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Development and Efficacy of a Bycatch Reduction Device for Wisconsin-Type FykeNets Deployed in Freshwater SystemsAuthor(s): Zachary W. Fratto, Valerie A. Barko, John S. ScheibeSource: Chelonian Conservation and Biology, 7(2):205-212. 2008.Published By: Chelonian Research FoundationDOI: http://dx.doi.org/10.2744/CCB-0687.1URL: http://www.bioone.org/doi/full/10.2744/CCB-0687.1
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Chelonian Conservation and Biology, 2008, 7(2): 205–212� 2008 Chelonian Research Foundation
Development and Efficacy of a Bycatch Reduction Device for Wisconsin-Type Fyke NetsDeployed in Freshwater Systems
ZACHARY W. FRATTO1,2,3, VALERIE A. BARKO
1,4, AND JOHN S. SCHEIBE2
1Missouri Department of Conservation, Open Rivers and Wetlands Field Station, 3815 East Jackson Boulevard,
Jackson, Missouri 63755 USA;2Department of Biology, Southeast Missouri State University, 1 University Drive, Cape Girardeau, Missouri 63701 USA;
3Present Address: Everglades National Park, 40001 SR 9336, Homestead, Florida 33034 USA [[emailprotected]];4Present Address: John A. Logan College, 700 College Road, Carterville, Illinois 62918 USA [[emailprotected]]
ABSTRACT. – Aquatic biologists throughout the United States use fyke nets to sample fish. Often,these nets have high turtle bycatch and mortality rates, especially when set in extremeenvironmental conditions. Because a previous study found increased turtle mortality usingWisconsin-type fyke nets, we designed and tested a bycatch reduction device (BRD) for this nettype and investigated its ability to reduce turtle bycatch without affecting fish capture. Over 68net-nights, the BRD significantly reduced turtle bycatch with no significant decrease in fishquantity or richness when compared to a control fyke net with no BRD. We argue that aquaticbiologists and managers should consider turtle mortality when sampling fishes and other aquaticorganisms. We also suggest that further studies be conducted to develop BRDs for all passivefreshwater sampling nets. Further, BRDs that have already been designed and tested and appeareffective at reducing turtle bycatch without significantly affecting fish catch, such as ours, shouldbe implemented in freshwater fisheries methodologies. This is the first known BRD developed forfreshwater trap nets.
KEY WORDS. – Reptilia; Testudines; Trionychidae; Chelydridae; Emydidae; turtle; mortality; fishsampling; fyke nets; bycatch reduction device; turtle excluder device; TED; BRD; USA;Mississippi River
Aquatic biologists often use fyke nets (otherwise
known as trap nets) to sample fish, and many protocols
require nets to be set for 24–72 hours (Gutreuter et al.
1995; Hubert 1996). These nets are usually set perpen-
dicular to the shore with the lead fixed to the bank and the
hoops of the net completely submerged. Consequently,
there is a high rate of turtle bycatch involved with passive
fishing techniques (Sullivan and Gale 1999; Michaletz and
Sullivan 2002; Barko et al. 2004). Because trapping is
often conducted during periods with extreme environmen-
tal conditions (e.g., high water temperature during summer
months or deep water during spring flooding), turtle
mortality can approach 100% because of low dissolved
oxygen content and drowning (Barko et al. 2004; Fratto et
al. 2008). For example, in 2001, fisheries biologists using
hoop nets set for 72 hours to sample 2 reservoirs in
southeastern Missouri captured 800 turtles per 100 net-
nights with nearly 100% mortality (J. Briggler, Missouri
Department of Conservation, unpubl. data). Barko et al.
(2004) identified some environmental variables correlated
with increased aquatic turtle mortality, including depth of
gear deployment and temperature. Unfortunately, these
conditions are often unavoidable when fish are sampled,
especially when spawning or young-of-the-year fishes are
targeted. Hence, revised methodologies and gear modifi-
cations should be considered to reduce bycatch and
bycatch mortality when deploying passive techniques for
fish and other aquatic organisms within waters occupied
by turtles.
