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

===== 3.2.3.1.4 Seabirds and marine mammals =====

Environmental alterations caused by global warming are resulting in phenological, behavioural, physiological, and distributional changes in Arctic marine mammal and seabird populations (Gilg et al., 2012 <sup>[[#fn:r631|631]]</sup> ; Laidre et al., 2015 <sup>[[#fn:r632|632]]</sup> ; Gall et al., 2017 <sup>[[#fn:r633|633]]</sup> ) ( ''high confidence'' ). These changes include altered ecological interactions as well as direct responses to habitat degradation induced especially via loss of sea ice. Population responses to warming have not all been linear, some have been particularly strong and abrupt due to environmental regime shifts, as seen in black-legged kittiwakes ( ''Rissa tridactyla'' ). A steep population decline in kittiwake colonies distributed throughout their breeding range coincided with an abrupt warming of sea surface temperature in the 1990s, while their population dynamics did not seem to be affected during periods of more gradual warming (Descamps et al., 2017 <sup>[[#fn:r634|634]]</sup> ).

Seabirds and marine mammals are mobile animals that respond to changes in the distribution of their preferred habitats and prey, by shifting their range, altering the timing or pathways for migration or prey shifting when this is feasible (Post et al., 2013 <sup>[[#fn:r635|635]]</sup> ; Hamilton et al., 2019 <sup>[[#fn:r636|636]]</sup> ) ( ''very high confidence'' ). However, some species display strong site fidelity that can be maladaptive in a changing climate and Arctic endemic marine mammals (all of which are ice-affiliated for breeding) in general have little scope to move northward in response to warming (Kovacs et al., 2012 <sup>[[#fn:r637|637]]</sup> ; Hamilton et al., 2015 <sup>[[#fn:r638|638]]</sup> ). Changes in the location or availability of polar fronts, polynyas, tidal glacier fronts or ice edges have impacted where Arctic sea birds and marine mammals concentrate because of the influence these physical features have on productivity; traditionally these areas have been key foraging sites for top predators in the Arctic (deHart and Picco, 2015 <sup>[[#fn:r639|639]]</sup> ; Hamilton et al., 2017 <sup>[[#fn:r640|640]]</sup> ; Hunt et al., 2018 <sup>[[#fn:r641|641]]</sup> ).

In some species, shifts in distribution in response to changes in suitable habitat have been associated with increased mortality. Increased mortality rates of walrus ( ''Odobenus rosmarus)'' calves have been observed during on-shore stampedes of unusually large herds, because Pacific walrus females are no longer able to haul out on ice over the shelf in summer due to the retraction of the southern ice edge into the deep Arctic Ocean (Kovacs et al., 2016 <sup>[[#fn:r642|642]]</sup> ). Shifts in the temporal and spatial distribution and availability of suitable areas of sea ice for ice-breeding seals have occurred (Bajzak et al., 2011 <sup>[[#fn:r643|643]]</sup> ; Øigård et al., 2013 <sup>[[#fn:r6|6]]</sup> 44) with increases in strandings and pup mortality in years with little ice (Johnston et al., 2012c <sup>[[#fn:r645|645]]</sup> ; Soulen et al., 2013 <sup>[[#fn:r646|646]]</sup> ; Stenson and Hammill, 2014 <sup>[[#fn:r647|647]]</sup> ).

Climate impacts that reduce the availability of prey resources can negatively impact marine mammals (Asselin et al., 2011; Øigård et al., 2014; Choy et al., 2017) ( ''very high confidence'' ). Sea ice changes have increased the foraging effort of ringed seals ( ''Pusa hispida'' ) in the marginal ice zone north of Svalbard (Hamilton et al., 2015 <sup>[[#fn:r651|651]]</sup> ), also causing diet shifts (Lowther et al., 2017 <sup>[[#fn:r652|652]]</sup> ). Ringed seals in Svalbard are using terrestrial haul out sites during summer for the first time in observed history, following major declines in sea ice (Lydersen et al., 2017 <sup>[[#fn:r653|653]]</sup> ), an example of an adaptive behavioural response to extreme habitat changes. Sea ice related changes in the export of production to the benthos (Section 3.3.3.1) and associated changes in the benthic community (Section 3.4.1.1.2) may impact marine mammals dependent on benthic prey (e.g., walruses and gray whales, ''Eschrichtius robustus'' ) (Brower et al., 2017 <sup>[[#fn:r654|654]]</sup> ; Udevitz et al., 2017 <sup>[[#fn:r655|655]]</sup> ; Szpak et al., 2018 <sup>[[#fn:r656|656]]</sup> ).

