Latvia starts work on removing barriers from rivers

Latvia starts work on removing barriers from rivers

Free-flowing waters will benefit migratory fish

The Latvian national Institute of Food safety, Animal Health and Environment (BIOR) is a consortium member of Life Goodwater IP, a project that aims to improve the status of water bodies at risk in Latvia by fully implementing the measures laid down in the Daugava, Gauja, Lielupe and Venta River Basin Management Plans (RBMPs).

Improving the status includes removing, as far as possible, barriers from rivers so that they can flow unimpeded down to the sea. The removal of barriers together with the restoration of breeding habitats (another expected outcome of the project) will have a positive impact on the ability of migratory fish species to swim upstream to spawn and thereby stabilise and increase fish populations. This in turn will have a positive impact on the environment as well as benefit commercial fishers and recreational anglers.

Allowing wild salmon to reproduce naturally is important for the stock

One of the species expected to gain from the project is salmon, which is considered either wild or reared. Unlike the reared salmon, the wild variety does not stem from hatcheries where salmon are bred for restocking purposes. In Latvia this breeding activity dates back well over 100 years and today in the Baltic Sea the number of stocked salmon exceeds natural salmon production in rivers. Researchers have also established that artificial propagation of salmonids without natural spawning will not ensure the viability of wild populations. This makes it all the more important to improve conditions in the rivers so that salmon can freely swim upstream to breed.

In Latvia salmon are divided into six assessment units. Didzis Ustups, Head of the Fish Resource Research Department at BIOR, says the resource is generally doing well except in Unit 5, which starts in the rivers on the coast of Estonia, Latvia, and Lithuania. Rivers on that coast in are not in a good situation. Moreover, on the Daugava river, Latvia’s biggest, there are three power stations, so the salmon have no chance to spawn. As a result, every year more than 500,000 smolts are released into the river to keep the Daugava salmon population alive. But, he adds, the direction that we are going not only in the Baltic Sea, but across Europe, is that we are trying to improve habitats, not just put juveniles or smolts in the river, but to create an environment where the fish can reproduce naturally. In this connection he and colleagues paid a visit to Estonia where work on removing barriers across rivers has been ongoing for a while. One of the main hindrances to improving the ecological status of rivers is the presence of hydro morphological barriers. Latvia has about 20,000 km of rivers and there are about 1,000 barriers which is a relatively high number. Of these about 150 are small hydropower stations, but many barriers have no function or are not making money for their owners. Perhaps a century ago they were used to run a flour mill or produce some electricity, but today they just create ponds or small lakes. The problem, however, is a knotty one, says Dr Ustups. For biologists like himself a free-flowing river is the best for nature and for the fish. But if a barrier creates a small lake that the owner of a guesthouse or hotel uses to offer rowboats or some other water-based activity to the guests, then there would certainly be protests if the barrier were to be removed. Among anglers too there is no clear preference for freeflowing rivers. Some anglers like to sit at the edge of a lake and fish for bream, for example, although others enjoy fishing for trout or salmon in a free-flowing river.

Dr Didzis Ustups, Head of the Fish Resource Research Department, Institute of Food safety, Animal Health and Environment (BIOR)

Fish passes are another way to help migratory fish

Enabling fish to swim freely up and down the length of a river is one of the reasons to remove barriers. This can also be achieved by building a fish pass. These structures can be divided into technical or natural fish passes. Technical fish passes are structures designed and built for a certain species of fish, usually a strong swimmer, such as salmon, trout, or sea trout. A natural fish pass is a channel that is built around the barrier which can then be used not only by fish, but also lampreys, or other benthos. Currently, Latvia has one natural fish pass. It was built a few years ago at a barrier on a river between

Surface water quality map of the Republic of Latvia

Liepaja and Ventspils and monitored by BIOR. Before the fish pass was constructed some sea trout were jumping the barrier, a sight that brought tourists to the area. Scientists from BIOR had noted the presence of juvenile sea trout upstream indicating that some fish were crossing the barrier. But after the natural fish pass was built the number of juveniles upstream from the barrier increased significantly suggesting that the fish pass was working. Of course, says Dr Ustups, simply demolishing the barrier would have been a far cheaper solution than building the fish pass, but for the local community the ability of the barrier to attract tourists outweighed the biological benefits of demolition. Compared with Estonia there are, however, not many examples of successful fish passes in Latvia.

In Estonia the Latvian delegation gained insights into how removing or bypassing barriers is managed. Demolishing a barrier and quantifying the benefits that follow would mean less resistance to the demolition of the next barrier. Even if tourists cannot see fish jumping a barrier, a free-flowing river offers other ways of attracting tourists. To identify and collate information about barriers in Latvia, BIOR launched a small project that involved citizen science. An app was developed that allowed people who discovered barriers to report them to the institute. This provided useful additional information that could be added to BIOR’s existing database of more than 1,000 dams. With this knowledge modellers could identify the currently most important rivers from the point of view of the fish. The list was divided into different categories that were colour coded. Green, for example, indicated rivers where the most improvement could be made. The categorisation made it apparent that rivers in categories one and two should be considered before those in three and four to create the greatest impact.

Latvian Environment, Geology and Meteorology Centre, 2020

Rivers grouped according to where the most improvement is possible

This grouping does not describe the least or the most affected rivers, clarifies Dr Ustups, but the rivers where it is most feasible and most efficient to improve conditions. Another aspect of the grouping is that rivers in a group are not organised in any sequence. Work can start on any river in the group and continue to any other within the group without following any order. In fact, if the river is already doing well then leave it alone and use resources where they will deliver the most improvement. The mapping of the rivers in this way shows where improvements can be made that will make a big change to the river, while the same improvement in another river will not result in the same degree of improvement. Barriers were found to be one of the most important factors and they were identified individually. The Daugava river is very important for salmon, but it has three power plants on it. In theory removing one would not do much for the river as the other two would continue to block it. It is therefore more useful to remove a barrier from a river, where salmon, sea trout, lampreys and bream could spawn, if it is the only obstacle. The mapping exercise, which focused on migratory fish, discovered that among the rivers with barriers causing the most impact was the Venta river and the barrier in question was the Rumba waterfall. The waterfall is Europe’s widest and a national and European heritage so a proposal to remove would not get far. Here it is possible to see vimba trying to jump the waterfall—a tragedy for a fisheries biologist. Other barriers in the most affected rivers included power stations and blockages on the Salaca, Latvia’s most important salmon river, which partially obstruct the river.

In the next stage of the project the institute will identify 50 or 60 barriers on Latvian rivers that, unlike the Rumba waterfall, can really be removed. Technical solutions will be discussed with the barrier owners insofar as they (the owners) exist. While individuals, municipalities, or the state often own these structures, in some cases they do not have an owner. Some funding should be available to pay for the demolition, but if the barrier is a power station or some other income-generating asset, it is likely that some form of compensation will have to be offered to the owner. The small power stations produce some power but not very much—the power generated by all these units together represents a very small fraction of the Latvian supply, unlike the three plants on the Daugava which are responsible for 30-40 of Latvia’s power. Biologists consider it