Subsistence harvest of ringed, bearded, spotted, and ribbon seals in Alaska is sustainable

Abstract

In 2012, climate-warming related decreases in sea ice led to listings of ringed Pusa hispida and bearded seals Erignathus barbatus as threatened under the United States Endangered Species Act (ESA) prior to evidence of population declines. These and 2 other ice-associated species (spotted Phoca largha and ribbon seals Histriophoca fasciata) are vital subsistence resources to coastal Alaska Native communities. ESA-related assessments concluded that subsistence removals (seals that were harvested as well as those that were struck and lost) were sustainable; however, limited data precluded a quantitative evaluation. Potential biological removal (PBR), defined as the maximum number of animals that can be removed from a stock while allowing the stock to reach or maintain its optimal sustainable size, is typically used to determine whether human-caused mortality is sustainable. Although developed to address commercial fisheries bycatch, PBR serves as a conservative measure of sustainability. We compiled annual subsistence removal of ice seals in Alaska between 1992 and 2014 for 41 of 55 ice seal hunting communities and used per capita (based on the 2015 human population) removal estimates from surveyed communities to estimate regional and statewide average removals. We used average per capita values of harvest, combined with struck and lost, for surveyed communities (average removals) to extrapolate to unsurveyed communities. To account for underreported harvest, we also extrapolated using maximum harvest values, providing a liberal estimate. Both the average and liberal estimates of removals were below PBR for all 4 species. Thus, the best available data indicate that subsistence hunting is currently sustainable for all 4 species of ice seals.