Routine maintenance of stormwater ponds and forebays is essential for maintaining functionality, managing water flow and flood risk, clearing debris and contaminants, and ensuring the health of urban and rural environments. However, maintenance activities can pose a significant risk to the delicate freshwater ecosystems that these ponds support.

Excavation, dewatering, and the removal of sediments and vegetation inadvertently impact populations of native freshwater species who have made these stormwater structures their home, leading to potential stranding, injury, or displacement from their habitats.

Recognising the importance of preserving Aotearoa’s unique freshwater biodiversity, Morphum is continuously engaged by a construction contractor to support the salvage and relocation of freshwater species, this time as part of a project at the Chelsea Sugar Factory Stormwater Pond Forebay.

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Assessment & Relocation

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Many construction projects benefit from integrating ecological considerations into the planning and execution of any work that could potentially affect terrestrial and freshwater ecosystems.

The first step in our approach was to conduct a thorough assessment of the watercourse prior to any disturbance. This allowed us to anticipate the expected species and abundance of fish present. This in turn informed the methodology for the targeted Fish Management Plan. Following our Fish Management Plan, our freshwater ecology team conducted humane overnight trapping of fish using a combination of fyke nets and Gee Minnow traps before the planned dewatering works. This may take two or three nights of fishing, the success of which we assess through a fish stock model.  

During the planned dewatering works, our team implement hand netting and visual and tactile searching of potential fish habitat, including excavated sediments to rescue any remaining fish.

Our team captured and relocated over 260 fish at Chelsea forebay consisting of longfin eel (Anguilla dieffenbachii), shortfin eel (Anguilla australis), banded kōkopu (Galaxias fasciatus) and common bully (Gobiomorphus cotidianus) from the works area to suitable habitat within the same catchment, ensuring that the fish were handled with care and experienced minimal stress.

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Proactive Fish & Wildlife Strategy

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Preparing wildlife management plans, including those for fish, provides two main benefits to contractors and the local communities.

Firstly, they provide a detailed method to protect native fish populations from harm, contributing to the overall health and resilience of freshwater ecosystems.

Secondly, they demonstrate a strong commitment to environmental stewardship (kaitiakitanga), aligning with regulatory requirements, as well as client and community expectations for responsible environmental practices. This creates trust with clients and builds rapport with the communities where the contractors operate.

When organisations prioritise the well-being of native ecosystems when undertaking waterway maintenance, they foster greater confidence in their operations and a brand reputation that potential future clients trust.

Embracing a proactive fish relocation strategy from the outset prevented unintended environmental incidents or the associated negative publicity and regulatory scrutiny that can occur on work sites like these. It also led to more sustainable outcomes for their project and business.

Fish Management Plans (FMPs) are designed alongside the construction plan and methodology to provide guidance on timing and expectations for the parties involved in the projects implementation. It’s built in close cooperation with the contractor to suit the project and the location.

Morphum’s science team is always ready to help support wildlife surveys, freshwater assessments and fish salvage and relocations to mitigate environmental and ecological risk in the industry. Ultimately, this approach has formed the ecological basis for essential stormwater management with the preservation of Aotearoa's precious freshwater biodiversity.

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