Area occupied by key marine non-indigenous species in New Zealand

Grid cell: an area of the harbour (100 by 100 metres) where the non-indigenous species is found.

To measure the spread of non-indigenous species over time, harbours are divided into squares (grid cells). Each year scientists measure the number of grid cells in which each monitored non-indigenous species is found. For this indicator, each grid cell is 100 metres by 100 metres.

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Marine non-indigenous (exotic) species arrive in New Zealand waters on the hulls of international vessels (biofouling) or in discharged ballast waters. Some have little impact or cannot survive in New Zealand waters; others have a negative impact on our native habitats and species and become pests. They can compete with, and prey on, indigenous species, modify natural habitats, affect marine industries or can alter ecosystem processes. The potential impact of non-indigenous species on our native habitats and species means they could threaten our cultural and natural heritage, as well as economic activities such as commercial and recreational fishing, shellfish harvesting, and aquaculture.

The Ministry for Primary Industries coordinates and undertakes monitoring to identify where exotic species have taken hold and determine what management measures to take. Monitoring focuses on sites where incursions by exotic marine species are most likely to occur. Species can occur at more than one location.
This data is informed by records from the national Marine High-Risk Site Surveillance (MHRSS) programme in monitored ports of first entry for international vessels.