Challenges in using genetics for European eel management: current status

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Marine organisms experience a wide range of intrinsic and extrinsic influences during their life cycle, which considerably impact their population dynamics and genetic structure. Subtle interpopulation differences reflect the continuity of the marine environment, but also pose challenges to define management units. The catadromous European eel Anguilla anguilla (Anguillidae; Teleostei) represents no exception. Its spawning habitat in the Sargasso Sea and vast migrations across the North Atlantic Ocean qualify it fully as marine. But the synergy between hydrographic variability and a shifting climate in the ocean, and the impact of habitat degradation and overfishing in continental waters has brought this intriguing species to the brink of extinction. The protracted spawning period, variance in age-at-maturity, parental contribution and reproductive success, and the difficulty to sample the spawning region, all may mask a weak geographical genetic differentiation. Recent molecular data report evidence for as well spatial as temporal differences between populations. However, temporal heterogeneity between intra-annual recruitment waves and annual cohorts exceeds spatial differences. Despite its common name of “freshwater eel”, the European eel should be managed on a North Atlantic scale. The fishery should be curtailed, migration routes kept open and water quality restored. Eel aquaculture has to focus on efficient rearing in the short term and controlled breeding in the long term. Future research in eel should focus on (1) establishing a biological baseline from pre-decline historical collections for critical long-term monitoring of genetic composition, (2) on the occurrence of adaptive genetic polymorphisms (genes under selection), to detect adaptive divergence between populations, requiring separate management, and (3) the joint validation of demographic and genetic models following various scenarios.