Estimation of In‐Water Density and Abundance of Harbor Seals

• Published in: The Journal of Wildlife Management
• Main Authors: Ampela, Kristen, Jefferson, Thomas A., Smultea, Mari A.
• Other Authors: U.S. Navy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: harbor seal; Phoca vitulina
• Online Access: http://dx.doi.org/10.1002/jwmg.22019; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jwmg.22019; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jwmg.22019; https://wildlife.onlinelibrary.wiley.com/doi/am-pdf/10.1002/jwmg.22019

ABSTRACT 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/km 2 , 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.