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

===== 3.2.3.2.3 Fish =====

Many Antarctic fish have a narrow thermal tolerance as a result of physiological adaptations to cold water (Pörtner et al., 2014 <sup>[[#fn:r721|721]]</sup> ; Mintenbeck, 2017 <sup>[[#fn:r722|722]]</sup> ), which makes them vulnerable to the effects of increasing temperatures (Mueller et al., 2012 <sup>[[#fn:r723|723]]</sup> ; Beers and Jayasundara, 2015 <sup>[[#fn:r724|724]]</sup> ). Increasing water temperatures may displace icefish (family ''Channichthyidae'' ) in marginal habitats (e.g., shallow regions around subantarctic islands) as they lack haemoglobin and are unable to adjust blood parameters to an increasing oxygen demand (Mintenbeck et al., 201250‹) ( ''low confidence'' ). Future warming may also reduce the planktonic duration and increase egg and larval mortality for fish species, which is predicted to affect dispersal patterns, with implications for population connectivity and the ability of fish species to adapt to ongoing environmental change (Young et al., 2018 <sup>[[#fn:r751|751]]</sup> ). The Antarctic silverfish ( ''Pleuragramma antarctica'' ) is an important prey species in some regions of the Southern Ocean, and has an ice-dependent life cycle (Mintenbeck et al., 2012 <sup>[[#fn:r752|752]]</sup> ; Vacchi et al., 2012 <sup>[[#fn:r753|753]]</sup> ). Documented declines in the abundance of this species in some parts of the West Antarctic Peninsula may have consequences for associated food webs (Parker et al., 2015 <sup>[[#fn:r754|754]]</sup> ; Mintenbeck and Torres, 2017 <sup>[[#fn:r755|755]]</sup> ) ( ''low confidence'' ).

Myctophids and toothfish are important fish groups from both a food web (myctophids) and fishery (toothfish) perspective. Species distribution models for ''Electrona antarctica'' , a dominant myctophid species in the Southern Ocean, project habitat loss for this species under RCP4.5 (6.2 ± 6.0% loss) and RCP8.5 (13.1 ± 10.2% loss) by 2090, associated with increased sea surface temperature (Freer et al., 2018 <sup>[[#fn:r756|756]]</sup> ) ''.'' There have been no observed effects of climate change on the two species of toothfish that are found in the Southern Ocean: Patagonian and Antarctic toothfish ( ''Dissostichus eleginoides'' and ''D. mawsoni'' ), but recruitment is inversely correlated with sea surface temperature for Patagonian toothfish at South Georgia (Belchier and Collins, 2008 <sup>[[#fn:r757|757]]</sup> ). Given differences in temperature tolerances for Patagonian toothfish (with a wide temperature tolerance) and Antarctic toothfish (limited by a low tolerance for water temperatures above 2°C), the latter may be faced with reduced habitat and potential competition with southward-moving Patagonian toothfish under climate change (Mintenbeck, 2017 <sup>[[#fn:r758|758]]</sup> ) ( ''very low confidence'' ).

<div id="section-3-2-3-2-southern-ocean-block-5"></div>

<span id="seabirds-and-marine-mammals-1"></span>