Do Endangered Lampreys Benefit from Water Pollution? Effect of Municipal Sewage Treatment Plant Operation on Growth and Abundance of the Ukrainian Brook Lamprey and the European Brook Lamprey

The impact of municipal pollution on the larvae of the Ukrainian brook lamprey and the European brook lamprey was studied in the River Gać, a left-bank tributary of the River Pilica. Both lamprey species share similar morphologies and habits, including filtration-based feeding and burial in soft river sediments. This study focused on a 200 m stretch of the river, divided by sewage discharge from a municipal wastewater treatment plant into unpolluted (above the discharge) and polluted (below the discharge) sections. The Ukrainian brook lamprey exhibited higher densities (1612 individuals in total over the study period) compared to those of the European brook lamprey (336 in total). Survival methods, such as body length-frequency charts, were used to determine age. These diagrams, showing multimodal distributions, facilitated the differentiation of age groups and the application of the von Bertalanffy growth function to determine growth parameters. The growth curves revealed that the Ukrainian brook lamprey achieve greater body lengths (246.7 mm for the unpolluted section; 256.3 mm for the polluted section) at the same age and asymptotic lengths when compared to those of the European brook lamprey (187.2 mm for the unpolluted section; 180.7 mm for the polluted section). Furthermore, the European brook lamprey exhibited inferior growth in the polluted river section compared to that of the Ukrainian brook lamprey. The response of both lamprey species to municipal pollution suggests that such pollution could promote the expansion of the Ukrainian brook lamprey, while causing the decline of European brook lamprey in areas of their overlapping habitat.