Growth and survival of Alaska stream-type Chinook salmon cultured in estuarine net-pens or freshwater raceways

The overwinter survival and growth and the subsequent marine survival of stream-type chinook salmon Oncorhynchus tshawytscha were compared between fish cultured in marine net-pens and their siblings cultured in freshwater. The net-pens were suspended in a stratified estuary with a low-salinity lens; the lens provided osmotic relief to the fish, and its depth and salinity varied seasonally. The median overwinter survival for chinook salmon from six brood years was 89.1% for the net-pen groups, significantly (P = 0.009) less than the median survival of 99.0% in freshwater. The median overwinter growth rate was 0.5% of body weight/d for the net-pen groups, significantly (P = 0.013) higher than the median growth rate of 0.2% for freshwater groups. The median marine survival of smolts from net-pen and freshwater groups was similar, 5.6% and 5.3%, respectively. These results demonstrate that juvenile stream-type chinook salmon can be cultured successfully over winter from the subyearling to smolt stage in marine net-pens suspended in a highly stratified estuary but that overwinter survival will be lower than in freshwater raceways.