Similar considerations have been made in oceanic
systems. For example, gear modifications were developed
for shrimp trawls in the 1980s (Seidel and McVea 1982)
and implemented by the National Marine Fisheries Service
and commercial shrimp trawlers to reduce loggerhead sea
turtle (Caretta caretta) bycatch. Crowder et al. (1995)
studied the effect of turtle excluder devices (TEDs) on
loggerhead turtle strandings and showed that TEDs
reduced beach strandings by 44%.
Wood (1997) developed a bycatch reduction appara-
tus to address mortality in diamondback terrapins
(Malaclemys terrapin) caught in crab traps, which are
passive gear like freshwater trap nets. The bycatch
reduction apparatus effectively reduced the number of
turtles caught in crab traps and increased the number of
harvestable crabs. Roosenburg et al. (1997) developed
crab pots that were taller than standard commercial and
recreational pots used in the Chesapeake Bay to allow
terrapins to surface for air. Roosenburg and Green (2000)
also developed bycatch reduction devices (BRDs) for crab
pots to reduce terrapin mortality. To date, we know of no
similar modifications made to freshwater sampling gears.
The lack of TEDs, bycatch reduction apparatuses, and
BRDs on passive fishing techniques, especially in
freshwater systems where few species are federally
protected, threatens all turtle species. Increased threats
occur in areas where fisheries studies and/or commercial
fishing are conducted over consecutive years. The
increased mortality these species incur can alter population
dynamics and sex-based ratios within a population
(Roosenburg et al. 1997).
Public attention has focused on charismatic marine
turtles because of numerous documented cases of turtle
mortality and beach strandings (see Crouse et al. 1987;
Magnuson et al. 1990). Also, many turtles in marine
environments are listed as threatened or endangered;
hence, the federally mandated use of BRDs. Because
marine turtles differ markedly in size or shape from target
species like shrimp or crab, the development of effective
TEDs and BRDs was less problematic. In freshwater
systems, turtles are often similar in size to fish species
found within their environment. For example, blue catfish,
Ictalurus furcatus, and common map turtles, Graptemysgeographica, have similar body widths. Thus, successful
BRDs in freshwater systems may depend on unique
aspects of turtle and fish behavior rather than size or
shape. Barko et al. (2004) reported fyke nets in the middle
Mississippi River had higher turtle mortality rates when
compared to other sampling gears. Thus, we developed a
BRD for this net type to provide aquatic biologists working
in river systems a tool to reduce turtle bycatch while not
significantly affecting fish species richness and abundance.
Study Site
Our study was conducted in Missouri within 3 river
systems: Mississippi River (MSR), Gasconade River, and
Missouri River. Sampling was conducted within MSR
floodplains and island side channels of Mississippi and
New Madrid counties, backwater sloughs of the Gasconade
River in Gasconade and Osage counties, the MSR
Diversion Channel of Cape Girardeau County, Mingo
National Wildlife Refuge of Stoddard and Wayne counties,
and behind wing dikes on the Missouri River in Gasconade
County. Fisheries studies in Missouri having the greatest
turtle mortality were conducted in lowland habitats (J.
Briggler, Missouri Department of Conservation, pers.
Figure 1. Design of the control Wisconsin-type fyke net with no modifications.
206 CHELONIAN CONSERVATION AND BIOLOGY, Volume 7, Number 2 – 2008
comm., February 2006). Study sites (public and private)
greater than 3.2 ha in size were identified using a
Geographic Information System (GIS). This minimum
size was chosen to provide ample room for paired net sets.
Floodplain sites were defined as water bodies within the
100-/500-year floodplain and were composed of levee
borrow pits, ditches, blew holes (e.g., scour holes created
by openings in the levee), and chutes. Side channels had
direct connection to the main river channel annually;
whereas, floodplain sites had no connectivity to the main
river except during extreme flood events. Sample sites were
demarcated into 100-m2 grids and net placement within
each site was chosen using a random number generator.
METHODS
Data were collected from July to October 2005 and
from May to July 2006 when water temperature generally
exceeded 158C, presumably ensuring turtle activity
(Finkler et al. 2004). The control Wisconsin-type fyke
net (Gutreuter et al. 1995) consisted of a lead (15 m long 3
1.3 m high), frame, and cab with 19-mm bar mesh (Fig. 1).
