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Marine Harvest Salmon Hatchery

From Moriston Matters, Issue 6, April 1978.

After operating a freshwater salmon rearing programme at Invergarry Hatchery since early 1971 Marine Harvest Limited, a subsidiary of Unilever, are planning to expand production by commissioning a new hatchery at Inchmore, Glenmoriston in the summer of 1978 after successfully rearing small trial batches of fish at the site in 1976 and 1977.

The unit will be supplied by water pumped from the river Moriston and rearing facilities will be based on the type evolved at Invergarry. The Invergarry hatchery will continue in its role both as a producer of smolts and as a development unit to continue evaluation of improved techniques in salmon rearing,

The basis of the artificial rearing of salmon is the natural life cycle. The adult salmon return from their sea migration to the rivers from spring until autumn and spawning takes place around November. The eggs are buried in about six inches of gravel by the hen fish during spawning and are then left. A major cause of loss at this stage is the action of other hen fish digging spawning redds and displacing previous hatches of eggs. Hatching takes place in March and the newly hatched alevin carries a substantial yolk sac as it is still buried in gravel and will not emerge to the river bed for about six weeks.

For this period the alevin lives on its yolk supply until after emergence when it will commence feeding on small aquatic larvae. The small fish, now termed fry, begin to establish territories on the river bed. At this early feeding stage losses from predation and starvation are very large.

Established fry soon become parr and will spend 2-3 years in fresh-water before migrating as smolts to the sea in May. Growth can be quite rapid in the summer months but will slow down as temperature and feed supply diminish in winter.

Once in the sea the smolts will migrate to various feeding areas, e.g. Western Greenland and around the Faeroes, until the spawning urge prompts them to return to their home river as grilse after one year at sea or as salmon after two or more years at sea.

The hatchery cycle follows exactly the same sequence with the difference that survival and growth rate are vastly improved because of the protected environment and regular feeding schedules.

Brood fish are taken either from the wild by arrangement with river boards and estates or from selected adult fish reared to maturity at the Marine Harvest sea farms. Stripping and fertilisation of the eggs is done manually in November and each batch, averaging about 7,000 eggs is placed in specially designed incubation trays kept undisturbed in total darkness apart from periodic inspections and maintained with a good flow of filtered water. The eggs become 'eyed' about mid February around a month prior to batching and at this stage it is safe to handle them if necessary for counting, stock adjustments etc. After hatching in March the alevins continue in the trays and in darkness until the bulk of the yolk sac is utilized. They are then transferred to feeding tanks about mid-April, light is gradually introduced and feeding commences.

This stage corresponds to the emergence of the wild fish from the gravel of the river bed.

There can be difficulty in establishing a steady feeding pattern in some fish because up to this stage they have been accustomed to nutrition from their own yolk supply; the instinct for 'normal' feeding must be developed by correct presentation of feed and by adjustment of water flows and depths.

Once feeding is established growth is rapid through the summer months and stock densities are perioically reduced either by dividing the population into new tanks or by transfer to larger tanks. At certain stages the fish will also be graded so that each population is fairly uniform in size. Later grading will differentiate potential smolts from parr requiring a further year in the hatchery. Since smolting is determined by size as well as other factors the majority of hatchery reared fish are ready to smolt after one year's growth whereas most river fish take longer.

Smolting always occurs in April/ May because it is thought that the final change to the streamlined shape and silver colouration of a migratory smolt is set off by increasing day length and temperature. Because of these internal and external changes together with a regime of heavy feeding and rapid growth the smolt stage is delicate and requires very careful handling both in hatchery and wild fish. Roughly handled fish tend to lose scales and die of stress or associated problems. In the hatchery situation migration to the sea is accomplished by transporting smolts in aerated tanks of chilled water, the whole operation being carried out with as little stress as possible. Marine Harvest smolts are normally transferred to sea farms either at Lochailort or Loch Leven and are maintained and fed in floating mesh pens until harvested either as grilse or salmon after one or two years at sea.

A large proportion of the harvest is sold fresh to wholesale outlets in the U.K. and increasingly for export while a substantial tonnage is reserved for processing, either for smoking or for frozen convenience packs. With the increase in production possible from Inchmore it is hoped that some fish will be available for stocking and fish farming purposes from 1979 onwards, in what is now a rapidly growing industry in the Highlands. Transfers from Invergarry will provide a nucleus of experienced staff for the unit but it is hoped that the staff complement will be made up by recruitment from the local area.

A.R. Hutchinson