Reducing the populations of planktivorous and benthivorous fish (either directly or through stocking of piscivorous fish)
may induce ecosystem changes that increase water transparency and decrease the risk of algal blooms and fish kills,
at least in the short term. However, the generality of biomanipulation effects on water quality across lake types and
geographical regions is not known. Therefore, we have undertaken a systematic review of such effects in eutrophic
lakes in temperate regions throughout the world.
Methods: Searches for literature were made using online publication databases, search engines, specialist websites
and bibliographies of literature reviews. Search terms were developed in English, Danish, Dutch and Swedish. Identified
articles were screened for relevance using inclusion criteria set out in an a priori protocol. To reduce the risk of bias, we
then critically appraised the combined evidence found on each biomanipulation. Data were extracted on outcomes
such as Secchi depth and chlorophyll a concentration before, during and/or after manipulation, and on effect
modifiers such as lake properties and amounts of fish removed or stocked.
Results: Our searches identified more than 14,500 articles. After screening for relevance, 233 of them remained. After
exclusions based on critical appraisal, our evidence base included useful data on 128 biomanipulations in 123 lakes.
Of these interventions, 85% had been made in Europe and 15% in North America. Meta-analysis showed that removal
of planktivores and benthivores (with or without piscivore stocking) leads to increased Secchi depth and decreased
chlorophyll a concentration during intervention and the first three years afterwards. Piscivore stocking alone has
no significant effect. The response of chlorophyll a levels to biomanipulation is stronger in lakes where fish removal is
intense, and in lakes which are small and/or have high pre-manipulation concentrations of total phosphorus.
Conclusions: Our review improves on previous reviews of biomanipulation in that we identified a large number of
case studies from many parts of the world and used a consistent, repeatable process to screen them for relevance
and susceptibility to bias. Our results indicate that removal of planktivorous and benthivorous fish is a useful means of
improving water quality in eutrophic lakes. Biomanipulation tends to be particularly successful in relatively small
lakes with short retention times and high phosphorus levels. More thorough fish removal increases the efficacy
of biomanipulation. Nonetheless successes and failures have occurred across a wide range of conditions.
Keywords: Biomanipulation, Planktivore, Benthivore, Piscivore stocking, Fish removal, Lake restoration, Eutrophication,
Water quality, Phytoplankton