The Mystery of Atlantic Salmon

Centuries ago Atlantic salmon were seen as mysterious for three very good reasons. They could leap through the air. They could live in both fresh and salt water. And they went somewhere and then reappeared, and no one knew where they went or how they did it.

Even well into the 20th century there were scientists, including the great A. G. Huntsman, who thought Atlantic salmon just roamed the oceans looking for food, and had nowhere particular to go.

Unfortunately for Atlantic salmon, one major feeding ground was discovered around 1960 near Greenland, and an over harvesting of Atlantic salmon began, ending in a crash of the population in the late 1980s.

At that time the rate of mortality at sea almost doubled, and we needed to find out where they were going, and where in the ocean they were dying.

Tracking Atlantic Salmon

Moving ahead to the present, we know infinitely more about where Atlantic salmon travel.

One major reason has been the Atlantic Salmon Federation's long and patient development of an efficient tracking technology.

ASF, together with its partners VEMCO, DFO, and lately the Ocean Tracking Network (OTN), developed an acoustic technology that now is extremely sophisticated.

Transmitters have been miniaturized to fit easily in Atlantic salmon smolts without affecting their swimming. At intervals, perhaps every 30 seconds, they give out a coded sound, that can be picked up by sensitive receivers either anchored to the bottom or on mobile carriers more than a half kilometre away.

Larger acoustic transmitters are inserted in kelts that in addition to identifying signals also provide information on water temperature and depth.

Wiring the Gulf of St. Lawrence

Rivers flowing into the Gulf of St. Lawrence host a high proportion of the Atlantic salmon returning to North America, and so it is absolutely vital to the health of the species.

In addition, the Gulf of St. Lawrence and its exits are potentially the site of further industrial development. There is interest in oil and gas drilling in the region known as Old Harry's. There is also the potential impact in future of extremely high voltage cables crossing the sea floor from Labrador to Newfoundland, and from southern Newfoundland to Cape Breton. Could strong magnetic fields affect the migration of these Atlantic salmon? No one knows, but baseline studies such as the smolt tagging are required.

We began with arrays of receivers that monitored the downstream migration of salmon in rivers like the Restigouche.

Since then, ASF has developed a system whereby receivers are deployed not just in the rivers, but across the Baie des Chaleurs, the exits of the Miramichi estuary, and even across the foggy and sometimes ice-laden Cabot Strait.

The Ocean Tracking Network (OTN) has added the other most important array of receivers - across the Cabot Strait between Cape Breton Island and Port aux Basques, Newfoundland, thus fully monitoring all exits from the Gulf of St. Lawrence.

In 2012, the OTN added a mobile receiver to seek smolts.  Called the Wave Glider, it uses the power of the waves to move forward, at speeds between one and four knots. Cruising the waters between NL and QC, it has detected in July 2012 at least one smolt with an ASF implanted acoustic tag.

On May 2013, with the Wave Glider deployed for a second year, it found, for the first time, one of the KELTS tagged by ASF in the Miramichi. READ FULL DETAILS

The Other Ways of Following Salmon Movements

For a second year, ASF in 2013, is utilizing satellite tags, that, together with a small balloon, ride attached to a harness near the Atlantic salmon’s dorsal fin. These tags pop off after five months and float to the surface. They transmit information on where the salmon has travelled, at what depth, and also the temperature of the water through which it swam.

These tags have the added advantage of pinpointing where an Atlantic salmon dies, even if it does not survive the full five months.

Other researchers are using other novel methods. In England, researchers are utilizing chemical analysis of Atlantic salmon otoliths, and comparing the profile of elements to known feeding areas in the ocean for Atlantic salmon originating in Europe.

Overall, this ability to track Atlantic salmon down rivers and out to sea has begun to offer a great range of insights on where mortality is occurring, and where Atlantic salmon are doing well at sea.

Solving the Puzzle

The salmon are proving that nothing is simple in their lives. Among the conclusions from the research:

  • Atlantic salmon in each river have different survival rates.
  • In some rivers, the estuary is a major source of mortality. For example, striped bass in the lower Miramichi feast on smolts as they are racing to the open sea.
  • Smolts can travel fast – one made it across the Gulf of St. Lawrence at 28 km. per day
  • Multi-year results have show that smolts from different rivers, along with older kelts, all travel through the Strait of Belle Isle in the same short space of a few days in early July.
  • In the summer of 2012, one of the smolts tagged by ASF was  found by the WaveGlider, proving this technology can work.

The results of the tracking in 2012 should be of great significance, since any travelling through the Cabot Strait should be registered on the receivers of that line. For the first time we will have reasonable knowledge of the proportion of wild Atlantic salmon leaving from each of the straits.