Where have the fish gone? Experts on climate change's toll on the Baltic Sea and Latvia's waters
Fisheries specialists discussed on the program "Klimata kurss" how warmer winters, rising water temperatures and human activity are reshaping fish populations in the Baltic Sea and Latvia's rivers and lakes, citing the collapse of cod stocks and the spread of invasive round gobies as examples.
On the program "Klimata kurss," Ivars Putnis, head of the Fish Resources Research Department at the Food Safety, Animal Health and Environment Scientific Institute "BIOR," and Aivars Rudzinskis, editor of the magazine "Copes Lietas," discussed how climate change is affecting Latvia's waters and the Baltic Sea.
Warmer winters reshape fishing habits
Rudzinskis noted that winters are becoming warmer and the ice season shorter, shrinking the window for ice fishing. He recalled that in his childhood, perch could be caught under ice from November through April, which is no longer the case. Warmer water favors heat-tolerant fish species, while cold-water species such as trout, salmon and char are struggling, since summer water temperatures can reach 25–28 degrees Celsius — conditions these fish cannot survive. Putnis added that fish, as cold-blooded animals, react very quickly to temperature shifts, which also affect oxygen solubility and habitat availability.
The Baltic Sea and the decline of cod
Putnis described the Baltic Sea as a volatile, relatively closed and shallow system with limited water exchange with the North Sea, making it especially sensitive to climate fluctuations. He noted that in 2006, research surveys across the entire sea caught more than 200 cod weighing five kilograms or more, while last year only one such cod was caught. Alongside the decline of native species, foreign organisms have spread — the first round gobies were caught in research surveys in 2004, and by 2018 their commercial catch exceeded 1,000 tons.
Human impact and the dam problem
Putnis emphasized that climate change amplifies existing problems caused by agriculture and land use, such as eutrophication and the overgrowth of water bodies. Both experts pointed out that small hydroelectric plants and old dams obstruct fish migration and contribute to water warming, since standing water in reservoirs heats up faster than flowing water. Rudzinskis added that Latvia still has hundreds of useless, often unregistered dams whose removal is hindered by legal obstacles, even though funding is available through European funds.
Possible solutions
Rudzinskis called for greater focus on freshwater fish farming in rivers and lakes, where municipalities could work with funds to replenish stocks. Putnis, meanwhile, urged a broader view of fish resources as an ecosystem service with potential for angling tourism, encouraging people to use the resource responsibly rather than always taking the full legal catch limit home.
