Tiakina Te Moana

Impacts of Seismic Surveys on Marine Mammals and Fish

What are seismic surveys?

Seismic surveys are used by the offshore oil and gas industry to help determine the location of oil and gas

deposits beneath the seafloor. These surveys utilize large, specialized ships which tow an array of powerful

air guns that generate sound waves by firing off explosive blasts of air. The sound waves are reflected off

the seafloor and create a picture of underwater geological formations.

A typical seismic survey lasts 2-3 weeks and covers a range of about 300-600 miles. The intensity of sound

waves produced by the firing of seismic air guns can reach up to 250 decibels (dB) near the source and can

be as high as 117 dB over 20 miles away. The sound intensity produced by a jackhammer is around 120

dB, which can damage human ears in as little as 15 seconds.

What impacts can seismic surveys have on marine mammals?

Unlike humans and other terrestrial animals, marine mammals rely on sound instead of sight as their

primary sense. Dolphins, whales and seals utilize their sense of hearing to locate prey, avoid predators,

choose migration routes, and to communicate across long distances. The noise associated with seismic

surveys can affect the ability of these animals to detect natural underwater sounds, thereby disrupting these

critical activities.

Numerous scientific studies have solidified what Eskimo subsistence hunters have known for years: that

whales avoid expansive areas where seismic surveys are being conducted. One recent study showed that

fall-migrating bowhead whales in the Beaufort Sea were displaced from an area within 12 miles of the

seismic source and began to show avoidance behavior up to 21 miles away. Researchers have also observed

signs of physical stress such as startle responses in humpback whales while seismic surveys were being

conducted many miles away (see Figure 1 below).

Scientists believe that pods of whales that include calves are at serious risk from seismic activities due to

their need to utilize critical habitats for feeding and resting. If seismic surveys continually displace whales

from these important areas, population-level consequences may result. Dr. Barret-Lennard, Senior Marine

Mammal Researcher at the Vancouver Marine Science Center, has asserted that seismic exploration is one

of the two greatest threats to whales and dolphins.

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What impacts can seismic surveys have on fish?

The powerful sound waves generated by seismic surveys can have a variety of harmful effects on fish.

Within close range, seismic surveys have been found to kill adult fish as well as larvae and fish eggs.

Scientific studies have also shown that air gun blasts can cause a variety of sublethal impacts on fish such

as damaging orientation systems and reducing their ability to find food. Researchers have noted

disturbances in the migration routes of salmon and other anadromous species as a result of seismic

operations.

Seismic surveys can cause physical damage to fish ears and other tissues and organs such as swim bladders.

Although such effects may not kill fish immediately, they may lead to reduced fitness, which increases

their susceptibility to predation and decreases their ability to carry out important life processes.

Furthermore, if important prey species in the food web such as squid and zooplankton are harmed by

seismic testing, the fish dependent on these creatures may also be negatively affected.

Proponents of offshore oil and gas production often argue that overall impacts of seismic surveys on fish

are negligible. However, Stanislav Patin, an international expert on the environmental impacts of offshore

oil and gas development, has warned that “…there seems to be no reason for the optimism that is

sometimes expressed regarding the ecological safety of seismic surveys and their harmlessness to fish

resources.”

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(over please)How do seismic surveys impact fishing efforts?

Seismic surveys not only threaten commercial and subsistence fishing by harming fish resources, but also

by interfering with fishing operations and dramatically affecting catch rates. Seismic ships tow streamers

that can be miles long. These can get tangled up with crab pots, set nets and trawl nets causing damage and

decreasing crucial fishing time. The best time to conduct seismic surveys in Arctic environments is during

the summer, which is also prime season for many Alaskan fisheries. As a result, seismic survey operations

can end up competing with fishing for time and space on the water.

Even if these kinds of conflicts can be avoided, several studies have shown that seismic operations have

greatly reduced catches of fish around areas where air guns were being fired. These studies have

demonstrated reduced catches over 20 miles away from the source with catch reductions continuing five

days after the testing was complete (See Table 1 below). Researchers believe these catch reductions are a

result of altered fish behavior due to seismic operations which cause them to be less likely to take hooks

and/or to move down and away from the seismic firing.

Table 1: Reductions in fish catch rates as a result of seismic survey activity

Species Gear type Noise level of

seismic testing

Catch reduction Source

Atlantic cod

(Gadus morhua)

Trawl 250 decibels (dB) 46-69% lasting at least

5 days

Engas et al. 1993

Atlantic cod

(Gadus morhua)

Longline 250 dB 17-45% lasting at least

5 days

Engas et al. 1993

Atlantic cod

(Gadus morhua)

Longline Undetermined, 9.32

miles from source

55-79 % lasting at least

24 hours

Lokkeborg and Soldal, 1993

Haddock

(Melanogrammus aeglefinus)

Trawl 250 dB 70-72% lasting at least

5 days

Engas et al. 1993

Haddock

(Melanogrammus aeglefinus)

Longline 250 dB 49-73% lasting at least

5 days

Engas et al. 1993

Rockfish

(Sebastes spp.)

Longline 223 dB 52%- effect period not

determined

Skalski et al., 1992