The frame and cab were 6.0 m long when fully extended
and 2 rectangular spring-steel rods (0.9 m high and 1.8 m
wide) formed the frame. Two mesh wings extended from
the sides of the first frame to the middle of the second
frame, forming a 5.1-cm vertical gap. The cab was
constructed of 6 steel hoops with a 0.9-m diameter. There
were 2 throats on the fyke net, one on the first hoop (40-
mm mesh aperture) and one on the third hoop (32-mm
mesh aperture). The cod end had a 2.4-m-long drawstring
to keep the cod closed with 19-mm bar mesh.
The modified fyke net had two 3.18-mm braided rope
vertical lines tied 38 mm apart where the wings came
together in the middle of the second frame for a total of 4
lines (Fig. 2). Horizontal lines were added for rigidity at
Figure 2. Design of the modified Wisconsin-type fyke net illustrating the pattern of braided rope configuration and placement ofmodification.
FRATTO ET AL. — Bycatch Reduction Device 207
127 mm and 101.6 mm from the bottom and halfway from
the top and bottom. Each net was set for 24 hours with the
lead tied to the bank, with the remainder of the net running
perpendicular from the bank into the water. Each modified
net and its paired control were set with � 1.5 m depth
differences and � 100 m apart to reduce bias. After each
24-hour period, nets were relocated to the next random
water body. Turtles and fishes were identified to species,
counted, measured for length (carapace length [CL] in
millimeters for turtles and total length [TL] in millimeters
for fish) and released at the point of capture. Because our
study focused on the development of an effective BRD, we
did not mark any fish or turtle species captured.
During 2005, the modified net and its paired control
were set at 10 different sites within the MSR (5 floodplain;
5 side channel). During 2006, the modified net and its
paired control were set in the Gasconade River (n ¼ 6),
Missouri River (n ¼ 4), Mingo National Wildlife Refuge
(n ¼ 5), MSR Diversion Channel (n ¼ 5), and floodplains
of the MSR (n ¼ 4) using the same methodology as in
2005. We conducted 34 paired net sets across all habitats
(i.e., 68 net-nights).
Statistical Analysis. — All statistical analyses were
performed using SAS v. 9.1.3 with significance assessed at
p ¼ 0.05 (SAS Institute 2002). Kolmogorov-Smirnov tests
were used to assess normality (Lilliefores 1967). Because
data transformations (i.e., log, log þ 1, square root, sin,
cosin, tangent, and 5%–10% trims) were unsuccessful at
normalizing the turtle abundance data, we used Wilcoxon
rank-sum test to determine if our modified net had an
effect on turtle abundance using the mean abundance of
each modified and control net (Sokal and Rohlf 1981). To
determine if there were differences among mean catch per
net-night for each turtle species with an overall abundance
� 10 (arbitrary sample size restriction) in either the control
or modified net, we used t-tests (Steel and Torrie 1980).
We also used t-tests to identify differences in mean fish
abundance (log þ 1 transformed) among the paired nets
and mean catch per net-night of each fish species (overall
abundance � 10 in either the control or modified net) and
fish species richness (log þ 1 transformed) among the
paired nets. Abundance of Lepisosteidae and Centrarchi-
dae fish families were compared using Wilcoxon rank-sum
tests because these families are often targeted in fyke nets
by aquatic biologists in large, midwestern river systems
(Boxrucker and Ploskey 1989; McInerny 1989; Hoffman
et al. 1990). Other families were not analyzed because of
the low frequency at which they occurred. We analyzed
length distributions of both fish and turtles using
Kolmogorov-Smirnov 2-sample tests. Fish mortality
among net types was compared using a Wilcoxon rank-
sum test.
RESULTS
We captured 1686 turtles in 68 net-nights during 2005
and 2006. The control fyke nets captured 80% of the
turtles (n ¼ 1355), while the modified fyke net captured
fewer turtles (n ¼ 331; Z ¼�3.314, df ¼ 1, p , 0.001).
There were differences in mean catch per net-night for 3
turtle species (midland smooth softshell, Apalone mutica;
eastern spiny softshell, A. spinifera; and common
snapping turtle, Chelydra serpentina; Table 1). In 48%
of the net-nights (n ¼ 14), the modified net captured no
turtles; whereas, the control net caught no turtles during
8% of the net-nights (n ¼ 3).
Over 68 net-nights, we captured 893 fishes (33
species), with 478 fishes (23 species) captured in modified
fyke nets and 415 fishes (29 species) in the control nets.
