Selected barriers to freshwater fish in Hawke’s Bay

  • Image, Selected barriers to freshwater fish in Hawke’s Bay

    Many of New Zealand’s iconic freshwater fish species are diadromous, which means they need to migrate between fresh water and the ocean to complete their life cycles. Some human-made structures such as culverts, weirs, stormwater pump stations, tide gates, and dams can obstruct diadromous fish migrations and prevent fish from reaching critical habitats. This can result in the gradual decline and loss of fish species from some rivers, streams and lakes. Protecting the connection between upstream and downstream habitats of our native fish is as important as protecting their habitats themselves.

    We do not yet have enough data to provide a national picture on fish barriers, so we report on the known barriers to freshwater fish passage in the Hawke’s Bay region – culverts, weirs, and stormwater pump stations.

    We classified Selected barriers to freshwater fish in Hawke’s Bay as supporting information.

    Key findings

    One-third (80) of the 240 culverts, weirs, and stormwater pump stations surveyed in the Hawke’s Bay region between 2002 and 2010 were identified as barriers to fish passage during some or all flow conditions.

    • More than half (44) of the 80 culverts, weirs, and stormwater pump stations identified as fish barriers were barriers in all flow conditions, depending on the fish biology. The following proportions of these structures were barriers in all flows: 
      • 71.3 percent for jumping fish 
      • 72.5 percent for fast-swimming fish 
      • 63.8 percent for climbing fish 
      • 56.3 percent for eel/tuna.
    • Of the assessed in-stream structures, 27 percent of culverts, 40 percent of weirs, and 71 percent of stormwater pump stations were identified as fish barriers in at least some flow conditions to some fish.
    • Many of these barriers occur in coastal areas, potentially preventing diadromous fish to access considerable upstream river habitat. 

    Figure 1

    Figure 2

    Note: This figure does not show culverts, weirs, and stormwater pump stations assessed as not being barriers to any fish passage.

    Definition and methodology

    Between 2002 and 2010, the Hawke’s Bay Regional Council (HBRC) assessed 240 culverts, weirs, and stormwater pump stations in the region to determine whether they are barriers to fish passage (HBRC, 2010). HBRC visited each structure and completed an in-stream structure assessment form (Kelly & Collier, 2006). This form records barrier type, as well as its severity in preventing fish passage to different fish groups (eels, jumpers, climbers, and fast-swimmers) under different flow conditions. Whether an in-stream structure is a barrier to fish depends on the fish (and life stage) and the flow conditions. Juvenile eels are able to climb wetted surfaces and can move through small spaces both in and out of water so are more able to get upstream past in-stream structures than other fish.

    The New Zealand Fish Passage Advisory Group are working to standardise monitoring of barriers to fish passage, so that the national extent of barriers to freshwater fish can be evaluated in the future.

    Data quality 

    Topic Classification   Relevance Accuracy 
     Resource use and management, and other human activities

    Supporting information

     Image, Partial relevance.

    Partial

    Image, Medium accuracy.

    Medium 

    See Data quality information for more detail.

    References

    Hawke’s Bay Regional Council (HBRC) (2010). A report on the known barriers to fish passage in Hawke’s Bay (PDF, 1.25MB). Environmental Management Group Technical Report. Retrieved from www.hbrc.govt.nz.

    Kelly, J, & Collier, K (2006). Assessment of fish passage within selected districts of the Waikato Region. Environment Waikato Technical Series 2007/03. Retrieved from www.waikatoregion.govt.nz.

    Published 27 April 2017

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