The exclusion efficiency of cylindrical wedge-wire screens was investigated at the Chalk Point Steam Electric Station in Aquasco, Maryland, by measuring entrainment of larval bay anchovies Anchoa mitchilli and naked gobies Gobiosoma bosci through screens with slot sizes of 1, 2, and 3 mm and through an unscreened intake. The degree of exclusion by the screens increased with fish size. Fish less than 5 mm long were not excluded by any of the screens. In contrast, more than 80% of larger ichthyoplankton were excluded by all screens. Virtually no ichthyoplankton larger than 10 mm were entrained through the 1-mm screen even when fish of this size were abundant and were entrained through the unscreened intake. The 2-mm and 3-mm-slot screens were not as effective at excluding ichthyoplankton as the 1-mm screen, but the effect of slot size on exclusion efficiency was small relative to the effect of fish size. These results suggest that entrainment through water intake structures can be successfully reduced by wedge-wire screens if the larval fish at risk exceed 5 mm in length.

The potential impacts of pile-driving noise on Hudson River sturgeon during construction of the New NY Bridge were predicted. Abundance data for shortnose and Atlantic sturgeon derived from fisheries sampling were combined with data about the spatial extent of pile-driving noise. This approach was used to calculate the number of sturgeon that could occur within sound level isopleths exceeding peak and cumulative noise criteria used by the National Marine Fisheries Service to determine the incidental take of sturgeon. The number of sturgeon subject to the potential onset of physiological effects during pile driving was predicted to be 35-41 fish for each species.

No abstract

A new bridge will be constructed to replace the aging Tappan Zee Bridge over the Hudson River in New York. Construction will potentially result in hydroacoustic impacts to the local fish fauna. As a consequence, a substantial environmental impact analysis had to be conducted to obtain construction permits. This paper describes the process of environmental analysis and some of the results of the studies that led up to the final permitting. The process included modeling of pile-driving acoustics, analysis of river ambient noise, analysis of test piling, and observations on fish behavior during these tests.

The National Marine Fisheries Service (NMFS) currently uses interim criteria developed on the US West Coast to assess the potential onset of peak and cumulative effects of noise on fishes. Analyses performed for this project provided adequate support for the NMFS to use the peak criterion (i.e., area ensonified by 206 dB re 1 μPa peak sound pressure level [SPL(peak)]) for estimating the incidental take of Hudson River sturgeon. Application of the peak criterion (rather than the cumulative criterion) could have implications for future construction projects because estimates of take using SPL(peak) will generally be considerably lower than estimates of take based on the cumulative sound exposure level.