Abstract Successful conservation of long‐lived species requires reliable understanding of long‐term trends and historical baselines. We present a framework for evaluating abundance trends and conservation outcomes for long‐lived marine species by integrating local ecological knowledge (LEK), ecological monitoring, and computer simulation, tested on a case‐study of long‐lived and heavily exploited green turtles ( Chelonia mydas ) in the Eastern Pacific. Models fit to LEK and monitoring data indicate that turtle abundance is increasing, but only after ∼40 years of safeguarding the species’ nesting and foraging habitats in Mexico. However, current abundance is at ∼60% of baseline levels and historic population structure has not been reestablished, indicating the need for sustained, long‐term conservation actions. We demonstrate the potential of linking LEK and ecological science to provide critical information for conservation, by establishing reference baselines and gauging population status with a long‐term historical perspective, while promoting equitable and sustainable futures.