There was no difference in fish quantity (Satterthwaite
method of unequal variances; t ¼ 0.96, df ¼ 59,
p ¼ 0.338) or fish species richness (t ¼�1.42, df ¼ 66,
p ¼ 0.161) among the modified and control nets. Also,
there was no difference in mean catch per net-night for any
of the fish species analyzed (Table 2). Much of the fish
catch was comprised of Centrarchidae (n ¼ 625, 70%) and
Table 1. Overall abundance, mean (x), and standard error (SE) of catch per net-night for turtle species captured in modified fyke net andits unmodified control net across all habitats sampled in 2005 and 2006. Mean catch per net-night (abundance � 10) was comparedusing t-tests, and significant results are bolded.
Family and species
Modified Control
t pN x SE N x SE
ChelydridaeCommon snapping turtle Chelydra serpentine 1 0.03 0.03 49 1.44 0.6 �2.32 0.027
KinosternidaeCommon musk turtle Sternotherus odoratus 51 1.5 0.88 33 0.97 0.54 0.51 0.610
EmydidaeSouthern painted turtle Chrysemys picta dorsalis 8 0.24 0.15 24 0.71 0.45 �0.99 0.330Common map turtle Graptemys geographica 1 0.03 0.03 27 0.8 0.03 �1.47 0.150Ouachita map turtle G. ouachitensis 2 0.06 0.06 2 0.06 0.04False map turtle G. pseudogeographica 104 3.06 1.58 167 4.91 1.61 �0.82 0.414River cooter Pseudemys concinna 2 0.06 0.04 12 0.35 0.21 �1.35 0.187Red-eared slider Trachemys scripta 156 4.59 2.4 994 29.24 12.44 �1.95 0.060
TrionychidaeMidland smooth softshell Apalone mutica 0 0 0 21 0.62 0.24 �2.59 0.014Eastern spiny softshell A. spinifera 6 0.18 0.15 26 0.76 0.25 �2.04 0.046
208 CHELONIAN CONSERVATION AND BIOLOGY, Volume 7, Number 2 – 2008
Lepisosteidae (n ¼ 142, 16%). We also found no differ-
ence in the quantity of Centrarchidae (Z ¼ 1.207, df ¼ 1,
p ¼ 0.228) or Lepisosteidae (Z ¼�1.866, df ¼ 1,
p ¼ 0.062) among control and modified nets.
We found a significant difference in the length
distribution of both false map, Graptemys pseudogeo-
graphica, and red-eared sliders, Trachemys scripta
(p , 0.001, Fig. 3), as well as white crappie, Pomoxis
annularis (p ¼ 0.008, Fig. 4), and bluegill, Lepomis
macrochirus (p ¼ 0.003). However, we found no differ-
ence in length distributions of longear sunfish, Lepomis
megalotis (p ¼ 0.459), or black crappie, Pomoxis nigro-
maculatus (p ¼ 0.4239). The number of dead fish per net-
night was significantly different among control and
modified nets (Z ¼�2.571, df ¼ 1, p ¼ 0.01) with 16 fish
dead in the modified net sets and 100 fish dead in the
control net sets.
DISCUSSION
Our data suggest that the modified fyke net did reduce
turtle capture when compared with its control without
significantly affecting fish quantity or fish species richness.
However, the modification was not very effective at
reducing turtles of smaller size (i.e., common musk turtles,
Sternotherus odoratus, and juvenile turtles of various
species), likely because the modification was not restric-
tive enough. Conversely, if the modification was too
restrictive, there may have been a decrease in fish quantity
or the frequency of larger fish.
Table 2. Overall abundance, mean (x), and standard error (SE) per net-night for fish species captured in modified fyke net and itsunmodified control net across all habitats sampled in 2005 and 2006. Mean catch per net-night (abundance � 10) was compared using t-tests and significant results are bolded.
