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

Abstract

Impact of climate changes on species is expected to be especially visible at the extremities of the species distribution, where they meet sub-optimal conditions. In Mauritania and Iberia, two genetically isolated populations of harbor porpoises form a distinct ecotype and are presumably locally adapted to the upwelling waters. By analyzing the evolution of mitochondrial genetic variation in the Iberian population between two temporal cohorts (1990-2002 vs. 2012-2015), we report a dramatic decrease in genetic diversity. Phylogenetic analyses including neighboring populations identified two porpoises in southern Iberia carrying a divergent haplotype close to the Mauritanian population, yet forming a distinctive lineage. This suggests that Iberian porpoises may not be as isolated as previously thought with immigration from Mauritania or an unknown population in between, but none from the northern ecotype. The rapid decline in the Iberian mitochondrial diversity may be driven by either genetic drift, or by a dramatic decline in census 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 Iberia.

Retrospective genomics highlights changes in genetic composition of tiger sharks (Galeocerdo cuvier) and potential loss of a south-eastern Australia population

“…Such relationship has also been reported in empirical studies (e.g. 37 , 38 ). We chose east coast Australia because of documented reductions in tiger shark CPUE in that region and because samples from this region are relatively abundant across both spatial and temporal scales; i.e.…”

Harbour Porpoise Abundance in Portugal over a 5-Year Period and Estimates of Potential Distribution

“…Even though the Iberian porpoise population was thought to be isolated from other porpoises [ 3 , 68 ], there is evidence of porpoise migration to the Iberian area from southern latitudes (Mauritania or an unknown population occurring between the Portuguese south coast and Mauritania) [ 1 ], emphasizing the need for studies on African porpoise genetics and population parameters.…”

“…A sharp decline in genetic diversity detected over the past 25 years indicates that the harbour porpoise population in the western Iberian Peninsula may be small and isolated [ 1 ]. Porpoises inhabiting upwelling areas in the western Iberian Peninsula and Mauritania are genetically differentiated from other populations [ 2 , 3 , 4 ] and a possible subspecies was proposed ( Phocoena phocoena meridionalis ) [ 3 ].…”

“…The harbour porpoises inhabiting Portuguese and Spanish waters (Iberian Peninsula) are considered a source population with individuals migrating to (but not from) northern and southern neighboring populations [ 3 ], and a hybridization zone for Iberian and north Atlantic porpoises was identified in the northern part of the Bay of Biscay [ 3 , 5 ]. However, migration from a southern population into the Iberian Peninsula was recently detected through molecular analysis of samples from individuals stranded in the Portuguese south coast [ 1 ].…”

Assessment of Harbour Porpoise Bycatch along the Portuguese and Galician Coast: Insights from Strandings over Two Decades

“…Recent genetic studies revealed that the harbour porpoise population in the upwelling areas of the Iberian Peninsula is small and isolated [ 1 , 2 ]. In fact, a new subspecies, Phocoena phocoena meridionalis, has already been proposed to include the so-called Iberian and Mauritanian harbour porpoise groups [ 1 ].…”