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

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 caterva..., 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..., , # 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

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## 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 t...