What's the deal with fish passage?

The Auckland Region is home to 21 species of native freshwater fish, most of which are found only in New Zealand and form a unique part of our biodiversity. Many of these fish species need to migrate between fresh and saltwater to complete their life-cycles, a huge challenge for these small fish, which can become impossible because of man-made barriers in streams and rivers.

If native fish are prevented from migrating into suitable habitats then their populations are affected, leading to fewer fish overall and the possibility of local extinction occurring. 

On this page:

• Swimming fish or climbing fish?
• What constitutes a barrier to fish passage?
• Do I need to provide fish passage?
• What can I do?
• How can I find out more?

Swimming fish or climbing fish?

Native fish can be divided into two broad groups depending on their swimming ability.

Swimmers – these species rely on short periods of ‘burst’ swimming to get around in-stream obstacles, such as chutes or rapids. They require areas of low velocity flow to rest in between periods of ‘burst’ swimming so that they don’t become exhausted. Species in this category include inanga, smelt and most bullies.

 

 

Climbers – species in this category are able to migrate over substantial obstacles, such as large waterfalls, by wriggling up the wetted margins at the edges of the water flow. Vertical surfaces can be overcome as long as they have a degree of roughness for the fish to adhere to and remain damp. Species that are known for their climbing ability include juvenile eels, kokopu and koaro.

 

Unlike some introduced fish, such as salmon and trout, our native species are unable to jump over obstacles while migrating upstream. This means that it’s important to take into account the types of native species likely to be present and their swimming abilities when designing fish passage solutions.

For more information on native freshwater fish species see the NIWA Atlas of NZ Freshwater Fishes.

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What constitutes a barrier to fish passage?

Whether a structure is a barrier to fish passage or not can depend on a number of factors:

Fish swimming ability

Climbing species are able to make their way over in-stream obstacles that would be total barriers to swimming species.

Fall height

Vertical differences in water level of as little as 10 cm can act as barriers to weaker-swimming species of fish. The higher the fall height, the more of a barrier it becomes.

Water velocity

High water velocities can exceed the swimming capabilities of native fish and prevent their migration upstream. It’s generally accepted that velocities above 1 m/s are likely to present a barrier to fish passage.

Water depth

Insufficient water depth can present a barrier to the larger species of fish and make them more susceptible to predation. Aprons at culvert outlets that cause flows to spread in a thin sheet during low flows are a common problem.

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Do I need to provide fish passage?

The rules surrounding the requirements for fish passage are contained within the Proposed Regional Plan:  Air, Land and Water. Section 7.5.2 (a) deals with existing structures, while sections 7.5.6 (a) & (b) contain the general conditions that apply to both new and existing structures. Refer to Chapter 7 (PDF) for more information.

Factors such as the availability of suitable upstream habitat and the presence of other barriers downstream can play a role in determining if fish passage is required.

ARC staff will be able to advise on any specific questions if more information is needed.

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What can I do?

Methods of incorporating fish passage into in-stream structures are always going to be site-specific, no two situations will be exactly the same. However, there are general principles that can be applied to both existing structures, where fish passage will be retrofitted, and to new structures, which will be designed with fish passage in mind.

More information on providing fish passage over specific in-stream structures can be found below:

• Culverts
• Weirs/Dams
• Fords
• Channelised streams
• Stormwater management ponds and wetlands

When undertaking any kind of construction or retrofitting work, the timing is important and the work should not be carried out during important migratory times – for most species this is between September and February.

Pollution control measures also need to be considered.  Please refer to ARC Technical Publication 90: Erosion and Sediment Control Guideline for Land Disturbing Activities in the Auckland Region, for regulations regarding earthworks near streams.

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How can I find out more?

• ARC Technical Report 2009/084: “Fish Passage in the Auckland Region – a synthesis of current research” contains the latest information on fish passage research and provides best practice guidelines for ensuring that in-stream structures are fish-friendly. Excerpts have been linked to throughout this website but the full version in pdf format can be downloaded here or a hard copy can be ordered here.
• If extensive modifications are needed for an existing in-stream structure, or if a new structure is being designed, then it is recommended that a suitably-qualified environmental engineer with experience in fish passage is engaged in the project at an early stage.
• ARC staff are able to provide advice and guidance if you have specific questions about fish passage at your site. Contact ARC on 09 366 2000.

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