ASF - Greenland Tracking Project Produces Crucial Data

Researchers fish for Atlantic salmon in West Greenland

ASF’s effort last fall marked a banner year in our satellite tracking in West Greenland. Seventy adult salmon were tagged with pop-up satellite tags (PSAT), quite an increase from 12 in 2018 and 20 in 2019. Scientists Jon Carr and Heather Perry spent about a month in Qaqortoq fishing and tagging with great success. With the help of locals Malu Ravn, Liili Petersen and Brian Jensen, as well as UNB Ph.D. candidate David Roth, who has a lot of experience salmon fishing in the Baltic, they spent very long days on the water trolling for salmon.

When a fish was captured and tagged, they also took length and weight measurements as well as a few scales and a small tissue sample, about the size of a grain of rice. The measurements provide basic information, and the scale sample allows us to examine the life history of that fish. Interpreting the growth marks on the scale allows us to determine, for example, how many years the fish spent in freshwater before smolting. The tissue samples were sent to a lab in Newfoundland where they were able to determine, for most of the fish, the continent and region of origin.

The pop off locations for the 56 tags that transmitted successfully. The numbers beside each mark show the “Days at Large,” the number of days between post-tagging release and the first transmission to a satellite. Twenty-six tags remained on fish over 100 days and nine of those recorded for over 200 days.

Of the 70 fish tagged, 36 were from North America and 29 from Europe, while five fish were undetermined. The North American fish all came from Canadian rivers in 2021, with two from the Gaspé Peninsula, six from the Gulf of St. Lawrence, 13 from southern Labrador, one from northern Labrador and three from the lower St. Lawrence North Shore area. The tagged fish ranged in length from 58.5cm to 89.0cm and 1.4kg to 9.0kg. Nine of the fish did not have any sea lice while others had as many as 20 sea lice on them at the time of capture.

For fish tagged in the fall of 2021, their tags are programmed to pop off and transmit data to satellites on a certain date, ranging throughout May 2022. However, tags may come off prematurely for a variety of reasons, like some predation events or going too deep. Of the 70 tags deployed, we have heard transmissions from 56 of them, a good proportion for this type of study. Of those 56 tags, four of them reached the programmed pop date, and 6 went too deep (the tag releases before it gets to its crush depth), one tag popped for yet unknown reasons (it may become clear later) and the rest were premature.

The explanations for premature pop offs will be investigated during the analysis and we are likely to decipher what happened to some of the fish. Predation events will certainly account for some. The amount of light, as well as temperature and depth profiles, can tell us if a salmon has been eaten by a marine mammal or larger fish.

While the information is preliminary at this point, much will be made of the data over the next months. All the data must be crunched and processed to yield a “most likely track,” a representation of where the fish likely travelled while the tag was on it. The geolocation for these tags is calculated using available light—tricky on land, let alone under water of varying depths, sea state and clarity. So, while an exact track is not possible, we rely on the most-likely track to indicate where the fish has gone. On top of that, we can build a temperature and depth profile for the fish, showing daily habits and environmental condition preference.

All of this is being done to discover not only where the fish are going, but what conditions they encounter along the way as well as behavioural information. The open ocean is one of the hardest environments to protect, and the more we know about Atlantic salmon’s habits and actions in that environment, the better prepped we are to fight for protection for them and the environment they, and all of us, depend upon.