Over the past 30 years, Atlantic salmon stocks appear to have declined in both North America and Europe. The decline, which has been observed by scientists and has raised concerns within the North Atlantic Salmon Conservation Organization (NASCO), is believed to be related to the characteristics of the salmon’s environment during its time at sea.
Salmon born in rivers leave their natal rivers at 2 to 8 year of age, i.e., the smolt stage, for the sea. It is there that they undergo significant growth: they can triple in size in one year. After three years at sea, salmon return to their natal rivers. “Salmon have a very well developed homing instinct,” explains Gérald Chaput, a biologist in the Gulf Region of Fisheries and Oceans Canada. Yet, some control rivers indicate a decline in salmon populations since the early 1980s. Not as many smolt that leave their natal rivers return as adults; more and more salmon are dying at sea. Why?
In 2004, in an effort to answer this question, NASCO began promoting the SALSEA research program. The program is designed to improve the understanding of the distribution and migration of salmon at sea and brings together experts from two continents.
Ross Jones, DFO scientist (at left) with the crew members of the research vessel showing the two smolts caught off Newfoundland and Labrador in August 2008.
Fisheries and Oceans Canada’s participation in the SALSEA program consisted of a research survey off the coast of Newfoundland and Labrador conducted by Gérald Chaput and his team in August 2008. The team members included representatives of several organizations from several Canadian provinces and the United States. The wide range of partners says much about the level of interest in Atlantic salmon.
For three weeks, the research vessel, towing its survey trawl, crisscrossed the northwest Atlantic. It covered both temperate and cold waters, ranging in temperature from 7 to 14° C. This first expedition was focussed on the geographic distribution of salmon. More than 40 salmon capture points were identified in the Atlantic off Newfoundland and Labrador. The team took samples on board the research vessel in accordance with a well defined protocol.
“This program was a first test with a surface trawl. We know that salmon stay primarily at the surface, but they can dive to significant depths to capture prey or for other unknown reasons,” said Gérald Chaput.
The salmon’s environment was also studied during the exploratory research at sea: what is the salinity and temperature of the waters in which they live? With what other species do they co-exist? What is the state of health of the captured salmon? Where are they captured?
In all the areas where surveys were conducted, only about 15 salmon were captured. The location of the captures was primarily in the more northern areas, i.e, in colder waters. The captured salmon were in very good health with no visible injuries.
Although the number of salmon captured was less than expected, the research confirmed the hypothesis that during its time at sea, salmon look for colder waters and migrate northward. “It would appear that they are intelligent enough to look for colder waters, ” explained Gérald Chaput. Would salmon that do not migrate to colder waters or that do not have the instinct to head towards them have a smaller chance of survival?
There are still a number of unanswered questions. Is there less predation in colder areas? Are colder waters more suitable to their metabolism? The team hopes to conduct a second survey at sea in 2009 to examine these questions and gain a better understanding of the factors that affect the survival of Atlantic salmon.