyke nets or hoop nets. Pound nets collected larger Bighead Carp than hoop nets and fyke nets. Hoop nets were ineffective at catching Asian carp in backwater lakes. Estimation of the effort required to deploy, maintain, and remove each gear type indicated that pound nets were the most cost effective gear due to their high catch rates of Asian carp relative to the labor hours invested to collect the catch. Pound nets appear to be an effective means of removing Asian carp in backwater lake habitats of the Illinois River.
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Knowledge of natal environments and dispersal of invasive Bighead carp (Hypopthalmichthys nobilis) and Silver carp (H. molitrix) inhabiting the Illinois River would be valuable for directing population reduction efforts intended to supplement electrical barriers in the Chicago Sanitary and Ship Canal and limit the probability of these species invading the Great Lakes. However, the extent to which Bighead carp and Silver carp (collectively referred to as bigheaded carps) stocks in the Illinois River are derived from recruits that originate within the Illinois River itself versus immigrants from the Mississippi and Missouri rivers is unknown. Bigheaded carps are also known to use connected floodplain lakes during early life, but the contribution of these habitats to recruitment of Bighead and Silver carps in the Illinois River is also unknown. The aim of this study was to identify natal environment of adult bigheaded carps collected from the Illinois River during 2010–2011 using stable isotope and trace element analyses of otolith cores. Both water and otolith strontium:calcium ratios (Sr:Ca) and water and otolith oxygen isotope ratios (expressed as δ18O) were strongly correlated for known-origin bigheaded carps, consistent with other fish species. Most Bighead and Silver carps collected from the Illinois River used river channel rather than floodplain lake habitats during early life. The majority of adult Silver carp originated in the Illinois River, although 11–39 % were immigrants from the Missouri or middle Mississippi Rivers. In contrast, 97 % of the Bighead carp originated in the Illinois River. Our results indicate that efforts to substantially reduce abundance of bigheaded carps in the Illinois River drainage should continue to focus on the Illinois River itself, but will likely need to be expanded to include the middle Mississippi and Missouri Rivers for sustainable control of Silver carp.
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Identifying how temporal variation in the environment affects reproductive success of invasive alien species will aid in predicting future establishment and tracking dynamics of established populations. Asian carp Hypophthalmichthys spp. have become a nuisance in recent years in the Mississippi River basin. Their populations are apparently expanding, indicating favorable conditions for reproduction. During 2004 and 2005, we quantified mean density of Asian carp larvae, mean monthly gonadosomatic index (GSI) of adult males and females, and number of eggs within mature females in the lower Illinois River, a major tributary of the Mississippi River. A flood (water velocity ≥ 0.7 m/s) and drought (<0.2 m/s) occurred during apparent spawning in 2004 and 2005, respectively. During 2004, Asian carp larvae were found during 32% of sampling weeks; mean GSI and fecundity were relatively low for adults, probably reflecting partially spawned individuals and perhaps low reproductive investment. During the drought of 2005, larval stages were present during only one (5%) of the sampling weeks, whereas mean GSI and fecundity of adults were high through summer. Females resorbed their eggs instead of spawning during this year. Spawning conditions during low water periods appear to be unsuitable for Asian carps, inhibiting adult spawning and yielding few larvae. Spawning conditions during 2004 were better but still yielded low densities of larvae relative to native fishes. Reproduction in the lower Illinois River appears to be linked to river flow and its impact on adult spawning decisions, but conditions for strong year-class production (i.e., high larval densities) may be rarer than previously expected.
