An evaluation of an experimental and a deepwater benthic fish trap in a large river system.

Hrabik, Robert A.

Abstract: Open River Field Station (ORFS) staff developed the Missouri trawl to capture small benthic fishes (e.g. Macrhybopsis spp.) in deep, swift areas of the Mississippi River. However, it was not possible to determine exactly where fish were caught during a trawl haul, thus it was difficult to describe microhbitats used by these fishes. The ORFS staff designed an experimental passive gear to capture benthic fishes in deep and swift water to better quantify microhabitat areas used by these fish. A modified mini-fyke net was used in conjunction with the experimental net for comparison. The nets were set in pairs within two habitat areas (i.e., main channel border and main channel border wing-dam). The experimental net captured a total of 121 fish and 1 Ohio Shrimp, Macrobrachium ohione. The modified mini-fyke net captured 126 fish and 1 M. ohione. There was no overall significant difference in catch rates between the two gears.

Key Words: Macrhybopsis, mini-fyke net, fishing gear, Macrobrachium ohione, passive gear, Mississippi River, wing dike.

Introduction

The Sicklefin Chub, Macrhybopsis meeki, and Sturgeon Chub, Macrhybopsis gelida, are listed as rare and uncommon in Missouri (MNHP, 2001). The decline in distribution and relative abundance of these chubs prompted the U.S. Fish and Wildlife Service (USFWS) to elevate these species to candidates for listing under the Endangered Species Act. However, they were not listed (see USFWS, 2001). M. gelida are thought to be a generalist species that tolerate a wide variety of habitat conditions (Young, 1997). However, Pfieger (1997) suggests M. gelida are confined to open channels of large rivers, preferring a strong current with sand and fine gravel substrate. Similarly, Pflieger (1997) states that M. meeki are confined to the main channels of large, turbid rivers, living in strong current over sand or fine gravel substrate. M. meeki are likely adapted to deep, swift water that often exceed 1 m/s and is > 3 m in depth (Young, 1997).

Open River Field Station (ORFS) staff used various methods to sample Macrhybopsis spp. and other benthic species including trawling, electrofishing, seining, and mini-fyke netting. While some of these methods were effective along the shoreline of the Mississippi River, only trawling was applicable to the main river channel where most Macrhybopsis spp. were found (ORES, unpubl. data). Unfortunately, it was difficult to determine where a fish was captured along a trawl haul. Standard trawl hauls used by ORES staff were 350 m long (Gutreuter et al., 1995). ORES staff wanted to design a stationary net that could be set in deep, swift water to better assess microhabitat use of Macrhybopsis spp. and other benthic fishes.

Gryska et al., (1998) designed a passive trap net to catch Kendall Warm Springs Dace, Rhinichthys osculus thermalis, a fish that lives in small streams. We modified their net (henceforth called the experimental net) by making it larger and sturdier to withstand the harsh environment of the Middle Mississippi River (MMR; that portion of the Mississippi River between the confluences of the Missouri and Ohio rivers). Although the experimental net was rigid and designed for deep, swift water, it could also be fished in areas of little or no water velocity. ORES staff preferred setting this type of passive gear because it could be handled without mechanized assistance, other than a boat, and it required little specialized training to operate (Hubert, 1996).

The objectives of this study were to compare the number of fish captured between the two net types to determine the usefulness of the experimental net in the MMR and describe microhabitat used by Macrhybopsis spp.

Methods

This study was conducted between MMR kilometers 48.3 to 128.7 (Fig. 1). Sampling was conducted from June-November 2000. Sites were selected subjectively to minimize net loss, maximize catch, and focus on deepwater habitats in wing dike (MCBW) and along the main channel border (MCBU) unstructured habitat (see Wilcox, 1993).

The experimental net consisted of a 0.95 cm steel rod frame and measured 107.9 cm wide, 30.4 cm high, and 152.4 cm long. The bottom of the frame was curved upward to give it a fusiform shape so the net would not be buried in the substrate or lost because of high velocity flows. This shape also decreased drag on the net. The experimental net was wrapped with 0.32 cm Ace style mesh. The entrance of the experimental net was V-shaped following Gryska and Hubert (1998) with an aperture diameter of 5 cm that was fixed using a stainless-steel ring following Gutreuter et. al. (1995). At the opposite end, a rope was sewn to the cod end mesh to support the throat to make a more durable and accessible catch chamber and to create a closing mechanism to seal the cod end (Fig. 2).

