Spotted wolffish are now rare in the Estuary and northern Gulf of St. Lawrence and are listed as a threatened species in Canada. To ensure the species’ recovery, the Department of Fisheries and Oceans wishes to better understand its key habitats. A team of scientists from the Maurice Lamontagne Institute (MLI) has been studying the relationships between wolffish, other demersal species and various aspects of their habitat including dissolved oxygen. In the deep troughs of the Estuary and Gulf of St. Lawrence, water is hypoxic (i.e. low oxygen levels). This can have a significant impact on the distribution and life cycle of wolffish.


Dissolved oxygen was measured with a newly designed apparatus based on an Aanderaa optode model 3830. The correlation between spotted wolffish, demersal fish communities and oxygen, a key feature of environmental conditions in the Gulf of St. Lawrence, can now be determined using this new tool avalaible to ocean sciences. This new instrument has been used successfully in several surveys, including the annual bottom trawl survey in the Estuary and northern Gulf of St. Lawrence at depths down to 500 m. It can also be combined with a towed camera system. The apparatus is fastened to the head rope of the trawl and records oxygen concentration, depth and temperature near the bottom during trawling.

Fish caught by the trawl, including many small species belonging to three poorly known families of the demersal community, Cottidae, Liparidae and Zoarcidae have been described.


Key habitats are thus determined by combining information from various sources, multibeam acoustic surveys, towed camera surveys, beam trawl catches, annual bottom trawl survey data, and oceanographic databases (salinity, temperature and dissolved oxygen).