Located in the township of Orewa is a large stormwater pond approximately 1.2 hectares in size that surrounds a number of residences. It acts as both a feature and stormwater waterway that is home to many native and exotic fish and bird wildlife. In 2016, grass carp were released due to the domination of the pest weed Egeria densa, and like many other sites was threatening to both the wildlife as a health risk, and interfering with the purpose of the site (being flooding control).
Auckland Council and NZWR, alongside Hon. Mark Mitchell (MP for Rodney) agreed that grass carp would be the most appropriate, and effective method. Other aquatic weed control methods are more costly, and the likes of herbicides and the mechanical removal of weeds results in considerable loss of aquatic life and can result in degradation of the habitat through rotting vegetation and disturbance of sediments; making it unsafe for humans or wildlife to consume safely. In a stormwater system this is important to avoid as the effects of such operations get flushed directly into the ocean.
Once introduced the grass carp reduced the weed levels on the eastern side of the pond (with a fish screen mesh divider running through the centre). This release allows for the process of improving the sites water quality to start and through on-going surveys it is evident that the fish will be required to have full site access.
Below are pictures of the effects of grass carp being present on the eastern side vs. the un-stocked western side.
Please note that this waterway is not open for fishing to the public, and course fishing is not permitted to anyone.
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