Discerning adaptive divergence within an endangered conservation unit - Gulf of Maine Atlantic salmon

Background: Conservation units for endangered or threatened species are often defined based on close genetic affinities. Seven populations of one such unit, the Gulf of Maine's Distinct Population Segment (GOM DPS) of endangered Atlantic salmon (Salmo salar), are listed as part of one, genetically cohesive conservation unit. All populations within GOM DPS are managed through a single captive rearing and supplementation conservation programme. Hypothesis: Significant adaptive trait variation exists among component populations within this unit. Time and location: Craig Brook National Fish Hatchery (2002-2003), a captive-rearing and supplementation facility in East Orland. Maine that manages the endangered, distinct population segment. Analytical methods: A common-environment rearing design assessed within and among population variation in fitness-related traits of adults (somatic vs. reproductive investment) and offspring (time-to-hatch, mass, and growth). Results: Significant heritable variation in fitness-related traits is evident within the GOM DPS. Salmon populations differ in ovarian-to-somatic tissue investment, time-to-hatch, and larval mass. Conclusions: Although the Gulf of Maine DPS of Atlantic salmon is defined based on close genetic affinities of component populations, those populations show considerable variation in fitness-related traits. Such variation indicates the presence of important adaptive diversity that should be monitored and conserved within the larger conservation unit. We also demonstrate how potential adaptive variation can be assayed within the confines of an active endangered species programme.