ORFS staff modified the mini-fyke net by removing the lead from the cab to make it more applicable for deepwater sets. Typically, this lead acted as a fence that was anchored on the shore to guide fish into the cab of the trap net. It was removed because it was impractical to use in main channel deepwater habitats. The net dimensions of the cab were 94.0 cm wide, 33.0 cm high, and 27.9 cm deep. The cod end measured 203.2 cm deep with a ring diameter of 38.1 cm. One throat was attached to the first hoop with an aperture diameter of 5 cm and was fixed using a stainless-steel ring (Gutreuter et. al. 1995). The modified mini-fyke was covered with 0.32 cm Ace style mesh (Fig. 3). The modified mini-fyke was collapsible and needed flow to hold the trap open. The mesh used on both nets was green dipped to protect it from deteriorating. Green dip is a water based latex dip used for coating netting.

A single set included both the experimental net and the modified mini-fyke net (paired set). These nets were set in close proximity to each other at each site and were anchored separately. Nets were set parallel to the shore by first anchoring a rope 15.2 to 30.5 m from the shoreline to a rock bag or cab weight. A rope was attached from the rock bag or cab weight to the net extending parallel to the shore. The nets were fished for 24 hours.

Water physical data were measured at each site, which included water depth (m), surface water velocity (m/s), substrate, secchi disc transparency (cm), and water temperature ([degrees]C). Predominant substrate type was determined at each site to further describe the habitat where Macrhybopsis spp. were captured. Chi-square analyses were used to test for differences (P[less than or equal to]0.05) in fish abundance (i.e. total number of individuals) between paired net sets (Steel and Torrie, 1980).

Results

A total of 19 paired sets were completed. Sixteen of the 19 sets were in MCBU and 3 were below MCBW. The MCBU sets consisted of 4 gravel substrate sets, 7 sand substrate sets, and 5 silt/sand substrate sets. The MCBW sets consisted of 3 sand substrate sets. Secchi visibility ranged from 17 to 48 cm (mean = 29 cm), depth ranged from 0.9 to 7.5 m (mean = 2.9 in), surface water velocity ranged from 0.10 to 0.70 m/s (mean = 0.31 m/s), and water temperature ranged from 4.1 to 29.5[degrees]C (mean = 26. 1[degrees]C, see Table 1).

The modified mini-fyke captured 126 fish while 121 fish were captured in the experimental net (Table 2). One Ohio Shrimp, M. ohione, was captured in each net type. Because of the small sample size, M. ohione data was not included in the statistical analysis. Macrhybopsis spp. chubs were not captured in either net. The modified mini-fyke net caught 11 species and the experimental net caught 9 species (Table 2). Channel Catfish, Ictalurus punctatus, dominated the catch in both nets. I. punctatus composed 87.4% of the catch in the modified mini-fyke net and 66.4% in the experimental net. No significant difference between fish abundance and net-type were detected ([X.sup.2] = 0.101, P > 0.75).

Discussion

Although both nets caught fish, neither captured Macrhybopsis spp. This may be because the nets created a velocity break that Macrhybopsis spp. may not seek. Pflieger (1997) suggested that both M. gelida, and M meeki prefer strong currents, which suggests they may avoid velocity breaks. Conversely, chubs could have avoided the nets. However, this was unlikely because the MMR is very turbid and does not allow light to penetrate very far below the surface. One way to lessen the magnitude of the velocity break and possibly increase chub capture would be to use a larger mesh. A larger mesh size would also reduce drag on the nets (Dickson, 1962). However, Macrhybopsis spp. chubs are small fish and an increase in mesh size may allow escapement.

The lack of chubs in the samples may also be related to temporal habits. Dettmers et al. (2001) suggested that there are numerous behavioral cues that may influence the locations and seasons that fishes use the main channel. Therefore, variables such as river stage height and time of year may affect the location and movement of fishes. Macrhybopsis spp. are thought to be early spring spawners and may not have been active in summer when we conducted this study (Pflieger, 1997).

The capture of M. ohione is important because this shrimp is rare in the MMR and techniques have not yet been developed to adequately sample this species. Conaway and Hrabik (1997) found that of 1,114 shrimp collected in 1992 only 4 were M. ohione, three of which were collected from wing dikes. ORFS biologists have captured 208 M. ohione from 1993 thru 2000, 35 of which were collected within MCBW habitat (ORFS, unpubl. data). One M. ohione captured in this study was collected from wing dike habitat.

Because the experimental net did not capture Macrhybopsis spp., ORFS staff could not assess microhabitat use. Further research is needed in developing a passive gear that will sample litho-psammophilic fishes that avoid crevice habitat.

