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

===== 3.2.3.2.4 Seabirds and marine mammals =====

Since AR5, there has been an increasing body of evidence of climate-induced changes in populations of some Antarctic higher predators such as seabirds and marine mammals. These changes vary between different regions of the Southern Ocean and reflect differences in key drivers (Bost et al., 2009 <sup>[[#fn:r759|759]]</sup> ; Gutt et al., 2015 <sup>[[#fn:r760|760]]</sup> ; Constable et al., 2016 <sup>[[#fn:r761|761]]</sup> ; Hunt et al., 2016 <sup>[[#fn:r762|762]]</sup> ; Gutt et al., 2018 <sup>[[#fn:r763|763]]</sup> ), particularly sea ice extent and food availability ( ''high confidence)'' across regions (Sections 3.2.1.1.1, 5.2.3.1, 5.2.3.2, 5.2.4). The predictability of foraging grounds and ice cover are associated with variations in climate (Dugger et al., 2014 <sup>[[#fn:r764|764]]</sup> ; Youngflesh et al., 2017 <sup>[[#fn:r765|765]]</sup> ; Abrahms et al., 2018 <sup>[[#fn:r766|766]]</sup> ) (Section 3.2.1.1) and are the main drivers of observed population changes of Southern Ocean higher predators ( ''high confidence'' ) (Descamps et al., 2015 <sup>[[#fn:r767|767]]</sup> ; Jenouvrier et al., 2015 <sup>[[#fn:r768|768]]</sup> ; Sydeman et al., 2015 <sup>[[#fn:r769|769]]</sup> ; Abadi et al., 2017 <sup>[[#fn:r770|770]]</sup> ; Bjorndal et al., 2017 <sup>[[#fn:r771|771]]</sup> ; Fluhr et al., 2017 <sup>[[#fn:r772|772]]</sup> ; Hinke et al., 2017a <sup>[[#fn:r773|773]]</sup> ; Hinke et al., 2017b <sup>[[#fn:r774|774]]</sup> ; Pardo et al., 2017 <sup>[[#fn:r775|775]]</sup> ). The suitability of breeding habitats and the location of environmental features that facilitate the aggregation of prey are also influenced by climate change, and in turn influence the distribution in space and time of marine mammals and birds (Bost et al., 2015 <sup>[[#fn:r776|776]]</sup> ; Kavanaugh et al., 2015 <sup>[[#fn:r777|777]]</sup> ; Hindell et al., 2016 <sup>[[#fn:r778|778]]</sup> ; Santora et al., 2017 <sup>[[#fn:r779|779]]</sup> ) ( ''medium confidence'' ). Finally, biological parameters (reproductive success, mortality, fecundity and body condition), life history traits, morphological, physiological and behavioural characteristics of top predators in the Southern Ocean, as well as their patterns of activity (migration, distribution, foraging and reproduction) are also changing as a result of climate change (Braithwaite et al., 2015a <sup>[[#fn:r780|780]]</sup> ; Whitehead et al., 2015 <sup>[[#fn:r781|781]]</sup> ; Seyboth et al., 2016 <sup>[[#fn:r782|782]]</sup> ; Hinke et al., 2017b <sup>[[#fn:r783|783]]</sup> ) ( ''high confidence'' ).

Trends of populations of Antarctic penguins affected by climate change include both increases for gentoo penguins, ( ''Pygoscelis papua'' ) (Lynch et al., 2013 <sup>[[#fn:r784|784]]</sup> ; Dunn et al., 2016 <sup>[[#fn:r785|785]]</sup> ; Hinke et al., 2017a <sup>[[#fn:r786|786]]</sup> ), and decreases for Adélie ( ''P. adeliae),'' chinstrap ( ''P. antarctica),'' king ( ''Aptenodytes patagonicus'' ) and Emperor ( ''A. forsteri'' ) penguins (Trivelpiece et al., 2011 <sup>[[#fn:r787|787]]</sup> ; LaRue et al., 2013 <sup>[[#fn:r788|788]]</sup> ; Jenouvrier et al., 2014 <sup>[[#fn:r789|789]]</sup> ; Bost et al., 2015 <sup>[[#fn:r790|790]]</sup> ; Southwell et al., 2015 <sup>[[#fn:r791|791]]</sup> ; Younger et al., 2015 <sup>[[#fn:r792|792]]</sup> ; Cimino et al., 2016 <sup>[[#fn:r793|793]]</sup> ) ( ''high confidence'' ). Yet population shifts in Adélie penguins (Youngflesh et al., 2017 <sup>[[#fn:r794|794]]</sup> ) may have resulted from strong interannual environmental variability in good and bad years for prey and breeding habitat rather than climate change ( ''low confidence'' ). New evidence suggests that present Emperor penguin population estimates should be evaluated with caution based on the existence of breeding colonies yet to be discovered/confirmed (Ancel et al., 2017 <sup>[[#fn:r795|795]]</sup> ) as well as studies that draw conclusions based on trend estimates from single colonies (Kooyman and Ponganis, 2017 <sup>[[#fn:r796|796]]</sup> ).

