SH1: Western Belfast Bypass SH1: Western Belfast Bypass SH1: Western Belfast Bypass SH1: Western Belfast Bypass

SH1: Western Belfast Bypass

Boffa Miskell relocates thousands of fish away from development work.

The Western Belfast Bypass (WBB) is a new four-lane section of the Western Corridor in Christchurch, one component of the NZ Transport Agency’s Christchurch Motorways project, a Road of National Significance. The WBB is a 5 km section of highway, which will help reduce congestion by bypassing Belfast between the Northern Motorway and SH1 at Johns Road.

The WBB alignment crosses an historic floodplain of the Waimakariri River, through what would have originally been wetlands but was drained for farmland pastures. Four human-made perennial waterways were to be culverted, diverted, or filled in to allow for building of the new road.

Boffa Miskell was commissioned by Fulton Hogan Ltd to oversee the aquatic ecology associated with the WBB project, including providing ecological advice on the reconstruction of new waterway channels and maintaining fish passage throughout the construction works, and carrying out the fish salvage as required by the project’s ecological management plan.

Our Aquatic Ecologist, Dr Tanya Blakely, has been leading the team responsible for the rescue and relocation of freshwater fish from the waterways located within the alignment. The fish relocation work required Tanya to work closely with engineers and contractors, so that the fish rescue works were perfectly timed with the road construction works. The fish rescue commenced in August 2015, with the last of the fish relocation works being completed in February 2016.

The specialised technique of electric fishing was initially used to capture fish and relocate them away from the construction zone. Electric fishing uses electricity to temporarily stun the resident fish so they can be relocated. However, electric fishing is best suited for use in faster flowing, stony-bottomed waterways. The waterways within the WBB were slow flowing and all had a thick layer of fine silt and sediment covering the gravel bottom, making it difficult to use electric fishing techniques.

So, the Boffa Miskell team then used a variety of trapping methods in order to rescue as many fish as possible from the waterways. Fyke nets (or hīnaki), Gee minnow traps, and Kilwell box traps were baited with tinned cat food or raw beef, cat biscuits, and NZ’s famous breakfast spread, Marmite. Traps and nets were set in the late afternoon and left overnight to catch nocturnally active fish out searching for food. The following morning, we checked the traps for fish. All fish captured were identified, measured and relocated to a suitable site downstream of the WBB work area and road alignment.

Nearly 1,500 native freshwater fish were captured during the electric fishing and in the traps and nets of approximately 500 m of freshwater habitat within the four farm waterways. The majority of these fish were shortfin eels, but also included longfin eels and inanga (one of the native whitebait species), both of which are of conservation interest due to the status of ‘at risk, declining’. A large number of giant bullies (not threatened, but may be of conservation concern) were also captured.

Despite this enormous number of fish captured, we knew there were still more fish in the waterways. So, once the electric fishing and trapping was completed, the contractors were able to carefully remove the top layer of fine silt and sediment from the stream bed. Boffa Miskell ecologists were on site to search through and rescue and fish from the wet sediment that was gently spread on the banks. A further 1,700 native fish, mainly shortfin and longfin eels, were salvaged from the construction area and relocated to suitable downstream habitat.

It was extremely rewarding to be a part of this huge fish rescue effort, assisting the NZ Transport Agency and Fulton Hogan in salvaging and relocating over 3,000 native freshwater fish species to suitable habitats downstream of the construction works.

Our role

Salvage and relocation of freshwater fish from waterways within the road construction area; aquatic ecology expert advice on the SH1: Western Belfast Bypass project.

The facts

ClientFulton Hogan and NZ Transport Agency
Project teamDr. Tanya Blakely
Project dateAugust 2015 – ongoing