Spatiotemporal reconstruction of species ranges
We estimated annual species range edges from the trawl survey data using
the spatial generalized linear mixed model implemented in the R package
VAST (Thorson and Barnett 2017, Thorson 2019). This model was designed
to estimate total abundance and spatial variation in density of species
using spatially referenced biomass observations. We fit VAST to data
that follow either stratified-random or fixed-station designs; in both
cases, VAST predicted densities over a fixed spatial domain. This
analysis enabled comparison across years even when survey methodologies
were revised and across regions with distinct survey protocols. In
addition, this approach controlled for differences in catchability,
enabling us to combine the two historical West Coast surveys (Thorson et
al. 2016a). The model structure is described in detail in the
supplementary materials (Appendix 2).
Of the 209 species-region combinations, VAST models converged for 205 of
them (72 of 74 in the Northeast, 53 of 54 on the West Coast, and 80 of
81 in the Eastern Bering Sea). This set included five species found in
both the West Coast and the Eastern Bering Sea (Atheresthes
stomias, Bathyraja interrupta, Clupea pallasii, Glyptocephalus
zachirus, and Hippoglossoides elassodon ), and one found in both
the Northeast and the West Coast (Alosa sapidissima ), so the
total number of unique species was 199.