This file documents counts of marine mammals (excluding Stellar sea lions) observed during aerial surveys to document Pacific herring in the Prince William Sound Area, Alaska, 2008–2021. Additional observations prior to 2008 are on paper maps and still need to be digitized. Prince William Sound Area (Registration Area E) is described in regulation (5 AAC 27.300) as follows: The Prince William Sound Area has as its western boundary a line extending south from Cape Fairfield, as its eastern boundary a line extending south from Cape Suckling and as its southern boundary 59 degrees N. lat. Aerial surveys are generally conducted between late March and mid-May as this brackets the majority of spring Pacific herring spawning events. A single observer was on most surveys prior to 2007 and subsequently two observers have been used on most surveys. Prior to 2008, all observations were marked on paper maps and summarized on paper data sheets. An ESRI ArcPad application was developed and began production use in 2008. From 2008-2021, observations were made using the ArcPad application on a tablet computer, using a bluetooth GPS to spatially locate observations. In 2021, ArcPad and computer were replaced with ESRI Field Maps on an iPad Pro using an external bluetooth Garmin GLO GPS. From 2008–2019, two observers generally split the duties as follows: one observer collected data on the ESRI Arcpad application, and the second observer collected data on paper maps and photographed spawn, herring schools; and marine mammal or sea bird observations. During 2020 and 2021, only one observer was present due to COVID-19 protocols. A few surveys were only collected on paper maps and digitized later. Photographs of large harbor seal groups were used to make adjustments to counts for some surveys.