On Tuesday, March 24, 2015, the National Marine Fisheries Service (NMFS) issued a 12-month finding (pdf) concluding that listing a distinct population segment (DPS) of the harbor porpoise (Phocoena phocoena) in the Baltic Sea as endangered or threatened under the Endangered Species Act (ESA) is not warranted. NMFS found that while a discrete subpopulation of harbor porpoises exists in the Baltic region, the subpopulation is not ecologically and biologically significant to the species.

In order to determine that a DPS exists, NMFS must find: (i) that a subpopulation is discrete either because it is markedly separated from other population of the same taxon as a consequences of physical, physiological, ecological, or behavioral factors, or because it is delimited by international governmental boundaries within which differences in control of exploitation, management of habitat, conservation status, or regulatory mechanism exist that are significant; and (ii) that the subpopulation is biologically and ecologically significant to the species. The significance consideration may take into account (1) persistence of the discrete subpopulation in an ecological setting that is unusual or unique for the taxon; (2) evidence that loss of the discrete subpopulation would result in a significant gap in the range of the taxon; (3) evidence that the discrete subpopulation represents the only surviving natural occurrence of a taxon that may be more abundant elsewhere as an introduced population outside its historic range; or (4) evidence that the discrete subpopulation differs markedly from other populations of the species in its genetic characteristics.

NMFS found that a discrete subpopulation of harbor porpoises exists in the Baltic region based on differences in genetics, skulls, contaminants, and teeth between Baltic harbor porpoises and other populations of the species. However, NMFS found that the discrete Baltic subpopulation was not significant under any of the possible significance factors. This finding stemmed from the fact that Baltic harbor porpoise prefers shallow coastal areas (the same habitat preferred by the general species) and that the Baltic subpopulation comprises only a small geographic area in the total range of the species. Additionally, NMFS found no evidence that the Baltic subpopulation either represents the only surviving natural occurrence of a taxon that may be more abundant elsewhere as an introduced population outside its historic range, or differs markedly from other populations in its genetic characteristics.

The 12-month finding was issued in response to a 2013 petition filed by WildEarth Guardians, which requested the listing of 81 marine species and subpopulations. NMFS has since found that the petitioned actions may be warranted for 24 species and 3 subpopulations. The findings issued Tuesday addressed only the Baltic Sea harbor porpoise. NMFS is still in the process of evaluating many of the other species for whom listing may be warranted.