Early marine migration of Atlantic salmon kelts, wild smolts and hatchery smolts

This study used acoustic tags in conjunction with an extensive offshore marine receiver array to compare the migration speed, directionality and overall detection rate (as a proxy for survival) between three distinct batches of Salmo salar (kelts, wild smolts and hatchery smolts) from the same river, the river Bush in Northern Ireland, tagged during spring 2021. Minimum survival rates through the river were higher for kelts (>95%) and wild smolts (84%) than for hatchery smolts (50%), while all three groups exhibited relatively high early marine survival (71%, 58% and 60%, respectively). Marine ground speed was significantly higher for kelts (>52 km day^-1) than for wild (>25 km day^-1) and hatchery (>31 km day^-1) smolts. The initial marine trajectory was similar between all three groups, with a mean bearing of 318° for kelts, 311° for wild smolts and 309° for hatchery smolts. Similarities between fish origins (wild and hatchery) and life stages (smolts and kelts) were suggestive of common drivers influencing early marine migration.