The effect of salinity on the development of freshwater pike ( Esox lucius ) eggs in the context of drastic pike population decline in Puck Lagoon, Baltic Sea

Over the past few decades, the number of available spawning grounds for anadromous pikes, Esox lucius, on the Baltic Sea coast has been significantly reduced resulting in a drastic pike population decline in those areas. It is therefore a question if saline Baltic waters may support the spawning of anadromous pike. In the present experimental study, salinity had a harmful impact on the development of eggs from pikes of freshwater origin. The hatching success rates were 0% at 7PSU and only 16.7% at 4PSU, while hatching success at 0PSU was 89.7%. However, when the eggs were fertilized in fresh water and transferred to the tested salinities after 1 h, salinity had a positive effect on egg development and hatching success (0PSU: 80%; 4PSU: 83.3%; and 7PSU: 93.7%). We concluded that the spawning of the freshwater pike population in the saline water of the Baltic Sea is most likely not successful. Simultaneously, inflows of coastal marine waters into near-shore spawning grounds do not have a harmful effect on egg development if the eggs are already fertilized. The main management measures that can be suggested are to rebuild the anadromous population by spawning ground reconstruction. Sea-spawning population introduction can also be considered.