Ю.А. Зуев, А.В. Шацкий, А.Ю. Тамулёнис.
Промысловые запасы мотыля (CHIRONOMUS: DIPTERA) ряда озер Ленинградской области
Keywords: Chironomus plumosus; Chironomidae larvae; distribution; macrobenthos; near-shore zone of lakes; stock; bloodworms; littoral
The harvestable stock of bloodworms (Chironomus sp.) has been investigated in some lakes of the Leningrad Region since 2010. Bloodworms were detected in 45 out of 51 lakes surveyed. Abundances sufficient for commercial harvesting of larvae were found in lakes Pobednoe and Vishnevskoe. Mean annual stocks in these lakes were 31 and 90tons. The highest recorded concentration was 311 tons in Lake Vishnevskoe in 2014 and the lowest concentration was 4.5 tons in Lake Pobednoe in 2020. Regular commercial harvesting of Chironomus larvae takes place only in Lake Pobednoe. In the absence of harvesting statistics, bloodworm stocks could not be estimated accurately. The distribution of Chironomidae larvae has been investigated on different substrates and in differentт lake areas (littoral and profundal) since 2018. According to the Kruskal-Wallis test, larval numbers were the highest in the nearshore zone. The nearshore zone was delineated through the analysis of the lake’s geomorphological characteristics. At the least, is was 30 meters wide. The biomass of larvae in this zone varies among years concurrently with the larval biomass in the central parts of the lakes. Nearshore stocks contribute in different years from a tenth to a half of the total bloodworm biomass in every lake. Among-year variations of the stock and harvesting effects on it cannot be estimated properly unless larvae in this zone are taken into account. Also, being inaccessible for regular harvesting gears, the nearshore zone is a natural refugium for bloodworms.
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