K. Douglas Blodgett

Larval Dynamics of a Riverine Metapopulation: Implications for Zebra Mussel Recruitment, Dispersal, and Control in a Large-River System

Zebra mussels (Dreissena polymorpha) in the Illinois River are likely to function as a metapopulation (a system of local populations connected by dispersal). River currents reduce or eliminate internal recruitment by local populations, making them dependent upon external recruitment from propagules (larvae) produced by upriver populations. Because of the importance of external recruitment, understanding the population dynamics of riverine zebra mussels requires knowledge of larval flux. In 1994 and 1995, larval drift past a fixed site on the Illinois River was characterized by pulses of similar-sized individuals. These pulses were composed primarily of D-stage (straight hinge) larvae, not yet competent to settle. The continual passage of pulses of young larvae suggests that the upriver source population(s) spawned in frequent distinct bursts throughout the summer months rather than spawning only once or twice. Overall larval abundance was a poor predictor of availability of competent larvae. Although larvae were frequently present in high numbers, larvae >200 μm in shell height (competent to settle) were present only sporadically at our fixed study site from May to November in 1994, and present only from June to early July in 1995. Settlement at a given site on the Illinois River is likely to be sporadic rather than constant. Colonization and population growth at a given site will occur only if suitable habitat and environmental conditions are available during the windows when competent larvae are available. Changes in mean size as a larval cohort drifted downriver suggested a growth rate of 6.72 μm/d. At this growth rate, most larvae probably travel a minimum of 304.6 km (190.4 miles) before settling. Thus, larvae spawned in the main channel of the lower 70% of the Illinois River are most likely to settle in the Mississippi River. We suggest that colonization and population growth in the upper 70% of the Illinois River are strongly dependent upon larvae produced at upriver source sites in Lake Michigan and the Chicago area waterways. Control of zebra mussels in a given stretch of the river will depend upon control of the upriver source populations.

Winter Habitats Used by Largemouth Bass in the Illinois River, a Large River-Floodplain Ecosystem

Abstract During the winter of 1993–1994, we characterized habitats used by 17 radio-tagged largemouth bass Micropterus salmoides in La Grange Reach of the Illinois River, a large river–floodplain ecosystem that has been significantly altered from its natural state. Radio-tagged largemouth bass wintered in backwaters, off-channel coves, ditches, and marinas from November through February. Electrofishing mean catch rates were higher in the study areas during winter than in other seasons, indicating fish were more concentrated in these areas during winter. Five of nine study areas received thermal inputs from springs or power plants, but water temperatures in all nine areas were warmer than the main channel during winter. Current velocities averaged 2 cm/s in the study areas and 19 cm/s in the main channel. We did not document movement of radio-tagged fish into the main channel during winter. River levels played a major role in determining the suitability of wintering habitats. When river levels declined, te...

Notes: Largemouth Bass Size Distributions under Varying Annual Hydrological Regimes in the Illinois River

Abstract Little is known about the population dynamics of largemouth bass Micropterus salmoides in temperate large river–floodplain ecosystems. However, the hydrological regimes in these systems are often similar to those of large reservoirs where fluctuating water levels during spawning have been shown to affect largemouth bass population dynamics. Most backwater lakes of the Illinois River have soft, silty substrates. These substrates are not conducive to nest building, so spawning centrarchids may use annual spring floods to access inundated terrestrial vegetation and previously dry, compacted substrates on the floodplain. We used electrofishing catch data from La Grange Reach of the Illinois River (1990–1995) to assess how spring and early-summer river levels influence the cohort strength of largemouth bass. Strong cohorts were produced during years with high spring floods (1990, 1993, and 1995) when largemouth bass could access the floodplain for spawning and nursery habitat. In both 1990 and 1993, f...

