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Dryad

Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change

Cite this dataset

Axler, Kelia et al. (2024). Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change [Dataset]. Dryad. https://doi.org/10.5061/dryad.9zw3r22jv

Abstract

The Pacific Arctic marine ecosystem has undergone rapid changes in recent years due to ocean warming, sea ice loss, and increased northward transport of Pacific‐origin waters into the Arctic. These climate‐mediated changes have been linked to range shifts of juvenile and adult subarctic (boreal) and Arctic fish populations, though it is unclear whether distributional changes are also occurring during the early life stages. We analyzed larval fish abundance and distribution data sampled in late summer from 2010 to 2019 in two interconnected Pacific Arctic ecosystems: the northern Bering Sea and Chukchi Sea, to determine whether recent warming and loss of sea ice have restricted habitat for Arctic species and altered larval fish assemblage composition from Arctic‐ to boreal‐associated taxa. Multivariate analyses revealed the presence of three distinct multi‐species assemblages across all years: (1) a boreal assemblage dominated by yellowfin sole (Limanda aspera), capelin (Mallotus catervarius), and walleye pollock (Gadus chalcogrammus); (2) an Arctic assemblage composed of Arctic cod (Boreogadus saida) and other common Arctic species; and (3) a mixed assemblage composed of the dominant species from the other two assemblages. We found that the wind‐ and current‐driven northward advection of warmer, subarctic waters and the unprecedented low‐ice conditions observed in the northern Bering and Chukchi seas beginning in 2017 and persisting into 2018 and 2019 have precipitated community‐wide shifts, with the boreal larval fish assemblage expanding northward and offshore and the Arctic assemblage retreating poleward. We conclude that Arctic warming is most significantly driving changes in abundance at the leading and trailing edges of the Chukchi Sea larval fish community as boreal species increase in abundance and Arctic species decline. Our analyses document how quickly larval fish assemblages respond to environmental change and reveal that the impacts of Arctic borealization on fish community composition spans multiple life stages over large spatial scales.

README: Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change

Date of data collection: 2010-2019

Geographic locations: Northern Bering Sea (>60 N) and the Chukchi Sea


NBS_Chukchi_Ichthyoplankton_haul_spp_CTD_2010_2019.csv

This spreadsheet is an ichthyoplankton species matrix with associated haul (ichthyoplankton sampling gear) and CTD (temperature, salinity) information of ichthyoplankton captured in the Northern Bering and Chukchi Seas between 2010-2019. The icthyoplankton taxa abundances were fourth-root transformed (ind. 10 m^-2). Ichthyoplankton sampling was conducted in late summer of 2010-2019 using paired 60-cm diameter bongo nets towed obliquely from the surface to a maximum depth of 300 m deep or 10 m off the bottom, whichever was shallower (only n = 11 of 1,114 stations [<1%] were >300 m). In 2010-2016, a few stations were also sampled using a 1-m^2 Tucker trawl affixed to a sled frame that was lowered to the seafloor and towed obliquely to the surface with a messenger-based opening-closing net system (Sameoto & Jaroszynski 1976). The bongo nets and Tucker trawls were equipped with either 333- or 505-m mesh before switching to only 505-m mesh beginning in 2015. All sampling configurations were used for analysis since previous studies showed no significant differences in ichthyoplankton catch rates between these gear types and mesh sizes (Shima & Bailey 1994, Boeing & Duffy-Anderson 2008). Flowmeters (General Oceanics) attached to each net were used to calculate the volume filtered for each net tow, enabling larval abundance estimation (ind. 10 m-2; Matarese et al. 2003). Samples were preserved in 5% formalin buffered with sodium borate and seawater and identified to the lowest taxonomic level at the Plankton Sorting and Identification Center in Szczecin, Poland. Taxonomic verifications took place at the National Oceanographic and Atmospheric Administration, Alaska Fisheries Science Center in Seattle, WA, USA.

Column headers explanation:

Ichthyoplankton sampling gear haul information: HAUL_ID, DATE, CRUISE, LON, LAT, YEAR, BOTTOM_DEPTH (meters), STATION_NAME, HAUL_NAME, GEAR_NAME (60 cm diameter bongo net or sled oblique trawl), NET, MIN_GEAR_DEPTH (meters), MAX_GEAR_DEPTH (meters), HAUL_PERFORMANCE (Good or Quest), MESH (microns), VOLUME_FILTERED, PURPOSE, DOY (Day of Year)

CTD sampling haul information: PROFILE_ID, TEMPERATURE1 (degrees Celsius), SALINITY1

Larval fish species abundances (fourth-root transformed ind. 10 m^-2) columns range from Acantholumpenus mackayi : Triglops pingelii taxa.


NBS_Chukchi_Environmental_Variables_2010_2019.csv

Mean environmental conditions during late summer (August-September averaged) in the northern Bering-Chukchi Sea region (2010-2019). regional climate data sets from the National Centers for Environmental Prediction (NCEP) reanalysis project. Monthly estimates of sea surface temperature (SST) and surface wind velocities (meridional [south-north] and zonal components [west-east], m s -1) were acquired for the northern Bering Sea (6065.9N, 155170W) and Chukchi Sea (6674N, 155170W). The National Snow and Ice Data Center Sea Ice Index provided estimates of sea ice concentration (%, Cavalieri et al. 1996), area (km^2), and extent (km^2), using the Defense Meteorological Satellite Program series of passive microwave remote sensing instruments (Fetterer et al. 2002). The ice retreat index was estimated as the time period from January 1 to July 15 where ice coverage consistently reached values below 15% in the Bering Sea based on the 7-day running mean of the daily sea ice data. Bering Strait advective transport (Sv) was acquired from a year-round subsurface Acoustic Doppler Current Profiler moored ~35 km north of the strait (Woodgate & Peralta-Ferriz 2021). All environmental data were averaged over the period of larval fish collection for each year of the study (August and September) to provide annual estimates of late summer ocean and climate conditions for each region.