Changes in the timing, distribution and thickness of sea ice and snow (Sections 3.2.1.1, 3.4.1.1) have been linked to phenological shifts, and changes in distribution, denning, foraging behaviour and survival rates of polar bears ( ''Ursus maritimus'' ) (Andersen et al., 2012 <sup>[[#fn:r657|657]]</sup> ; Hamilton et al., 2017 <sup>[[#fn:r658|658]]</sup> ; Escajeda et al., 2018 <sup>[[#fn:r659|659]]</sup> ) ( ''high confidence'' ). Less ice is also driving polar bears to travel over greater distances and swim more than previously both in offshore and in coastal areas, which can be particularly dangerous for young cubs (Durner et al., 2017 <sup>[[#fn:r660|660]]</sup> ; Pilfold et al., 2017 <sup>[[#fn:r661|661]]</sup> ; Lone et al., 2018 <sup>[[#fn:r662|662]]</sup> ). Cumulatively, changes in sea ice patterns are driving demographic changes in polar bears, including declines in some populations (Lunn et al., 2016 <sup>[[#fn:r663|663]]</sup> ; McCall et al., 2016 <sup>[[#fn:r664|664]]</sup> ), while others are stable or increasing (Voorhees et al., 2014 <sup>[[#fn:r665|665]]</sup> ; Aars et al., 2017 <sup>[[#fn:r666|666]]</sup> ). This is because protective management measures have been successful in allowing severely depleted populations to recover or because new food sources, such as carrion, are becoming available to polar bears in some regions (Galicia et al., 2016 <sup>[[#fn:r667|667]]</sup> ; Stapleton et al., 2016 <sup>[[#fn:r668|668]]</sup> ). Changes in the spatial distribution of polar bears and killer whales can have top-down effects on other marine mammal prey populations (Øigård et al., 2014 <sup>[[#fn:r669|669]]</sup> ; Breed et al., 2017 <sup>[[#fn:r670|670]]</sup> ; Smith et al., 2017a <sup>[[#fn:r671|671]]</sup> ).

Several studies from different parts of the Arctic show evidence that changing temperatures impact seabird diets (Dorresteijn et al., 2012 <sup>[[#fn:r672|672]]</sup> ; Divoky et al., 2015 <sup>[[#fn:r673|673]]</sup> ; Vihtakari et al., 2018 <sup>[[#fn:r674|674]]</sup> ), reproductive success and body condition (Gaston et al., 2012 <sup>[[#fn:r675|675]]</sup> ; Provencher et al., 2012 <sup>[[#fn:r676|676]]</sup> ; Gaston and Elliott, 2014 <sup>[[#fn:r677|677]]</sup> ) ( ''high confidence'' ). Recent studies also show that changes in sea surface temperature and sea ice dynamics have impacts on the distribution and abundance of seabird prey with cascading impacts on seabird community composition (Gall et al., 2017 <sup>[[#fn:r678|678]]</sup> ), nutritional stress and decreased reproductive output (Dorresteijn et al., 2012 <sup>[[#fn:r679|679]]</sup> ; Divoky et al.; Kokubun et al., 2018 <sup>[[#fn:r680|680]]</sup> ) and survival (Renner et al., 2016 <sup>[[#fn:r681|681]]</sup> ; Hunt et al., 2018 <sup>[[#fn:r682|682]]</sup> ).

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