Lake survival of hatchery-reared adfluvial brown trout-A case study in a large natural lake in Sweden

Throughout their native range, adfluvial brown trout populations have declined due to habitat degradation and over exploitation. As a consequence, numerous restoration projects that include stocking of hatchery-reared trout have been conducted; however, estimates of survival in large lakes remain scarce. Here, we use telemetry to evaluate the survival of stocked trout smolts and sub-adults in a large lake in central Sweden. Of the smolts released in the main tributary, 42% entered the lake. Both life stages suffered high rates of mortality. Only 8% of smolts survived the first 10 months after entering the lake and 10% of those released as sub-adults survived 23 months post-release. In agreement with studies on anadromous trout, we conclude that stocking of hatchery-reared individuals is not an efficient method to recover population numbers due to poor performance in the wild. Similar studies from other large lakes and comparisons with wild conspecifics would increase the applicability of the results and promote further understanding of the utilization of hatchery-origin trout to rebuild wild populations and sustain fisheries.