Impacts of land-based activities on coastal and estuarine fisheries and ecosystems
What people do on land can have major impacts on coastal ecosystems and fisheries.
In many cases these are not instantly obvious and effects build up gradually over many years.
Occasionally, these effects reach a point where we start to notice them – often when a fishery we care about is affected.
Sediment washed into the sea from urban development, catchment deforestation, agriculture and roading is a particular problem.
Already we have seen important shellfish fisheries around New Zealand suffer or collapse, at least in part because of too much sediment in the water. These include intertidal shellfish like pipi and cockle, as well as paua, kina and scallop fisheries.
Over the past 50 years, sediment build-up in harbours and sheltered inshore waters around northern New Zealand has probably damaged or destroyed important nursery areas for young snapper and other inshore species.
Our west coast North Island snapper fishery may be particularly affected. Many of these fish are thought to spend their juvenile years in sub-tidal seagrass beds and other three-dimensional ‘living’ habitats in our main west coast harbours. These west coast nursery areas have been shrinking in recent years (seagrass has now largely disappeared from the Manukau Harbour). So with fewer nursery grounds there may be fewer fish to catch.
Nutrient run-off from the land also has an effect, particularly in estuarine ecosystems. And in some places around New Zealand, high levels of bacteria in the water from humans and animals have closed shellfish fisheries by making them unsafe to eat.
Seagrass is an important habitat and provides shelter for young fish. Whangapoua Harbour.
The government’s goal is to see all these effects turned around and the health of affected ecosystems and fisheries restored .
This work involves everyone, because we are all a part of the problem and a part of its solution.
Some of the groups working together to address land-based effects have already had success.
In Whaingaroa (Raglan) Harbour, water quality and biodiversity are now improving through a local initiative to fence and plant waterways leading into the harbour.
Similarly, in Golden Bay, dairy farm run-off has been reduced through an initiative involving local marine farmers, dairy farmers, Fonterra and the Tasman District Council.