Migration Patterns and Spawning Distribution of Adult Hatchery Sockeye Salmon Released as Parr from Net-Pens in Lake Wenatchee, Washington

Abstract

Artificial propagation of sockeye salmon Oncorhynchus nerka interrupts the early phases of their life history cycle, typically between the egg and smolt stages. Sockeye salmon reared initially in a hatchery and subsequently released as parr from freshwater net-pens suspended in a lake cannot imprint on a specific tributary water source. As a result, the spawning distribution of returning adults may differ from that of naturally produced fish. We used radio tags and carcass surveys to determine whether the spawning distribution and location of adult hatchery sockeye salmon reared and released from net-pens in Lake Wenatchee, Washington, were similar to the spawning distribution and location of their naturally produced counterparts. Over 2 years, 100 hatchery sockeye salmon were radio-tagged and tracked to their spawning location. No radio-tagged sockeye salmon were found spawning in Lake Wenatchee, the lake outlet, or other nearby rivers. All radio-tagged sockeye salmon that were tracked into tributaries of Lake Wenatchee spawned in locations (i.e., river reaches) similar to those of naturally produced fish. Based on carcass surveys, the spawning distribution of hatchery sockeye salmon among spawning tributaries was different from that of naturally produced fish; this difference was attributed to the inability of hatchery fish to imprint on a natal stream during their early life history. Although the spawning distribution among tributaries differed between hatchery and naturally produced fish, the mean difference was small (10.8%) and ranged between 0% and 29%.