ST. ANDREWS, N.B. – A 14 year tracking study provides a range of unmatched data to scientists on young Atlantic salmon in the four major rivers of the East Coast.
The iconic species is famous for taking fishermen to the region, but researchers wanted to know more about their young survival rates.
The findings, from the Atlantic Salmon Federation in partnership with Canadian Fisheries and Oceans and the Ocean Tracking Network, are in a paper published on Thursday at ICES Journal of Marine Science.
"The study started due to an interest and lack of understanding of how these fish behaved and survived as they mobilized downstream," said Jason Daniels, a research scientist with the federation and reported -awdur.
"Acoustic telemetry has enabled us to have a little window to what's happening."
The complex technical study traces more than 2,800 young wild Atlantic salmon, known as smolt, of four-river populations that are empty to St Lawrence's WC. They include the Miramichi river, the Northwest Miramichi, and the Restigouche rivers in New Brunswick and the Cascapedia River in Quebec.
Smolt was collected every spring as they made their way down and they were tagged with small acoustic transmitters that monitored the pace of migration and survival rates.
"During the 14 years of study survival estimates ranged without the population trends of Bay Chaleur, but the migrant populations dropped through Miramichi Bay," said the study report.
The data collected indicated that fish survival was dependent on factors such as smolt size, distance traveled to open water, the conditions faced, and the presence of predators.
"There was a reliable size-size probability of survival through freshwater areas and estuary," said the study. "The possibility of surviving smoln was 16 centimeters 1.5 to 1.7 times higher than 13.5 centimeters smuggled by tagging."
The survival rates for tagging in the Restigouche and Cascapedia through the shared estuary at Chaleur Bay ranged from year to year but remained relatively high – 67 to 95 per cent over the a period of 14 years.
In the first instance, those rates were similar for scabbards leaving the South West and Northwest Miramichi rivers and to Miramichi Bay, but it changed in 2010 when a "declined trend" began with rates Survival ranges from 28 to 82 per cent.
The reduction in survival rates on the Miramichi has been attributed to an increase in the population of the population passing prey. The population increased silhouette from a strip bass in the river of about 15,000 at the beginning and the study to around 300,000 by 2016.
"The spawning period overlaps timing with the migration down the smell," said the report. "Atlantic salmon smolves have been identified in stomachs from strap strips sampled by the Miramichi."
Other factors that affect the overlap survival estimates may include water chemistry in the North West Miramichi and alter experimental conditions.
Daniels said that the higher mortality numbers for the North West Miramichi were a cause of concern given that the average return rates of the river smolk were about two to three percent.
"When you see 80 to 90 percent of those smolks disappear in the estuary before they even reach the sea, you scratch your head and wonder how you're going to see three or four percent of those who make it back as adults, "he said.
The study confirmed that most deaths occurred during the first few days or weeks after smokers left fresh water. However, the researchers said that fish survival is improving as the smolt moves in the sea.
"The estuary is where most of the deaths appear," said Daniels. "These fish have lived their entire lives in a freshwater environment and have many different physiological changes, so they are already in a state where they are emphasized."
Apart from adapting to the saltwater environment, he said they also had to deal with another set of predators, so the results are not really a surprise.
"The ability to study a number of rivers at the same time over a number of years allows you to see these trends and compare to rivers that do not have the same type of pressure," said Daniels. "You can see the relative effect that some of these pressures may be on salmon populations."
Not Keith Doucette in Halifax