Collaborating to help our freshwater fish
species to complete their lifecycle,” says Tim Olley, Field Ecologist for Fish & Wildlife Services. “This is an important piece of the puzzle for helping conserve our native fish.”
B Y J A C Q U I E WA LT E R S | P H O T O G R A P H Y T I M O L L E Y
Stream crossings have been added in the Nelson Forests estate over many years, some dating back to the days of the Forest Service. The crossings were put in place to allow access across rivers and streams to various parts of the estate for tree planting, forest management and tree harvesting activities. The natural migratory process of fish can be seriously impeded by poorly constructed and maintained stream crossings. Smooth concrete culverts can create something akin to a hydroslide, because of the way that they focus and intensify water flow, which fish can find impossible to swim through. Other structures, such as battery culvert fords, can become perched (raised above the level of the stream bed) as the stream bed downstream of the structure is eroded with time. These are significant, but not irreversible, barriers to many of Aotearoa New Zealand’s native fish. To solve the problem, Fish & Wildlife Services retrofit fish ramps, baffles and ropes to existing stream crossings that are an issue for fish passage. Heather Arnold, Environmental Planner for Nelson Forests has spearheaded the project to ensure unimpeded fish passage in streams in the company’s forest estate since 2017. The first task was to locate and map out stream crossings based
A
otearoa New Zealand has more than 50 native freshwater fish species. Around 70 per cent of these are threatened. Many of these fish access different habitats during their lifecycles. Some species, such as inanga (one of the whitebait species), are migratory. They move between fresh and sea water environments to complete their lifecycles. Other species spend their entire life in freshwater. Fish are found in a variety of freshwater habitats. For example, giant kōkopu and īnanga tend to be found in lowland rivers, streams
45° cut
and wetlands, whereas kōaro live in high, mountainous, bouldery streams. Many instream structures e.g. culverts across New Zealand are blocking fish migration and impacting our freshwater fish species. Nelson Forests has been collaborating with Fish & Wildlife Services to help ensure that fish can travel through streams in the Nelson Forests estate. “Nelson Forests’ commitment to improving fish passage at their structures aims to reconnect waterways and provide all habitats necessary for our freshwater
45° cut
Above: From top - Kōaro; Diagram: The culverts are fitted with fish baffles to slow water velocities and create pools for fish to rest as they move through the culverts. The baffles are cut at 45 degrees so fish have the option of swimming around or over the top of the baffles; the baffles are flexible, therefore they can flex over during high flows and maintain culvert capacity (an engineering friendly solution to fish passage). 70
Removing obstacles
