As the climate changes, lamprey are starting to go to their spawning grounds later, according to researchers from the BIOR Institute for Food Safety, Animal Health and the Environment, who have identified the river lamprey population in Latvia and Lithuania. The onset of migration is delayed by the fact that rivers have been keeping warm for longer in recent years, which does not create suitable conditions for the migration of lamprey.
The lamprey travels from the sea to spawning grounds from August, and the greatest activity is usually reached in October and November. Due to the different environmental conditions in the rivers, the researchers say that it is not possible to determine exactly how many weeks or months the spawning route is delayed. However, in general, trends in other countries also suggest the impact of global warming on water temperature and changes in lamprey migration patterns.
Lamprey fishing is only allowed when they are on their way to their spawning grounds, from August to February.
As lamprey has recently started later, Lithuanian fishermen have even started talking about the need to extend the permitted fishing season.
It must be said here – how many rivers, so many views, because, for example, the owner of the fishing farm “Kurķis” Aleksandrs Rozenšteins, who has been fishing for lamprey in Salaca for more than 20 years, does not complain about changes in their migration.
Rosenstein’s observations show the opposite – this year the fisherman considers it good, because already in August managed to catch almost a ton of lamprey, September was also productive, when 2 tons were caught compared to the experience of other years, when such catches were achieved during the whole season.
“Everything is determined by weather conditions for lampreys. If there is a suitable wind and a strong river current, then lampreys in the sea feel fresh water and it “drowns” them in the river. If there has been rain, then the river also brings much more fresh water to the sea, which lamprey feels and follows. For us, the southwestern and western winds are favorable for lampreys in Salaca. It will be different in another river. For example, the northwest wind will be decisive in the Gauja, ”says Rosenenstein.
Lamprey spawns in the nearest place
One would think that lampreys, like salmon, also return to their native rivers and expect favorable conditions in their vicinity. However, as explained by BIOR leading researcher Ruta Medne, lampreys are less demanding in this respect. “We once performed an experiment and marked the Daugava lampreys before entering the sea. We expected them to return directly to the Daugava during spawning. But nothing – we found them in other rivers, and it only suggests that the lamprey, as soon as it feels favorable conditions, uses the nearest opportunity, ”says Medne.
River lamprey in Latvia are fished in 16 rivers. Most, about 80%, is extracted only in four rivers – Salaca, Gauja, Daugava and Venta.
Latvia is one of the few countries in the Baltic Sea where lamprey is a delicacy.
Lamprey is also fished in Lithuania and Estonia, but mainly for export to Latvia. In 2018, almost 25 tons were caught in Estonia, 44 tons in Latvia, but only 6-7 tons per year in Lithuania, ”explains Medne.
There are three species of lamprey in the territory of Latvia – stream lamprey, river lamprey and sea lamprey. The lamprey population is most directly affected by migration opportunities and the quality of spawning grounds and larval habitats. “Venta’s hub is disturbing in Venta – the lamprey can’t get over it. In addition, there are many dams, not just dams for small hydropower plants (HPPs), which often have neither use nor the need to be in the river. The remnants of the pape factory dam in Rīva, the Lubes mill in Roja and other man-made obstacles also have a significant impact, ”explains the researcher. Fisherman Rozenstein also mentions that in addition to the small HPP rivers, there are enough other obstacles – for example, although there are no small HPP buildings in Salaca, the Staicele paper mill dam is a major burden for lampreys.
Losses are compensated with babies
Although there is no doubt about the negative impact of small and large HPPs on the lamprey migration route, Medne also draws attention to population compensating activities: “Although it often seems that the Daugava HPP cascade has caused the greatest damage to fish resources, it should be noted that fish fry are reared in farms and released into the Daugava basin ”.
More than 10 million artificially propagated lamprey larvae are released into Latvian rivers every year.
Two methods are used to propagate lamprey in Latvia, and obtaining lamprey larvae in fish farms is only one of them. Adult spawning migrating lampreys are also released into potential spawning grounds already above obstacles. “Lamprey is released in places where [šķāršļus] the upward migrants cannot overcome, but the downward migrating young lamprey will already be able to overcome. The results of the project look promising, but we will only get the final conclusions in a few years, ”explains Medne. The challenge in this respect is that the duration of a lamprey breeding project is shorter than the life cycle of the lamprey, but as lamprey monitoring is planned for at least the next four years, there is promise more clarity on how many lampreys successfully overcome migration barriers.
In Latvia, lampreys have been studied since the middle of the last century – their feeding and spawning, as well as breeding possibilities have been analyzed. Lamprey larvae have also been monitored in rivers, and scientists have now gone a step further and performed genetic analyzes of river lamprey. The aim was to find out how close Latvian lamprey are to those spawning in Lithuanian rivers. It turned out that lampreys as a resource are common to both countries and should be managed jointly.
Lamprey is one of the oldest and most primitive vertebrates currently found on our planet. Fossils show that they have changed very little in the last 380 million years. As lampreys are in danger of extinction in most of Europe, they are protected by both European Union law and the Berne Convention for the Protection of Species and are an integral part of the International Union for Conservation of Nature and Natural Heritage (IUCN) list of endangered species. Along with Lithuania, Estonia, Finland and Sweden, Latvia is one of the few countries where commercial use of lamprey is allowed.
The publication has been prepared with the financial support of the Latvian Environmental Protection Fund.
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