| Summary: | The goal of this study is to reveal the temporal variation of biological backscatter in a region of the Beaufort Shelf known for intense upwelling. Acoustic Zooplankton Fish Profilers (AZFPs, ASL Environmental Sciences Inc.) were deployed on moorings for two years. The AZFP was equipped with 38, 120, 200, and 455 kilohertz (kHz) frequencies. The first deployment took place from Aug. 29, 2017 – Aug. 10, 2018 at the 80 m isobath in the mid-Beaufort Sea shelf. The instrument was moored 7.8 meters (m) off the bottom and collected data using 90 pings with a 20 second ping interval every 20 minutes for the deployment period. The second deployment took place from Aug. 24, 2018 – Aug. 20, 2019 at the 115 m isobath on the Beaufort Shelf just east of the mouth of Barrow Canyon. The instrument was moored 7.8 m off the bottom and collected data in two different configurations over the year designed to optimize battery life (5-minute burst interval with 30 pings per burst and a 2 second ping interval from August to the end of November and from June until recovery and 20-minute burst interval with 30 pings per burst and a 2 second ping interval from December through May). Only the 38 and 455 kHz transducers operated throughout the 2-year deployment period. The 200 kHz transducer failed in January 2018 and the 125 kHz transducer failed in August 2018, making frequency differencing to differentiate taxa difficult/impossible for much of the record. Statistical measures of acoustic backscatter, known as Echometrics, as defined in Urmy et al. 2012 were calculated using the Echoview version 12.1 software for 38 kHz data over the entire AZFP time series between August 2017 and August 2019. Acoustic data were be adjusted for sound speed and absorption using temperature and salinity measurements from a Seabird CTD (Conductivity, Temperature, and Depth) moored nearby.
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