Does Seismic Exploration Harm Whales and Fish?
Every swimmer learns the startling efficiency of underwater sound propagation. When someone at a distance taps two rocks together, it seems to be happening next to your eardrums. Many marine creatures make and react to sounds. Whales in particular vocalize to sing, communicate, and navigate.
But what happens when man-made noises mix with those of the ocean? Millions of boat engines, the giant propellers of ships, military and commercial sonar equipment, coastal construction operations, and the drills of offshore oil rigs all pour sounds into the sea. And in recent decades, concern has mounted over oil exploration using seismic methods.
In this approach, a towed array of "airgun" releases blasts of compressed air, generating seismic pulses that penetrate the seabed. Echoes picked up by hydrophones tell commercial geologists the nature of the seabed and the likelihood of oil.
Conservationists and commercial fishermen fear that the seismic pulses will interfere with sea life. Researchers at the Bedford Institute of Oceanography (BIO) in Halifax, Nova Scotia, have tackled the issue for two Atlantic marine areas, one known for its beauty and diversity, the other for its rich fishery.
The first area, known as the Gully, lies about 150 nautical miles off Halifax, just east of Sable Island, whose many shipwrecks made it known as "the graveyard of the Atlantic." The underwater Gully, a deep indentation at the edge of the continental shelf, is winning a different kind of fame, for its ecological importance.
Dr. Kenneth Lee, head of the BIO-based Centre for Offshore Oil, Gas and Energy Research (COOGER), calls the Gully "an underwater Grand Canyon." Some 65 kilometres long, the area shelters a profusion of plants, including many deep-sea corals. It provides crucial habitat for many species of fish and marine mammals, including the northern bottlenose whale, an endangered species. The Department of Fisheries and Oceans (DFO) in 2003 made the Gully Canada's first Marine Protected Area.
The northern bottlenose whale.
Although its MPA status protects the Gully from oil and gas exploration, nearby seismic surveys can still send sound waves into the area. That's where the COOGER study comes in.
"Millions have been spent in other parts of the world to study seismic exploration," Dr. Lee says, "showing some effects under certain conditions. But studies elsewhere don't answer all our regional questions."
"Sound propagation can vary according to water temperatures, shape of the bottom, and other factors. Evaluating the effects on different creatures at different life stages can be difficult. Our research will build up data about specific effects in our area."
COOGER co-ordinates DFO's research on offshore exploration, drawing on scientists across the country. For the Gully project, Dr. Lee brought in researchers from the Institute of Ocean Sciences in Sidney, British Columbia, the Maurice Lamontagne Institute in Mont-Joli, Quebec, Newfound-land's Marine Institute, and other centres in the private sector and academia. At-sea research took place in 2003, before and during commercial surveys nearby.
"We documented the occurrence of northern bottlenose whales, to supplement earlier information on their numbers and distribution," Dr. Lee says. "We observed humpback, blue, fin, and sperm whales, along with seals and dolphins, and recorded their vocalizations and other ocean sounds under natural conditions. We have provided the scientific community with a major amount of new baseline data."
"Then we monitored what happened during seismic explorations. The energy companies have models of sound propagation. We need to validate how well they work for this area, and to document seismic effects in general."
The researchers used Ocean Bottom Seismometers and hydrophones to measure sounds. They developed new instrument-ation for monitoring noise and vocalizations in the process. Marine mammal observers also did visual observations. The study catalogued multiple aspects of sound propagation and fish and mammal behaviour.
Deploying an ocean bottom seismometer from a DFO ship during the Gully project. (DFO photo)
Researchers found no significant changes in the general distribution of Gully whales during seismic explorations. "It's not that we've ruled out all effects," Dr. Lee said. “But we've seen no evidence of the most-feared results, such as abandonment of the area.
"We're still completing our evaluation of the energy-company models. And we'll continue our research on more subtle effects of seismic explorations."
The Gully study has built a strong framework for future research. "We know better what questions to ask," Dr. Lee says, "and how to answer them."
COOGER's second major Atlantic study to date took place off the west coast of Cape Breton, home of some of the richest snow-crab grounds in the world.
When the Canada-Nova Scotia Offshore Petroleum Board allowed airgun surveys in the area, commercial fishermen feared bad effects. Previous laboratory experiments had suggested that high-energy sound could affect crab reproduction.
Dr. Mikio Moriyasu of DFO's Gulf Fisheries Centre in Moncton, New Brunswick, led COOGER's 2003 crab study in the area. The researchers captured female crabs and placed some in the path of seismic exploration, leaving others in a non-seismic control area. Ocean Bottom Seismometers monitored sound levels.
The researchers assessed the physiology of the captured crabs just after the seismic explorations took place, and again months later. All the crabs survived, with no clear damage to animals, eggs, or larvae.
"It's seemingly reassuring," Ken Lee says. "But, there is a preliminary suggestion of cell damage in some crabs in the seismic survey area, whether from the airguns or another cause. We're following up with lab research to nail that down."
As in the Gully, the crab study gave researchers the protocols to ask tighter questions about current and emerging issues of concern. Besides follow-up research in these two areas, COOGER is also assessing seismic effects on Newfoundland lobster and on freshwater species in the Northwest Territories' Mackenzie River.
The end result will be concrete, reliable, and tested data on Canadian seismic research and its effects. The studies will contribute to governmental guidelines on seismic explorations.
The seismic work forms part of a long list of COOGER projects. "We operate as a virtual research centre within DFO," Dr. Lee says. "With the co-operation of the department's research centres, universities, and provincial institutions, we can bring together an array of talent to match the questions."
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