Extremely shallow spawning of perch (Perca fluviatilis L.) : the roles of sheltered bays, dense semi-terrestrial vegetation and low visibility in deeper water

摘要

The roles of wind protected bays, presence of littoral vegetation and light attenuation in the water column on spawning site selection and depth of egg strands deposition by perch Perca fluviatilis was studied in ?ímov Reservoir, Czech Republic, in the years 2007 and 2011 using boat observation and SCUBA divers. The data were compared with results from Chaba?ovice Lake, Czech Republic, where similar monitoring took place in 2007–2010 and 2012. In shallow water of ?ímov Reservoir, the density of egg strands was significantly higher in grass bays compared to both rocky bays and the main reservoir body. Most egg strands were deposited in water less than 0.5 m deep on reed canarygrass Phalaris arudinacea. In year when the littoral vegetation was absent perch were forced to spawn significantly deeper on various types of woody structures. In ?ímov Reservoir, which is less vulnerable to wind, 91.1% of egg strands were spawned in water ≤3 m deep. In contrast, in the wind exposed Chaba?ovice Lake, even in the presence of littoral vegetation, 90.5% of egg strands were found at depths greater than 3 m. In Chaba?ovice Lake, the light penetrated to three times greater depth compared to ?ímov Reservoir and, similarly, the depth limit to which 95% of egg strands were spawned was three times greater in this lake compared to ?ímov Reservoir. This study is the first contribution showing the role of water transparency in controlling the depth distribution of perch egg strands in lakes and reservoirs.