To determine the proportion of seabed in the saltwater portion of the St. Lawrence that is directly affected by mobile fishing gear, a quick estimate was made by multiplying the number of trawl or drag passes by the area affected by each pass of the gear. Readers should note, however, that trawling has almost totally ceased in recent years due to the closure of the cod fishery. Boats may also trawl the same area several times to optimize their use of a good fishing spot, which may decrease the area affected. The next question to be answered is what effects mobile fishing gear has on the biodiversity of the saltwater part of the St. Lawrence. Maps are not available for marine invertebrates, particularly benthic species, however.
Some marine ecosystems appear to be affected on a large scale by mobile gear.
The proceedings of a workshop on the effects of mobile gear on marine biodiversity, which brought together researchers from many countries, were published in December 1998 in the journal Conservation Biology. According to some estimates, nearly half of the world's continental shelves are scraped by trawls and other such gear annually, which represents an area 150 times the area of forest clearcut worldwide each year. Losses in biodiversity could eventually occur at a more local scale in the St. Lawrence. Frequent trawl passes in the same region result in fragmentation of the original habitats, which are transformed increasingly into habitats that are structurally and biologically less diverse. As the bottom trawling and dragging of the seafloor intensifies, the diversity of benthic communities may decrease in areas where fishing activities are concentrated.