Editing IPCC:AR6/SROCC/Chapter-3 (section)

===== 3.2.3.1.3 Fish =====

Since AR5, additional evidence shows climate-induced physical and biogeochemical changes are impacting, and will continue to impact, the distribution and production of marine fish ( ''medium confidence'' ). Changes in the spatial distribution and production of Arctic fish are best documented for ecologically and commercially important stocks in the Bering and Barents Seas (Box 3.4; Figure 3.5), while data is severely limited in other Arctic shelf regions and the Central Arctic Ocean (CAO).

Higher temperature and changes in the quality and distribution of prey is already affecting marine fish (Wassmann et al., 2015 <sup>[[#fn:r601|601]]</sup> ; Dalpadado et al., 2016 <sup>[[#fn:r602|602]]</sup> ; Hunt et al., 2016 <sup>[[#fn:r603|603]]</sup> ; Section 3.2.3.1) ( ''high confidence'' for detection '', medium confidence'' for attribution). In the northern Barents Sea, Atlantic Sector, higher temperatures (Section 3.2.1.2) have expanded suitable feeding areas for boreal/subarctic species (Box 3.4) and has contributed to increased Atlantic cod ( ''Gadus morhua'' ) production (Kjesbu et al., 2014 <sup>[[#fn:r604|604]]</sup> ). In contrast, Arctic species like polar cod ( ''Boreogadus saida'' ) are expected to be affected negatively by a shortened ice covered season and reduced sea ice extent through loss of spawning habitat and shelter, increased predatory pressure, reduced prey availability (Christiansen, 2017 <sup>[[#fn:r605|605]]</sup> ), and impaired growth and reproductive success (Nahrgang et al., 2014 <sup>[[#fn:r606|606]]</sup> ). These changes may cause structural changes in food webs, with large piscivorous and semipelagic boreal fish species replacing small bodied Arctic benthivores (Box 3.4; Fossheim et al., 2015 <sup>[[#fn:r607|607]]</sup> ; Frainer et al., 2017 <sup>[[#fn:r608|608]]</sup> ).

Time series on responses of anadromous fish (including salmon) in the high Arctic are limited, although these stocks will also be exposed to a wide range of future stressors (Reist et al., 2016 <sup>[[#fn:r609|609]]</sup> ). There is some evidence that environmental variability influences the production of anadromous species such as Arctic char ( ''Salvelinus alpinus'' ), brown trout ( ''Salmo trutta'' ), and Atlantic salmon ( ''Salmo salar'' ) through its influence on growth and winter survival (Jensen et al., 2018 <sup>[[#fn:r610|610]]</sup> ).

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'''Figure 3.5'''

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'''Schematic summary of key drivers that are causing, or are projected to cause, direct effects on Arctic marine ecosystems (Section 3.2.1.2). Effects presented here are described in the main text (Sections 3.2.3.1; 3.2.4.1.1; 3.2.4.2; 3.2.4.3) with associated confidence levels and citations. For mixed effects, no confidence level is given (see main text for details on […]'''
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[[File:b9febfe6dc3285f5ce48ec8097e23c96 IPCC-SROCC-CH_3_5.jpg]]

Schematic summary of key drivers that are causing, or are projected to cause, direct effects on Arctic marine ecosystems (Section 3.2.1.2). Effects presented here are described in the main text (Sections 3.2.3.1; 3.2.4.1.1; 3.2.4.2; 3.2.4.3) with associated confidence levels and citations. For mixed effects, no confidence level is given (see main text for details on how multiple drivers cause interacting positive and negative effects). Projected effects are conceptual representations based on high emission scenarios (Section 3.2.1.2). The cross-sectional view of the Arctic ecosystem shows the association of key functional groups (marine mammals, birds, fish, zooplankton, phytoplankton and benthic assemblages) with Arctic marine habitats. Species depicted in the fishing net are not a comprehensive depiction of all target species.

The scope for adaptation of marine fish to a changing ocean conditions is uncertain, but knowledge is informed by previous biogeographic studies (Chernova, 2011 <sup>[[#fn:r611|611]]</sup> ; Lynghammar et al., 2013 <sup>[[#fn:r612|612]]</sup> ). The present niche partitioning between subarctic and Arctic pelagic fish species is expected to become more diffuse with potential negative impacts on cold adapted species such as polar cod (Laurel et al., 2017 <sup>[[#fn:r613|613]]</sup> ; Alabia et al., 2018 <sup>[[#fn:r614|614]]</sup> ; Logerwell et al., 2018 <sup>[[#fn:r615|615]]</sup> ) ( ''low confidence'' ). Winter ocean conditions in the high Arctic are projected to remain cold in most regions (Section 3.2.3.1), limiting the immigration of subarctic species that spawn in positive temperatures onto the high Arctic shelves (Landa et al., 2014 <sup>[[#fn:r616|616]]</sup> ). Projected increases in summer temperature may open gateways to subarctic pelagic foragers in summer, particularly in the inflow regions of the Kara and Chukchi Seas, and the shelf regions of east and west Greenland (Mueter et al., 2017 <sup>[[#fn:r617|617]]</sup> ; Joli et al., 2018 <sup>[[#fn:r618|618]]</sup> ). For example, t he pelagic capelin ( ''Mallotus villosus'' ) are capable of entering the CAO, but may be restricted in winter by availability of suitable spawning areas and lack of antifreeze proteins (Hop and Gjøsæter, 2013 <sup>[[#fn:r619|619]]</sup> ; Christiansen, 2017 <sup>[[#fn:r620|620]]</sup> ).

Regional climate scenarios, derived from down-scaled global climate scenarios, have been used to drive environmentally linked fish population models (Hermann et al., 2016 <sup>[[#fn:r621|621]]</sup> ; Holsman et al., 2016 <sup>[[#fn:r622|622]]</sup> ; Ianelli et al., 2016 <sup>[[#fn:r623|623]]</sup> ; Hermann et al., 2019 <sup>[[#fn:r624|624]]</sup> ). Hermann et al. (2019) <sup>[[#fn:r625|625]]</sup> contrasted future production of copepods and euphausiids in the eastern Bering Sea under scenarios derived from projected downscaled high spatial and temporal resolution ocean habitats under RCP4.5 and RCP8.5. Consistent with AR5, these updated scenarios project future declines in the abundance of large copepods under RCP8.5, a result that has been shown to negatively impact production of walleye pollock, Pacific cod ( ''Gadus microcephalus'' ) and arrowtooth flounder ( ''Atheresthes stomias'' ) (Sigler et al., 2017 <sup>[[#fn:r626|626]]</sup> ; Kimmel et al., 2018 <sup>[[#fn:r627|627]]</sup> ) ( ''medium confidence'' ). Hedger et al. (2013) predicts increases in Atlantic salmon abundance in northern Norway (river Alta around 70°N) with future warming ( ''low confidence'' ). Under end of century RCP8.5 projections, ocean acidification and higher ocean temperatures are expected to reduce production of Barents Sea cod (Stiasny et al., 2016 <sup>[[#fn:r629|629]]</sup> ; Koenigstein et al., 2018 <sup>[[#fn:r630|630]]</sup> ) ( ''low confidence'' ).

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