DOI: 10.5061/dryad.dfn2z356g
title: Phenological shifts in out-migrating juvenile Pacific salmon

description: This dataset contains the rates of change in juvenile migration timing of
 66 Pacific salmon populations ranging from Oregon to Alaska, the rates of
 change in timing of the initiation of spring phytoplankton bloom in nearby
 coastal regions, and covariates. Species represented in this dataset
 include coho salmon (Oncorhynchus kisutch), sockeye salmon (O. nerka),
 Chinook salmon (O. tshawytscha), pink salmon (O. gorbuscha), chum salmon
 (O. keta), and steelhead trout (O. mykiss). Rates of change in salmon
 phenology includes rate of change in peak date, and rate of change in
 range (number of days between 25th and 75th quantile of migration).
description: This dataset represents the rates of
 change in juvenile salmon outmigration phenology. Rates of change were
 determined using the 'phenomix' R package from either daily
 outmigration counts, or mark-recapture corrected abundance estimates. In
 general, juvenile salmon were intercepted during their migration to the
 ocean using a full fence weir, partial fence weir, rotary screw trap,
 incline plane trap, floating trap, or seine. Individuals were identified
 to species, counted, and released. Mark recapture expanded estimates were
 only used when more than three stratified time estimates within a year
 were made. All rates of change were calculated from datasets with at least
 20 years of outmigration timing data, with at least 15 sampling days per
 year. The longest dataset began in 1951. Rates of change in phenology were
 determined for the full dataset and for a subset of years spanning 1999 -
 2019 (to match with availability of chlorophyll-a concentration
 data). In addition to rates of change in
 juvenile salmon outmigration phenology, this dataset contains rates of
 change in the corresponding coastal ocean spring phytoplankton bloom
 timing. Bloom timing estimates were derived from level-3 processed daily
 global composites (9 km x 9 km) of surface chlorophyll-a concentration
 from two satellites, Sea-viewing Wide Field-of-view Sensor (SeaWiFS; 1999
 - 2010) and the Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua;
 2003 - 2019) from the Goddard Space Flight Center. 2x2 degree grid cells
 along the coastal ocean between 42 – 60<sup>o</sup>N, 161.5 –
 124.5<sup>o</sup>W were subset from global composites.
 Sequential 8-day chlorophyll-a concentration estimates from Jan 1 to Aug 1
 for 20 years spanning 1999 – 2019 for each grid cell were generated. The
 day of year of initiation of the coastal spring phytoplankton bloom was
 determined to be the mid-date of the first 8-day chlorophyll-a
 concentration estimate that exceeded 5% of the median chlorophyll-a
 concentration estimate for that year. Rate of change in bloom date was
 determined using a linear regression of year and bloom day of year. Each
 population of salmon was linked to a rate of change in initiation of the
 spring phytoplankton bloom by both grid cell and river outlet. Thus, the
 coastal ocean grid cell corresponded to areas where juvenile salmon would
 enter the ocean.  Rates of change in seasonal air
 temperature and precipitation were determined for each population.
 Seasonal air temperature and precipitation were estimated using ClimateNA
 (v.5.21) and the latitude, longitude, and elevation where the juvenile
 salmon were intercepted, for each year salmon were counted, up to 2013
 (limit of ClimateNA v.5.21). The rate of change in seasonal air
 temperature and precipitation were determined for each salmon population
 using a weighted linear regression of year and seasonal air temperature or
 precipitation value for that year, weighted by the inverse variance in the
 estimate of air temperature or precipitation.