Ocean experiments help protect environment

Press, Volume CXIV, Issue 33448, 1 February 1974, Page 14

Ocean experiments help protect environment

(Sy

GLENN HASZARD)

Little white cards enclosed in clear plastic envelopes have been washing up on Canterbury beaches in the last two months. Information obtained from them could have implications for the fishing industry and environmental prolection.

The card shown m the illustration is one of about 2000 released in Pegasus Bay by the New Zealand Oceanographic Institute from the research vessel Tangaroa in October. They are waterproof inside their plastic covers and float on or near the surface of the sea until they are washed ashore and stranded. Instructions on the cards request tinders to return them to the oceanographic institute.

The drift card illustrated was found between Waimairi Beach and Spencer Park Beach last November 11, having been released by the institute about 15 miles offshore exactly one month before. About the same time as the cards were released, 1000 objects like the one shown in the other illustration were released. They are called sea-bed drifters and are made of light plastic rods about 2ft long with an Bin plastic disc at one end and a brass weight at the other. When released these drifters fall to the bottom and the brass weights anchor them in a vertical position. They are kept moving by the light weight of the disc at the top. and drift along the floor of the sea with the prevailing currents until they are either washed ashore or fished up in trawling nets. 70 recovered About 70 drifters have been recovered so far. Like the cards, the drifters are clearly labelled. Because of the possibility of their being fished up by Japanese or Russian trawlers, they are labelled in three languages. Although drifters have been used extensively overseas, this is the first time they have been used in New Zealand, according to Mr R. H. Herzer, a student from Victoria University in Wellington, who is working with the institute while doing his Ph.D. thesis. Sea-floor currents “The function of the seabed drifters is to establish on a regional basis the direction of bottom current movement." he said. Information obtained by this means could be used to explain the direction solid or chemical pollutants would travel if discharged into the sea. said Mr Herzer. It could also be used to locate the source of an offshore mineral deposit if traces of the mineral were washed ashore, he said. Research by the oceanographic institute has shown that there is a noticeable difference between the drift from onshore and offshore releases. Cards dropped at points up to 20

miles off shore in the southern part of Pegasus Bay have been recovered mainly <>n the Pegasus Bay beaches after a nett drift due west. Cards dropped 20 to 60 miles offshore have moved north-east parallel to the coastline as far as Gisborne. The implications of this pattern for Christchurch are clear. If factories were permitted to discharge solid pollutants into the sea they would all find their way back on to our beaches. Similarily, if solid pollu*ants were discharged from Timaru there would be a good chance that they would find their way up'to the Canterbury area. Litter on beaches The westward drift in Pegasus Bay also goes a long way towards explaining the amount of litter, cast from fishing and other commercial vessels, which has been found on Christchurch beaches. Now that patterns of drift around the New Zealand coasts have been established more specific studies are being made, said Mr Herzer. One study of importance

to fishermen is the tracing of the movement of larval forms of sea life. This can be done by using a device called a parachute drogue. It

is released at a specific depth and attached to a buoy on the surface. The buoy can be tracked by a vessel and hydrological measurements such as temperature and salinity can be taken. “Having found cards which we released we can predict whether areas of upwelling (cold deepwater currents moving on to continental shelves) are rich in nutrients, which provide favourable conditions for plankton and hence other fish,” said Mr Herzer. The oceanographic institute, attached to the Department of Scientific and Industrial Research in Wellington, has also been studying the possible environmental effects of hot-water discharge from the New Plymouth thermal power station. Scientists from the institute are finding out the direction the hot water will take and its effects on fish and other marine life. The need for environmental impact reports before major projects affecting the environment are sanctioned is becoming increasingly apparent. The New Zealand Oceanographic Institute, with its staff of about 30 scientists and technicians, is well equipped to provide this information.