Evidence for climate change impacts on Antarctic flying birds indicates that contraction of sea ice (seasonally and in specific regions), increases in sea surface temperatures, extreme events (snowstorms) and wind regime shifts can reduce breeding success and population growth rates in some species: southern fulmars ( ''Fulmarus glacialoides'' ), Antarctic petrels ( ''Thalassoica antarctica'' ) and black-browed albatrosses ( ''Thalassarche melanophris'' ) (Descamps et al., 2015 <sup>[[#fn:r797|797]]</sup> ; Jenouvrier et al., 2015 <sup>[[#fn:r798|798]]</sup> ; Pardo et al., 2017 <sup>[[#fn:r799|799]]</sup> ) ( ''low confidence)'' . Poleward population shifts with increased intensity and frequency of westerly winds affect functional traits, demographic rates, foraging range, rates of travel and flight speeds of flying birds (Weimerskirch et al., 2012 <sup>[[#fn:r800|800]]</sup> ; Jenouvrier et al., 2018 <sup>[[#fn:r801|801]]</sup> ) but also increase overlap with fisheries activities thus increasing the risk of bycatch and the need for mitigation measures (Krüger et al., 2018 <sup>[[#fn:r802|802]]</sup> ) ( ''medium confidence)'' .

Changes in local- and regional-scale oceanographic features (Section 3.2.1.2) together with bathymetry control prey aggregation and distribution, and affect the ecological responses and biological traits of higher predators (particularly marine mammals) in the Southern Ocean (Lyver et al., 2014 <sup>[[#fn:r803|803]]</sup> ; Bost et al., 2015 <sup>[[#fn:r804|804]]</sup> ; Jenouvrier et al., 2015 <sup>[[#fn:r805|805]]</sup> ; Whitehead et al., 2015 <sup>[[#fn:r806|806]]</sup> ; Cimino et al., 2016 <sup>[[#fn:r807|807]]</sup> ; Hinke et al., 2017a <sup>[[#fn:r808|808]]</sup> ; Pardo et al., 2017 <sup>[[#fn:r809|809]]</sup> ) ( ''medium confidence'' ) and ''likely'' explain most of the observed population shifts (Kavanaugh et al., 2015 <sup>[[#fn:r810|810]]</sup> ; Hindell et al., 2016 <sup>[[#fn:r811|811]]</sup> ; Gurarie et al., 2017 <sup>[[#fn:r812|812]]</sup> ; Santora et al., 2017 <sup>[[#fn:r813|813]]</sup> ). Decadal climate cycles affect access to mesopelagic prey by southern elephant seals ( ''Mirounga leonina'' ) in the Indian Sector of the Southern Ocean and breeding females are excluded from highly productive continental shelf waters in years of increased sea ice extent and duration (Hindell et al., 2016 <sup>[[#fn:r814|814]]</sup> ) ( ''medium confidence)'' . To date there is no unified global estimate of the abundance of Antarctic pack ice seal species (Ross seals ( ''Ommatophoca rossi)'' , crabeater seals ( ''Lobodon carcinophaga)'' , leopard seals ( ''Hydrurga leptonyx)'' and Weddell seals ( ''Leptonychotes weddellii)'' ) as a reference point for understanding climate change impacts on these species (Southwell et al., 2012 <sup>[[#fn:r815|815]]</sup> ; Bester et al., 2017 <sup>[[#fn:r816|816]]</sup> ), although some regional population estimates for pack ice seals are available (Gurarie et al., 2017 <sup>[[#fn:r817|817]]</sup> and references therein). Analysis of long-term data suggests a genetic component to adaptation to climate change ( ''low confidence'' ) in Antarctic fur seals ( ''Arctocephalus gazella'' , Forcada and Hoffman (2014)) and pigmy blue whales ( ''Balaenoptera musculus brevicauda'' , Attard et al. (2015)).

Population trends of migratory baleen whales have been associated with krill abundance in the Atlantic and Pacific sectors of the Southern Ocean which is reflected in increased reproductive success, body condition and energy allocation (milk availability and transfer) to calves (Braithwaite et al., 2015a <sup>[[#fn:r818|818]]</sup> ; Braithwaite et al., 2015b <sup>[[#fn:r819|819]]</sup> ; Seyboth et al., 2016 <sup>[[#fn:r820|820]]</sup> ) ( ''high confidence'' ). There have been predictions of negative future impacts of climate change on krill and all whale species, although the magnitude of impacts differs among populations (Tulloch et al., 2019 <sup>[[#fn:r821|821]]</sup> ) as for other higher predators (Section 5. 2.3 ). Pacific blue (Tulloch et al., 2019 <sup>[[#fn:r822|822]]</sup> ) ( ''Balaenoptera musculus'' ), fin ( ''B. physalus'' ) and southern right whales ( ''Eubalaena australis'' ) are the most at risk but humpback whales ( ''Megaptera novaeangliae'' ) are also at risk, as consequence of reduced prey and increasing interspecific competition. Importantly, climate-related risks for whale populations are a product of environmental conditions and connectivity between whale foraging grounds (Southern Ocean) and breeding grounds (lower latitudes) (Section 5.2.3.1 ).

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