Dredging activity and associated sound have negligible effects on adult Atlantic sturgeon migration to spawning habitat in a large coastal river

Abstract

Dredging is considered a major threat/impedance to anadromous fish migrating to spawning habitat. Due to the perceived threat caused by dredging, environmental windows that restrict dredge operations are enforced within many rivers along the east coast. However, it is generally unknown how anadromous fish react to encountering an active dredge during spawning migrations. Atlantic sturgeon (ATS) are an endangered, anadromous species along the Atlantic slope of North America. To determine if and how an active dredge may affect ATS spawning migration, a Vemco Positioning System array was deployed around an active hydraulic-cutterhead dredge that adult ATS must traverse to reach spawning habitat in the James River, VA. Telemetry data showed that all ATS that entered the study area survived. ATS that migrated upstream during dredge operations (N = 103) traversed the dredge area and continued upstream to spawning habitat. Many ATS made multiple trips through the study area during dredge operations. There was no noticeable difference in swim behavior regardless of whether the dredge was absent or working within the study area. We suggest that dredging in the lower James River does not create a barrier for adult ATS migrating to spawning habitat or cause adults to significantly modify swim behavior. This is the first study to utilize fine-scale telemetry data to describe how an organism moves in relation to an active dredge. This methodology could be used to describe dredge-sturgeon interactions on different life stages and in other locations and could be expanded to other aquatic organisms of concern.

Juvenile Atlantic Sturgeon Survival and Movement in Proximity to an Active Cutterhead Suction Dredge

“…Results of the present study are summarized in Table 4 and supplement those of a previous study by Balazik et al [10] in which survival and movements of adult ATS in the James River were examined. In that study fine spatial scale telemetry was used to follow the migration of 103 tagged adult ATS upstream to spawning habitat while a CSD was operating in the Dancing Point reach of the river.…”

“…Collectively 298 transits of the dredge were recorded with no indication of altered swimming speed or degree of meandering. Popper and Calfee [32] noted that Balazik et al [10] did not collect concurrent underwater sound data, as is the case for the present study. However, in tandem the two studies provide strong evidence that the presence of an active CSD did not affect survival or movements of either juvenile or adult ATS.…”

“…ATS are a long-lived species with a relatively high generation time making recovery from low numbers a slow process [3,4,5,6,7]. A number of obstacles to the recovery of ATS have been identified, with navigation dredging being listed as a potential threat by altering habitat and macroinvertebrate communities [5,6], hydraulic entrainment [8], and impediments to migration [9,10]. Research into how sturgeon species might be affected by dredging operations is very limited.…”

“…No evidence of injury, mortality or migratory impairment was observed. In a later study based on telemetry of 1m position accuracy, Balazik et al [10] similarly showed that CSD had no noticeable effect on ATS migrating to spawning habitat in the James River, Virginia.…”