LAUSR

There is growing interest in the phenology of juvenile Salmo trutta and evidence of significant downstream migration during the autumn in some anadromous populations. The present study used acoustic telemetry to examine the phenology of potamodromous trout parr across a region encompassing two large lake catchments. 167 trout parr were tagged in late summer across 4 lake tributaries between 2018-2020. In total, 75 tagged parr migrated into the lakes with 67 (89%) migrating between September-December and 8 (11%) migrating between March-June. Autumn migration was highly prevalent across all the tributaries, with 16-66% of each tagged sample exhibiting autumn migration, and 0-15% of each tagged sample exhibiting spring migration. Autumn migrants were significantly longer and heavier than spring migrants but condition factor was similar. Autumn migrants were associated with higher river discharge levels and lower water temperatures than spring migrants. The management challenges posed by extensive autumn migration behavior in migratory trout stocks are examined and discussed. This article is protected by copyright. All rights reserved.