... Monitoring Program, and the Missouri Department of. Conservation. iii ...... Robins C.R., R.M. Baily, C.E. Bond, J.R. Brooker, E.A. Lachner, R.N. Lea, and W.B.. Scott. ... Simons, D.B., M.A. Stevens, P.F. Lagasse, S.A. Schumm, and Y.H. Chen.
CAPTURE EFFICIENCY AND HABITAT USE OF STURGEON CHUB (MACRHYBOPSIS GELIDA) AND SICKLEFIN CHUB (MACRHYBOPSIS MEEKI) IN THE MISSISSIPPI RIVER.
by DAVID P. HERZOG
A THESIS
Submitted in partial fulfillment of the requirements for the degree of Master of Natural Science in the Department of Biology in the School of Graduate Studies and Research of Southeast Missouri State University
CAPE GIRARDEAU, MISSOURI
March 2004
ACKNOWLEDGEMENTS The efforts of everyone who assisted in this thesis are appreciated. I thank Mike Petersen, David Ostendorf, Joe Ridings, Jason Crites, Collin Beachum, Larry Evans, Wayne Dunker, Lesly Conaway and Bob Hrabik for field assistance. I thank Ed Peters (Nebraska), Steve Delain (Minnesota), Mike Steuck and Andy Thompson (Iowa) for guiding us while sampling in their perspective states. Valerie Barko, John Scheibe, Matt Winston and John Stanovick provided information for data analysis and gear comparison. Matt Winston, David Etnier, and Brooks Burr provided recent collection records of these species. Steve Gutreuter provided significant input into gear design. I thank A. J. Hendershott for completing the pencil sketch of the Missouri trawl and John Vallaza and Mike Roell for professional review. I thank Darrel Snyder (for initial identification of Scaphirhynchus albus specimens and for providing us with taxonomic keys. I thank Paul McKenzie (USFWS) for funding previous work efforts and providing insight into developing this project. To conclude, I thank John Scheibe and John Holbrook for serving on my graduate committee. I thank Rex Strange for chairing my graduate committee. This project was funded by the U. S. Fish and Wildlife Service, Endangered Species Act, Section 6 Program, Agreement Number E-1-37, and by the U. S. Army Corps of Engineers, and the U. S. Geological Survey, Biological Resources Division, Upper Midwest Environmental Sciences Center through the Upper Mississippi River System Long Term Resource Monitoring Program, and the Missouri Department of Conservation.
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CONTENTS ACKNOWLEDGEMENTS…………………………………………………………..
iii
LIST OF FIGURES………………………………………………………………….. vi LIST OF TABLES…………………………………………………………………...
ix
ABSTRACT…………………………………………………..………………………
xi
GENERAL INTRODUCTION………….……………………………………………
1
CHAPTER 1 Size selectivity and efficacy of a benthic trawl for sampling small-bodied fishes in large river systems ………………………………………… 6 Introduction………………………………………………………………......
6
Methods………………………………………………………………………
8
Results………………………………………………………………………..
11
Discussion……………………………………………………………………
13
Conclusion…………………………………………………………………..
17
Figures……………………………………………………………………....
18
Tables…………………………………………………………………….....
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CHAPTER 2 The status and habitat use of sicklefin chub (Macrhybopsis meeki), sturgeon chub (Macrhybopsis gelida), and pallid sturgeon (Scaphirhynchus albus) in the Middle and Lower Mississippi rivers.………………………………………………………………… 31 Introduction………………………………………………………………….
31
Methods……………………………………………………………………..
33
Results……………………………………………………………………….
34
Discussion…………………………………………………………………...
36
Conclusion………………………………………………………………......
42
Figures………………………………………………………………………
43
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Tables……………………………………………………………………….
62
CHAPTER 3 Concluding Recommendations for future research…………...…….
77
LITERATURE CITED…………………………………………………………......
80
APPENDIX A………………………………………………………………………
86
APPENDIX B………………………………………………………………………
88
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LIST OF FIGURES Chapter 1 Figure 1.
Long Term Resource Monitoring Program, study area of the Upper Mississippi River monitored by the Open River Field Station. This reach extends from RK 48 to RK 129………………………………………. 18
Figure 2.
Modified two-seam balloon trawl (Missouri trawl) sketch illustrating the individual components.……………………………………………….. 19
Figure 3.
Digital image showing the small mesh cover (4.76 mm) wrapped over the standard trawl body (19.05 mm) mesh.………………………………. 20
Figure 4.
Results of the logistic regression showing cumulative probability of capture against length for the standard trawl portion of the Missouri trawl (▲=codend observed: ● =cover observed). Codend curve and cover curve are indicated by the solid lines.………………………………………... 21
Figure 5.
Results of the logistic regression showing cumulative probability of capture against length for the standard trawl without cover (▲=codend w/cover observed: ● =codend w/o cover observed). Codend curves, with and without cover, are indicated with solid lines. ……………………. 22
Figure 6.
