2007 Status Review of Atlantic sturgeon - National Marine Fisheries ...

Merrimack) have been severely impacted by dams, as access to large portions of historical
sturgeon spawning habitat have been eliminated or restricted. This may be the primary cause of
the extirpation of several subpopulations. 21 Thus, it warrants consideration when assessing the
extinction risk of subpopulations that are currently impacted by loss of accessible spawning
habitat.
3.1.2. Dredging and Blasting
Riverine, nearshore, and offshore areas are often dredged to support commercial shipping and
recreational boating, construction of infrastructure, and marine mining. Dredging activities can
pose significant impacts to aquatic ecosystems by removing, disturbing, disposing, and
resuspending bottom sediments, modifying substrate and impacting the community structure of
benthic macrofauna. Environmental impacts of dredging include the following: direct
removal/burial of organisms; turbidity/siltation effects; contaminant resuspension;
noise/disturbance; alterations to hydrodynamic regime and physical habitat and actual loss of
riparian habitat (Chytalo 1996, Winger et al. 2000). According to Smith and Clugston (1997),
dredging and filling impact important habitat features of Atlantic sturgeon as they disturb benthic
fauna, eliminate deep holes, and alter rock substrates. Nellis et al. (in press) documented similar
impacts as dredge spoil was documented to drift 12 km downstream over a 10 year period in the
Saint Lawrence River, and those spoils have significantly lower amounts of macrobenthic
biomass compared to control sites. Using an acoustic trawl survey, researchers found that
Atlantic and lake sturgeon were substrate dependent and avoided spoil dumping grounds
(McQuinn and Nellis, In Press). Similarly, Hatin et al. (In press) tested whether dredging
operations affected Atlantic sturgeon behavior by comparing CPUE before and after dredging
events in 1999 and 2000. The authors documented a three to seven-fold reduction in Atlantic
sturgeon presence after dredging operations began, indicating that sturgeon avoid these areas
during operations.
Indirect impacts to sturgeon from either mechanical or hydraulic dredging include destruction of
benthic feeding areas, disruption of spawning migrations, and deposition of resuspended fine
sediments in spawning habitat. In addition to these indirect impacts, hydraulic dredging can
directly harm sturgeon by lethally entraining fish up through the dredge drag-arms and impeller
pumps. Dickerson (2005) summarized observed takings of sturgeon from dredging activities
conducted by the ACOE; overall 24 sturgeon (2 – Gulf, 11 – Shortnose, and 11 – Atlantic
sturgeon) were observed during the years of 1990-2005 (Table 8). Of these 24 sturgeon
captured, 15 (62.5%) were reported as dead. Overall take during this time can be partially
calculated as 100% of hopper dredges have been observed since 1995 during seasonal
restrictions for shortnose sturgeon and sea turtles, with an unknown proportion of hydraulic
pipeline and bucket-and-barge dredging operations being observed (Dena Dickerson, USACOE-
ERDC, Pers. Comm. 2006). The SRT calculated a minimum take of 0.6 Atlantic sturgeon per
year, based simply on hopper dredge takes since 1995 and that dredging efforts were relatively
similar among years (USACOE 2006). It should be noted that all Atlantic sturgeon takes
associated with dredging projects may not have been observed because seasonal restrictions for
21 Within this report a subpopulation is considered a population unit of the species range or its DPS and is
sometimes used interchangeably with the term population when referring to specific population units (e.g., Hudson
River Population = Hudson River subpopulation)
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