Passive capture techniques involve the capture of fishes or other aquatic animals by entanglement, entrapment, or angling devices that are not actively moved by humans or machines while the organisms are being captured (Lagler 1978). The behavior and movements of the animals themselves result in their capture. The techniques used in passive sampling of fish populations are similar to those used for food gathering over the centuries. Nets and traps have been widely used among various cultures, and many of the currently applied techniques were used by the ancient Egyptians, Greeks, and Romans (Alverson 1963). Based on their mode of capture, passive sampling devices can be divided into three groups: (1) entanglement, (2) entrapment, and (3) angling gears. Entanglement devices capture fish by holding them ensnared or tangled in webbing or mesh made of natural or artificial materials. Gill nets and trammel nets are examples of entanglement gears (Figure 6.1). Entrapment devices capture organisms that enter an enclosed area through one or more funnel- or V-shaped openings that hinder escape after entrance. Hoop nets, trap nets, and pot devices are examples of entrapment gears (Figures 6.2 and 6.3). Angling devices capture fish with a baited hook and line. Trotlines and longlines are examples of passive angling gears (Figure 6.4). Gear selectivity and gear efficiency are important considerations with respect to passive sampling devices. Often these terms are used interchangeably, but they have different, specific definitions. Gear selectivity is the bias of a sample obtained with a given gear (Box 6.1). Selectivity for species, sizes, and sexes of fishes occurs in samples taken with specific types of gear. Species selectivity refers to overrepresentation of particular species in samples as compared with the assemblage of species present. Similarly, size or sex selectivity refers to overrepresentation of specific sizes (lengths) or one sex within samples from a fish population. Fisheries scientists may use gear selectivity to their benefit when targeting specific species or sizes of fishes, thereby enhancing their sampling efficiency. The efficiency of a gear refers to the amount of effort expended to capture target organisms (Box 6.2). It is generally desirable to maximize the efficiency of a sampling gear to save time and money in single-species assessments of fisheries. Even with efficient sampling gear, the sampling effort needed to estimate the relative abundance and other descriptive statistics for a given species may be unrealistic (Gerow 2007).
Extensive research has been conducted on Silver Carp Hypopthalmicthys molitrix in the heavily modified Illinois River in the midwestern United States due to the potential for populations to enter the Great Lakes; however, little research has been conducted on populations in unimpounded rivers. The Wabash River is an unimpounded large river in the U.S. Midwest that may be a good model for studying Silver Carp in unregulated river ecosystems that could potentially be invaded if reproducing populations in the Great Lakes are established. In this study we compared population demographics of Silver Carp in the Wabash and Illinois rivers. Abundance was over three times greater in the Illinois than in the Wabash River, although Wabash River Silver Carp had significantly greater mean length, age, and condition and a higher growth rate than did Illinois River Silver Carp. Although the heavily modified and degraded environment in the Illinois River may have aided in the rapid expansion of Silver Carp, intraspecific competition, increased commercial fishing, and competition with native species have likely reduced condition, decreased growth rate, and increased mortality rate of the population. Differences between Silver Carp populations in the Illinois and Wabash rivers suggest that the impacts of invasion may be reduced in ecosystems with little modification.
Conference Paper
Bigheaded carps, including the non-native bighead Hypophthalmichthys nobilis and silver carps H. molitrix, have been present in the Illinois River since the mid 1990's. The Long Term Resource Monitoring Program (LTRMP) is part of the Environmental Management Program on the Upper Mississippi River System (UMRS) and has monitored fish communities in La Grange Reach, Illinois River since 1990. Standard LTRMP protocols have collected abundance, age and growth, and maturation and recruitment information for these carps as they have invaded the UMRS. Bigheadded carps have been collected in La Grange Reach by the LTRMP since 1995 and 1998 respectively. Since 2000, LTRMP catches of bigheaded carps have increased, and substantial spawning and recruitment has been evident. Length-frequency distribution analyses for both species have provided insight into growth rates, mean sizes at age, and cohort strength. Maturation schedules of bigheaded carps have been variable during the invasion, yet recruitment was positively correlated with Illinois River flow. The LTRMP provides a unique perspective into the invasion of these species and gives initial insights into possible ecological impacts within a large river basin. Biological and life history data collected by the LTRMP may also be useful in understanding and predicting future effects of bigheaded carps within other waterbodies.