Comparison of the rate of fish species captured after 100 samples using the standard mesh trawl (grey line) and Missouri trawl (black line) in the Open River Field Station reach of the Upper Mississippi River. Solid lines represent cumulative number of fish species captured at selected sampling intervals…………………………………………………….. 23
Chapter 2 Figure 1.
Sampling locations in sections of the Middle/Lower Mississippi Rivers (15) and in the Lower Missouri River (6), during trawling (2000-2001)… 43
Figure 2.
Longitudinal profile of catch per unit effort of sicklefin chub during 20002001 sampling using benthic trawling in sections of the Middle/Lower Mississippi and Missouri Rivers……………………………………… 44
Figure 3.
Longitudinal profile of catch per unit effort of sturgeon chub during 20002001 sampling using benthic trawling in sections of the Middle/Lower Mississippi and Missouri Rivers……………………………………… 45
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Figure 4.
Depth partitioning of Sturgeon chub observed during trawling (20002001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers…………………………………………………………………. 46
Figure 5.
Temperature partitioning of Sturgeon chub observed during trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers……………………………………………………….. 47
Figure 6.
Surface water velocity partitioning of Sturgeon chub observed during trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers……………………………………………….. 48
Figure 7.
Length frequency of sturgeon chub captured during trawling (Feb-Mar) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 49
Figure 8.
Length frequency of sturgeon chub captured during trawling (May-Jun) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 50
Figure 9.
Length frequency of sturgeon chub captured during trawling (Aug-Sep) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001……………………………………………………... 51
Figure 10.
Length frequency of sturgeon chub captured during trawling (Nov-Dec) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001……………………………………………………… 52
Figure 11.
Depth partitioning of Sicklefin chub observed during trawling (20002001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers………………………………………………………………….. 53
Figure 12.
Temperature partitioning of Sicklefin chub observed during trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers………………………………………………………. 54
Figure 13.
Surface water velocity partitioning of Sicklefin chub observed during trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers……………………………………………….. 55
Figure 14.
Length frequency of sturgeon chub captured during trawling (Feb-Mar) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 56
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Figure 15.
Length frequency of sturgeon chub captured during trawling (May-Jun) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 57
Figure 16.
Length frequency of sturgeon chub captured during trawling (Aug-Sep) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 58
Figure 17.
Length frequency of sturgeon chub captured during trawling (Nov-Dec) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers during 2000-2001…………………………………………………….. 59
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LIST OF TABLES Chapter 1 Table 1.
Species captured using a modified two-seam balloon trawl (i.e., Missouri Trawl) and Chi-square values associated with abundance comparison of codend and cover……………………………………………………… 24
Table 2.
Logistic regression results for the linearized cumulative probability of capture against length up to 28 cm using Standard cod of the Missouri trawl…………………………………………………………………… 27
Table 3.
Logistic regression results for the linearized cumulative probability of capture against length up to 28 cm using the cover of the Missouri trawl…………………………………………………………………… 28
Table 4.
Logistic regression results for the linearized cumulative probability of capture against length using the Standard codend of the Missouri trawl over all lengths captured……………………………………………… 29
Table 5.
Logistic regression results for the linearized cumulative probability of capture against length using the Standard trawl without cover over all lengths captured………………………….…………………………… 30
Chapter 2 Table 1.
Effort allocation by time period and location during trawling samples (2000-2001) within section of the Middle/Lower Mississippi and Lower Missouri Rivers……………………………………………………….. 60
Table 2.
Number and catch per unit effort ( ) of sicklefin chub by time period and location during bottom trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers………………. 61
Table 3.
Number and catch per unit effort ( ) of sturgeon chub by time period and location during bottom trawling (2000-2001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers………………. 62
Table 4.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Pelican Island, MO--Lower Missouri River………………………………………………………………….. 63
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Table 5.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Grand Tower Island, MO--Middle Mississippi River………………………………………………………………….. 64
Table 6.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Cape Girardeau, MO area--Middle Mississippi River……………………………………………………... 65
Table 7.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Thebes, IL area--Middle Mississippi River.. ………………………………………………………………… 67
Table 8.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Cairo, IL area--Middle Mississippi River………………………………………………………………….. 68
Table 9.
Relative abundance values and species totals by location and time period during trawling (2000-2001) at Wolf Island, KY--Lower Mississippi River…………………………………………………………….......... 69
Table 10.
Overall abundance of fishes captured during trawling samples (20002001) in sections of the Middle/Lower Mississippi and Lower Missouri Rivers…………………………………………………………………. 71
Table 11.
Percent occurrence of sicklefin and sturgeon chub during trawling (20002001) in selected areas of the Middle/Lower Mississippi and Lower Missouri Rivers at varied temperature habitats………………………. 74
Table 12.
