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Despite the fact that cetaceans provide significant ecological contributions to the health and stability of aquatic ecosystems, many are highly endangered with nearly one‐third of species assessed as threatened with extinction. Nevertheless, to date, few studies have explicitly examined the patterns and processes of extinction risk and threats for this taxon, and even less between the two subclades (Mysticeti and Odontoceti). To fill this gap, we compiled a dataset of six intrinsic traits (active region, geographic range size, body weight, diving depth, school size, and reproductive cycle), six environmental factors relating to sea surface temperature and chlorophyll concentration, and two human‐related threat indices that are commonly recognized for cetaceans. We then employed phylogenetic generalized least squares models and model selection to identify the key predictors of extinction risk in all cetaceans, as well as in the two subclades. We found that geographic range size, sea surface temperature, and human threat index were the most important predictors of extinction risk in all cetaceans and in odontocetes. Interestingly, maximum body weight was positively associated with the extinction risk in mysticetes, but negatively related to that for odontocetes. By linking seven major threat types to extinction risk, we further revealed that fisheries bycatch was the most common threat, yet the impacts of certain threats could be overestimated when considering all species rather than just threatened ones. Overall, we suggest that conservation efforts should focus on small‐ranged cetaceans and species living in warmer waters or under strong anthropogenic pressures. Moreover, further studies should consider the threatened status of species when superimposing risk maps and quantifying risk severity. Finally, we emphasize that mysticetes and odontocetes should be conserved with different strategies, because their extinction risk patterns and major threat types are considerably different. For instance, large‐bodied mysticetes and small‐ranged odontocetes require special conservation priority. [ABSTRACT FROM AUTHOR]

Ecologists and managers require accurate population estimates of marine mammals to assess potential anthropogenic threats to these animals. We present estimates of in‐water density and abundance of a distinct stock of harbor seals (Phoca vitulina richardii) in Hood Canal, Washington, USA. We used aerial line‐transect survey data collected from 2013 to 2016 to directly estimate harbor seal density and abundance in the waters of Hood Canal, a deep‐water fjord in the Salish Sea. We estimated a correction factor for trackline detection probability from dive and surface time data gathered from regional seal tagging studies, and applied this factor to correct for seals missed on the trackline during surveys. We applied conventional and multiple covariate line‐transect approaches in the analysis. The resulting best estimate of in‐water density of harbor seals in the Hood Canal study region was 5.80 seals/km2, with an estimated abundance of 2,009 seals. We did not derive a correction factor to account for the number of seals on land (i.e., hauled out). Therefore, these estimates do not reflect total stock size but provide a starting point to evaluate potential influences of anthropogenic activities, particularly those involving underwater noise, on this marine mammal stock. © 2021 The Wildlife Society. Using aerial survey data collected from 2013 to 2016, we estimated the in‐water density and abundance of a distinct stock of harbor seals in Hood Canal, Washington, USA, to help assess potential anthropogenic threats to these animals. We used conventional and multiple covariate line‐transect approaches in the analysis, and the resulting best estimate of in‐water density of harbor seals in the study region was 5.80 seals/km2, with an estimated abundance of 2,009 seals. [ABSTRACT FROM AUTHOR]