Long before the first drop of oil or gas is extracted from
the sea bottom, there is a serious threat from offshore oil
and gas development. To begin, seismic tests are conducted
to gather information about rock formations and where or not
oil or gas might be found. Seismic testing uses air guns that
send explosive shock waves into the seabed, which then reverberate
through the marine environment. Although the direction of
the greatest sound intensity is downward, a considerable amount
of energy is radiated horizontally. Seismic testing can be
heard many kilometres from the source. For example, the seismic
activity off Nova Scotia is heard off the Bahamas, several
thousands of kilometres away.
During seismic surveys, high intensity and low frequency
sounds are emitted into the marine environment. An array of
air guns, which typically include between 15 and 45 air guns,
fires shots approximately every ten to 25 seconds, twenty
four hours a day. Surveys can last several months and an area
of the ocean may have more than one seismic survey performed
on it. Seismic testing occurs throughout the entire lifetime
the offshore oil and gas industry operates in a particular
area. For example, on the east coast of Canada, in the waters
off Newfoundland and Labrador, more than one million kilometres
of seismic have been shot between 1964 and 2002.
This deafening noise causes fish swim bladders to explode,
it kills marine larvae and disrupts the traditional migratory
paths of some fish species and marine mammals, such as whales
and dolphins. In some places, these disturbances have resulted
in reductions in commercial fish catches up to 50 percent,
and have caused whales to leave waters where they are habitually
The sounds emitted from seismic air guns travel a far distance
in the ocean environment. For example, seismic testing that
took place off the coast of Cape Breton was recorded in the
Bahamas. According to Dr. Chris Clarke, Director of the Bioacoustics
Research Program at Cornell University, seismic testing is
the modern form of exploratory dynamite, and “the air
guns represent the most severe acoustic insult to the marine
environment that [he] can imagine short of naval warfare.”
Read Dr. Clarke’s submission to the hearings on seismic
testing in Cape Breton.
Because marine mammals are extremely acoustically sensitive,
international concern has grown regarding threats of seismic
testing to marine mammals. Evidence suggests high-intensity
sound from sonar and air guns leads to strandings and subsequent
mortality of beaked whales. Meanwhile, other species of marine
mammals have shown a tendency to react to seismic testing.
The critically endangered Sakhalin gray whale population in
the western North Pacific has been found to react to seismic
surveys at distances greater than 30 kilometres, and high
levels of seismic surveys in that region seem to have displaced
the whales from their critical habitat.
more about the impacts of seismic testing on the Sakhalin
gray whale population.
A recent DFO study on the impact of seismic testing on the
snow crab found crabs had damaged ovaries and internal organs.
Changes were also observed in crab behaviour, while some lost
the entire DFO study.
For further reading on the impacts of
seismic testing check out the reports in our library.