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Mississippi-B1 301 STATUS AND MANAGEMENT OF MISSISSIPPI RIVER FISHERIES H.L. Schramm Jr. U.S. Geological Survey, Mississippi Cooperative Fish and Wildlife Research Unit Mississippi State, Mississippi 39762 USA E-mail: hschramm atcfr.msstate.edu ABSTRACT The Mississippi River has been variously altered for navigation and flood control but supports a diverse and rel- atively productive fish assemblage. In the upper, impounded reach, commercial fish harvest has increased for most species since 1945. The upper reach provides an extensive and moderately used recreational fishery resource. Limited information for the lower, un-impounded reach of the Mississippi River indicates commercial harvest is increas- ing. Neither the commercial nor recreational fisheries appear to be over harvested; however, fisheries for sturgeon and paddlefish should be carefully monitored. Future fish- eries production may be threatened by loss of aquatic 302 Status and management of habitat, altered spatial and temporal aspects of flood- ured in the lower river at Vicksburg, Mississippi) plain inundation and nuisance species invasions. Water ranges from 3 568 to 55 558 m3 s-1 and averages 17 358 quality in most reaches has improved substantially m3 s-1. The Mississippi and its major tributaries - the from formerly severely degraded conditions. Arkansas, Illinois, Missouri and Ohio rivers - have Navigation traffic affects fish survival and recruitment been central to the social and economic development and increases in navigation are forecast. Future conser- of the United States. As a major transportation corri- vation and management of the fisheries and aquatic dor, the river has been greatly altered for navigation resources of the Mississippi River will require substan- and by developments in its watershed and floodplain tial investment in effective assessment programs and for agriculture, industry and urbanization. achieving societal recognition of the diverse values of Comprehensive treatments of the historic and present the resource. conditions in the Mississippi River are provided in INTRODUCTION Scarpino (1985); Fremling et al. (1989); Baker, Killgore and Kasul (1991); Rasmussen (1994); Weiner The Mississippi River is the largest river in et al. (1998); U.S. Geological Survey (1999) and North America. Its 3.25 million km2 watershed Fremling and Drazkowski (2000). includes parts of two Canadian provinces and parts or all of 31 U.S. states (Figure 1). Daily discharge (meas- Figure 1. Mississippi River basin and Mississippi River. Mississippi River basin figure from Meade (1995). Mississippi river fisheries 303 Ten thousand years ago, the Mississippi River The Upper Mississippi River (UMR) reach was a continuum typical of a floodplain river. stretches 1 075 km from St. Anthony Falls to Alton, Beginning as a small stream in the forested headwaters Illinois, a few km above the confluence with the of Lake Itasca, Minnesota, the river flowed through Missouri River1. The UMR is impounded by 28 locks virgin forests and unbroken prairie to its deltaic outlet and dams built for commercial navigation and one dam into the Gulf of Mexico in Louisiana. From headwaters (Keokuk, Iowa) built for navigation and hydropower to the mouth, the river increased in size and discharge generation. These dams are operated to maintain mini- and decreased in slope. Initially, the young river mum navigation channel depth (9 feet, 2.7 m); thus, flowed through a small valley bordered by wetlands the dams have little effect on the river stage and dis- and lakes. Along its downstream course, the river charge during spring floods. The dams, however, have changed from a single to a braided channel in its mid- increased the river elevation throughout the annual reaches and finally to a meandering, constantly chang- cycle (Figure 2). The timing and relative increase dur- ing channel downstream. Its valley changed rather ing the spring rise resembles the pre-dam condition, steadily from a narrow floodplain flanked by tall bluffs but the natural summer drawdown and the autumn rise upstream to a vast, flat floodplain downstream. are missing. Throughout the UMR, the dams have increased the area of aquatic habitat at low-water river In its present form, the Mississippi River stage from 971 km2 before dams to 1 495 km2 after changes dramatically and rather incrementally along dam construction, essentially permanently inundating its 3 731 km journey from headwaters to the Gulf of 23 percent of historic wetlands and seasonally inundat- Mexico. The headwaters reach, the upper 824 km from ed floodplain (49 km2 of marsh and 820 km2 of flood- Lake Itasca to St. Anthony Falls, Minnesota, flows plains; J. Rogala, U.S. Geological Survey, unpublished alternately through forests and wetlands. Dams have data). Navigation channel depth and alignment in the been built to form 11 small reservoirs and modify the open river is maintained by wing dykes2, closing elevation and discharge of several natural river lakes. dykes3, bank revetment4 and dredging. Most of these These dams variously function for flood control, elec- structures are remnants of the former channel before tric generation, water supply, or recreation. impoundment, but some are new and many require 1 Terminology for different reaches of the Mississippi River is not uniform among different management agencies. For example, the Upper Mississippi River Conservation Committee defines the UMR as the reach of the Mississippi River from St. Anthony Falls, Minnesota, to the confluence with the Ohio River at Cairo, Illinois. The terminology adopted in this paper was chosen for its ecolog- ical utility. 