Fake seagrass could help boost fish numbers: New Zealand study

Andre Hueber NZ Herald 30 Jan 11;

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.

Fish battling to survive with seagrass decline
TVNZ 30 Jan 11;

Fewer young fish are surviving because it's becoming harder to find enough food and shelter in New Zealand waters.

The National Institute of Water and Atmospheric Research (NIWA) said the alarming decline of seagrass is having a major impact on fish numbers.

Fisheries ecologist from NIWA Mark Morrison said fish use seagrass for protection.

"To them it's not the fact that it's sea grass per se but it's structure and they can hide in it from and protect themselves from being eaten by bigger fish and other predators," Morrison told ONE News

But that protection has been deteriorating for the last century.

Whangarei Harbour had 14 square kilometres of it in 1960 and now it's almost all gone.

Tauranga Harbour lost 90% of its seagrass between 1959 and 1996.

Morrison said the decline and loss is a world wide problem.

"We're not alone in it and in fact some areas are much worse off," he said.

The cause of the long term decline is thought to be sediment from land developments running into the ocean.

"What you do on the land goes down through the catchments, the rivers and it goes into the estuaries and seas. It has these big cascade effects down to the open coast," Morrison said.

NIWA is trying to help fish protect themselves in some areas, by putting plastic seagrass in its Coromandel estuary reserve to imitate the natural plant.

Morrison said 16 species have already flocked to the reserve.