History of expansion and anthropogenic collapse in a top marine predator of the Black Sea estimated from genetic data

Two major ecological transitions marked the history of the Black Sea after the last Ice Age. The first was the postglacial transition from a brackish-water to a marine ecosystem dominated by porpoises and dolphins, once this basin was reconnected back to the Mediterranean Sea (ca. 8,000 years B.P.). The second occurred during the last decades, when overfishing and hunting activities brought these predators close to extinction, deeply impacting the structure and dynamics of the ecosystem. Estimating the extent of this decimation is essential for characterizing this ecosystem's dynamics and for formulating restoration plans. However this extent is poorly documented in historical records. We addressed this issue for one of the main Black Sea predators, the harbor porpoise, using a population genetics approach. Analyzing its genetic diversity using an Approximate Bayesian Computation approach, we show that only a demographic expansion (at most 5,000 years ago) followed by a contemporaneous ...