Abstract
The paper presents data on some biological indices, i.e. size and age structure, of ruff in the Curonian Lagoon throughout 1993–2006. It analyses year-to-year dynamics of ruff catches, identifies the factors determining their abundances, and examines possible reasons for variation in ruff stocks. The size of ruff spawning shoals was found to have no effect on ruff reproduction. Pikeperch and pike stocks were the most important determinants limiting ruff abundance. Ruff catches increased up to several thousand tons in the years when pikeperch catches were below 50–70 t. Effectiveness of ruff spawning was dependent on the course of spring and water yield in summer. Below-zero temperatures and increased water yield of the Nemunas River in March created favourable conditions for ruff reproduction and abundance. Similar natural conditions for reproduction can explain similar catches of fish species belonging to different ecological groups, such as ruff and smelt.
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