Percent occurrence of sicklefin and sturgeon chub during trawling (20002001) in selected areas of the Middle/Lower Mississippi and Lower Missouri Rivers at varied depth habitats……………………………… 74
Table 13.
Percent occurrence of sicklefin and sturgeon chub during trawling (20002001) in selected areas of the Middle/Lower Mississippi and Lower Missouri Rivers at varied surface water velocity mesohabitats………. 75
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ABSTRACT I conducted this study from 1998 to 2001 to determine size selectivity and efficacy of a trawl with the purpose of increasing species detection and reducing zero catch of small-bodied fishes. Emphasis was placed on Macrhybopsis gelida (sturgeon chub) and Macrhybopsis meeki (sicklefin chub) because of a perceived decline in their range that prompted the U.S. Fish and Wildlife service to consider listing them as threatened under the endangered species act in 1994. Scaphirhynchus albus (pallid sturgeon) was also included because of its current federally endangered status. A twoseam slingshot balloon trawl was modified by covering the trawl body and codend with a small mesh cover. After completing 281 trawl hauls, I discovered that most fish passed through the body of the standard trawl and were captured in the cover. Chi-square tests indicated that abundance of 18 of the 45 species was significantly higher in the small mesh cover. Logistic regression analysis indicated that cumulative probability of capture was higher in the small mesh cover than the standard trawl codend for all fish up to 28 cm total length. The cumulative probability regressions of the original standard trawl and the modified standard trawl with cover were nearly identical. Therefore, there was no noticeable effect of the cover on the catch entering the standard codend of the modified trawl. Some fish, such as S. albus and Scaphirhynchus spp., were captured exclusively in the small mesh cover. Catch of small-bodied adult fish, such as Macrhybopsis species, was significantly improved using the small mesh cover design. A modified two-seam slingshot balloon trawl (a.k.a. the Missouri trawl) increased significantly the number and species of fish captured over previously used designs. During 2000-2001, these 3 species were studied with emphasis on spawning and rearing habitats during 4 sampling periods
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at 6 sampling stations. Two-hundred-thirty-one benthic trawl hauls captured 636 sturgeon chub, 190 sicklefin chub, and 3 larval pallid sturgeon. Habitat use of Macrhybopsis chubs differed by time period, species, and size classes within species. Larval Scaphirhynchus were captured with highest frequency at downstream island tips.
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GENERAL INTRODUCTION Habitats used by fish have been altered in the Upper Mississippi River (UMR) through dredging, siltation (Southall and Hubert 1984), and the creation of both flood control and navigation structures. U.S. Congress passed a bill in 1927 that authorized the creation of a 9 ft deep and 300 ft wide navigation channel in the section of the Mississippi River extending from the mouth of the Missouri River to the mouth of the Ohio River (Yin and Nelson 1995). This section of the Mississippi River is under the authority of the U.S. Army Corps of Engineers (USACE), St. Louis District to maintain a 9 ft (minimum depth) navigation channel (Farabee 1986). The maintenance of this navigation channel included historically the clearing of snags/debris and annual dredging, but now includes creation and maintenance of structures such as wing dikes and levees (Farabee 1986; Pitlo 1998). Wing dikes cause reduced river width, increased sedimentation, and loss of side channels (Simons et al. 1975; Theiling 1999). Consequently, sedimentation allows for plant colonization and subsequent plant succession. This vegetation can restrict or block the entrance to side channels, and make them unavailable to fish (Bradford and Gurtin 2000). Disturbance (e.g., dredging) to habitats used by fish occur commonly in the UMR. The depth of the Mississippi River has increased at all discharges because of channel maintenance activities (Simons et al. 1974). The increase in depth increases water column pressure on fish. Many species may not be adapted to withstand the physical stress of increased water pressure. Therefore deep water, although beneficial to navigation, cannot be used by some fish species. Also, maintenance activities disturb habitats used by fish species at critical life stages. These activities have reduced large
1
2
