Over the past 3 years, we have been involved in a project to tag sea trout in the Skaftá watershed(Battle Hill Fisheries), Skaftá is one of the largest glacial rivers in Iceland and receives the biggest run of Sea run browns in Iceland, in collaboration with the biologists at Laxfiskar. Although it is far too early to draw concrete conclusions from these studies, several interesting patterns have emerged.
Widely Traveled Female
In late October 2022, a 24-inch female, tagged number #1377, was marked in Þverárvatn (the upper region of Fossálar) approximately 20.5 miles from the sea. On April 14, 2023, this female was caught again in Breiðbalakvísl(the lower part of River Geirlandsá). She had traveled about 8 miles down Þverárvatn to Vatnamót and 3 miles up Skaftá and Breiðbalakvísl, where she was caught for the second time.
She likely preferred to spend the winter in Breiðbalakvísl/Geirlandsá rather than in Fossálar/Þverárvatn after spawning, as the water temperature in Fossálar/Þverárvatn is lower then in Geirlandsá
We have seen this pattern a few times now in our tagged fish. They don’t seem to stick to 1 tributary in the system as several have been re-caught in a different tributary they were originally tagged in.
Growth Rate
It is important to note that measurements are never 100% accurate, but it is still interesting to examine the growth rate of sea trout in the Skaftá area.
- #1371 was tagged in Vatnamót on September 3, 2022, at 17 inches and caught again in Vatnamót just over a year later at 23 inches. This represents a growth of 6 inches in just over a year.
- #823 Female was tagged in Vatnamót on May 1, 2023, at 18.5 inches. She was caught again in Fossálar on September 6, 2023, at 21.5 inches, having grown 3 inches.
- #1477 Male was tagged on May 6, 2022, in Vatnamót at 24.5 inches. He was caught again in Geirlandsá in September 2022 at 30 inches! This shows a growth of 5.5 inches in just over 4 months.
Fish tagged in the fall and caught again in the spring generally showed little to no growth, which is not surprising, though some were measured to be 0.5-1 inch larger, possibly within the margin of measurement error. Fish caught in the spring and again in the fall invariably showed significant growth, from 1.5 to 6 inches, though usually 1.5-2.5 inches.