Column headers explanation:

Year (2010-2019)
Chukchi_SST (Sea Surface Temperature, degrees Celsius, averaged over the Chukchi Sea during August-September)
NBS_SST NBS_U_Wind (Northern Bering Sea Zonal Eastward Wind Velocity, m/s, +/- depending on wind direction; averaged over the Northern Bering Sea during August-September)
NBS_V_Wind (Northern Bering Sea Meridional Northward Wind Velocity, m/s, +/- depending on wind direction; averaged over the Northern Bering Sea during August-September)
Chukchi_U_Wind (Chukchi Sea Zonal Eastward Wind Velocity, m/s, +/- depending on wind direction; averaged over the Northern Bering Sea during August-September)
Chukchi_V_Wind (Chukchi Zonal Northward Wind Velocity, m/s, +/- depending on wind direction; averaged over the Northern Bering Sea during August-September)
Chukchi_SI_Area_km2 (Chukchi Sea Ice Area, km^2, averaged over August and September)
Chukchi_SI_Extent_km2 (Chukchi Sea Ice Extent, km^2, averaged over August and September)
BS_Transport (Bering Sea transport, Sverdrups, averaged over August and September)
Mean_DOY (Mean Day of Year of ichthyoplankton sampling)
IRI (Index of Ice Retreat for the Bering Sea, Mean Day of Year)

Methods

Data Collection and Methods

Field collections of environmental and ichthyoplankton data were conducted by a variety of research programs across the eastern (U.S.) region of the northern Bering-Chukchi seas in August and September of 2010-2019 and included coordinated efforts by the Distributed Biological Observatory, North Pacific Research Board’s Arctic Integrated Ecosystem Research Program (Baker et al. 2020), and the National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center. Hydrographic data were collected using a lowered conductivity-temperature-depth (CTD) profiler (SeaBird Electronics 911 plus) and in-line CTD system (SeaBird Electronics FastCAT SBE 49) attached to the ichthyoplankton nets to provide in situ temperature and salinity measurements from surface to bottom. If hydrographic data were not collected at a station, data from the nearest station and closest date in time were used. CTD-derived temperature and salinity measurements at each station were averaged over the entire water column to align with ichthyoplankton sampling protocols.

Environmental Dataset

Additionally, we collated regional climate data sets from the National Centers for Environmental Prediction (NCEP) reanalysis project. Monthly estimates of sea surface temperature (SST) and surface wind velocities (meridional [south-north] and zonal components [west-east], m s -1) were acquired for the northern Bering Sea (60–65.9°N, 155–170°W) and the Chukchi Sea (66–74°N, 155–170°W). The National Snow and Ice Data Center Sea Ice Index provided estimates of sea ice concentration (%, Cavalieri et al. 1996), area (km2), and extent (km2), using the Defense Meteorological Satellite Program series of passive microwave remote sensing instruments (Fetterer et al. 2002). The ice retreat index was estimated as the time period from January 1 to July 15 where ice coverage consistently reached values below 15% in the Bering Sea based on the 7-day running mean of the daily sea ice data. Bering Strait advective transport (Sv) was acquired from a year-round subsurface Acoustic Doppler Current Profiler moored ~35 km north of the strait (Woodgate & Peralta-Ferriz 2021). All environmental data were averaged over the period of larval fish collection for each year of the study (August and September) to provide annual estimates of late summer ocean and climate conditions for each region.

Ichthyoplankton Dataset

Ichthyoplankton sampling was conducted in late summer of 2010-2019 using paired 60-cm diameter bongo nets towed obliquely from the surface to a maximum depth of 300 m deep or 10 m off the bottom, whichever was shallower (only n = 11 of 1,114 stations [<1%] were >300 m). In 2010-2016, a few stations were also sampled using a 1-m2 Tucker trawl affixed to a sled frame that was lowered to the seafloor and towed obliquely to the surface with a messenger-based opening-closing net system (Sameoto & Jaroszynski 1976). The bongo nets and Tucker trawls were equipped with either 333- or 505-µm mesh before switching to only 505-µm mesh beginning in 2015. All sampling configurations were used for analysis since previous studies showed no significant differences in ichthyoplankton catch rates between these gear types and mesh sizes (Shima & Bailey 1994, Boeing & Duffy-Anderson 2008). Flowmeters (General Oceanics) attached to each net were used to calculate the volume filtered for each net tow, enabling larval abundance estimation (ind. 10 m-2; Matarese et al. 2003). Samples were preserved in 5% formalin buffered with sodium borate and seawater and identified to the lowest taxonomic level at the Plankton Sorting and Identification Center in Szczecin, Poland. Taxonomic verifications took place at the National Oceanographic and Atmospheric Administration, Alaska Fisheries Science Center in Seattle, WA, USA.

Funding

National Oceanic and Atmospheric Administration