Food-web manipulation in a small, eutrophic Lake Wirbel, Poland: long-term changes in fish biomass and basic measures of water quality. A case study

• Published in: Hydrobiologia Vol. 342-343; pp. 383 - 386
• Main Authors: Prejs, Andrzej, Pijanowska, Joanna, Koperski, Pawe, Martyniak, Andrzej, Boro, Sawomir, Hliwa, Piotr
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Dordrecht Springer Nature B.V 01.01.1997
• Subjects: Eutrophic lakes; Eutrophication; Freshwater; Prey; Rotenone; Water quality; Water quality measurements; Zooplankton; Poland; Poland, Wirbel L
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1017047625303

A whole-lake experiment was carried out for seven years(1988-1994) in a shallow, eutrophic lake. In the first phase(1989-1991), repeated introductions of young-of-the-year pike(Esox lucius) were used to control the density ofjuvenilestages of the dominant planktivores (roach Rutilusrutilus,white bream Blicca bjoerkna and Leucaspiusdelineatus).The successive introductions of juvenile pike were accompaniedbyselective removal of large pike, roach, bream Abramisbramaand white bream. No visible improvement in water quality wasregistered in the first three years. Assessments made afterthelake was treated with rotenone, revealed the high efficiencyofjuvenile pike in controlling prey of vulnerable size. Thoughthefirst three age-classes were nearly exterminated, older fish(3+ to6+) remained abundant enough to keep their planktonic prey incheck. Indeed, the non-altered density of dominant cladoceransindicated that they were still heavily preyed upon. Algalbiomassremained high.In October 1991, rotenone was applied to remove all fish.Immigrating fish were gradually recolonizing the lake fromspring1992 onwards. However, the process was kept under control bycontinued stocking with juvenile pike and intensive fishing.Theyears following the rotenone treatment witnessed aconsiderableimprovement in water quality, with water transparency 30%higher,a significant 2.2-fold decrease in seston dry weight and2.8-folddecrease in algal biomass, averaged for the summer months.Theseevents can largely be attributed to substantial changes in theherbivorous zooplankton, above all increased density of LakeWirbel's largest cladoceran, Daphniacucullata.[PUBLICATION ABSTRACT]