Calculation of the expected commercial return after stocking the lagoons in the Kaliningrad region with juvenile european eel Anguilla Anguilla

The population of european eel Anguilla anguilla is in critical condition, having reached a historic low. In the framework of the Eel Management Plans, juvenile eels have been stocked in the Kaliningrad and Curonian Lagoons since 2022. The key indicator for effectiveness of these measures is the commercial return, but its calculation is complicated by lack of systematic monitoring. To justify the volume of stocking and effect of measures for restoring the population, the expected commercial return is estimated by three methods of calculation: i) direct calculation based on expected catch and planned escapement of spawners to the spawning grounds; ii) interpolation of data from scientific literature; and iii) modified formula proposed by S.V. Shibaev. As the result, the expected value of commercial return for juvenile eels weighing 1–5 g is estimated as 12–14 % for these two vast lagoons in the Kaliningrad Region. This value can be used as a basis for planning resource activities, but require further clarification within the long-term monitoring program that conducts annual assessments of the eel stock taking into account the species features, as separate counting the yellow and silver stages of eel in catches.