Environmental Engineering Reference
In-Depth Information
Thompson et al., 2008). Because the transport of planktonic (drifting) life stages is
affected by water velocity (DiBacco et al., 2001; Epifanio, 1988), localized reduction
of water velocities by large, multi-unit projects could influence recruitment of some
species. A variety of aquatic organisms use magnetic, chemical, and hydrodynamic
cues for navigation (Cain et al., 2005; Loghmann et al., 2008a). Thus, in addition
to mechanical obstructions, the electrical and magnetic fields and current and wave
alterations produced by energy technologies could interfere with local movement or
long-distance migrations.
Alteration of Local Movement Patterns
Anchors and other permanent structures on the bottom will create new habitats and
thus may act as artificial reefs (Wilhelmsson et al., 2006). Artificial reefs are often
constructed in order to increase fish production, but some studies suggest that they
may be less effective than natural reefs (Carr and Hixon, 1997) and that they may
even have deleterious effects on reef fish populations by stimulating overfishing and
overexploitation (Grossman et al., 1997).
Similarly, new structures in the pelagic zone (e.g., pilings or mooring cables for
floating devices) will create habitat that may act as fish aggregation/attraction devices
(FADs). These devices are extremely effective in concentrating fish and making them
susceptible to harvest (Dempster and Tacquet, 2004; Michel et al., 2007; Myers et
al., 1986). Sea turtles are also known to be attracted to floating objects (Arenas and
Hall, 1992). Fish are attracted to the devices as physical structures/shelter, and they
may feed on organisms attached to the structures (Boehlert et al., 2008). Artificial
lighting used to distinguish structures at night may also attract aquatic organisms.
The aggregation of predators near FADs may adversely affect juvenile salmo-
nids or Dungeness crabs moving through the project area. Wilhelmsson et al. (2006)
found that fish abundance in the vicinity of monopiles that supported wind turbines
was greater than in surrounding areas, although species richness and diversity
were similar. Most of the fish they observed near the structure were small (juvenile
gobies), which may in turn attract commercially important fish looking for prey.
Dempster (2005) observed considerable temporal variability in the abundance and
diversity of fish associated with FADs moored between 3 and 10 km offshore. The
variability was often related to the seasonal appearance of large schools of juve-
nile fish. Fish assemblages differed between times when predators were present or
absent; few small fishes were observed near the FADs when predators were present,
regardless of the season. Using FADs as an experimental tool, Nelson (2003) found
that fish formed larger, more species-rich assemblages around large FADs compared
to small ones, and they formed larger assemblages around FADs with fouling biota.
Devices enriched with fish accumulated additional recruits more quickly than those
in which fish were removed.
It is likely that floating wave energy devices will act as FADs, but the effect on
fish populations may be difficult to determine. FADs are attractive to fish because
they provide food and shelter (Castro et al., 2002); subsequently, they also attract
predators (Dempster, 2005) that can in turn attract commercial and sport fisher-
ies. Without well-designed monitoring, it will be difficult to determine whether an
energy park will enhance populations of aquatic organisms (by providing more
