PRELIMINARY FIELD OBSERVATIONS OF LAKE TROUT (SALMO TRUTTA M. LACUSTRIS L.) REDD STRUCTURE, AND FRY EMERGENCE IN THE UPPER WDA RIVER SYSTEM (NORTHERN POLAND)
The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. Some parameters of spawning redds and the emergence of lake trout fry were investigated at spawning areas in the upper Wda River system. Redds were located and selected in late fall 2003 and a few of their parameters were identified, i.e., dimensions, water velocity, and grain fraction content. The sand content varied in particular redds from 5.1 to 24.8%. Fry was captured with traps at five of the six observed redds. Trout emerged from late April until mid May when temperatures increased within the range of 11.0-16.0°C. The most numerous trout fry was observed in the two biggest redds, which had less sand and high water velocities.
Keywords: Lake trout (Salmo trutta m. lacustris), spawning redds, fry emergence
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