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Posted January 11, 2000

The Farming of Atlantic Salmon in the State of Maine

By Linda J. Kling and H. Michael Opitz, Associate. Professor and Associate Extension Professor

The Maine salmon aquaculture industry has a farm-gate value of $65 million dollars, with the economic impact to the region being three times this value. The Maine salmon industry is a small player in the global production of salmon, with Norway and Chile leading the pack. Current husbandry methods follow those practiced worldwide. Maine farmers have successfully competed for the global market, by continuing to reduce production costs. Further improvements in efficiency of production will determine Maine's continued presence as a supplier of farmed-reared salmon to the global market.

Atlantic salmon life-cycle patterns . . .

The Atlantic salmon is an anadromous fish, which is it spends its early life in freshwater and then migrates to sea, only to return to reproduce. In the wild, the young fish may spend several years in freshwater until they reach an appropriate size. In mid April to early May, young Atlantic salmon, now called smolts, undergo physiological changes that adapt them to living in sea water. They migrate seawards and spend two winters at sea. Some of the salmon migrate to feeding areas probably not beyond the continental shelf and some may actually remain in coastal waters within the influences of the rivers where they were born, but the majority of the salmon migrate well beyond the continental shelf and spend much of their sea life in the rich feeding grounds off west Greenland before returning once again to freshwater to reproduce or spawn. Survival rates for fish in the wild are naturally low, with values of less than 1 percent common but sufficient to sustain the population if not over harvested.

Good husbandry practices necessary . . .

The life cycle of the cultured salmon reflects the natural cycle, but like any farming enterprise, the implementation of good husbandry practices allows for improved survival and growth over their wild counterparts. Production begins with the removal of eggs from mature females, a process called stripping. Eggs are then fertilized with the sperm from male salmon, taken in a similar fashion. The eggs are incubated under controlled conditions in a freshwater hatchery until they hatch. The young salmon, called fry, are nurtured throughout the year until they are physiologically capable of responding to the increasing light conditions of springtime, that is, they smolt. In captivity, the freshwater period seldom exceeds 16 months. Survival of farmed salmon from fry to smolt is typically higher than 80%, reflecting the excellent husbandry practices of Maine's fish culturists.

Prior to transport to sea cages, the smolts are vaccinated against common salmon diseases, much as children are routinely vaccinated against common human diseases. All hatcheries in the state of Maine must be certified to be free of certain diseases before smolts can be transferred to sea cages. Hatcheries undergo twice annual health inspections by an independent laboratory to verify their disease-free status. Similarly, broodfish, or parents, are tested and must be free from disease before off-spring can be generated.

The smolts are placed in large insulated boxes and moved by truck to the harborside. In most cases the boxes are loaded on barges and moved to the cage site, a series of cubic or cylindrical net bags or pens open at the top and suspended from a floating collar. The net hangs freely and its shape is maintained by leaded ropes and weights at the base and corners. They are hung from rails or posts extending above the floating collar to prevent the fish from jumping out.

Cage site selection . . .

Cage site selection is an arduous task. Few areas in Maine have perfect conditions, and selection is a compromise between optimal fish health and growth, worker safety, and cost. The cage site must be well sheltered from heavy seas for the protection of the net pen, as well as the workers. Cages can be built for the most exposed sites, but fish feeding and handling can be extremely hazardous and costs are prohibitive. The tides allow for continual exchange of clean, oxygenated water, but, nets can distort severely in strong currents, reducing the "real" volume of the net and cause the fish to crowd.

The cage site has to be located where the winter water temperature does not drop below 31o F, the lower lethal temperature for Atlantic salmon and the summer water temperatures do not exceed 60o F for any length of time. Higher water temperatures, while promoting rapid growth, subject the fish to lower oxygenated water and make them more susceptible to disease. There are only a few areas in the Bay of Fundy and northeast Maine, where there is sufficient tidal turnover to bring the warmer deeper water to the surface and prevent freezing in the winter, but where the summer water temperatures do not exceed unfavorable growing conditions.

Survival rates of farmed salmon in net pens typically average higher than 90%, but as in all farming enterprises, problems can arise. The threat of predation is always a serious concern for farmers. The net pens are further enclosed with anti-predator nets, to deter birds and seals from attacking. But occasionally, during storms or high currents, the predator net is pushed against the fish net, allowing the seals to penetrate and cause damage to the fish, and more seriously, to the net pen itself, allowing salmon to escape from the net pen enclosure. Seal attacks cause serious loss to fish farms due to fish mortality, escapees, stress and loss in weight gain.

Occasionally severe storms hit our coast and damage the integrity of the net pens, allowing fish to escape. Losses attributable to parasitic infection and infectious disease are managed through good husbandry practices but even healthy fish can succumb to the most virulent agents. Timely development of new vaccines, continued good husbandry practices and implementation of stock rotation and separation of year classes can significantly reduce risk of disease. Losses from predator-induced fish injury, disease and escaped fish can seriously affect production costs and every attempt is made to prevent these losses.

Feed and genetics . . .

As for all farmed animals, feed cost represent over 50% of the production cost to produce a farmed salmon. However, with improved feeding technologies and practices, salmon farmers can boost one of the most efficient animal systems, with feed conversions of 1.3 pounds of feed required for each pound of fish produced. This compares with 1.8 pounds of feed required to produce a pound of chicken, the most feed efficient of our land-farmed animals. Most salmon farmers in Maine now use under-water video cameras to monitor when the fish have had enough to eat. Reducing feed wastage improves the 'bottom-line' and reduces organic load into the environment.

As in all animal industries, ie poultry, swine, cows, farmers are interested in improving the genetic potential of their stock. Significant gains in growth rates, feed efficiency, flesh pigmentation, and disease resistance, to name a few selected traits, can be achieved through a well-planned genetic selection program. Gains have already been achieved in Norway, Scotland and Chile, where it once took 20-24 months in sea cages to produce a market-sized fish, it now takes 17 months, reducing production cost significantly. Maine's farmed salmon is derived from a variety of local (Penobscot and St. John's) and non-local (Icelandic and European) strains.

Atlantic salmon, once a dining delight for the wealthy, at greater than $10 per pound, has now reached the table of average Americans everywhere, and demand is increasing. Maine's salmon farmers aim to meet this demand while at the same time abating pressure on the wild salmon fishery.

Keywords: Atlantic salmon, aquaculture, farming

For further information, please feel free to contact:

Linda J. Kling, Associate Professor, School of Marine Sciences, 581-2735, lkling@maine.edu or

H. Michael Opitz, Assoc. Extension Professor, Cooperative Extension, 581-2771, moptiz@umext.maine.edu

Dr. Kling is an Associate Professor in the School of Marine Sciences. Her research involves the development of diets for cultured fish. Her research has been supported mostly through the Maine-New Hampshire Seagrant College Fund, NOAA, and the Maine Agricultural and Forest Experiment Station.

Dr. H. Michael Opitz is an Associate Extension Professor in University of Maine Cooperative Extension. He is a veterinarian with expertise in diseases of fish and poultry.

If you would like to receive addition copies of this white paper or any other papers in the series, please contact:

Judith Round, College of Natural Sciences, Forestry, and Agriculture, University of Maine, 5782 Winslow Hall, Orono, Maine 04469-5782

Telephone: (207) 581-3229, E-Mail: judy.round@umit.maine.edu

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