shallow expanses of sand and gravel bar habitats adjacent to deeper off-channel areas. Reducing the size of these habitats creates longer distances between them (Peacock and Smith 1997). Dispersal patterns, mating behavior, and genetic variation of populations are influenced by this habitat fragmentation (Peacock and Smith 1997). These shallow areas may be important feeding areas for many Cyprinids. Algal and detrital material are important food sources for many minnows. Algal growth is found mostly in shallow waters of the Mississippi River because turbidity prevents sunlight penetration in deep water. Furthermore, water temperatures are typically warmer in shallow areas because of increased sunlight effects on the water column. Therefore, shallow waters may be important for reproduction and rearing. Habitat modifications of the Mississippi River are associated with the noticeable decline in some species. For example, Alligator gar (Atractosteus spatula) are now extirpated from Missouri as a result of the reduction of overflow waters or floodplain waters of large rivers (Pflieger 1997). Habitat diversity loss is a common issue in many large rivers of the world. Homogeneity among habitats results in homogeneous fish assemblages. Therefore, it is important to determine the habitats and requirements of fish species. Reducing disturbances to habitats during critical life stages will assure fish assemblage stability. The decline in distributional area and relative abundance of two small minnows (Family Cyprinidae), 1) sturgeon chub, Marchybopsis gelida, and 2) sicklefin chub, Macrhybopsis meeki, prompted the United States Fish and Wildlife Service (USFWS) to elevate these species to candidates for 'threatened' status on the Endangered Species list in 1994 (USFWS 2003). The state of Missouri lists these as special concern species. Little published information exists on the habitat requirements or life histories of these
3
species and macrohabitat requirements of these species are described only generally (Werdon 1993a, 1993b; Jackson 2002). However, microhabitat requirements during reproduction, feeding, and rearing are unknown. The historic distribution of these species encompasses several river systems and involves multiple interest groups and state agencies. Recently, several studies have been undertaken to describe population demographics or habitat characteristics of these species in portions of their historic range (Kopf 2003; Herzog and Ostendorf 2002; Jackson 2002; Everett 1999; Gelwicks et al.1996). This new information about these species’ habitat use has been useful in protecting critical habitats in the study areas. The sturgeon chub (M. gelida) can be described as a slender minnow with reduced eyes, long fleshy snout, and a small horizontal mouth (Pflieger 1997). This species has scales with ridges or keels only on its back and sides. Adults are typically 43 to 64 mm total length and have a maximum length of 76 mm. Visually, the keels or ridges on the scales, along with dark pigment and long snout, provide a quick identification for this species (Appendix A). The sicklefin chub (M. meeki) is as a long slender minnow with small eyes, small horizontal mouth, and long, sickle-shaped pectoral fins (Pflieger 1997). Visually, the pale yellowish back and sides, long pectoral fins, and relatively small scales that make the body reflective, create distinguishable characters for field identification (Appendix B). Adults are typically 61 to 94 mm total length and have a maximum length of 102 cm. Both sicklefin chub and sturgeon chub have a small conical barbel at the corners of the mouth (Pflieger 1997).
4
The sturgeon chub and sicklefin chub occupy open channels of large rivers, in strong current over a sand and fine gravel substrate (Pflieger 1997). The sturgeon chub has been noted to prefer gravel, whereas sicklefin chub may prefer firm sand. Within the UMR, little information exists about the distribution of these species. Pflieger (1997) described distribution of the sicklefin chub and sturgeon chub in the Missouri River, and Mississippi River downstream of the mouth of the Missouri River. Also, Pflieger (1997) described these species as absent in the Mississippi River, (sturgeon chub), or occasional strays (sicklefin chub). Furthermore, a seine survey in the UMR completed by Grace and Pflieger (1985) found that sicklefin chub and sturgeon chub were absent from all sites sampled. Grady and Milligan (1998) reported that trawling, when compared to seining, captured 98 percent of all sicklefin chub and 100 percent of sturgeon chub. In addition, Everett (1999) noted trawling as the gear used for capturing sicklefin and sturgeon chub. Both Grady and Milligan (1998) and Gelwicks et al. (1996) captured adult sicklefin and sturgeon chub in the Missouri River using trawling. Trawling methods used on the Mississippi River at the Open River Field Station (ORFS) captured no sturgeon chub and only 44 sicklefin chub from 1991 through 1996 (LTRMP 2000). Therefore, it is evident that sampling gear can have an effect on distribution and abundance if the species are not susceptible to the gear being used. For that reason, effort should be made to determine capture efficacy of gear on the species or community being studied. As a result, recent modifications to the ORFS trawl gear have been made to provide information on capture of small-bodied fishes in large river systems (Herzog et al. In review). However, efforts to identify effectiveness of this gear relative to others has not been completed.
5
Accordingly, the objectives of this study are to: 1) Determine effectiveness of capture of small bodied fishes using two types of benthic trawls, 2) Summarize habitat use of sicklefin chub and sturgeon chub in the Mississippi river.
