Delineating population structure of resilient sea/river‐type sockeye salmon

Conserving wild fisheries requires identifying and monitoring distinct populations, yet prevalent genetic approaches often do not integrate habitat data and may not fully delineate these structures. This issue is critical in sea/river‐type sockeye salmon (Oncorhynchus nerka), an ecotype whose specific spawning habitats better define distinct breeding populations. Despite possessing traits that confer greater resilience to climate change and significant contributions to wild fisheries, gene flow among groups dilutes genetic structure, making it difficult to track populations. We focus on sea/river sockeye from one of the Pacific Rim's largest Sockeye fisheries, combining river strontium (Sr) isotope predictions, otolith Sr isotope measurements, and a Bayesian assignment model with a 4‐yr radiotelemetry and genetic dataset (n = 1994) to delineate the geographic structure of spawning habitats. Our results identify four distinct subpopulations with unique natal habitat Sr isotope ratios previously undifferentiated by genetic methods, providing a novel approach to monitor critical groups over multiple years.