Here we present a newly digitized fish monitoring dataset for two major Lithuanian inland ecosystems – Curonian Lagoon and Kaunas Water reservoir. The data comprises fish surveys conducted during 1950s to 1980s, using a range of fishing gears and sampling methods. Three different definitions or methods describe the level of detail for each fish community study: Method 1 surveys include individual fish sizes and weights, Method 2 surveys record frequencies of fish in length or weight groups, whereas Method 3 only records the total catch biomass of a given species. 

Fish abundance, biomass and sizes were surveyed by national Lithuanian agencies using a range of gillnets and trawls during 1950-1980s. For each survey fish abundances, sizes and biomasses were recorded and stored in archival journals, currently available at Nature Research Centre (Lithuania). In this dataset, the archival journals were digitized and data was standardized using available information on gear types and fishing effort.

 Gear information, such as mesh size and gear length or type, was collected as accurately as possible. When specific details were not provided in the original archival journals, expert opinion was used to make the best guess and recorded in separate columns, defining broad categories (for the mesh size, gear length and also soak time).