Table 1

Water physical measurements of sites sampled using experimental and
modified mini fyke nets

 Secchi Depth Velocity Temperature utm
Site (cm) (m) (m/s) Substrate ([degrees]C) Easting

 1 18 6.0 0.35 Sand 28.1 810089
 2 24 3.0 0.23 Silt/Sand 26.8 807446
 3 40 7.5 * Silt/Sand 28.1 808801
 4 39 2.0 0.65 Sand 28.1 808613
 5 35 1.0 0.12 Sand 28.6 811178
 6 27 1.0 0.70 Gravel 28.5 812056
 7 29 3.0 0.22 Sand 28.6 810550
 8 30 7.5 0.21 Silt/Sand 29.3 809342
 9 34 6.0 0.39 Silt/Sand 29.2 816228
10 28 1.0 0.38 Sand 29.1 821811
11 26 0.9 0.35 Sand 29.5 821811
12 23 0.9 0.60 Sand 29.0 810539
13 17 1.8 0.21 Gravel 29.3 812084
14 19 1.8 0.16 Sand 28.9 808608
15 30 2.1 0.20 Silt/Sand 25.0 808786
16 34 3.0 0.17 Sand 25.4 810811
17 24 3.0 0.25 Sand 20.0 810925
18 26 2.1 0.10 Gravel 21.2 811576
19 48 1.6 * Gravel 4.1 811605

 utm
Site Northing

 1 4136226
 2 4164116
 3 4132393
 4 4131673
 5 4137061
 6 4137484
 7 4136742
 8 4134691
 9 4119337
10 4110872
11 4110817
12 4136655
13 4137549
14 4131576
15 4132342
16 4136647
17 4136876
18 4137055
19 4137542

* velocity readings were unobtainable

Table 2

Catch and relative abundance of fishes and Macrobrachium obione by gear
and substrate type in the Middle Mississippi River from June-November
2001

 number relative
Modified mini-fyke net abundance Sand Silt/Sand

Bluegill, Lepomis macrochirus 2 1.6% 2 (100.0%)
Channel catfish, 111 87.4% 73 (65.8%) 3 (31.5%)
Ictalurus punctatus
Channel shiner, Notropis 1 0.8% 1 (100.0%)
wickliffi
Emerald shiner, Notropis 1 0.8% 1 (100.0%)
atherinoides
Flathed catfish, Pylodictis 2 1.6% 2 (100.0%)
olivaris
Freckled madtom, Noturus 2 1.6% 2 (100.0%)
nocturnus
Freshwater drum, Aplodinotus 4 3.2% 4 (100.0%)
grunniens
Ohio shrimp, Macrobrachium 1 0.8% 1 (100.0%)
ohione
Striped bass, Morone 1 0.8% 1 (100.0%)
saxatilis
Stonecat, Noturus flavus 1 0.8% 1 (100.0%)
White bass, Morone chrysops 1 0.8% 1 (100.0%)

Total 127 100.0%


Modified mini-fyke net Gravel

Bluegill, Lepomis macrochirus
Channel catfish, 3 (2.7%)
Ictalurus punctatus
Channel shiner, Notropis
wickliffi
Emerald shiner, Notropis
atherinoides
Flathed catfish, Pylodictis
olivaris
Freckled madtom, Noturus
nocturnus
Freshwater drum, Aplodinotus
grunniens
Ohio shrimp, Macrobrachium
ohione
Striped bass, Morone
saxatilis
Stonecat, Noturus flavus
White bass, Morone chrysops

Total

 number relative
Experimental net captured abundance Sand

Blue catfish, Ictalurus furcatus 3 2.5% 2 (66.7%)
Channel catfish, 81 66.4% 40 (49.4%)
Ictalurus punctatus
Channel shiner, Notropis 1 0.8% 1 (100.0%)
wickliffi
Flathed catfish, Pylodictis 3 2.5% 3 (100.0%)
olivaris
Freckled madtom, Noturus 4 3.3% 2 (50.0%)
nocturnus
Freshwater drum, Aplodinotus 25 20.5% 13 (52.0%)
grunniens
Ohio shrimp, Macrobrachium 1 0.8%
ohione
Red shiner, Cyprinella 1 0.8% 1 (100.0%)
lutrensis
Stonecat, Noturus flavus 3 2.5% 3 (100.0%)

Total 122 100.0%


Experimental net Silt/Sand Gravel

Blue catfish, Ictalurus furcatus 1 (33.3%)
Channel catfish, 11 (13.6%) 30 (37.0%)
Ictalurus punctatus
Channel shiner, Notropis
wickliffi
Flathed catfish, Pylodictis
olivaris
Freckled madtom, Noturus 1 (25.0%) 1 (25.0%)
nocturnus
Freshwater drum, Aplodinotus 9 (36.0%) 3 (12.0%)
grunniens
Ohio shrimp, Macrobrachium 1 (100.0%)
ohione
Red shiner, Cyprinella
lutrensis
Stonecat, Noturus flavus

Total

Acknowledgements

Funding for this project was provided, in part, by the U. S. Fish and Wildlife Service, Endangered Species Act, Section 6 Program, Agreement Number E-1-37. Fieldwork was made possible with assistance by D. P. Herzog, D. E. Ostendorf, J. W. Ridings, L. Evans, C. Beachum, and W. Dunker. Illustrations were provided by D.E. Ostendorf. Thanks to the anonymous reviewers for taking time and effort to look over this manuscript.

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