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THE QUEBEC REGION BULLETIN
AUGUST - SEPTEMBER 2010/VOLUME 13/NUMBER 4
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Underwater imagery on a sled...
Learning more about the seabed
The research team makes some final adjustments before deploying the sled in the water.

DFO  C. Nozères

For some years now, the scientists at Maurice Lamontagne Institute have been using an innovative tool to see and better understand what’s happening deep beneath the surface of the St. Lawrence. The optical imagery system, updated and improved over the years as technology advances, provides highly precise information about the biology and geology of the seabed.

Benthic habitats can be characterized much more easily than in the past using the exceptional quality photos and the videos that are produced. The selected photos are meticulously analyzed to identify all the invertebrates that can be seen and the nature of the seabed (sand, clay, pebbles, shells, boulders and bedrock). As for the videos, they more generally help to identify fish and other mobile organisms such as crabs. In this way, scientists can evaluate their density and verify the particular associations that might exist between some marine species and the type of seabed. The video is also used to see the transition from one substrate to the next, from sand dunes to gravel, for example.

These data are all tied to a precise geographical position. They can therefore be used for a variety of research projects; examples include studies to learn more about the ecosystem in a given area, the species that live there and the type of sediments present there. Furthermore, physical and chemical data such as the temperature, depth, salinity, and oxygen concentration associated with each location examined can be recorded.

The technology

An Institute team designed and developed the equipment used, a sled that is dragged along the seabed at a constant speed by a research vessel. This sled is equipped with a vertical camera, which takes photos at regular intervals, a high-definition video camera facing forward which records continuously, high-efficiency lighting, and a device that records depth, temperature and dissolved oxygen. Other measurement devices can be added to the benthic sled as research needs dictate.

The results are obtained rapidly, and they provide more detailed information about larger areas at depths not accessible to scuba divers. For instance, the information on sediments is complementary to that obtained using a dredge. Moreover, this technique causes little damage to the seabed under study.

Images with many uses

So far, seabed imagery has been used particularly in the St. Lawrence estuary, in the Saguenay fjord and along the Gaspé Peninsula, notably to characterise beluga habitat, spot natural gas vents and study habitats suitable for the wolffish.

The images are analyzed, compiled and made available to document other research work dealing with the seabed in the areas covered. The some 10,000 photos obtained to date constitute a significant data base on the ecosystem, and bear witness to the current state of the environment and biological diversity of the St. Lawrence.

IMAGERIE_02_HIRES.png
83 m below the surface north
of Île Verte
IMAGERIE_03_HIRES.png
41 m below the surface south
of Île Rouge
IMAGERIE_04_HIRES.png
62 m below the surface near
Île aux Basques
IMAGERIE_05_HIRES.png
83 m below the surface north
of Île Verte

IMAGERIE_06_HIRES.png
315 m below the surface near
Les Escoumins


Photos : DFO   R. Larocque

Richard Larocque
Sciences