| Summary: | 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 Římov Reservoir, Czech Republic,
in the years 2007 and 2011 using boat observation and SCUBA divers. The data were compared
with results from Chabařovice Lake, Czech Republic, where similar monitoring took place in
2007–2010 and 2012. In shallow water of Římov 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
Římov 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 Chabařovice Lake, even in the
presence of littoral vegetation, 90.5% of egg strands were found at depths greater than 3
m. In Chabařovice Lake, the light penetrated to three times greater depth compared to
Římov Reservoir and, similarly, the depth limit to which 95% of egg strands were spawned
was three times greater in this lake compared to Římov 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.
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