SOME CHARACTERISTICS OF LAKE TROUT SALMO TRUTTA M. LACUSTRIS L. REDDS IN THE UPPER WDA RIVER SYSTEM (NORTH POLAND)
Department of Migratory Fish, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. Observations of lake trout, Salmo trutta m. lacustris L., spawning, including recording redd parameters, were conducted in the 2003-2004 to the 2007-2008 seasons at spawning grounds located in the upper Wda River system. Spawning was noted from mid October to early January at a temperature range of 1.1-10.8°C, but primarily within the 3.0-8.0°C range. Redds were measured following spawning in selected segments of the spawning grounds. The parameters measured were as follows: tailspill size, pot depth, water depth near the tailspill, water velocity above the tailspill. Substrate samples were taken from some of the redds in spring to determine particle size distribution. In total, 51 redds were measured, and substrate samples were collected from fifteen of them. The tailspill length ranged from 40-150 cm, and water depth was from 15 to 55 cm. The geometric mean diameter of the substrate (Dg) ranged from 3.0-17.4 mm, and the sand content (fraction < 1 mm) was from 3.0-36.5%. Water velocity above the redds ranged from 40 to 120 cm s-1, and this differed significantly statistically among the streams investigated; the lowest rates were noted in the upper reaches of the system (Pilica). Furthermore, in this part of the system the mean geometrical diameter of the substrate was twofold smaller and the share of sand twofold higher than in the lower part of the river system. The size of the tailspills was positively correlated with female size, pot depth, and water velocity. In practical terms, it can be generalized that female length corresponded to approximately 55% of the tailspill diameter.
Key words: SALMO TRUTTA, SPAWNING REDDS, SUBSTRATE STRUCTURE, REDD DIMENSIONS