Good scientists fully understand that complex
issues with high uncertainties require two or more working hypotheses. NOAA
failed to communicate the great uncertainties and alternatives. Instead NOAA’s
report card made claims that hinge on the
unproven hypothesis that a reduction in sea ice is detrimental by denying
walruses access to foraging habitat. In the Pacific the number of calves per
cow increased as has calf survival, both indicators of a growing population,
contradicting NOAA’s claim,. As detailed in Hijacking
Successful Walrus Conservation, historical records for the
Pacific walrus (Fay 1982, 1989) observed
an overall increase in the use of land haulouts coinciding with increasing
populations of recovering walrus. In the Barents Sea’s Svalbard archipelago,
despite the greatest decline of sea ice, recent research has also observed an increased
use of land haulouts coinciding with an exponential population growth, a 48%
increase in abundance between 2006 and 20012 (Kovacs 2014). Yet
despite all the positive indicators, NOAA downplays growing populations and
makes the empty assertion, “the overall carrying capacity of the region for
walruses is almost certainly declining because of sea ice declines.”
The full weight of evidence suggests an
alternative hypothesis is more likely. Less
sea ice allows more access to larger areas of bountiful foraging habitat
that had been previously covered by heavy ice. The carrying capacity of walrus
habitat - its ability to nourish and sustain a population - will only decline
if the following are true but perusal of the evidence suggests the carrying
capacity has increased.
1) Carrying capacity will decline if the
population becomes so abundant it reduces the prey base and
competition for dwindling food
creates nutritional stress
2) Carrying capacity will decline if there is a
general decline in marine productivity
3) Carrying capacity will decline if the areal
extent of potential foraging habitat is reduced, and/or
4) Carrying capacity will decline if access to
foraging habitat is reduced.
1. Food
Competition, Density-dependent Regulation, and Healthy Vital Rates
Populations are naturally regulated by
“density-dependent” factors. As a growing population adds more individuals to a
given area, the density increases. As the density approaches the carrying
capacity of that habitat, competition for a limited food supply increases
nutritional stress. Marine mammals such as polar bears, ringed seals and
walruses respond to nutritional stress by reducing their reproductive output,
which ultimately reduces population growth. The ratio of calves to cows
decreases because pregnancy rates decline, young cows defer their first year of
pregnancy to an older age, and calf survival rates decrease. Conversely when
the food supply is abundant, walruses’ pregnancy rates increase, cows give
birth at an earlier age, and calf survival rates increase. When those critical
factors raise the ratio of calves to cows the population increases.
Based on 20th century surveys,
researchers believed the Pacific walrus had rebounded from an overhunted
population reduced to ~ 50,000 in the 1950s which then grew to ~250,000 to
300,000 walrus by 1980 (Fay 1989).
Consistent with density-dependent theory, when the population was below the
carrying capacity in the 1950s and 60s, researchers observed the highest ratios
of calves per cows. As the population grew subsistence hunters reported
increasing numbers of leaner individuals and a steady decline in the ratio of
calves to females suggesting walruses were reaching or exceeding the region’s
carrying capacity. The resulting decline in reproductive output caused the
population growth rate to stop and the population peaked around 1980.
Researchers then calculated a brief population decline during 1980s exacerbated
by an uptick in Russian walrus harvests (Fay 1997). But the
calves:cows ratio then began to increase throughout the 1990s and some
researchers believed population growth had resumed. The calves:cows ratio is
now as high as it was in the 1960s when the recovering population was rapidly
growing (McCracken
2014). Presently calf survival rates have nearly
doubled (Taylor 2015) and cow’s
age of first pregnancy has been increasingly younger (Garlich-Miller
2006). All those vital signs usually suggest a well
fed, growing population, supporting early research but contradicting NOAA’s
current argument that the carrying capacity is “certainly declining”.
2.
Marine Productivity is Improving
The shallow shelves of the Bering and Chukchi
seas prevent nutrients from sinking to a dark abyss far from the reach of
photosynthesizing plankton. Shallow seas more readily upwell nutrients enabling
high rates of productivity. Furthermore ocean currents bathe large sections of
those shallow shelves with nutrient rich subtropical waters further enhancing
productivity. And because surface productivity more rapidly reaches the floor
of those shallow shelves, bottom dwelling organisms collectively called the
“benthos,” receive over 70% of the energy sequestered at the surface. As a
result the Bering and Chukchi seas sustain some of the earth’s richest bounty
of bottom dwelling prey sought by walrus, gray whales and bearded seals (Sirenko
2007). Contrary to earlier suggestions that global
warming may possibly decrease
productivity (Grebmeier
2006), satellite observations have determined marine
productivity has increased by 30% since the 1990s (Arrigo 2015). The
reason for this increase is elementary. Less sea ice allows more
photosynthesis. Grebmeier
2015 has now reported that the Bering and Chukchi
Sea “hotspots” she has studied have sustained high levels of biomass over the
past 4 decades.
