Scientists Study Fish

Press, Volume CVI, Issue 31121, 26 July 1966, Page 18

Scientists Study Fish

Flounders are scarce at this time of the year. Marine Department scientists, using a net of only half the mesh of the commercial kind, caught only one flounder in a day’s fishing out from Lyttelton on Friday, and did only slightly better with 30 on Saturday.

They did not expect many, and their trawling was done purely in the interests of research into the behaviour and population of flounders. The fish were tagged with loops of yellow plastic and returned to the sea. Commercial fishermen are paid a bounty for those they recover, and the information they provide helps the biologists to learn such things as the spawning rate of the fish, the age at which they mature, and their movement habits. While the scientists were trawling for slim catches of flounders in Pegasus Bay in the chartered boat Marewa, the rest of the commercial fleet was out in deep water fishing for tarakihi. The trawling done on Friday and Saturday was the first of an expanded programme of flounder catching and tagging, with the purpose of assemb--ling information of practical' value to commercial fishing. Similar trips are being made tfMk from the port of Timaru. When flounders are caught ■HH they are sexed, measured andi weighed. The purpose of the MB finer-mesh net is to catch the i

young fish that would normally escape from commercial nets. The fine-mesh net is tied over the ordinary commercial net.

More than 16,000 flounders have been tagged in the last two years in the Lyttelton, Akaroa and estuary areas, ana some have been recovered as far away as the Otago Heads. In the next 12 months the Marine Department intends to charter a fishing boat on three successive days a month to ensure a comprehensive coverI age of the areas being studied, over the entire year, j At the same time, Mr A. I Coakley, assistant fisheries scientist for the Canterbury area, is beginning a similar line of research into the biology, growth rate, number and age structure of the population of elephant fish. Elephant fish are third In importance on the list of commercial varieties caught from Canterbury ports (after tarakihi and gurnet), but landings have steadily decreased in the last three years. Demand for elephant fish Is growing—for fish and chips, fish fingers and exports to Australia as “white fillets”— but in spite of increased efforts to catch them, the total catch has not been growing. Mr Coakley is trying to find out why. He particularly wants to discover whether i there are local populations of elephant fish or whether there ■is a continuous population around the coast. Timaru, Akaroa and Lyttelton are the main landing ports, but they have also been caught at other places between New Plymouth and Bluff.

“If there is a continuous population, there is a chance that they will move into these areas,” said Mr Coakley. “We want to see if there is a problem. It may be necessary to take conservation measures, as is done with oysters.” He plans to catch elephant fish in all size ranges, from the very young ones just hatched up to the adults of 30 lb or so. He will measure and weigh them and determine their ages at various sizes in an attempt to find out at what age they mature sexually, how many young they produce and how successful their breeding is. He is tagging elephant fish to help pin-point their growth rate, and, from fishermen’s returns, to check seasonal migrations and coastal movements. From the information he has already, he thinks they probably mature in three to four years, but it could take about three years’ research to collect enough information to be sure about the things he wants to know. The main fishing season for elephant fish—Callorhynchus mill!—is from October to January, when they come in to spawn on the beaches, and leave their familiar black egg cases behind. The photograph shows Mr Coakley about to weigh an elephant fish caught in a trawl about six miles off the mouth of the Ashley river on Saturday. Mr A. McKenzie, a laboratory technician, is recording the statistics, with another technician, Mr B. Richardson, standing by.