Christmas trees becomes habitat for fish

For several years, Strömma, in collaboration with partners such as the City of Stockholm and SportFiskarna, has engaged the public in collecting discarded Christmas trees. The trees are then submerged in the waters around Stockholm in bundles of three to five, so-called “risvasar”. The aim is to create new spawning areas and nursery habitats for Stockholm’s fish, as pristine areas crucial for fish upbringing are threatened by rapid exploitation.

Fish habitats are impacted by urban explotation

Today, Stockholm, with its archipelago and city center, faces significant challenges due to exploitation. For example expanded shoreline areas, dredging, heavy boat traffic, docks, and marinas. This results in the gradual disappearance of previously untouched fish habitats. This leads to a decline in the reproduction of fish offspring.

Studies indicate that approximately 40% of the fish’s breeding grounds along the coast are already gone. And 0.5% of the remaining pristine areas are being exploited each year. If this trend continues, all untouched breeding areas around Stockholm could be lost within 50 years.

Christmas trees transforms into fish playgrounds

One day in January, Christmas trees are collected from the public. Three to five trees are bundled together to form “risvasar”. Theese are transported to the water and lowered to a suitable depth with the help of securely bound stones. As the water warms up in the spring and the fish’s spawning season begins, the branches of the trees serve as new playgrounds and habitats for fish offspring. Fish move into the trees to build beds, nests, and spawn. Here the fry hatch. And the tight and dense habitat of the trees provides fry with small areas to get into and grow.

Positive outcomes of the project

The Stockholm City Environmental Barometer reports positive effects of the project. Divers have confirmed this with underwater cameras, observing perch playing in the branches of the trees. They have witnessed fish laying eggs on, and swimming around, the Christmas trees.

Aborr-rom i en risvase.
New fish habitat in a bundle of old Christmas trees. Photo: Sportfiskarna

Using “risvasar” to create nursery habitats is an old yet proven fish management method. Yet, at a low cost, it yields significant benefits. The ecological gains are substantial. The project fosters public engagement in the well-being of Stockholm’s water and its inhabitants.

By participating in the creation of “risvasar” with the help of Christmas trees and submerging them in Stockholm’s waters, Strömma contributes to strengthening the ecosystem. (14.2)