| Summary: | Sea otters are apex predators that can exert considerable influence over the nearshore communities they occupy. Since facing near extinction in the early 1900s, sea otters are making a remarkable recovery in Southeast Alaska, particularly in Glacier Bay, the largest protected tidewater glacier fjord in the world. The expansion of sea otters across Glacier Bay offers both a challenge to monitoring and stewardship and an unprecedented opportunity to study the top-down effect of a novel apex predator across a diverse and productive ecosystem. Our goal was to integrate monitoring data across trophic levels, space, and time to quantify and map the predator-prey interaction between sea otters and butter clams (Saxidomus gigantea ), one of the dominant large bivalves in Glacier Bay and a favored prey of sea otters. To do so, we developed a modeling framework to account for both bottom-up and top-down drivers of butter clam abundance and dynamics. For the bottom-up driver, we used the root-mean-square current speed (m/s) predicted by a tidal circulation model of Glacier Bay developed by Drew et al. (2013). For top-down sea otter dynamics, we used the posterior mean sea otter abundance estimates from Lu et al. (2019). This repository contains the current speed raster (100m x 100m resolution) produced by Drew et al. (2013) and the files and model output from Lu et al. (2019) necessary to generate a time series of rasters (400m x 400m resolution raster brick with 26 layers for the years 1993-2018) of estimated posterior mean sea otter abundance. These data layers are used in Leach et al. (2023) to model butter clam dynamics at sampling sites across Glacier Bay. R scripts to read and process both the current speed and sea otter rasters are available at https://github.com/clint-leach/otter-clam and in the linked Zenodo archive. Code to load the current speed raster and extract its values at a set of lat-long coordinates is provided in the script 'align_data.r' provided in that repository. After extracting the zip, the ...
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