In 2012, all populations of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus were listed as either threatened or endangered under the U.S. Endangered Species Act. During 2007–2010, researchers documented 31 carcasses of adult Atlantic sturgeon in the tidal freshwater portion of the James River, Virginia. Twenty‐six of the carcasses had gashes from vessel propellers, and the remaining five carcasses were too decomposed to allow determination of the cause of death. The types of vessels responsible for these mortalities were not explicitly demonstrated. Most (84%) of the carcasses were found in a relatively narrow reach that was modified to increase shipping efficiency. To explore the number of Atlantic sturgeon being hit and their horizontal and depth distributions in relation to vessel draft, we conducted telemetry experiments on three living fish (all males) and six dead specimens. While staging (holding in an area from hours to days, with minimal upstream or downstream movements), the adult male Atlantic sturgeon spent most (62%) of the time within 1 m of the river bottom. Assuming that behavior is not modified by vessel noise, adult male Atlantic sturgeon in the James River would rarely encounter small recreational boats or tugboats with shallow drafts; instead, mortalities are likely caused by deep‐draft ocean cargo ships, which have drafts that coincide with the distribution of the tracked adult males. Dead specimens (n = 6) drifted with the current for several hours to almost 4 d before beaching at distances ranging from 0.5 to over 50 river kilometers from the point of release. We estimated that current monitoring in the James River documents less than one‐third of vessel strike mortalities. A better understanding of Atlantic sturgeon behavior in the presence of vessels will aid in restoring this federally endangered species. Received February 20, 2012; accepted July 19, 2012

Sound recordings were made of two dredging operations at hydrophone depths of 3 and 9.1 m at distances up to 1.2 km from the source in shallow waters (<15 m) of New York Harbor. Sound sources included rock fracturing by a hydraulic cutterhead dredge and six distinct sources associated with a mechanical backhoe dredging operation during rock excavation. To place sound emitted from these dredges in perspective with other anthropogenic sounds, recordings were also made of several deep-draft commercial vessels. Results are presented as sound pressure levels (SPLs) in one-third octave versus range across the 20 Hz to 20 kHz frequency band. To address concerns for protection of fishery resource occupying the harbor, SPL were examined at frequency bands of 50-1000 Hz and 100-400 Hz, the ranges where the majority of fishes without hearing specializations detect sound and the range of greatest sensitivity, respectively. Source levels (dB re 1 μPa-1 m rms) were back calculated using fitted regression (15LogR). The strongest sound sources (180-188.9 dB) were emitted by commercial shipping. Rock fracturing produced a source level of 175 dB, whereas six distinct sources associated with rock excavation had source levels ranging from 164.2 to 179.4 dB re 1 μPa-1 m (rms).

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Underwater sounds were characterized for three trailing suction hopper dredges (TSHD) during the removal of 3.1 million yd 3 of sand from an offshore borrow area and during offloading of the escavated sediment at the pump-out stations in support of the Wallops Island, Virginia Beach Stabilization Project. Sounds were recorded simutaneoulsy at two depths, 3 and 9.1 m from the surface. Sound sources included sediment removal, pump-out of material, pump-out of clear water during pipe flushing, and transit to the borrow site (hopper empty) and to the pump-out stations fully loaded. Received and 1/3-octave Sound Pressure Levels (dB re 1 µPa, rms) are reported for each sound source. Source Levels (dB re 1µPa-1m, rms) were back-caculated using fitted regression (15.788LogR). Source Levels (SL) ranged from 161.3 dB to 176.7 dB re 1µPa-1m rms. Highest SL were obtained for the dredge Liberty, which is nearly twice the size (e.g. hopper volume, displacement) of the dredges Padre and Dodge Islands. Sounds emitted during transit produced the highest SL, whether the hopper was empty or full. Attenuation to ambient was dependent on the sound source, and ranged from 0.85 km (flushing pipes) to 2.65 km during transit with the hopper at maximum capacity.

This report assesses potential impacts to aquatic resources resulting from proposed navigation channel expansion activities within Mobile Bay, Alabama. This work was conducted for the U.S. Army Corps of Engineers (USACE) Mobile District, to support development of a supplemental Environmental Impact Statement. Changes in water quality and hydrodynamics were evaluated for potential impacts to benthic macroinvertebrates, wetlands, submerged aquatic vegetation, oysters, and fish. The assessment includes extensive characterization of baseline conditions, evaluation of estimated post-project conditions related to aquatic resource habitat (e.g., changes in salinity, dissolved oxygen). An analysis of potential impacts related to a 0.5-m sea level rise (SLR) scenario were also evaluated. Results suggest that no substantial impacts in aquatic resources within the study area are anticipated due to project implementation, as the area of greatest potential changes to environmental conditions are already adapted to natural shifts in salinity (and other factors), and to conditions resulting from the existing navigation channel. Although SLR has the potential to alter aquatic resource habitats with Mobile Bay, additional impacts related to project implementation remain negligible under the 0.5-m SLR scenario. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.