Summeringen är på Engelska:

2018 field season: Project update

Trapping Migrating Smolt

This spring, downstream migrating smolt were captured and processed at three new wolf traps in addition to the smolt wheel located at Ekeberg. Trapping began during the last week of April for two of these traps located in the Hemsjö HEP system. The first trap was constructed at the Hemsjö Övre ice gate and was the similar in design to the trap used by Simon Karlsson in 2013 to film downstream migrating kelt. Unlike this previous design however, the current model held captured fish in a holding box until they were processed. Further downstream, a second trap was constructed within the Hemsjö Nedre intake channel at the same location as a trap initially constructed in 1999 for a project testing the efficacity of a bubble guidance devise. A third trap was constructed at Laxens hus. Construction of the additional traps occurred in April and was performed by Olle Calles and Niclas Carlsson of Kau and Zakarias Mibesjö of Sveaskog.

Throughout the smolt migration period, the trap at Laxens hus was checked daily by Sveaskog employees in conjunction with, and following the same protocols set up by SLU and employed at the smolt wheel at Ekeberg. The two traps situated at the Hemsjö HEP system were monitored by Andrew Harbicht (KAU) and either Johanna Högvall (KAU) or Zakarias. During initial trap construction and monitoring, all work performed at Upper Hemsjö were supervised by Patrik Svensson of One Nordic AB. Prior to working unsupervised on the upper trap, all three of the project members mentioned above completed the SSG Basics and Sydkraft safety courses. In addition to these two courses, Andrew Harbicht also completed the ESA Hydropower course, giving him clearance to operate the ice gate controls.

Both Hemsjö traps were inspected daily and all captured trout and salmon smolt were weighted, measured, classified in terms of their smoltification status (0-4), and PIT tagged. A tissue sample was also collected from every 5th smolt for genetic analysis. Processed smolt were then released into the natural fishway parallel to the Hemsjö Nedre intake channel. These PIT tagged smolt will be used to assess the proportion of smolt captured downstream that originated above the Hemsjö HEP system.

Smolt Migration Study

A subsample (n = 48) of the Atlantic salmon smolt captured at the two Hemsjö traps were included in a study to monitor smolt movement within the Mörrumsån. These smolt received an internal radio transmitter in lieu of a PIT tag, which was surgically implanted by Andrew at the processing site at the lower Hemsjö trap. These smolt were also individually photographed during processing, which was not done for PIT tagged smolt.

The movement patterns of radio-tagged Atlantic salmon smolt were monitored between the last week of April and the last week of May with an array of 14 antennas/receivers situated along the length of the Mörrumsån, from the Hemsjö HEP system to the Södra Cell AB pump house near the river mouth. For much of the river's length, these antennas were located at roughly equal distances from one another. Exceptions to this occurred at locations where supplemental information was required: the Marieberg dam and Laxens hus in Mörrum. At these locations, four and two antenna/receiver stations were used respectively.

The data produced by this array will be used by Andrew to assess smolt movement and mortality rates in relation to environmental conditions and anthropogenic features (the Marieberg dam) in the river as well as to estimate path choice at Laxens hus. This data will also be used by Johana for her Masters project in which she will be assess the relationship between the smolt status of tagged Atlantic salmon and their migratory speeds/mortality rates.

The initial goal of tagging 80 smolt was not achieved this spring due to limitations with the turnover rate of tagged smolt in the river. However, the remaining tags will provide an opportunity to repeat the study in the future in order to a) collect additional data on smolt migrations in the river in spring 2019, or b) assess changes in the migratory patterns of Atlantic salmon smolt following the removal of the Marieberg dam (spring 2020). Of the smolt that were tagged, 29 reached the dam, 27 passed the dam and 20 made it as far as Mörrum.

During the course of this project, Olle and Anders Nilsson also participated in checking the Hemsjö Nedre trap along with 14 students attending a Master course entitled "Scientific methods". During two days of visits, the students assisted with checking/maintaining the lower trap and observing/participating with smolt tagging methods. Students also assisted with the construction of the third smolt trap at Laxens hus.

Monitoring Adult Migrations

Pending good health among the adults returning to the Mörrumsån in the fall of 2018, a second radio tagging experiment will be conducted on upstream migrating spawners. This will involve the installation of antennas throughout the river, with the majority of antennas being concentrated at key locations in close proximity to the hydroelectric stations (Marieberg and the Hemsjö system). The remaining antennas will be distributed evenly throughout the river to permit the upstream progress of migrating salmon to be monitored over the length of the Mörrumsån.

Antenna setup will occur in September, followed closely by a tagging period in which several adults will be tagged each day and monitored as they move upstream. Naturally this work will be conditional on the returning salmon being in good health. In the event that tracking does occur, we have received the necessary ethical permits to conduct a parallel experiment with the tagged salmon involving thiamine injections. Previous work on this subject has found that the migratory behaviour of thiamine deficient salmon can be influenced by injecting deficient salmon with thiamine along their spawning migration. The purpose of this parallel experiment will therefore be to determine whether thiamine injections improve spawning returns to upper sections of the Mörrumsån by testing for differences in mortality rates and behaviour during the upstream spawning migration. Apart from the treatment of returning spawners with thiamine, this section of the project will remain the same as was originally proposed.

Holistic Monitoring

This summer, we will once again be setting out sampling stations throughout the river to assessing the microbial decomposition rates within the river prior to dam removal. This will establish a summer baseline value to accompany the winter values calculated earlier this year. Combined with the collection of stable-isotope and benthic invertebrate samples and the assessment of littoral vegetation conducted last summer and the monitoring of the sediment during dam removal, these measures will provide us with an overall understanding of the riverine ecosystem before and during dam removal. These samples will then be collected again following dam removal to allow direct comparisons of before and after to be made along with the control samples collected in unaffected sections of the river.