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Publications
Science Information By:
Sea Floor Mapping: Ocean Knowledge from the Bottom Up
Multi-beam sonar has brought multiple benefits to a fishing area off southwest Nova Scotia. Through detailed mapping of the ocean floor, the advanced technology has opened up a multi-million dollar scallop fishery. And while providing their skills to the project, fishermen, fishery scientists, geologists, oceanographers, and the hydrographers who create nautical charts have all learned more from it.
“It’s a notable increase of both knowledge and co-operation,” says Stephen Smith, research scientist at the Bedford Institute of Oceanography in Halifax, Nova Scotia. “The two went together.”
The research project addressed a poorly known, L-shaped fishing area covering about 1,500 square kilometres. Lying south of the famous scallop grounds in the Bay of Fundy and north of offshore fisheries on German’s Bank and Georges Bank, this in-between sector – technically, the western part of Scallop Fishing Area (SFA) 29 – supported some fishing in the past, but regulations after 1986 kept it minimal.
When a resource downturn struck Bay of Fundy scallop beds in the 1990’s (they have since recovered), fishermen pressed for access to SFA 29. But fishery scientists worried about the strength of the resource, and fishery managers in the Department of Fisheries and Oceans (DFO) sought more information before allowing more fishing.
How to assess the scallop beds in timely fashion? Part of the answer emerged from another part of DFO, the Canadian Hydrographic Service (CHS ), responsible for nautical soundings and charts, and recognized as among world leaders in using multi-beam sonar to picture the ocean floor.
Sonar devices
convert electrical signals to sound pulses through an underwater
transducer, and trace the echoes to show the bottom, rocks, fish,
submarines, or whatever’s down there. The technology has made great
advances in recent decades.
One view of the western part of Scallop Fishing Area 29, showing relative catches by area. Sea-floor mapping can show many aspects of the sea-bed, including bathymetry, geology, flora and fauna.
Multi-beam sonars now use transducer arrays to send out many narrow beams at slightly different angles. This allows unprecedented delineation of the depth, shape, and nature of the bottom. CHS and other experts, including researchers at the University of New Brunswick, have developed computerized methods to integrate sonar and other data, such as precise locations from the satellite-based Global Positioning System.
Sea-floor mapping soon found fishery applications. Scallop vessels tow sack-like metal drags along the bottom. CHS worked with the offshore industry to outfit a fishing vessel for sonar surveys on German’s and Georges Banks. Fishermen found they could home in on mature scallops, avoid nursery areas, and reduce bottom disruption.
Further inshore, in SFA 29, a more elaborate project took shape. First, BIO technician Mark Lundy, on the DFO research vessel J.L. Hart, conducted a fishing survey in 2000. He found surprising abundance. Demands for access grew, by Bay of Fundy and other fishermen.
But besides resource worries, other factors complicated the picture. “The area is also a major lobster-fishing ground,” Stephen Smith explains. “Scallop drags can take a bycatch of lobsters. If the fishery was to expand, we needed to know all we could about both scallops and bycatch.”
Budget constraints hindered DFO from undertaking all the required research by itself. But new partnerships made it happen. Fishermen’s groups anted up nearly $400,000 over three years to help pay incremental cost for sea-floor mapping. And fishing vessels, such as the Julie Ann Joan under Capt. Kevin Ross and the Branntelle, under Capt. Vance Hazelton, carried out fishing surveys.
More confident but still cautious, fishery managers allowed a fishery starting in 2001, but only outside the November-May lobster season, and with catch and other restrictions. Boats had to carry observers as required and to install Vessel Monitoring System (VMS) devices that reported their exact location by satellite. They also recorded tows and catches in log books. All such information feeds into BIO’s computer data banks.
BIO -developed instrumentation added more layers to the picture. The Campod, a drift camera, provided photographs and videos of the bottom, its plant and animal life. BIO’s Towcam, a towed-camera system, will also find use in future obtaining more information on the geology and benthic communities in this area. Sonar, photography, and catch sampling documented a good abundance of scallops. And sea-floor mapping and reports by on-board observers help to avoid bycatches of lobster.
To complement those data, BIO researchers with the Geological Survey of Canada (Atlantic ), of the Department of Natural Resources, took grab and core samples along with photographs to catalogue the various sea-floor substrates. Scallops are most plentiful on sand and larger-grained glacial till.
BIO’s research has given fishermen new eyes underwater. They can now slip a disk into an on-board computer and see the bottom in great detail, enabling more effective and conservationist fishing. And fishermen are enhancing that ocean picture, often calling Stephen Smith from the fishing grounds to relay extra information.
The fishing industry is only one beneficiary of the project. Hydrographers now have a picture of the sea floor that, compared with earlier charts, is like daylight compared with flashlights. Geologists have gained major amounts of information. Oceanographers too have learned more; for example, the orientation of small sand dunes reveals the direction of sea-bed currents. And researchers are exploring ways to enrich the integrated, computerized picture with other variables, such as the ocean’s salinity, temperature, and plankton production at different times of year.
All told, in SFA 29, fishermen and government are creating one of the world’s fullest pictures of the sea floor, the creatures it nourishes, and the workings of the water column above.
