QERM alum, Cole Monnahan, will be presenting at the UW School of Aquatic and Fishery Sciences (SAFS) Quantitative Seminar on June 7. He is currently a postdoc in SAFS and the Alaska Fisheries Science Center at NOAA. See the Quantitative Seminar page for more information about the series.
Cole Monnahan (Postdoc, SAFS and AFSC)
Title: Combining data series within a spatio-temporal index standardization model to improve estimates and reduce uncertainty, with application to Eastern Bering Sea Pollock
For semi-pelagic fish the acoustic and bottom trawl surveys sample from different subsets of the vertical distribution of fish. Taken together the two surveys cover the total vertical column, but overlap to an unknown degree in the midwater. Considering these surveys independently can thus lead to unreliable estimates of trends in fish abundance for use in stock assessments because fish can either be missed (i.e., are unavailable) or counted twice. The extent of this variation in availability is further complicated because vertical distribution is driven by unknown physical and biological processes and varies spatially within, and among, years. Thus to better understand the change in fish abundance over time, it is important to account for the vertical distribution. Here we use Walleye pollock as a case study and extend the spatio-temporal modeling software VAST to explicitly model the vertical distribution of fish in space and time as part of an index standardization. In this talk I will focus on the technical features and challenges we encountered fitting this model to the two pollock survey data sets. Our preliminary results show substantial vertical shifts in space and time, and thus highly variable availability by survey type, and we argue our combined approach results in an improved index of abundance.
Date/Time: June 7, 2019, 12:30pm-1:30pm
Location: FSH 203