Freshwater biodiversity is steadily decreasing. A research team headed by IGB and the Humboldt Universität zu Berlin (HU), in collaboration with angling clubs, performed whole-lake experiments in 20 lakes to enhance ecological conditions. Improved habitat was the most effective method of increasing fish populations, while stocking failed completely.
The research, which was published in the journal Science, emphasizes the significance of restoring habitats and enhancing natural ecosystem processes to benefit fish populations, conservation, and fisheries.
Many conservation efforts concentrate on a single species. An alternative method is to holistically improve ecological processes and habitats, thus supporting entire species communities. However, because it is costly, this so-called ecosystem-based management is rarely implemented. There is also an absence of evidence that ecosystem-based habitat management is more efficient than obvious alternatives, like an animal release to boost stocks.
Important Lesson for Fish Conservation
A study team based in Berlin described breakthrough research in collaboration with multiple angling clubs organized in the Angler Association of Lower Saxony. Over a six-year period, scientists and practitioners collaborated to conduct a series of whole-lake experiments and compare results of ecosystem-based habitat enhancement versus fish stocking in 20 gravel pit lakes. Additional shallow water zones were formed in some of the lakes.
To increase structural diversity in other lakes, coarse wood bundles were added. Other study lakes were filled with five fish species of interest to fisheries; control lakes were unmanipulated. The research was based on a sample of over 150,000 fish.
The key result: Creating shallow water zones was the most efficient method to increase fish populations. These zones are ecologically vital for numerous fish species, particularly as spawning grounds and nursery areas for young fish. The introduction of coarse wood had only positive effects in selected lakes; fish stocking completely failed.
Restoring central ecological processes and habitats—ecosystem-based management—is likely to have stronger long-term effects for rebuilding fish species and populations than narrow, species-focused conservation actions.
Johannes Radinger Study Lead Author, Leibniz-Institute of Freshwater Ecology and Inland Fisheries
From The Laboratory to Jointly Executed Whole-Lake Experiments
Never before have fish communities been studied on such a large-scale set of whole-lake experiments involving numerous angling clubs and other practitioners.
In contrast to studies in the laboratory, field experiments that consider natural ecosystem variation as well as ecological and social interactions allow to gain robust evidence about the effectiveness of management measures.
Thomas Klefoth, Professor, Hochschule Bremen
Thomas Klefoth is the co-initiator of the project.
“To include multiple gravel pit lakes in the experiments was only possible through close cooperation between research and practice. The transdisciplinary approach contributed to a rethinking of fish stocking and fostered the acceptance of more sustainable, ecosystem-based management alternatives,” states study leader Robert Arlinghaus, Professor of Integrative Fisheries Management at the HU and the IGB.
Two Key Messages for Freshwater Conservation and Fisheries Management
The research emphasizes two key messages that are applicable to other aquatic ecosystems besides gravel pit lakes: restoring ecological processes has a more long-term effect on communities and species than narrow, species-focused conservation actions.
Furthermore, the conservation of freshwater biodiversity is most efficient when user groups, like angling clubs, feel responsible and are supported in their efforts by authorities, associations, and science. This method allows for the reconciliation of conservation and use, as ecosystem-based management benefits both species and fisheries.
Radinger, J., et al. (2023) Ecosystem-based management outperforms species-focused stocking for enhancing fish populations. Science. doi.org/10.1126/science.adf0895.