Family and species
Modified Control
t pN x SE N x SE
LepisosteidaeLongnose gar Lepisosteus osseus 1 0.03 0.03 4 0.12 0.07Spotted gar L. oculatus 11 0.32 0.21 12 0.35 0.16 �0.11 0.912Shortnose gar L. platostomus 26 0.76 0.19 85 2.5 0.97 �1.76 0.087
AmiidaeBowfin Amia calva 6 0.18 0.09 4 0.12 0.06
ClupeidaeGizzard shad Dorosoma cepedianum 11 0.32 0.1 15 0.44 0.22 �0.49 0.624
CyprinidaeCommon carp Cyprinus carpio 6 0.18 0.08 8 0.24 0.09Bighead carp Hypophthalmichthys nobilis 0 0 0 1 0.03 0.03
CatostomideaBigmouth buffalo Ictiobus cyprinellus 0 0 0 1 0.03 0.03Smallmouth buffalo I. bubalus 0 0 0 7 0.21 0.08River carpsucker Carpiodes carpio 5 0.15 0.06 9 0.26 0.1Black redhorse Moxostoma duquesnei 3 0.09 0.09 0 0 0Spotted sucker Minytrema melanops 1 0.03 0.03 0 0 0
IctaluridaeChannel catfish Ictalurus punctatus 0 0 0 9 0.26 0.13Blue catfish I. furcatus 0 0 0 1 0.03 0.03Flathead catfish Pylodictis olivaris 0 0 0 1 0.03 0.03Yellow bullhead Ameiurus natalis 2 0.06 0.04 1 0.03 0.03Brown bullhead A. nebulosus 0 0 0 2 0.06 0.04Black bullhead A. melas 1 0.03 0.03 5 0.15 0.15
MoronidaeYellow bass Morone mississippiensis 0 0 0 3 0.09 0.06White bass M. chrysops 2 0.06 0.06 3 0.09 0.05Striped bass M. saxatilis 0 0 0 4 0.12 0.07White bass 3 Striped bass hybrid Morone spp. 0 0 0 1 0.03 0.03
CentrarchidaeLargemouth bass Micropterus salmoides 5 0.15 0.12 5 0.15 0.12Warmouth Lepomis gulosus 3 0.09 0.05 1 0.03 0.03Green sunfish L. cyanellus 0 0 0 2 0.06 0.06Orangespotted sunfish L. humilis 1 0.03 0.03 2 0.06 0.06Longear sunfish L. megalotis 60 1.76 0.88 39 1.15 0.57 0.59 0.557Bluegill L. macrochirus 182 5.35 2.05 66 1.94 0.59 1.60 0.118Redear sunfish L. microlophus 14 0.41 0.22 2 0.06 0.06 1.58 0.123Flier Centrarchus macropterus 3 0.09 0.09 0 0 0Rock bass Ambloplites rupestris 2 0.06 0.04 1 0.03 0.03Black crappie Pomoxis nigromaculatus 55 1.62 0.61 59 1.74 0.62 �0.13 0.893White crappie P. annularis 68 2 0.94 55 1.62 0.53 0.35 0.726
SciaenidaeFreshwater drum Aplodinotus grunniens 11 0.32 0.16 7 0.21 0.09 0.63 0.531
FRATTO ET AL. — Bycatch Reduction Device 209
When sampling requires nets to be submerged, the
application of this modification may prevent high numbers
of aquatic turtles from drowning, especially when set in
extreme environmental conditions such as high water
temperature (Barko et al. 2004). Turtles rely on environ-
mental temperatures to control their internal temperature
and metabolism (Pough et al. 1998). Cooler waters and
low stress conditions allow turtles to remain submerged for
longer periods of time before drowning. When turtles are
captured in nets, the stress incurred may raise metabolic
rates, creating a greater demand for oxygen (Pough et al.
1998). This becomes problematic when turtles are
captured in warm temperatures because the submersion
time before drowning is shortened.
Our BRD captured fewer large and small turtles when
compared to the control net. A reduction in turtle size is
important because few sexually mature turtles will be
killed or removed from the population. Turtles are long-
lived and growth is slow in most adults (Cagle 1946;
Gibbons and Semlitsch 1982; Pough et al. 1998). When
high rates of adult or older juvenile turtles are harvested or
captured as bycatch in commercial fishing or biological
sampling nets, the age structure of these populations
cannot remain stable (Congdon et al. 1993, 1994). A study
on the demographics of Blanding’s turtles, Emydoideablandingii, found that population stability was most
sensitive to changes in adult and/or juvenile survivorship
(Congdon et al. 1993). One consequence of an unstable
age distribution is large density fluctuations in different
age groups. Because turtles are long-lived, recovering to a
stable age distribution can take many years (Gibbons and
Semlitsch 1982).
