Fake seagrass could help boost fish numbers

Artificial seagrass, used to promote population growth in snapper. Photo / Supplied

Scientists are using fake grass mats under the sea to prove how New Zealand's fish stocks can be boosted.

The plastic mats are being used at Coromandel by NIWA scientists to test how seagrass attracts fish such as juvenile snapper and trevally.

A large amount of New Zealand's seagrass has been lost from sediment from land development washing into harbours. Seagrass at Whangarei Harbour has gone from 14 sq km in the 1960s to virtually none, while Tauranga Harbour lost 90 per cent of its seagrass between 1959 and 1966.

There has been a resurgence in the greater Auckland region, with seagrass expanding in the lower Kaipara, at Snells Beach and St Heliers.

NIWA fisheries ecologist Dr Mark Morrison said scientists had created artificial beds at Whangapoua Estuary. The "plants" were made from plastic fronds 5cm to 30cm long and tied to wire frames to form an artificial mat.

"We made them with tantalising long blades of artificial grass, the things fish really go for," Dr Morrison said.

Fish numbers reached their highest towards the highest seagrass densities. This summer fish are being tagged to track their survival and growth rates.

"What we found, initially, is that fish are really looking for shelter and seagrasses provide good protection to fish."

New Zealand Recreational Fishing Council president Geoff Rowling said the research and steps to enlarge seagrass areas was vital.

Council vice president Sheryl Hart said fishermen needed to get smart, but it was ultimately up to local body authorities to stop agricultural run-off and sediment run-off from development - the best way to encourage regrowth.