Chapter I Size selectivity and efficacy of a benthic trawl for sampling small-bodied fishes in large river systems. INTRODUCTION Trawling has been used to sample aquatic organisms in coastal marine systems (Matsushita and Shida 2001), reservoirs (Michaletz et al. 1995), and rivers (Dettmers et al. 2001). Trawl size and design varies depending on the intended use. For example, researchers may target an individual species and use a trawl that is known to capture that group (Van Den Avyle et al. 1995; Pine 2000; Madsen and Holst 2002). During many trawl surveys, the loss of other species is unimportant and at times, because of catch regulations, considered beneficial (Kelley 1994). Therefore, many trawl surveys use a large mesh trawl. Large mesh trawls reduce drag while in tow and are noted for fuel efficiency and reduced bycatch (Dickson 1962; Naidu et al. 1987). Also, some studies show that large mesh trawls tend to capture more large fish (Mous et al. 2002). In addition, shape, configuration, and environmental factors can influence catch of a trawl (Glass and Wardle 1989; Kunjipalu et al. 1992; Chopin and Arimoto 1994; Kim and Wardle 1997; Godo and Walsh 1998; Dahm 2000; Ryer and Olla 1999; Matsushita and Shida 2001). Furthermore, catch is affected by trawl design components. For example, the codend (i.e. distil end) is where most of the trawl catch is collected. Millar (1992) modeled trawl selectivity based on total catch, which he determined was influenced by size and shape of the mesh openings in the codend. The codend is often modified to capture a particular size of organism (Lowry and Robertson 1996), although many factors could affect catch entering the codend. For example, the escape of organisms through the
6
7
body of a trawl may result in variable codend retention (Dremiere et al. 1999; Polet 2000). The covered codend method is often used to determine mesh codend selectivity (Madsen and Holst 2002). However, the body of the trawl in addition to the codend determines total catch. Therefore, the whole catch of a trawl is determined by the sum of its parts. Trawls have been used to sample the Mississippi River although techniques varied among researchers (Pitlo 1992; Dettmers et al. 2001). From 1991 through 1997 a two-seam balloon ‘standard’ trawl (Gutreuter et. al. 1995) was used to sample benthic fishes; however, the catch was highly variable (D. Herzog, unpubl. data) and small benthic fish (e.g., Macrhybopsis species) or larval and juvenile fishes (e.g. Scaphirhynchus species) were not well represented in the total catch. The objective of this study was to design a trawl that would increase species detection and reduce zero catches of small-bodied fishes. To accomplish this, a two-seam slingshot balloon trawl-body and codend--was modified using a dual mesh design (i.e., pass through technique). The body of the trawl in addition to the codend was covered to determine mesh selectivity of the entire standard trawl.
STUDY SITE This study was conducted in the unimpounded section of the Upper Mississippi River (Figure 1). Trawling effort was conducted between river kilometers (RK) 48.3 and 128.7; the Long Term Resource Monitoring Program -Open River Field Station (ORFS) reach. This reach contains few side channels and has been channelized for commercial navigation. Water surface elevations in the ORFS reach rise and fall annually
8
approximately 8 m. Samples were at depths that ranged from 0.6 to 10 m, with a mean depth of 3.2 m. Water surface velocity ranged from 0.02 to 1.94 m/s with a mean of 0.81 m/s. Secchi disk transparency averaged 28 cm and ranged from 2 to 61 cm. Sample area substrates varied but were mostly comprised of sand. Channel maintenance structures (e.g., wing dikes) occur throughout the ORFS reach and vast expanses of limestone rock (i.e., revetment) cover much of the river bank.
METHODS The modified trawl, (hereafter referred to as the Missouri Trawl; Figure 2) was made of a two-seam 19.05 mm mesh body (i.e., standard) slingshot balloon trawl (Gutreuter et. al.1995) completely covered with a 4.76 mm heavy delta mesh cover (i.e., cover; Figure 3). The standard trawl originally contained a codend lined with 3.18 mm mesh. Therefore, I added the same mesh to the cover codend. The footrope was 4.87 m long with a 4.76 mm diameter chain attached. The chain helped the footrope maintain contact with the substrate when trawling under heavy current, fast tow speeds, or undulating bottom surfaces (e.g., sand waves). The head rope was 4.57 m long with floats spaced every 0.91 m. The Missouri Trawl was attached to the boat with 30.48 60.96 m towlines. Towline length was dependant on water depth (i.e., deeper water required longer towlines; Brabant and Nedelec 1979). The towlines were comprised of 15.87 mm twisted nylon ropes and attached to the bow of the boat. The otter boards were 38.10 cm high, 76.20 cm long, and weighed 13.6 kg each. A buoy was attached to a single 22.86 - 30.78 m rope line that was attached to the codend of the trawl to assist in retrieval if the trawl snagged.
