Research has often shown that hatchery salmon perform less well than their wild counterparts. The reason for this has often been attributed to genetic factors such as parent selection or to the lack of opportunity for Mother Nature to cull misfits.
Recent research indicates that poor performance of hatchery fish may stem more from the their environmental experiences than from their genetics. Some older theories that suggested that hatchery fish were just raised dumb now have gained a new following. New research from Canada suggests that atypical food and feeding combined with overcrowding in hatcheries weakens inherent genetic abilities to cope with the natural environment.
In California’s Central Valley, we have added the burden of releasing hatchery smolts late in the natural emigration season outside of peak flow periods, into warmer waters that are full of other fish that want to eat them. When the salmon from the hatcheries get hungry, there is no flood of fresh food pellets. Their new environment results in starvation, thermal stress, and much higher vulnerability to predation. Still, hatchery fish make up 70-90% of California’s salmon runs, because Valley habitats no longer support historic levels of wild salmon production.
In recent posts, I have advocated raising hatchery fry in Valley floodplain habitats. UC Davis studies have shown high rates of growth of hatchery fry raised in flooded rice fields during the winter. New planning efforts call for more flooded Valley habitats, including rice fields, but these efforts focus primarily on wild juvenile salmon. There has been no testing to date of the performance of hatchery fry that rear under controlled floodplain conditions. In light of the recent Canadian research, the ability of floodplain-reared hatchery fish to survive, and the degree to which they stray, warrant evaluation.