An Endangered Population of Harbour Porpoise Phocoena phocoena Hidden in Plain Sight: Biology, Ecology and Conservation of the Iberian Porpoise

The Iberian harbour porpoise (Phocoena phocoena) reaches a larger body size than most other harbour porpoise populations and is genetically distinct, albeit closely related to the population in Northwest Africa. Currently comprising an estimated 3000–4000 individuals, genetic evidence and strandings data suggest that the population has declined in recent times, and it is considered to be at risk of extinction. It is distributed all around the Atlantic coast of the Iberian Peninsula, with the highest densities off Galicia in Northwest Spain and Northern and Central Portugal, a highly productive upwelling area characterised by cold-water upwelling. There are occasional reports from the Mediterranean and Macaronesia and some evidence of emigration into the Celtic Sea. It feeds mostly on fish, with pelagic fish being more important than in the diet of porpoises from northern Europe, perhaps due to excursions beyond the narrow continental shelf. The population faces a number of anthropogenic threats. Historically, porpoises were used for human consumption while current threats include polychlorinated biphenyls (PCBs), with some individuals having concentrations in their blubber above the threshold for impairment of reproduction, and nematode infections, probably also prey depletion, underwater noise and fatal attacks by bottlenose dolphins. The most serious current threat is fishery bycatch mortality. Stranding data suggest that the bycatch mortality increased in the last decade. Although based on information from a small number of documented mortalities (reflecting limited observer coverage especially for small-scale fishing as well as a low number of reported strandings), annual bycatch mortality estimates are in the order of a few hundred animals, which is clearly unsustainable. There is, however, an apparent incompatibility between the high bycatch estimates and the rather similar abundance estimates obtained from large-scale abundance surveys in 2005, 2016 and 2022. Consistent with population status assessments by Spain and Portugal, OMMEG 1 (Convention for the Protection of the Marine Environment of the North-East Atlantic) concluded that bycatch mortality in Iberian porpoise “is critically exceeding the agreed threshold” of zero. There are several national initiatives in Spain and Portugal including the development of species conservation plans. Continuous reduction of bycatch mortality, preferably until such mortality is eliminated, is a priority to ensure that this population does not disappear in the near future.