Improved trawling setup for sampling pelagic juvenile fish communities in small inland bodies of water

Trawling juveniles is an effective method to estimate 0+ fish assemblages in inland bodies of water. Trawlers are usually moved between bodies of water by ground transport, which restricts the size, weight and type of the equipment able to be transported, and as such do not always come equipped with machinery for trawl operation. Having to lift the trawl onto the deck of the trawler after each tow also makes small-scale juvenile trawling time-consuming and personnel intensive and deep water trawling is especially hard work. This study introduces a new two-boat setup for continuous trawling that enables faster and easier operation of the trawl, even in deep water layers, and more accurate distance and depth measurements

Extremely shallow spawning of perch ( Perca fluviatilis

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

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

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