Abundance of Fishes in the Navigation Channels of the Mississippi and Illinois Rivers with Implications for Estimation of Entrainment Mortality Caused by Towboats

ID: 8834; issued December 1, 1998INHS Technical Report prepared for Office of Resource Conservation, Illinois Department of Natural Resource

Estimating Mortality Rates of Adult Fish From Entrainment Through the Propellers of River Towboats

We developed a method to estimate mortality rates of adult fish caused by entrainment through the propellers of commercial towboats operating in river channels. The method combines trawling while following towboats (to recover a fraction of the kills) and application of a hydrodynamic model of diffusion (to estimate the fraction of the total kills collected in the trawls). The sampling problem is unusual and required quantifying relatively rare events. We first examined key statistical properties of the entrainment mortality rate estimators using Monte Carlo simulation, which demonstrated that a design-based estimator and a new ad hoc estimator are both unbiased and converge to the true value as the sample size becomes large. Next, we estimated the entrainment mortality rates of adult fishes in Pool 26 of the Mississippi River and the Alton Pool of the Illinois River, where we observed kills that we attributed to entrainment. Our estimates of entrainment mortality rates were 2.52 fish/km of towboat travel (80% confidence interval, 1.00-6.09 fish/km) for gizzard shad Dorosoma cepedianum, 0.13 fish/km (0.00-0.41) for skipjack herring Alosa chrysochloris, and 0.53 fish/km (0.00-1.33) for both shovelnose sturgeon Scaphirhynchus platorynchus and smallmouth buffalo Ictiobus bubalus. Our approach applies more broadly to commercial vessels operating in confined channels, including other large rivers and intracoastal waterways

A Comparison of Shoreline Seines with Fyke Nets for Sampling Littoral Fish Communities in Floodplain Lakes

We compared shoreline seines with fyke nets in terms of their ability to sample fish species in the littoral zone of 22 floodplain lakes of the White River, Arkansas. Lakes ranged in size from less than 0.5 to 51.0 ha. Most contained large amounts of coarse woody debris within the littoral zone, thus making seining in shallow areas difficult. We sampled large lakes (greater than 2 ha) using three fyke nets; small lakes (less than 2 ha) were sampled using two fyke nets. Fyke nets were set for 24 h. Large lakes were sampled with an average of 11 seine hauls/ lake and small lakes were sampled with an average of 3 seine hauls/lake, but exact shoreline seining effort varied among lakes depending on the amount of open shoreline. Fyke nets collected more fish and produced greater species richness and diversity measures than did seining. Species evenness was similar for the two gear types. Two species were unique to seine samples, whereas 13 species and 3 families were unique to fyke-net samples. Although fyke nets collected more fish and more species than did shoreline seines, neither gear collected all the species present in the littoral zone of floodplain lakes. These results confirm the need for a multiple-gear approach to fully characterize the littoral fish assemblages in floodplain lakes. © Copyright by the American Fisheries Society 2007

Comparison of Gears for Sampling Littoral‐Zone Fishes in Floodplain Lakes of the Lower White River, Arkansas

Gear comparison studies are useful to fisheries managers because many aquatic systems require multiple gears to assess fish assemblages. Many previous studies have emphasized comparisons of catch per unit effort or basic community measures such as richness and diversity. Our objectives were to (1) compare fish assemblage richness, diversity, and evenness across sampling gears, (2) assess the similarity of fish assemblage structure as depicted by the different gears, and (3) compare fish assemblage-environment relationships depicted by the different gears. Assessments were conducted in littoral-zone areas of 16 floodplain lakes in the lower White River, Arkansas. Four sampling gears were used: 500-V, 60-Hz (highpulse) and 1,000-V, 15-Hz (low-pulse) boat-mounted nighttime electrofishing, mini-fyke nets, and experimental gill nets. Species richness and diversity were significantly greater using boat-mounted electrofishing (both pulses) than the other gears. Experimental gill nets exhibited the lowest richness of all gears (less than 50% of the other gears), and mini-fyke nets exhibited significantly lower evenness owing to the tendency for 1-2 species to dominate catches. Procrustean analyses indicated that the lake-specific fish assemblages depicted by the different gears were significantly different during all paired-gear comparisons except between the two electrofishing configurations. Regardless of gear, multivariate direct gradient analyses indicated that lake depth, water clarity, and morphoedaphic index were consistently important variables associated with the structuring of littoral-zone fish assemblages. The results support the idea that multiplegear approaches are useful in assessing floodplain lake fish assemblages and that, in the case of lower White River floodplain lakes, the assemblage information collected from the different gears was not redundant. Additionally, if a large-river sampling program is using only one or two gears, major fish-environment relationships that are depicted may not be gear dependent. © by the American Fisheries Society 2010