Haringvliet Sluices Blocked Migratory Fish Passage for 18 Years

For 18 years, fewer than 30% of migratory fish could pass Haringvliet sluices. This is a significant barrier to their migration.
By Newsroom | Environment, Netherlands |

Analysis of 18 Years of Data Shows Limited Opportunities for Salmon, Trout, and Lamprey

A new analysis spanning 18 years, from 1996 to 2018, demonstrates that migratory fish like salmon, sea trout, and sea lamprey faced severely restricted passage through the Haringvliet sluices. During this period, prior to changes in sluice management, fewer than a third of these fish were able to enter the Rhine-Meuse delta, and their successful passage through the sluices occurred only within very narrow timeframes.

The study, published in Movement Ecology, utilized data collected before the implementation of "Kierbeheer," a management strategy involving the partial opening of the sluices to allow limited saltwater intrusion and aid fish migration. Researchers found that river discharge played a significant role in attracting migratory fish for their upstream journeys. However, when the sluices were discharging water, high flow velocities actually limited passage opportunities. When no discharge occurred, passage was solely reliant on the operation of fish locks.

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The findings underscore a global issue where dams and other artificial structures disrupt the crucial migration routes of anadromous fish. This research offers a baseline understanding of fish behavior at the Haringvliet barrier before management adjustments, with ongoing studies now examining the impact of Kierbeheer on fish migration patterns.

Species-Specific Behaviors and Data Sources

While the study highlights general challenges, evidence suggests different species exhibited distinct passage preferences and timing. Data underpinning the publication, made available by Wageningen University & Research, was compiled from environmental and sluice management records provided by Rijkswaterstaat and meteorological data from the Royal Netherlands Meteorological Institute (KNMI). Fish tagging and detection data were collected using the NEDAP Trail System®, owned by Rijkswaterstaat.

The dataset aims to improve understanding of fish behavior to optimize sluice gate management and support the rehabilitation of migratory fish populations.

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Frequently Asked Questions

Q: How did Haringvliet sluices affect migratory fish between 1996 and 2018?
A study found that migratory fish like salmon and trout had very limited passage through the Haringvliet sluices during this period. Fewer than a third of these fish could enter the Rhine-Meuse delta.
Q: What made it difficult for fish to pass through the Haringvliet sluices?
High water speeds from the sluices discharging water made passage difficult for the fish. When the sluices were not discharging, passage depended only on special fish locks.
Q: Did all fish species have the same problems passing the Haringvliet sluices?
No, the study suggests that different fish species had different preferences and timing for passing through the sluices.
Q: What is being done to help migratory fish at the Haringvliet sluices now?
A new management strategy called 'Kierbeheer' partially opens the sluices to allow some saltwater in and help fish migration. Ongoing studies are looking at how this new method is working.