Lack of ‘Personal Space’ Causes Hatchery Salmon to Falter in Wild

For decades, fisheries managers have reared hatchery salmon and released them into rivers to supplement declining populations of wild salmon. And for years, a large percentage of hatchery-raised Atlantic salmon have perished in the wild, returning to their native streams far less frequently than wild salmon. Now, researchers at the University of Gothenburg in Sweden think they know one reason why: Young salmon, or smolts, reared in tightly-packed pens have lower rates of survival than smolts raised in less-crowded surroundings. The researchers compared smolts raised in high-density cages and those raised in low-density cages and found that young fish given more “personal space” fared better in the wild than smolts reared in close quarters. The researchers also suspect that the high-fat food pellets given to hatchery salmon also make them less suited to survive in the wild. And their research also suggests that instead of placing very young smolts in crates, the fish should be raised in an environment with structures on the bottom, such as rocks, to stimulate brain development. The University of Gothenburg research is part of a larger, government-funded effort to make hatchery practices and commercial fish farming more sustainable.