THE TRANSCRIPTOMIC PROFILES AND MARINE MIGRATION SUCCESS OF ATLANTIC SALMON SMOLTS (SALMO SALAR) FROM FIVE POPULATIONS IN CANADA

Abstract

Atlantic salmon smolts frequently experience high mortality during the marine phase of their migration, especially during the initial period after entering the sea. However, the mechanisms underlying marine mortality are difficult to determine due in part to the difficulty of observing freely migrating fish in the open ocean. I combined transcriptomic sampling with acoustic telemetry by non-lethally tissue sampling smolts (n = 262) from four stocks of wild Canadian Atlantic salmon as they emigrated down natal rivers, and followed their migration across the Gulf of St. Lawrence to the Labrador Sea ~800 km away. On average, it took fish ~40 days to emigrate to the Strait of Belle Isle. From the activity of 49 genes examined, there was no generalized transcriptomic profile that predicted mortality across populations over the time and distances covered in this study. However, I identified population-specific genes that contributed to mortality during migration. These genes played a role in immune system function and thermal stress, suggesting that smolts were under pressure from these stressors. Finally, I found that larger smolts were more likely to be successful migrants than smaller smolts.