In regards to the differences in length distributions of
bluegill and white crappie among modified and control
nets, this shift in the distribution may be a consequence of
the greater number of turtles found in the control nets and
the increased chance of fish consumption by turtles.
Another explanation for these results may be that these
fishes avoided nets with greater numbers of turtles as a sort
of predator avoidance. There also was a decrease in
shortnose gar, Lepisosteus platostomus, abundance in the
modified nets. Although not significant, the apparent
decrease in gar may also help explain the significant
difference in length distributions of bluegill and white
crappie. Shortnose gar are known to be generalist in their
food habits, and they may prey on fishes within the nets
(Pflieger 1997). There was also greater fish mortality in the
control nets, likely because of increased turtle capture.
Figure 3. A comparison of length-frequency distributions of red-eared sliders (A) and false map turtles (B) among control andmodified nets.
Figure 4. A comparison of length-frequency distributions ofwhite crappie (A) and black crappie (B) among control andmodified nets.
210 CHELONIAN CONSERVATION AND BIOLOGY, Volume 7, Number 2 – 2008
Many of the dead fish had missing fins, heads, and other
body parts, presumably a result of turtle consumption.
Because we found no turtles lodged in the throats of the
fyke nets, we do not believe turtles blocked the entrance to
these nets and that fish could continuously be trapped.
Further, fyke nets used in our study had 2 finger-style
throats that were larger than the girths of any of the turtles
captured. Because of our findings, we suggest that a
reduction in turtle capture within the nets may yield more
accurate fish population assessments.
To our knowledge, no papers have been published on
BRDs in freshwater systems on passive or active fishing
techniques. Further investigation of TEDs and BRDs for
freshwater fishing techniques is essential because riverine
turtle numbers are declining (Moll and Moll 2000), and
turtle mortality figures from commercial fishing are
lacking (Barko et al. 2004). These factors are troubling
because aquatic turtle habitats, such as rivers, streams,
lakes, and other such wetlands, are threatened and
declining (Gosselink and Maltby 1990). For instance,
floodplains and side channels are becoming disjunct from
mainstem rivers because of extensive levee systems, wing
dikes, and closing structures (Simons et al. 1975;
Buhlmann and Gibbons 1997; Theiling 1999). Bodie and
Semlitsch (2000) studied habitat use of lentic and lotic
aquatic turtles with the use of radiotelemetry and found
that riverine species such as false map and red-eared slider
turtles spend most of the year in the Missouri River, but
during the warmer months, habitat use was more diverse
and included offshore wetlands and even flooded agricul-
tural fields and forests.
Of the 160 freshwater aquatic and semi-aquatic turtle
species in the United States, at least 62 require conservation
action, and 18 of these are federally endangered (Burke et
al. 2000). With these declines and the negative human
influence on worldwide turtle populations, incidental
mortality by biologists and commercial fisherman using
passive sampling techniques should not add to the decline.
Our study provides useful information for aquatic manag-
ers because our modified nets did not significantly reduce
the quantity or richness of fishes captured, yet reduced
turtle captures. We suggest further evaluation of this gear in
other systems as well as additional research into the
development of TEDs and BRDs for other passive and
active sampling nets commonly deployed in freshwater
systems (e.g., hoop nets). Further, we urge state and federal
agencies to support the development, testing, and imple-
mentation of these BRDs.
ACKNOWLEDGMENTS
We thank B. Swallow, A. Given, J. Wallace, J. Ridings, J.
McMullen, and R. Sitzes of the Open Rivers and Wetlands
Field Station for aiding us in collection of field data. We
thank G. Cwick and J. Kraemer for providing guidance
needed to complete this project. We also thank the
Resource Science Division within the Missouri Depart-
ment of Conservation for funding this project and the
private landowners in Mississippi and New Madrid
counties of Missouri who granted us permission to conduct
our study on their property. Reviews were provided by D.
Herzog, A. Hendershodt, and 2 anonymous reviewers.
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Received: 13 February 2007
Revised and Accepted: 13 May 2008
212 CHELONIAN CONSERVATION AND BIOLOGY, Volume 7, Number 2 – 2008
