Sea grass pollution threatens snapper
Sun, 17 Mar 2013 6:23p.m.
By Sanele Chadwick
New Zealand pasture has taken a battering from the drought. But under the sea, grass pastures are facing a different threat, and it could impact on our snapper stocks.
The sea grass in the Kaipara Harbour is a crucial feeding ground for snapper. But there are fears the fish numbers will drop as the sea grass is being destroyed by sediment and pollution.
Baby snapper and a host of other fish filmed over the past few days have been having a feed in the Kaipara Harbour.
"We know it's really important for snapper," says Dr Mark Morrison, NIWA scientist. "We know the habits in there support large numbers of snapper and other species as well – travelly, sharks, school sharks, grand mullets. So the harbour itself is really, really important for the West Coast ecosystem."
But scientists are worried that pollution and runoff from nearby farms could kill the sea grass and the fish, particularly the snapper, will start to disappear.
"If those critical habitats were knocked out by an intervention, by man, or whatever, then you're looking at a much reduced number of small fish that migrate to the coast subsequently," says Dr Morrison. "Then you're looking at smaller stock sizes and productivity from fisheries."
That means there would be less fish to catch, and that's worrying locals.
"We have to seriously consider in terms of what's happening on the land and the runoff that comes from farmlands, developments around the eastern shores of the Kaipara Harbour," says Richard Nahi of Ngati Whatua.
Scientists have begun using aerial photos to get a better picture of what's happening.
"What we're doing now is trying to go towards mapping out those habitats and where they are and what extent they are – where the important areas are – and look after them over time," says Dr Morrison.
The sea grass needs light to grow. Without it, it dies. It's already happened in Tauranga, the Waitamata and Manukau Harbours, dramatically reducing snapper numbers. But hopefully it will not happen in the Kaipara Harbour.
Local iwi, council and community are working together to prevent runoff and pollution from reaching the water.
Researchers will spend another few weeks completing their research and the next few months analysing their results.
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