DOI: 10.5061/dryad.2280gb66b
title: Widespread phenological shifts with temperature in Alaska’s marine fishes

description: Changes in the timing of fish spawning and early life stage development
 can affect the temporal match or mismatch of larvae with production of
 preferred prey as well as their availability to predators, with potential
 consequences for recruitment success, food-web dynamics, and fisheries.
 Using &gt;370,000 observations from over four decades of spring
 ichthyoplankton surveys in the Gulf of Alaska and Bering Sea, we
 investigated long-term changes in the phenology of 29 fish species,
 including commercially important taxa such as Pacific cod, walleye
 pollock, and Pacific halibut. Larval size on a standardized date
 (size-at-date) was used as a proxy for larval developmental timing in
 spring, and reflects a combination of hatch timing (larval age), growth,
 and mortality. Spatiotemporal generalized linear mixed models were used to
 account for variable sampling effort in space and time in order to isolate
 long-term trends and thermal effects on larval size. For a majority of
 species, interannual variation in mean size-at-date was significantly and
 positively related to temperature, demonstrating widespread thermal
 effects on the phenology of fish early life stages. Despite the wide
 diversity of life history traits exhibited by the 29 species examined,
 patterns in size-at-date over time were similar across most species within
 each ecosystem, reflecting the common effect of temperature on phenology.
 While temperature affected size-at-date, there was little evidence of
 long-term trends, likely due to the lack of a linear trend in
 winter-spring temperatures observed in recent decades. We demonstrate a
 novel analytical method to assess changes in phenology from larval size
 observations sampled at variable locations and times, and detect
 phenological shifts that were not necessarily identifiable from larval
 abundance data alone. Our results suggest that earlier spring phenology
 due to warming will be a common response among fishes to projected future
 climate change in high-latitude ecosystems.
description: Survey Data
 Ichthyoplankton surveys in Alaska’s waters have been conducted by
 the National Oceanic and Atmospheric Administration’s Alaska Fisheries
 Science Center (NOAA AFSC) and partners since the 1970s, becoming more
 frequent in the 1980s (GOA) and 1990s (EBS). At each survey station,
 paired 60-cm bongo nets were towed obliquely from a depth of at least 100
 m, or 10 m off the bottom in shallower waters. Net mesh sizes were either
 333-µm or 505-µm. For each tow, the contents of one net were preserved in
 5% formalin and later sorted and identified to the lowest taxonomic level
 possible at the Plankton Sorting and Identification Center in Szczecin,
 Poland. Up to 50 larvae of each taxa from each tow were measured for
 standard length after preservation. Species identifications were verified
 by expert taxonomists at NOAA AFSC. Survey coverage and timing has varied
 over the years due to differing survey objectives and ship time
 allocations, although many earlier surveys were specifically targeted for
 studying pollock eggs and larvae. For this analysis, we selected study
 areas that represented the most consistently sampled areas within each
 region and used only samples collected within the most consistently
 sampled temporal window (days 98-162 in the EBS and 117-160 in the GOA).
 This spring (April-June) sampling window captures a high diversity and
 abundance of larval fishes, reflecting common patterns of winter-spring
 spawning in these systems. Species Selection
 Only taxa identified to the species level were included for
 analysis. From those, we chose species that were present in at least 10
 different years, with at least 10 observations in each of those
 years.
description: # Widespread phenological shifts with temperature in Alaska’s marine
 fishes Dataset DOI:
 [10.5061/dryad.2280gb66b](https://doi.org/10.5061/dryad.2280gb66b) ##
 Description of the data and file structure #### Survey Data
 Ichthyoplankton surveys in Alaska’s waters have been conducted by the
 National Oceanic and Atmospheric Administration’s Alaska Fisheries Science
 Center (NOAA AFSC) and partners since the 1970s, becoming more frequent in
 the 1980s (GOA) and 1990s (EBS). At each survey station, paired 60-cm
 bongo nets were towed obliquely from a depth of at least 100 m, or 10 m
 off the bottom in shallower waters. Net mesh sizes were either 333-µm or
 505-µm. For each tow, the contents of one net were preserved in 5%
 formalin and later sorted and identified to the lowest taxonomic level
 possible at the Plankton Sorting and Identification Center in Szczecin,
 Poland. Up to 50 larvae of each taxa from each tow were measured for
 standard length after preservation. Species identifications were verified
 by expert taxonomists at NOAA AFSC. Survey coverage and timing has varied
 over the years due to differing survey objectives and ship time
 allocations, although many earlier surveys were specifically targeted for
 studying pollock eggs and larvae. For this analysis, we selected study
 areas that represented the most consistently sampled areas within each
 region  and used only samples collected within the most consistently
 sampled temporal window (days 98-162 in the EBS and 117-160 in the GOA).
