Polar Bear

Appendix A—Background
Sea ice is rapidly thinning and retreating throughout
the Arctic. Ice conditions that affect polar bear
habitat include: (1) fragmentation of sea ice; (2) a
dramatic increase in the extent of open water areas
seasonally; (3) reduction in the extent and area of
sea ice in all seasons; (4) retraction of sea ice away
from productive continental shelf areas throughout
the polar basin; (5) reduction of the amount of
heavier and more stable multi-year ice; and (6)
declining thickness and quality of shore-fast ice,
if it restricts access to seals. These combined and
interrelated events change the extent and quality
of sea ice during all seasons, but particularly during
the spring-summer period.
Climate change will continue to affect Arctic sea ice
for the foreseeable future. A further review of new
information since 2008 indicates that climate change,
resulting in the loss of sea ice habitat for polar bears
continues to be the primary threat to the species.
Due to the long persistence time of certain greenhouse
gases (GHGs) in the atmosphere, the current
and projected patterns of GHG emissions over the
next few decades and interactions among climate
processes, climate changes over the next 40–50
years are already largely set (IPCC 2007; Overland
and Wang 2007, 2013). Climate change effects on
sea ice and polar bears will continue during this
time and likely further into the future (IPCC 2014;
Atwood et al. 2016a).
The ultimate effect will be that polar bear subpopulations
will decline or continue to decline. With a
diminished sea ice platform, bear distribution and
seasonal onshore abundance will change. Not all
subpopulations will be affected evenly in the level,
rate, and timing of effects (Atwood et al. 2016a).
Below, we discuss the various threats that have
been identified, organized by the ESA listing factors
(section 4(a)(1)) addressed in the Final Rule. In addition
to the factors identified in the listing, additional
threats were investigated during development of
this Plan.
A. The present or threatened destruction,
modification, or curtailment of the species’
habitat or range
A.1. Loss of access to prey
Without sea ice, polar bears lack a platform that
allows access to ice seal prey. Longer melt seasons
and reduced summer ice extent will likely force
bears to increase use of habitats where hunting
success will decrease (Derocher et al. 2004; Stirling
and Parkinson 2006). Highly-selected summer sea
ice habitat by polar bears in the CS subpopulation
has declined by 75% in the past 30 year (Wilson et
al. 2016). Once sea ice concentration drops below
50 percent, polar bears have been documented
to quickly abandon sea ice for land, where access
to their primary prey is almost entirely absent.
Bears may also retreat northward with the more
consolidated pack ice over the polar basin, which
may be less productive foraging habitat. The
northward retreat is most likely related to reduced
hunting success in broken ice with significant open
water and need to reduce energetic costs once
prey availability and food intake drops below some
threshold (Derocher et al. 2004, p. 167; Stirling et
al. 1999, pp. 302–303). A recent study (Ware et al.
in review) found that polar bears are increasingly
found on ice over less productive waters in summer,
with activity levels indicating that they are not
hunting. Similarly, Whiteman et al. (2015) found that
bears summering on sea ice had similar metabolic
rates to those on land, indicative of fasting. During
summer, ice seals typically occur in open water and
therefore are virtually inaccessible to polar bears
(Harwood and Stirling 1992) although bears have
rarely been reported to capture ringed seals in open
water (Furnell and Oolooyuk 1980). Thus, hunting
in ice-free water will not compensate for the loss of
sea ice and the hunting opportunities it affords polar
bears (Stirling and Derocher 1993; Derocher et al.
2004). Additionally, Rode et al. (2010a) demonstrated
that available terrestrial food resources are likely
inadequate to offset the nutritional consequences of
an extended ice-free period.
Reduced duration of sea ice over shallow, productive
waters of the continental shelf is likely to have
significant impacts on the polar bears’ ability
to access prey, and continued declines in sea ice
duration are expected in the future (Durner et al.
2009, Castro de la Guardia et al. 2013, Hamilton et
al. 2014). Polar bears have two options to respond to
these changes, 1) remain on the sea ice as it moves
over less productive waters, or 2) move to land. In
both instances, polar bears are likely to find limited
prey items and employ similar energy saving strategies
(Whiteman et al. 2015). While observations
exist of polar bears eating terrestrial-based foods
(e.g., Rockwell and Gormezano 2009), the general
consensus is that these food items are unlikely to
compensate for lost hunting opportunities while on
the sea ice (Rode et al. 2015b); with rare exceptions
(e.g., Miller et al. 2015, Rogers et al. 2015, Whiteman
et al. 2015). Further, Rode et al. (2010a) demonstrated
that available terrestrial food resources are likely
inadequate to offset the nutritional consequences of
an extended ice-free period.
Reduced access to preferred prey (i.e., ice seals;
Thiemann et al. 2008) is therefore likely to have
demographic effects on polar bears. For example,
in the SB subpopulation, the period when sea ice is
Polar Bear Conservation Management Plan 65