. Bulletin. Natural history; Natural history. \ug., 1975 Spabks & Starrett: Electrofishing Survey of Illinois River 321. 6 NOVEMBER 1953 MILE MID-CHANNEL OXYGEN O O SURFACE A MID-DEPTH D n BOTTOM i BARGE PASSAGE ⢠⢠TURBIDITY 1500 1600 CENTRAL STANDARD TIME Fig. 2.âThe effects of towboat passage on dissolved oxygen concentrations and turbidity it the same location on 6 November, 1963. The symbols are the same as in Fig. 1. situ oxygen demand, and could logi- ;ally be equated to the effects of dis- iirbances created by barges (Butts 1974:6). It is not knowTi why oxygen levels ncrease
. Bulletin. Natural history; Natural history. \ug., 1975 Spabks & Starrett: Electrofishing Survey of Illinois River 321. 6 NOVEMBER 1953 MILE MID-CHANNEL OXYGEN O O SURFACE A MID-DEPTH D n BOTTOM i BARGE PASSAGE ⢠⢠TURBIDITY 1500 1600 CENTRAL STANDARD TIME Fig. 2.âThe effects of towboat passage on dissolved oxygen concentrations and turbidity it the same location on 6 November, 1963. The symbols are the same as in Fig. 1. situ oxygen demand, and could logi- ;ally be equated to the effects of dis- iirbances created by barges (Butts 1974:6). It is not knowTi why oxygen levels ncreased slightly at the bottom on 6 SJovember, and at mid-depth on 7 *>Iovember, following passage of tow- Doats. It may be that turbulence from owboats results in uneven mixing of parcels of water aerated by turbulence vith parcels of water deoxygenated by esuspended sediment. The water temperatures in Starved â lock, Marseilles, and Dresden Pools vere generally higher than in the upper )art of Peoria Pool, even though the eadings in the upper pools were taken I weeks later and the weather had umed colder. The upper river is evi- lently warmer because of warm in- lustrial and municipal discharges. Star- ett (1971:370-373) reported the same trend of warmer temperatures in the upper river in July and August, 1966. ELECTROFISHING RESULTS The electrofishing results for those species that were frequently taken are presented below in phylogenetic order. Shortnose Gar (Table 3) Table 3 shows that shortnose gar (Lepisosteus platostomus) were occa- sionally taken in the three downstream pools, but never taken in the three up- stream pools. Judging by the reports of commercial fishermen, shortnose gar are more abundant in the downstream pools than our records indicate, and these fish are probably less vulnerable to electric shock than other species. Although garfish are listed in the com- mercial catch from the Illinois River (Table 28) most fishermen consider them a nuisance because
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