 This spring (April-June) sampling window captures a high diversity and
 abundance of larval fishes, reflecting common patterns of winter-spring
 spawning in these systems. #### Species Selection Only taxa identified to
 the species level were included for analysis. From those, we chose species
 that were present in at least 10 different years, with at least 10
 observations in each of those years. ### Files and variables #### File:
 EBS_spring_d98to162_11spp_Apr2024_larval.csv **Description:** Larval fish
 catch data and length measurements from NOAA EcoFOCI and partner surveys
 in the Bering Sea, collected between day of year 98 and 162. Data queried
 in April 2024. ##### Variables * SPECIES_NAME: Scientific name of
 specimen. * HAUL_ID: Unique identifier for haul (bongo net sampling event
 from a particular station and survey). * CRUISE: Survey identifier. *
 HAUL_NAME: Sequential haul number within a station. * NET: 1 or 2,
 indicating which of two sampling nets was preserved and used for analysis.
 * MESH: Mesh size of sampling net in microns. * LAT: Latitude, degrees. *
 LON: Longitude, degrees. * GEOGRAPHIC_AREA: Region of sampling, either GOA
 (Gulf of Alaska) or BS (Bering Sea). * YEAR: Year of collection. *
 GMT_DATE_TIME_TXT: Date and time of sampling. * GMT_DATE_TIME: Date of
 sampling. * CORRECTED_LENGTH: Standard length of formalin-preserved larvae
 (mm). * LARVALCATCHPER10M2: Calculated catch of larvae of this species per
 10 m2 from this haul. * LARVALCATCHPER1000M3: Calculated catch of larvae
 of this species per 1000 m3 from this haul. *
 NUMBER_MEASURED_COUNTED: Number of larvae of this species measured for
 length at this station (not necessarily equal to total number caught). *
 COMMON_NAME: Common name of species. * YDAY: Day of year of sampling. *
 nyrs: Total number of years this species is present in dataset (by
 region). #### File: GOA_spring_d117to160_32spp_Jul2024_larval.csv
 **Description:** Larval fish catch data and length measurements from NOAA
 EcoFOCI and partner surveys in the Gulf of Alaska, collected between day
 of year 117 and 160. Data queried in July 2024. ##### Variables *
 SPECIES_NAME: Scientific name of specimen. * HAUL_ID: Unique identifier
 for haul (bongo net sampling event from a particular station and survey).
 * CRUISE: Survey identifier. * HAUL_NAME: Sequential haul number within a
 station. * NET: 1 or 2, indicating which of two sampling nets was
 preserved and used for analysis. * MESH: Mesh size of sampling net in
 microns. * LAT: Latitude, degrees. * LON: Longitude, degrees. *
 GEOGRAPHIC_AREA: Region of sampling, either GOA (Gulf of Alaska) or BS
 (Bering Sea). * YEAR: Year of collection. * GMT_DATE_TIME_TXT: Date and
 time of sampling. * GMT_DATE_TIME: Date of sampling. * CORRECTED_LENGTH:
 Standard length of formalin-preserved larvae (mm). * LARVALCATCHPER10M2:
 Calculated catch of larvae of this species per 10 m2 from this haul. *
 LARVALCATCHPER1000M3: Calculated catch of larvae of this species per 1000
 m3 from this haul. * NUMBER_MEASURED_COUNTED: Number of larvae of this
 species measured for length at this station (not necessarily equal to
 total number caught). * COMMON_NAME: Common name of species. * YDAY: Day
 of year of sampling. * nyrs: Total number of years this species is present
 in dataset (by region). ####