Demonstration of salmon farming as a net producer of fish protein and oil

To date aquaculture’s reliance on dietary marine sources has been calculated on a fish weight‐to‐weight basis without considering the absolute amounts of nutrients but this approach neglects the often considerable differences in the nutritional value of fish. We propose simple nutrient‐to‐nutrient‐based dependency measures that take into account these nutritional differences. In the first study reported here, individually tagged Atlantic salmon (Salmo salar) were reared in seawater supplied tanks with feed collection facilities. In the second, commercial net pens were used to grow over 200 000 fish. For both studies, a low marine ingredient feed containing approximately 165 g kg^?1 fishmeal was compared to a control feed (approx 300 g kg^?1 fishmeal) whilst fish oil inclusion was less markedly reduced. The low marine feeds supported similar growth and feed efficiency compared to the control feeds. With the low marine ingredient feeds, the weight of salmon protein and lipid produced through growth exceeded the weight of marine protein and lipid consumed by the fish meaning that salmon farming can be a net producer of fish protein and oil. The amount of n‐3 long‐chain polyunsaturated fatty acids deposited was sufficient to meet current recommendations from human health organizations.     

Soils, Forests, and Pastures in South Wales

Marginal upland soils may be used for forestry or sheep grazing.In the State Forests of South Wales a study of selective plantingshows the greatest volume yield is generally obtained from Sitkaspruce (Picea sitchensis) planted in ridge-crest soils. Yieldsfrom Sitka spruce on ridge-flank soils are reduced by the presenceof Ericaceae on upper slopes and the dryness of the soils onlower slopes. Contrary to this trend, the nutritional valueof the pasture for sheep is lowest on ridge crests and increasesdownslope, being greatest on the Agrostis pastures of lowerslopes. Further, reclamation is most economically accomplishedon ridge flanks where they are not too steep. Although profitcomparisons are very difficult to make, ridge slopes might bemore usefully allocated to sheep grazing and ridge crests toSitka spruce forests. To be economically viable, a forest mustbe large, but within any new forestry acquisitions the largerareas occupied by slope soils might be reclaimed or utilizedas sheep pastures.