A R C T I C I N T E G R A T E D E C O S Y S T E M R E S E A R C H P R O G R A M
Warmer waters and swifter northward currents changed fish communities in the Chukchi Sea Rising summer sea temperatures were associated with an increased presence of warmer-water larval fishes in Arctic habitats historically occupied by colder water fishes. The larvae of many Arctic fish species experienced declines in abundance during recent warm years (2017-2019) that were also characterized by increased advection of waters from the south and a reduction in sea ice. During 2017, young Arctic cod were highly abundant over the Chukchi shelf, but in 2019, they were restricted to only the northeastern Chukchi Sea, likely due to increased northward flow of warm water from the Bering Sea. Large numbers of young walleye pollock were present in the Chukchi Sea in 2017-2019, and young Pacific cod inhabited the eastern Chukchi Sea during recent warm summers. Adult Pacific cod were also present in low densities in the western Chukchi Sea during the recent warm period. The presence of age-1 Pacific cod in the eastern Chukchi Sea may indicate that young Pacific cod are surviving through the winter. Changes in fish communities will impact the food web of the Chukchi Sea. Salmon, whitefish, herring, and sand lance have the highest caloric content of
fish in the Chukchi Sea, but they are not particularly abundant or widespread, and some of them are only seasonally available. Arctic cod have slightly more than half the caloric content of salmon, but because they are the most abundant Arctic fish species, they are crucial prey for many predators. Capelin are nearly as calorie-rich as Arctic cod, but large fluctuations in their abundance make them less dependable prey. A comparison of the fat storage in young Arctic cod from the summer of 2017 showed that they had only half the fat storage relative to that measured in fish from earlier colder years (i.e., 2013). The use of chemical biomarkers as well as stomach diet analyses indicate that reduced Arctic cod fat storage is linked to a dietary decrease of large fatty zooplankton. When sea ice is absent, young fish feed on lower quality prey items that originate from warmer waters from the south. If lower-fat fish such as walleye pollock or Pacific cod displace Arctic cod as ocean temp- eratures rise, their lower caloric content will require predators to consume more fish to meet their energy needs. Arctic cod likely spawn in the northern Bering and southern Chukchi seas, hatch in winter and spring, and grow in the Chukchi Sea over the summer.
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