18 Months On: Progress Update from Swedish Case Study

Over the past half year, we have carried out less field work than in previous months, mainly because there is less fishing going on at this time of year.

However on land, we have been busy, analysing data, disseminating our initial results and planning for the forthcoming field activities over the autumn and winter.

We also conducted a test of discard and catch-and-release mortality of undersized Arctic char, working with two Masters’ students.

Catch & Release Test in Depth

In this test, recreational fishermen worked with scientists to see whether Arctic char suffered any injuries or mortality when they were released after being caught.

Recent changes to rules about the size of fish which can be landed means that many of the fish caught are now too small to be landed, and so need to be released by the fishermen. However, as Arctic Char are caught in deep waters, it was feared that some of the released fish would be injured (or killed) due to the rapid change in depth, as well as by the handling the fishermen.

The test assessed the mortality rate and the effect the capture had on fish behavior and physiology by catch and release.

Scientists accompanied local recreational fishermen on their fishing trips and marked any fish caught with acoustic tags. These tags transmitted a signal allowing the scientists to record the fish’ location, depth and temperature. The researchers from Uppsala University also helped to attempt measurements of physiological stress.

Unsurprisingly, the tests showed that fish caught and released have a higher mortality rate than those left in the water. But importantly, it was also shown that if a fish manages to escape death for the first few hours after release, it is likely to return to “normal behaviour” after a few days. This suggests that it is not the change in depth which causes fish mortality, but their handling by the fishers.

Therefore, to maximise survival rates for the fish in these first few hours after capture, it was concluded that changes would have to be made to how the fishers handled the fish.

It is now important to share this understanding with recreational fishermen and to work closely with them to develop ways to avoid this problem in the future.

Next Steps

Over the next six months it is the main fishing season for whitefish and scientists will continue sampling and data collection as new fishing gear is trialed. GAP2 scientist Dr. Sandstrøm will also participate in the EIFAAC international symposium “Towards responsible future in inland fisheries” and the rare phenomenon of deep-spawning white fish will also be investigated and documented.


This entry was posted in Case Study 6 - Lake Vattern Whitefish, Progress. Bookmark the permalink.