9
The trawl was deployed manually and retrieved. I began by powering the boat in reverse (bow upstream) with continued movement downstream. Reverse direction trawling is safer with small jon boats in large rivers. For example, when a snag is encountered, the towlines pull downward at the attachment point. Using stern mounted towlines in rivers may cause small jon boats to take on water or capsize whereas bow mounted towlines utilize the buoyancy of the bow and dampen downward pull. In addition, the power from outboard motor propellers is generated in forward gear. When a trawl is snagged while reverse trawling, forward gear allows the driver more power to remove the downward pull of the towlines. I continued a trawl haul by tossing the buoy line off the bow of the boat followed by the codend of the net. The trawl and otter boards were deployed into the water while the boat reversed downstream. Tension was kept on the towlines so the otter boards did not twist while the towlines were being deployed. A standard haul was approximately 375 m and lasted approximately 6 minutes (Gutreuter et al. 1995). The Missouri Trawl was towed at speeds slightly faster than the surface current velocity by a 7.32 m jon boat equipped with a 90 HP outboard motor. Trawling speed (km/hr) and distance (m) were monitored using a Garmin GPSMAP 168 Sounder global positioning system (GPS) with differential correction. Effort was recorded in time trawled and distance traveled (i.e., when towlines were taut to when the net was retrieved into the boat). Trawling location and duration were limited by water depth less than 0.5 m and bottom snags. Catch of the standard trawl codend portion and cover were kept separate to determine extent of trawl mesh selectivity. Fish were identified to species, measured, and enumerated. All common and scientific names follow Robins et al. (1991). To compare
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abundances of species captured in the standard codend of the Missouri trawl and the cover of the Missouri trawl I used chi-square tests for equal proportions (Steel and Torrie 1980, SAS Institute Inc. 1988). The effect of trawl body mesh size on probability of capture was assessed using logistic regression (SAS Institute Inc. 1988). The cumulative probability of capturing a fish was linearized using the logit transformation: p' = ln⎛⎜ p ⎝ 1−
⎞ p ⎟⎠
(1)
where p is the cumulative probability of capturing a fish of a given length or shorter. Thus, the linear regression model had the form: p' = β 0 + β1 X .
(2)
where X represented fish length. Transforming the linearized cumulative probabilities back to their original form resulted in the logistic regression model: e ( β 0 + β1 X ) E (Y ) = . 1 + e ( β 0 + β1 X )
(3)
With this formulation, the dependent axis was the expected cumulative probability of capturing a fish with a length of at least X cm, and varied from 0 to 1. The regression was performed three times. Cumulative probability of capture was regressed against length using the 1998-2001 data set, first for the standard trawl codend of the Missouri trawl and second for the cover of the Missouri trawl. Lastly, to determine effect of the cover, cumulative probability of capture was regressed against length for the standard trawl codend without the cover using the 1991-1997 data. Species data from the standard trawl without cover, 1991-1997, were compared to the Missouri trawl data set, 1998-2001. I estimated the rate of species capture by
11
randomly selecting 100 observations in both the 1991-1997 and 1998-2001 data sets. The data were randomized by assigning a random number to each sample. The data were then sorted by the random numbers. The first sample listed was plotted by the number of species captured in that sample/haul. I continued plotting samples until 100 observations were reached. A logarithmic trend line was used to plot each “sample” for both trawls.
RESULTS Two hundred eighty-one Missouri trawl hauls were completed over a 4-year period from 1998-2001. I captured 3,217 fish (32 species) in the standard trawl codend portion of the Missouri trawl and 10,549 fish (43 species; i.e., 77 percent of the total catch) in the 4.76 mm mesh cover. Chi-square tests indicated that abundance of 18 of the 45 species was significantly higher (P ≤ 0.05, df = 1) in the 4.76 mm mesh cover. However, shovelnose sturgeon (Scaphirhynchus platorhynchus) had significantly higher abundance in the standard trawl codend portion of the Missouri trawl (Table 1). Larval Scaphirhynchus species were captured entirely in the 4.76 mm mesh cover. Several additional species were captured entirely in either the 4.76 mm mesh cover (i.e., Pimephales vigilax, Menidia beryllina, Hybognathus nuchalis, Scaphirynchus spp and S. albus) or the standard trawl codend portion of the Missouri trawl (i.e., Lepisosteus platostomus) and were represented by more than one occurrence (Table 1). The remaining species did not differ significantly in abundance in either the standard codend of the Missouri trawl or the cover of the Missouri trawl. Sturgeon chub (Macrhybopsis gelida) and larval Scaphirhynchus spp. were captured using the Missouri trawl and had not been captured by ORFS researchers during 1991-1997 using the standard mesh trawl.
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Two hundred fifty-two standard trawl hauls were completed over the 7-year period 19911997. I captured 3,035 fish (30 species) in 223 hauls. The logistic regression models for all scenarios were significant at the 0.05 level and explained 82.33% (standard codend of Missouri trawl), 90.27% (standard trawl without cover), 91.51% (4.76 mm cover up to 28 cm), and 87.8% (standard codend of Missouri trawl up to 28 cm) of the variance in cumulative capture probability (Tables 25; and Figures 4-5). The slopes for the regression models between the standard codend portion of the Missouri trawl and the cover differed markedly, with that for the 4.76 mm cover being steeper (Figure 4). It is clear that use of the 4.76 mm cover resulted in greater probability of capture for fish lengths up to 23 cm, and that for fish longer than 15 cm the cumulative probability of capture approached one (Figure 4). The standard trawl codend portion of the Missouri trawl accumulated captures at a slower rate, and the cumulative probability of capture approached one for fish longer than 26 cm. Fish larger than 28 cm were not captured in the 4.76 mm mesh cover because they did not pass through the standard 19.05 mm mesh trawl body. The slopes for the regression models between the standard codend portion of the Missouri trawl with cover (1998-2001) and the standard trawl without cover (1991-1997) were similar. It is clear that use of the 4.76 mm cover did not affect the cumulative probability of capture of fish in the standard codend portion of the Missouri trawl (Figure 5). Therefore, the cumulative probability of capturing fish at length in the codend using the standard trawl with cover is the same as using the standard trawl without the cover. Species detection was higher with the Missouri trawl than with the standard trawl. Random sampling of the data indicated shorter response times of species detection by
13
sample using the Missouri trawl (Figure 6). After eight samples the Missouri trawl captured 50 % of the overall detected species, whereas it took the standard trawl 56 samples to reach the same level of species detection.
