Environmental Engineering Reference
In-Depth Information
Marra (1989) described the interactions of elasmobranchs with submarine optical
communications cables. The cable created an iE field (1 µV/m at 0.1 m) when sharks
crossed the magnetic field induced by the cable. The sharks responded by attacking
and biting the cable. Marra (1989) was unable to identify the specific stimuli that
elicited the attacks but suggested that at close range the sharks interpreted the electri-
cal stimulus of the iE field as prey, which they then attacked.
The weak electric fields produced by swimming movements of zooplankton can
be detected by juvenile freshwater paddlefish (
Polyodon spathula
). Wojtenek et al.
(2001) used dipole electrodes to create electric fields that simulated those created by
water flea (
Daphnia
sp.) swimming. They tested the effects of alternating current
oscillations at frequencies ranging from 0.1 to 50 Hz and stimulus intensities ranging
from 0.125 to 1.25 µA peak-to-peak amplitude. Paddlefish made significantly more
feeding strikes at the electrodes at sinusoidal frequencies of 5 to 15 Hz compared to
lower and higher frequencies. Similarly, the highest strike rate occurred at the inter-
mediate electric field strength (stimulus intensity of 0.25 µA peak-to-peak ampli-
tude). Strike rate was reduced at higher water conductivity, and the fish habituated
(ceased to react) to repetitive dipole stimuli that were not reinforced by prey capture.
Gill and Taylor (2002) carried out a pilot study of the effects on dogfish of electric
fields generated by a DC electrode in a laboratory tanks. They reported that the dog-
fish avoided constant electric fields as small as 1000 µV/m, which would be produced
by 150 kV cables with a current of 600 A. Conversely, the dogfish were attracted
to a field of 10 µV/m at 0.1 m from the source, which is similar to the bioelectric
fields emitted by dogfish prey. The electrical field created by the three-phase, AC
cable modeled by CMACS (2003) would likely be detectable by a dogfish (or other
similarly sensitive elasmobranch) at a radial distance of 20 m. It is possible that the
ability of fish to discriminate an electrical field is a function of not only the size and
intensity but also the frequency (Hz) of the emitted field.
Like elasmobranchs, sturgeon (closely related to paddlefish) can utilize electro-
receptor senses to locate prey and may exhibit varying behavior at different elec-
tric field frequencies (Basov, 1999). For this reason, electrical fields are a concern
as they may impact migration or ability to find prey. The National Marine Fisheries
Service (NMFS, 2008) proposed designating critical habitat for the Southern Distinct
Population Segment of the threatened North American green sturgeon (
Acipenser
medirostris
) along the coastline out to the 110-m isobath line. One of the principal
elements in the proposal is safe passage along the migratory corridor. Green sturgeons
migrate extensively along the nearshore coast from California to Alaska, and there is
concern that these fish may be deterred from migration by either low-frequency sounds
or electromagnetic fields created during operation of marine energy facilities.
Magnetic Fields
Many terrestrial and aquatic animals can sense the Earth's magnetic field and
appear to use this magnetosensitivity for long-distance migrations. Aquatic species
whose long-distance migrations or spatial orientation appear to involve magneto-
reception include eels (Westerberg and Begout-Anras, 2000), spiny lobsters (Boles
and Lohmann, 2003), elasmobranchs (Kalmijn, 2000), sea turtles (Lohmann and
Lohmann, 1996), rainbow trout (Walker et al., 1997), tuna, and cetaceans (Lohmann
