Kittiwake and murre abundance comparison between colony and at-sea data trends in Alaska, 1975-2022

This analysis uses at-sea seabird sightings collected from 1975-2022, and seabird counts from 10 different island colonies in Alaskan maritime waters (time range is variable), to model and compare abundance trends. Specifically, we investigated three different species (black-legged kittiwakes, common murres and thick-billed murres using two different models: 1) a 2000-2022 contemporary model modeling the three species separately both at-sea and on land; 2) a 1975-2022 historical model modeling that grouped the two murre species into a common "Murre spp." category, and thus modeled murre spp. and black-legged kittiwakes. Input data for at-sea seabird observations used in modeling were extracted from the publically available North Pacific Pelagic Seabird Database V.4, hosted by the United States Geological Survey. The Historic_model_density_prediction.csv data represents modeled seabird density predictions for three species, encompassing May-August and 1975-2022 at a spatial resolution of approximately 100 x 100-km grid cells. It was produced using a gamma-distribution joint dynamic species distribution model using the VAST modeling approach. Density estimates are available in a combined June-July period for each year between 1975-2022. The Modern_model_density_prediction.csv.csv data represents modeled seabird density predictions for three species, encompassing May-August and 2000-2022 at a spatial resolution of approximately 200 x 200-km grid cells. It was produced using a gamma-distribution joint dynamic species distribution model using the VAST modeling approach. Density estimates are available in 4 monthly intervals for each year between 2000-2022. The Colony Model Study Area Shapefile provides the study area boundaries for the seabird density predictions used in a Colony VAST model on 3 species, encompassing May-August and 1975-2022. The Colonies Shapefile provides 200km buffer circles around each of 10 seabird colonies used in the Colony VAST model analysis comparing at-sea versus colony trends in 3 seabird species, encompassing May-August and 1975-2022. The Raw_Colony_data.csv data represents colony subsample counts obtained from plots and census count for three seabird species at 10 different colonies in Alaskan region, from 1975 - 2022. These counts were collected as part of regular monitoring efforts maintained by the Alaska Maritime National Wildlife Refuge system.