Initial Occurrences of Zebra Mussels (Dreissena polymorpha) on Freshwater Mussels (Family Unionidae) in the Upper Mississippi River System

ABSTRACT The exotic zebra mussel (Dreissena polymorpha) was found attached to native freshwater mussels (Unionidae) in La Grange, Peoria, and Alton Pools of the Illinois River and Pools 4, 13, and 26 of the Mississippi River. From 1% to 27% of native bivalves collected within these pools in 1992 had one or more zebra mussels attached with the highest densities of zebra mussels found in the Illinois River. At one site in the Alton Pool of the Illinois River, 27% of native mussels had a mean of 2.2 zebra mussels attached. Densities were lower in the Mississippi River sites, ranging from 1% to 12%, with the highest density occurring below the confluence of the Illinois and Mississippi Rivers. Of the 25 native species collected, nine had zebra mussels attached. In the Alton Pool of the Illinois River, Amblema plicata longer than 82 mm had more zebra mussels upon them than A. plicata smaller than 82 mm. The large numbers of young-of-the-year zebra mussels found in the Illinois and Mississippi Rivers indicate D...

Establishment of Daphnia lumholtzi (an Exotic Zooplankter) in the Illinois River

Abstract Daphnia lumholtzi, an exotic zooplankter, recently has become established in the Illinois River. This species was first detected at Illinois River Mile (IRM) 121.1 near Havana, Illinois in June of 1995, and exhibited a peak abundance of 22.5/L in August. Population trends and densities in the Illinois River resemble those reported in lakes and reservoirs of the southeastern United States, suggesting D. lumholtzi is adaptable to lotic as well as lentic systems. Individuals were found at sampling sites as far upriver as IRM 195.9.

Post-Extirpation Recovery of the Freshwater Mussel (Bivalvia: Unionidae) Fauna in the Upper Illinois River

ABSTRACT Freshwater mussels are recolonizing the upper Illinois River following their extirpation by pollution in the early part the 20th century. From 1990 to 1999, we collected 332 individuals of 18 species between river miles 232.0 and 271.2. Age structure of the community suggests mussels began recolonizing in the early 1980s, which coincides with improvements in water quality and the upper river fish community. We found four sites with five or more species, which we considered to be recently formed mussel beds. We collected live individuals of six species (Actinonaias ligamentina, Alasmidonta marginata, Lampsilis cardium, Lasmigona costata, Pleurobema sintoxia, and Strophitus undulatus) thought to have been extirpated from the entire Illinois River mainstem, and one species (Anodonta suborbiculata) that has recently expanded its range into the upper river. Upper Illinois River tributaries and lower reaches of the Illinois River harbored source populations for the recolonizing mussels. Although the present community does not approximate the pre-disturbance fauna, these data show that given adequate time and improved conditions, mussel communities may recover from a devastating disturbance.

Application of key ecological attributes to assess early restoration of river floodplain habitats: a case study

The Nature Conservancy acquired the Emiquon Preserve along the Illinois River, Illinois, with the primary objective of restoring ecological floodplain processes and habitats that promote and sustain native species and communities. The Conservancy convened an Emiquon Science Advisory Council prior to restoration implementation that identified key ecological attributes (KEAs) for riverine and backwater targets, KEA indicators, and acceptable ranges for those indicators. We assessed the application of this methodology to evaluate status of conservation targets and to inform future science and management at Emiquon. The KEA framework provided an important function of directing a systematic monitoring program that provided fundamental data on changing environmental conditions that were incorporated into annual target evaluations. Data show that 46–55% of all indicators were within acceptable ranges prior to reconnection of the preserve with the Illinois River. Recent completion of a water control structure represents a critical intervention that provides potential to improve conservation status of those floodplain and riverine targets that depend on water management and river connectivity. Continued review and modification of the KEA model in conjunction with a strategic monitoring program will provide critical information to guide relevant management decisions and testable hypotheses to reduce potential threats and achieve future restoration goals.

Sediment toxicity in Reach 15 of the Upper Mississippi River : technical report to the Illinois Department of Natural Resources./ Denise B. Stoeckel, K. Douglas Blodgett, and Richard E. Sparks.

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