DISCUSSION My data show that many small fishes passed through the trawl body. Previous variability in the catch of small benthic fishes in the standard trawl, (1991-1997), was because of the relatively large (19.05 mm) mesh of the trawl body. I used a small mesh codend in the standard trawl for seven years before implementing the Missouri trawl, and was not able to detect as many fish or species. Thus, I captured more fish and fish species using a smaller mesh trawl body than I captured using a small mesh codend in the standard trawl. Seventy-seven percent of the total fish captured passed through the trawl body before they entered the codend of the standard trawl. Young and larval fish (e.g., Scaphirhynchus spp.) and smaller bodied adult species, (e.g., Macrhybopsis spp.) passed through the 19.05 mm mesh body of the standard trawl. The lack of several historically common species (e.g. M. gelida, M. meeki) in community samples from 1991 through 1997 was previously troublesome. It is possible that one reason for low frequency of occurrence was gear selectivity toward species catch at length. Researchers continue to modify codend specifications to study the size of fish captured (Mous et al. 2002). The modifications are usually not associated with community sampling. Instead they are usually conducted to increase catch of large fish and reduce small fish or unwanted catch. The body of the trawl can reduce unwanted catch. The unwanted catch or ‘bycatch’ is a regulated component of the trawling industry
14
and could be reduced substantially by modifying the mesh size of the trawl body. This study supports the idea that body of the trawl can affect capture as much or more than the codend. The standard trawl design does capture small fish. However, the design may have contributed to escape through the trawl body because the fish may have impinged against the mesh prior to entering the codend. Although the general shape of the standard trawl is funnel-shaped, the operational procedures may have caused the trawl to act more like a sieve rather than funneling fish to the codend. However, trawling procedures did not change from using the standard trawl (1991-1997) to using the Missouri trawl (19982001). Therefore, any changes to catch composition should be attributed to a change in trawl design rather than methodology. When using a trawl with a cover, there is a chance that mesh interactions affect the catch. Cover effects were not noticed when comparing cumulative probability of capture from the standard trawl portion of the Missouri trawl (1998-2001) to the standard trawl codend without cover (1991-1997). Cumulative probability of capture at length was nearly identical across all length ranges. These results are similar to findings of Madsen and Holst (2002). They found no obvious masking effects caused by the codend with cover on the catches of a single species. However, fish larger than the mesh cannot pass through to the small mesh. Therefore, comparisons of lengths greater than the maximum escape length through the trawl body would be redundant. Many shovelnose sturgeon were larger than the 19.05 mm mesh. This explains the significantly higher abundance of shovelnose sturgeon in the standard codend portion of the Missouri trawl. Shape, texture, behavioral response (e.g. predator avoidance), and size are important
15
factors in determining susceptibility to fishing gear (Pope et al. 1975). Shovelnose sturgeon are not strong swimmers and use "substrate appression" to maintain themselves in the current (Adams et al. 1997). Thus, this species is less likely to escape an encounter with a bottom trawl. Conversely, larval sturgeon pass through large mesh because of their size and shape. Gunderson (1993) addressed differences in trawl capture based on the size of fish and the ability to out-swim the trawl. Also, some fish species will not be captured because of habitats they occupy (e.g. pelagic fishes) and are not susceptible to bottom trawling. All eighteen species that were significantly more abundant in the small mesh cover portion of the Missouri trawl were either small or had streamlined bodies. Although there was no apparent effect of the cover on cumulative probability of catch at length, there is an affect on drag. The small mesh cover of the Missouri trawl increases the power required by the motor to pull the trawl and requires substantially more manpower to retrieve than does the standard trawl without cover. In addition, the small mesh cover is susceptible to damage because it is on the outside of the trawl. However, the utility of the cover for community sampling outweighs any negative aspect of drag or maintenance. For example, the use of the Missouri trawl may reduce catch mortality of small fish. Large mesh trawls capture larger fish, reduce drag, and allow reduced bycatch (Dickson 1962; Naidu et al. 1987) yet they may injure or kill fish. Fish escape through the large mesh trawls may cause delayed mortality because of the trauma of impingement or passing through the trawl body (Chopin and Arimoto 1994). Because there were two mesh sizes in the Missouri trawl, smaller fish that passed through the standard trawl portion of the Missouri trawl remained separate from large debris and larger fish. This design prevents unnecessary damage by the impingement of larger fish
16
