Applying landscape fragmentation analysis to icescape environments: potential impacts for the Pacific walrus (Odobenus rosmarus divergens)

Abstract

Sea-ice cover across the Arctic has declined rapidly over the past several decades owing to amplified climate warming. The Pacific walrus (Odobenus rosmarus divergens) relies on sea-ice floes in the St. Lawrence Island (SLI) and Wainwright regions of the Bering and Chukchi seas surrounding Alaska as a platform for rest, feeding and reproduction. Lower concentrations of thick ice floes are generally associated with earlier seasonal fragmentation and shorter annual persistence of sea-ice cover, potentially affecting the life history of the Pacific walrus. In this study, 24 Landsat satellite images were classified into thick ice, thin ice or open water to assess sea-ice fragmentation over the spring-summer breakup period. Geospatial fragmentation analyses traditionally used in terrestrial landscapes were newly implemented in this study to characterize the icescape environment. Fragmentation of sea ice was assessed based on the Percent of Landscape, Number of Patches, Mean Area, Shape Index, Euclidean Nearest Neighbor and Edge Density. Results show that lower sea-ice concentrations in both the SLI and Wainwright regions were associated with smaller sea-ice floes. In the Bering Sea, lower sea-ice concentrations were also associated with increases in the number of ice floes, floe isolation and edge density. By contrast, lower sea-ice concentrations in the Chukchi Sea were associated with ice floes that were more circular in shape. The continuation of sea-ice decline with shifting icescape characteristics may result in walruses having to swim longer distances in the northern Bering Sea and adapt to use less-preferred, rounder ice floes in the Chukchi Sea.

Archaeological evidence of resource utilisation of walrus, Odobenus rosmarus, over the past two millennia: A systematic review protocol

“…As walruses and ice cover are intrinsically linked, good documentation on the past distribution of this taxon is also vital in order to understand both the response of northern ecosystems to global change (cf. 36 ) and potential temporal changes in the behaviour of walrus vis-a-vis sea ice 35 , 37 , 38 . Further information will help to understand how northern hemisphere (predominantly Arctic and subarctic) ecosystems and human societies have previously varied in response to environmental and cultural pressures.…”

“…Over the Holocene, northern hemisphere habitats have undergone both cooler and warmer periods, particularly affecting regions with seasonal ice cover like Arctic and subarctic environments, potentially influencing walrus populations 75 – 78 . Reductions in sea ice platforms are already forcing walrus populations to haul-out on land, and they are now frequently observed congregating in large groups 38 , 79 . Such sea ice reductions will increasingly require individuals to swim longer distances to visit current feeding sites which is energetically costly and may result in changes to foraging site usage 35 , 38 , 80 , 81 .…”

“…Reductions in sea ice platforms are already forcing walrus populations to haul-out on land, and they are now frequently observed congregating in large groups 38 , 79 . Such sea ice reductions will increasingly require individuals to swim longer distances to visit current feeding sites which is energetically costly and may result in changes to foraging site usage 35 , 38 , 80 , 81 . A good understanding of how walruses have historically responded to environmental change may help to predict how they will respond to the ongoing climatic change of the 21 st century.…”