Adult Herring Biomass Survey Data, 1993-2021, Prince William Sound, EVOS Herring Program

These data are part of the Herring Program of the Exxon Valdez Oil Spill Trustee Council, which is a multi-faceted study to determine why herring populations in Prince William Sound remain depressed since the early 1990s. Since 1993 the Prince William Sound Science Center has annually conducted surveys of the spawning biomass using hydroacoustic techniques. This information can be used as a biomass index in the age-structure-analysis model for determining the population biomass. In most years the focus has been on the main spawning stock in eastern Prince William Sound (there are other smaller stocks in Prince William Sound that are not quantified). It is possible that fish spawning outside the primary spawning area may include a significant portion of the biomass; this project focused on expanding survey areas to quantify the biomass of fish spawning outside of the primary spawning location. Surveys were conducted during the spring of each year (late March to early April period) during 2012-2021. This effort is a continuation of similar adult herring acoustic surveys conducted within Prince William Sound from 2007 to 2012. Location of surveys were based in part on historical information and evidence garnered from aerial surveys of the distribution of dominant predators (particularly whales, seabirds, orcas and sea lions). Surveys were conducted using a 70 kHz single-beam hydroacoustic unit towed beside a vessel in a zig-zag survey design. During the surveys, the returned sound intensity from the sonar were recorded and stored for later processing and estimation of adult herring biomass in metric tons. The expanded survey effort was primarily focused on the spawning areas along Montague Island, where there have been consistent small spawning events since the mid-2000s. The main location of spawning has been in Port Gravina and Fidalgo bays in Prince William Sound. The dataset consists of raw acoustic source data files (in *.DT4 format generated by BioSonics DT system) with embedded GPS coordinates; intermediary echointegration files (in CSV format) of acoustic backscatter generated by Biosonics or Echoview software in the form of the area backscatter coefficient (sa, m2 m-2); and final biomass summary (in CSV format) of the acoustic survey area, and the upper and lower biomass estimate of adult herring (>150 mm TL) from 1993-2021. While the time series of acoustic data dates back to 1993, this dataset represents intermediary acoustic data files for 2016 -21 for which full acoustic analysis has been completed.