Survival of coho salmon ( Oncorhynchus kisutch) cultured in fresh water and in estuarine net pens

Growth, survival during culture, and subsequent marine survival are compared for two broods of juvenile coho salmon ( Oncorhynchus kisutch) cultured in freshwater raceways or in net pens suspended in a highly stratified estuary. Two strategies for use of estuarine net pens were examined: (1) transfer as subyearlings from fresh water to net pens in fall, and (2) transfer as presmolt yearlings to net pens in early spring, prior to their normal migration or release time. Overwinter survival of juveniles cultured in net pens exceeded 90% and was only slightly lower than that of fish cultured in fresh water; however, fish cultured in fresh water were slightly larger at release. Time of release had a much greater effect on subsequent adult return than did culture environment. Return rates were significantly higher for fish released in late spring than for fish released in fall or early spring. Return rates of fish cultured in net pens were similar to or greater than that of fish cultured in fresh water. Results demonstrated that juvenile coho salmon can be cultured overwinter in estuarine net pens, thereby freeing rearing units for culture of subsequent broods and increasing the number of yearling smolts that can be produced in a hatchery.