Freshwater Fishery Research

Press, Volume CVIII, Issue 31724, 6 July 1968, Page 5

Freshwater Fishery Research

written for "The Press" by

R. C. KINGSBURY)

Better fishing for the New Zealand angler and a significant contribution to the country’s economic potential as an earner of overseas funds from tourism are the equally welcome results likely to come from fish management investigations being carried out by the Marine Department in Lake Coleridge and the Glenariffe Stream, a tributary of the Rakaia River.

The two-year survey of Lake Coleridge completed this season was undertaken to provide information from scientific investigations on which a sound fish management nolicv for the lake could be based.

taken into account indicated that the angler may catch the larger, older fish from the run.

Although the figure for this year is still open to correction, present indications are that the run was unusual for the large proportion of three-year-old fish. The 1967 run was unusual for its large numbers of two-year-old -fish and decreased numbers of four-year-olds, compared with 1966 and 1965. Busy Periods Mr Flain said the Glenariti. Stream was chosen from a number of spawning areas off the Rakaia River because it was a particularly good one, was readily accessible, and because it was normally free from flooding. The trap is about 30 miles from Methven on the south bank of the R&k&ia. The Glenariffe field staff comprises a senior technical field officer (Mr J. Galloway), who is in charge of the project, field officers (Messrs W. S, Johnston, R. A. Dougherty, and S. J. Wing), and several head office trainees. They live in a comfortable cottage equipped with dieselgenerated electricity and a radio telephone. Two or three times a year the men are isolated by road slips, but they normally spend two weeks at the trap and then a week in Christchurch taking their days off and working at the Kyle Street office of the department. At the height of the spawning run when an average of 100 adult salmon have to be counted, weighed and tagged a day, they work during the day and night to keep up with the run. Lake Coleridge Mr Flain said it would be some time before his report on the Lake Coleridge survey would be finished. The actual investigations and sampling were completed several weeks ago, but much of the laboratory work had yet to be done Investigations had showed, however, that the lake water was almost as free of mineral content as distilled water, and the plankton count had been very low. This suggested that the addition of trace elements might prove beneficial in providing food for the fish population. By far the greatest proportion of fish caught in the lake were land-locked quinnat salmon. Ten per cent were rainbow trout and 1 per cent was brown trout.

The long-term quinnat salmon survey which has already run for four years in the Glenariffe Stream will also enable the department to advocate a management policy, and possibly predict good and poor fishing seasons.

This information will be released by the chairman of the Freshwater Fisheries Advisory Council in a report cent to all acclimatisation societies. The societies will then make it available to anglers.

returned to the spawning grounds in their third year. Some returned in the fourth year, a small proportion in the fifth year, and there were some precocious fish of both sexes which returned in the second year.

The Glenariffe salmon trap is worked by the technical field service of the Marine Department with the co-oper-ation of the South Island Council of acclimatisation societies. The installation is designed to obtain on a moderately long-term basis information and biological samples from the yearly quinnat salmon run. The installation consists of an upstream trap for adults and a downstream trap for fry. Over a period of years it will provide comparative information which should throw considerably more light on the behaviour of quinnat salmon in New Zealand rivers. Predicting Season Controlled experiments at the trap to test theories suggested by investigations made there could provide information applicable to other rivers without putting traps in them. The information will continue to be available to acclimatisation societies through the Freshwater Fisheries Advisory Council. The result will be that accurate predictions of future salmon season prospects should be possible. If an unusually small number of fry come down the stream in a particular season it will be an indication that the season of their return a certain number of years ahead will probably be a poor one.

There had been an unusually large number of two-year-old fish of both sexes recorded last year at the trap, but they had in the main been males.

The main spawning time for quinnat salmon is in April and May. The eggs hatch in August to October and the majority of the fry begin their long journey to the sea almost immediately. The count of adult fish through the trap and the count of returning fry gives a spawning success figure for the season. A comparison of these results over a number of years can indicate the optimum number of spawning fish for a given area.

The age composition of the 1967 quinnat salmon run determined from otoliths obtained at the Glenariffe trap and examined at the department's laboratory in Christchurch showed that 69.6 per cent were three-year-old fish. 19.7 per cent were two-year-old fish (an unusual feature of which was that 0.6 per cent were precocious females), 8.2 per cent were four-year-old fish, and 0.4 per cent were five-vear-old fish. Results from this season's run are at present being compiled. There were indications from a sampling programme at the Rakaia River mouth that the angler may catch the older fish from the run before they can reach the spawning grounds. Count Of 3000 Mr Flain said the count of more than 3000 fish this year through the trap was the greatest so far recorded. There had been 1772 last vear, compared with 1132 in 1966, and 2120 in 1965. A much larger proportion of the fish tagged up to that time were recovered last year. This was 59.3 per cent, compared with 37.8 per cent in 1966, and 34.1 per cent in 1965. The trap sex ratio was males 58.3 per cent, and females 41.7 per cent. The presence of mature two-year-old females in a sea run of quinnat salmon was considered unique. Post mortem examinations for residual ova indicated that two out of six two-year-old females had retained some eggs. The variable growth rate I for year groups indicated that it would be difficult to separate the year classes by measurement alone. The average length of the two-year-old i females was greater than that of the two-year-old males, but in all other age groups it was smaller, the difference increasing with increasing age. Of 56 fish sampled at the Rakaia mouth last year, two were five-year-olds, compared with four out of 1028 which passed through the trap. This and other factors

The Glenariffe trap is 110 ft long and built of hardwood and treated pine. It sits on the stream bed so that water runs through adjustable gates j and across screens. Adult i salmon swimming upstream to > spawn are channelled into a pen to be counted, weighed, measured and tagged. The fry coming down the stream are counted in their millions and smolts fin-clipped for later identification and age check. After spawning, without exception. all quinnat salmon die. Many of the spent salmon are recovered from the gratings of the trap or from upstream over a distance of about 15 miles. Their age is assessed by examination of their otoliths, chalky bone structures of the inner ear, and the number of unlaid eggs counted. The original pilot trap was built in the stream in 1965. and 2120 salmon were counted on their spawning run. It was so successful that the more elaborate version was installed the next year, and has been manned continuously since then.

The investigation will determine the physical and chemical aspects of the lake Samples of water have been taken from different depths for analysis, samples of weed and food organisms have been i obtained, bullies counted on a I pre-determined area of the .lake bottom, vertical and seasonal temperatures recorded, light penetration recorded at various depths, and the shape of the lake mapped by bathymetry. The survey has required the use of a wide variety of scientific recording and laboratory equipment during the past two years, the use of a power boat on the lake, and diving by navy-trained Marine Department divers using wet suits. When finally compiled and correlated the information obtained will provide a factual basis for the stocking and management of the lake. In addition to Mr Flain, divers employed on the survey have been Messrs I. D. McFarlane, C. R. Docherty, D. J. Broomhead, and R. Goode. All are Marine Department laboratory technicians.

Mr M. Flain, assistant fishery scientist for the Marine Department in Christchurch, said that he was primarily engaged in the Glenariffe project to determine the age structure of salmon runs in the Rakaia River. Although there were large variations, present indications were that the great majority of fish