2 Wing dikes are large rock riprap structures that extend from the shore into the main channel. The surface elevation of most dikes is 2-3 m above low water elevation in the MMR and LMR. In the UMR, dikes constructed before impoundment remain in place and, for the most part, remain at or below normal navigation pool surface elevation. The dikes are placed to divert the flow of water, there- by both controlling the path of the main channel and directing the energy to scour the navigation channel. Usually multiple dikes are placed in a longitudinal series, with shorter dikes upstream; these groups of three or more dikes are called dike fields. 3 Closing dikes, like wing dikes, are large rock riprap structures placed to block or reduce flow to a secondary channel or backwa- ter, thereby increasing flow in the main channel. The main channel contains the thalweg and is used for navigation. Secondary chan- nels are former main channels or channels created when the flow of the river cuts across a point bar forming a new channel. Dike fields often are used to close secondary channels and backwaters. 4 Revetments are installed on high energy banks to armor the river bank against erosion. Although various materials have been used in the past, present-day revetments consist of large (>0.3 m) rock riprap or, in the LMR, articulated concrete mattress (concrete slabs approximately 30 cm x 70 cm x 7 cm thick connected by stainless steel wire) for lower bank (from 1-3 m above low water elevation to the toe of the channel) protection and large rock riprap for upper bank protection. 304 Status and management of Figure 2. Average stage at Upper Mississippi River Lock and Dam 15 tailwaters, Rock Island, Illinois. 1900-1925 is pre-impoundment; 1940-2002 is post-impoundment. routine maintenance. The navigation channel retains Mexico. The 314 km reach from the mouth of the substantial flow even during low river stages; howev- Missouri River to the mouth of the Ohio River is er, flows through aquatic habitats lateral to the naviga- referred to as the Middle Mississippi River (MMR) by tion channel are greatly reduced resulting in off-chan- management agencies. Flows from the Missouri River nel sedimentation, stagnation and deep-water habitat almost double the volume of water flowing through the loss. Because the dams, to maintain a minimum navi- MMR (Meade 1995). The 1 570 km reach from the gation depth, dampen drawdown, less floodplain is Ohio River to Head of Passes is referred to as the exposed during lower-flow periods and less floodplain Lower Mississippi River (LMR). Water from the Ohio area is inundated during the annual spring rise. In the River increases Mississippi River discharge 150 per- lower third of the UMR, the natural bluffs flanking the cent (Meade 1995). Although discharge and channel floodplain diminish and the floodplain expands lateral- size differ between the two reaches, both share similar ly. Here, levees and railroad embankments have been hydrologic conditions, methods and levels of channel- built relatively close to the riverbank to contain flood- ization and loss of connectivity with the historic flood- waters and reclaim fertile bottomlands for agriculture, plain. Thus, I will refer to the MMR and LMR collec- reducing the floodplain to a fraction of its former area. tively as the Aopen River reach. The MMR fluctuates an average of 4 m throughout the year (Figure 3), Downstream from the confluence of the while the LMR, influenced by Ohio River discharge Missouri River, the Mississippi flows un-dammed for (60 percent of LMR discharge), fluctuates an average 1 834 km to Head of Passes where it branches into sev- of almost 10 m (Figure 4). Nevertheless, hydrographs eral distributaries that carry water to the Gulf of of the two reaches are similar. As in the UMR, the U.S. Mississippi river fisheries 305 Army Corps of Engineers is mandated to maintain a 9- Classification of river reaches based on the feet (2.7 m) deep, 300-feet (91 m) wide navigation form and consequences of anthropogenic perturbations channel in the open river reach. To maintain access to is convenient, even desirable, from both ecological and harbours and cargo ports and to preserve waterfront management perspectives. The ecological structure developments, it is also necessary to maintain current and function of the headwaters, UMR and open river channel alignment.
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