Harbor porpoise losing its edges: genetic time series suggests a rapid population decline in Iberian waters over the last 30 years

• Main Authors: Ben Chehida, Yacine, Stelwagen, Tjibbe, Hoekendijk, Jeroen, Ferreira, Marisa, Eira, Catarina, Pereira, Andreia, Nicolau, Lidia, Thumloup, Julie, Fontaine, Michael C.
• Other Authors: Groningen Institute for Evolutionary Life Sciences Groningen (GELIFES), University of Groningen Groningen, Maladies infectieuses et vecteurs : écologie, génétique, évolution et contrôle (MIVEGEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD France-Sud )-Université de Montpellier (UM)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: cetacean conservation genetics; genetic time series; genetic diversity; bycatch; approximate Bayesian computation; population genetic modelling; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDV.BID.EVO]Life Sciences [q-bio]/Biodiversity/Populations and Evolution [q-bio.PE]; Phocoena phocoena
• Online Access: https://hal.science/hal-04303383; https://hal.science/hal-04303383/document; https://hal.science/hal-04303383/file/Ben_Chehida_MS_IBeria_V4_withoutTrackChange.pdf

International audience Impact of climate change is expected to be especially noticeable at the edges of a species’ distribution, where they meet sub-optimal habitat conditions. In Mauritania and Iberia, two genetically differentiated populations of harbor porpoises (Phocoena phocoena) form an ecotype adapted to local upwelling conditions and distinct from other ecotypes further north on the NE Atlantic continental shelf and in the Black Sea. By analyzing the evolution of mitochondrial genetic variation in the Iberian population between two temporal cohorts (1990-2002 vs. 2012-2015), we report a substantial decrease in genetic diversity. Phylogenetic analyses including neighboring populations identified two porpoises in southern Iberia carrying a divergent haplotype closely related to those from the Mauritanian population, yet forming a distinct lineage. This suggests that Iberian porpoises may not be as isolated as previously thought, indicating possible dispersion from Mauritania or an unknown population in between, but none from the northern ecotype. Demo-genetic scenario testing by approximate Bayesian computation showed that the rapid decline in the Iberian mitochondrial diversity was not simply due to the genetic drift of a small population, but models support instead a substantial decline in effective population size, possibly resulting from environmental stochasticity, prey depletion, or acute fishery bycatches. These results illustrate the value of genetics time series to inform demographic trends and emphasize the urgent need for conservation measures to ensure the viability of this small harbor porpoise population in Iberian waters.