Scientist Discusses Pipi Population

Press, Volume CI, Issue 29898, 11 August 1962, Page 13

Scientist Discusses Pipi Population

In the summer at 1953-54, there was an estimated population of 430 million adult pipie—in size from lfin to 2in—in a strip 40 yards wide from South Brighton to the

Wsumakariri river mouth. Thus information was given yvsrterday by Mr E. W. Dawson, a senior scientific officer of the Department of Scientific and Industrial Research in Wellington, commenting on recent correspondence in ‘The Press" about the disappearance of the pip. beds. However, because of the lack of “settling" of young pipis since 1947 (calculated from an examination of annual rings of growth on pipis in 1953-54) he had concluded that by 1957 or 1958 the pifi beds would have decreased considerably, and would eventually disappear, said Mr Dawson.

“During a recent visit to the New Brighton beach I was unable to locate any sign of the extensive beds formerly situated near the pier, between 80 and 100 yards below high-tide mark.” said Mr Dawson. Some years ago, Mr Dawson carried out a monthly sampling of the pipd population at 1000 yard intervals along a 30-«n:le stretch of the Canterbury beaches.

His rerearcbee Stowed it was “no easy task” to be ■ pipi. Ito struggle for existence was a very real one. “Each individual pipe found on trie beach was certainly lucky to have found a resting place.” he said. Describing the life cycle of the pipi. Mr Dawson says that a single female pusx may cany up to 30 million eggs during the breeding season—an insurance against the tremendous losses after hatching. The eggs are shad into the sea, where they are fertilised by sperm from the male pipis. The fertiUsed eggs develop into feeblyswimming larval stages known as “veligers.” which for two weeks are at the mercy of tides, currents, and drifts, and predators such ss fish, crabs and guMs. “If they have then avoided death they will settle down in the sand of the nearest part of the beach where the currents bane swept them,” says Mr Dewwon. “Here, they will increase in size from their tiny Larval Shells of about one-hundredth of an inch, until in four or five years they become the foilsized pipis known to everyone who visits the beach.” Ocean currents are largely responsible for carrying the larvae to the particular beaches along the shores of Pegasus Bay. says Mr Dawson. The settling of the pipi larvae on the beach is known as a “spetfaß.” In some years there is no “apatfaU” at certain places, or one insufficient to establish a population.

If any readers have observations on the depletion of the pipi beds along the foreshore from South Brighton to Brooklands, Mr Dawson would be glad if they would communicate with bim at the New Zealand Oceanographic Institute, P.O. Box 8009, Wellington.