or debris on smaller fish. Matsushita and Shida (2001) noted separation of marine debris by selective gear (e.g., small mesh panels) avoided much damage to the catch. This is extremely important when there is potential for encountering an endangered species (e.g., S. albus) while trawling. The Missouri trawl proved effective in the ORFS reach, consequently I tested its efficacy in several other areas. Sample sizes were too low to include in any analysis, but the data provided meaningful results. For example, in 2001 I captured M. gelida in the Platte River, Nebraska using the Missouri trawl. This species had not been detected using other sampling gear during the previous 9 years (Ed Peters personal communication). As a result, a smaller version of this trawl was used to complete a Master thesis on chubs in the Lower Platte River, Nebraska (Kopf 2003). Also, in 2001, I captured stonecat (Noturus flavus) in Pool 4 of the Upper Mississippi River using the Missouri trawl. This species was represented previously by single collections in 1993, 1994, 1995 (Steve Delain personal communication). In addition, Bowler (in press) used the Missouri trawl in Pool 13 of the Mississippi River to capture freckled madtom (Noturus nocturnus)--an Iowa endangered species. The species was previously captured in few areas prior to these collections and records for Iowa in the Mississippi River are from 1989 in Pool 14. Furthermore, sampling was conducted in Cedar River, IA; Pools 19, 20, 22, 24, 26 of the Upper Mississippi River; the Lower Illinois River; the Middle and Lower Missouri River; the Lower Mississippi River at locations from Cairo, Ill to Vicksburg, MS; and in the Pascagoula River, MS. The efficacy of the Missouri trawl has been tested in many areas and may provide utility to future researchers.
17
CONCLUSION It is important to address how many species are being captured as well as the total number of each species when using a single gear to sample a fish community. Many sampling protocols are designed to capture species-specific information using best methods and are effective tools for resource managers. However, sampling gear that is effective for multiple species and diverse areas provides more utility per unit effort. I have shown that the Missouri trawl is a practical method for sampling fish communities in different sized river systems. The advantages of this trawl include low equipment cost, simple operation, and improved capture of fish species and abundance compared to a 19.05 mm mesh body two-seam slingshot balloon trawl with 3.18 mm codend mesh. This methodology will improve the effectiveness of benthic fish community sampling in moderate to large river systems.
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Figure 1. Long Term Resource Monitoring Program, study area of the Upper Mississippi River monitored by the Open River Field Station. This reach extends from RK 48 to RK 129. River KM 129
Cape Girardeau
Mi d dl
e s M i
si
ss
i
p
pi
R
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(M
M R
R
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)
i v
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i o
O
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N W
E S
River KM 48
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Figure 2. Modified two-seam balloon trawl (Missouri trawl) sketch illustrating the individual components (Illustration not to scale).
20
Figure 3. Digital image showing the small mesh cover (4.76 mm) wrapped over the standard trawl body (19.05 mm) mesh.
21
Figure 4. Results of the logistic regression showing cumulative probability of capture against length for the standard trawl portion of the Missouri trawl ( ▲=codend observed: ● =cover observed). Codend curve and cover curve are indicated by the solid lines. 1
Cumulative probability of capture
0.8
0.6 Codend curve Cover curve Codend Observed Cover Observed 0.4
0.2
0 0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 length (cm)
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Figure 5. Results of the logistic regression showing cumulative probability of capture against length for the standard trawl without cover (▲=codend w/cover observed: ● =codend w/o cover observed). Codend curves, with and without cover, are indicated with solid lines. 1
Cumulative probability of capture
0.8
0.6 Cod with cover curve Cod without cover curve Cod with cover Observed Cod without cover observed
0.4
0.2
0 0
10
20
30
40 length (cm)
50
60
70
23
Figure 6. Comparison of the rate of fish species captured after 100 samples using the standard mesh trawl (grey line) and Missouri trawl (black line) in the Open River Field Station reach of the Upper Mississippi River. Solid lines represent cumulative number of fish species captured at selected sampling intervals. 45 n=40
40
35
Number of species
30 n=25
25
20
15
10
5
0 0
5
10
15
20
25
30
35
40
45
50
55
60
Number of samples
65
70
75
80
85
90
95
100
24
Table 1. Species captured using a modified two-seam balloon trawl (i.e., Missouri trawl) and X2 values associated with abundance comparison of codend and cover. Total Catch Common name
Scientific Name
Cover Codend
X2
P
0
.
ACIPENSERIDAE Pallid sturgeon
Scaphirhynchus albus
2
0
Shovelnose sturgeon
Scaphirhynchus platorynchus
22
83
Larval sturgeon
Scaphirhynchus spp.
26
0
Polyodon spathula
181
24
Lepisosteus platostomus
0
4
0
.
Goldeye
Hiodon alosoides
22
8
6.53