From a marine productivity perspective, the
evidence does not support NOAA’s claim of a declining carrying capacity; just
the opposite. Increased productivity has increased the carrying capacity.
3.
Areal Extent of Foraging Habitat Has Increased
 |
| Depth Ppofiles of Bering and Chukchi Seas. Walrus prefer depths less than 60 meters |
The key
variable that determines walrus foraging habitat is depth. Telemetry
studies found walrus spent nearly 98% of their time foraging in shallow water
no deeper than 60 meters (Jay 2005) and other
observations suggest foraging at depths deeper than 80 meters is unlikely. As
seen in Figure 1, much of the Arctic is not suitable for walruses. The darkest
blue regions represent inaccessible regions of great depth. The 3 lightest
shades of blue-gray outline the only
depths with potential walrus foraging habitat.
The white mass in the upper right of Figure 1
represents the summer minimum of the 2007 ice pack. The average historic summer
minimum (the yellow line in Fig.1) indicates large portions of the Chukchi
Sea’s foraging habitat have been covered with summer ice concentrations of 50%
and greater for much of the 20th century. Because walrus avoid ice-covered waters where sea ice
concentration is 80% or greater, any heavy ice concentrations reduce the
areal extent of walrus foraging habitat.
Notice that along the northern coast of Alaska
in the Beaufort Sea, sea ice historically retreated over deep waters every
year. Thus the most recent retreat of sea ice further northward did not impact
the areal extent of foraging habitat in that region. Likewise once the Chukchi
summer sea ice retreated over the deep Arctic Ocean, any additional retreat had
little consequence. In contrast, the initial reduction in summer sea ice over
the western Chukchi Sea opened vast regions of potential foraging habitat.
It is believed that 70 to 80% of the total
Pacific walrus population exploits the western Chukchi habitat especially
during the autumn when reduced sea ice exposes the most habitat. Russian
researchers surveying the western Chukchi in September of 1980, estimated
approximately 150,000 walrus had hauled out in roughly equal numbers on sea ice
and on land. A repeat of that survey in October as freezing conditions
increased, revealed the number of walrus hauled out on ice had been greatly
reduced but walrus on land remained unchanged (Fedoseev
1981). Clearly 75,000 walrus were not forced onto the
Russian coast due to the lack of ice. Although the lack of sea ice in 2007 very
likely increased the numbers of walrus hauling out on land, media hyperbole
that sensationalized terrestrial haulouts are solely due to global warming,
inexcusably ignores all historical observations of natural land haulouts. Based
on observations that roughly 50% of the walruses use land haulouts despite
plentiful potential resting platforms of sea ice, any occupation of land
haulouts serves as an indicator of where walrus accessed Chukchi habitat as sea
ice cover waxed and waned.
In Figure 3 below (from
Garlich-Miller 2011) the numbers locate known land
haulouts. The red arrow I added points to Cape Serdse-Kamen (#50) that has
always been occupied in September and October during past surveys. The numbers
to the west of Cape Serdse-Kamen and to the north around Wrangel Island
represent traditional haulouts that are used only in years of light sea ice but
unoccupied in years of heavy ice (Fay 1984). For example despite the shallow
foraging habitat north of Wrangel Island, walruses were not observed there in
the 1980s (Fedoseev 1981). When sub-freezing winds removed much of the thick
Arctic ice from this region in the 1990s when Arctic Oscillation shifted,
walrus rapidly exploited the region’s resources and over 120,000 walruses
hauled around Wrangel Island. Such observations support the hypothesis that
reduced ice increases available foraging habitat and consequently the western
Arctic’s carrying capacity.
 |
| Location of Known Walrus Land Haulouts. From Garlich-Miller 2010 |
Due to heavy sea ice cover, access to rich
foraging habitat on shallow shelves naturally fluctuates between seasons,
years, decades and millennia. The heavy ice of the last Ice Age must have been
the nadir for walrus populations. Not only was there maximum sea ice coverage,
but also the drop in sea level left the shallow shelves of the Arctic Seas high
and dry. Although this allowed humans to enter North America, it relegated
walrus populations to narrower shelf waters as far south as central California.
Eventually Holocene warmth raised sea level and reduced sea ice allowing walrus
populations to once again flourish in the Arctic. Flexible migratory patterns are
likely an adaptation to the constant changes in sea ice even during the warm
Holocene. Proxy data covering the past 9000 years from Point Barrow revealed
annual sea ice covering the eastern Chukchi Sea varied from only 5.5 to 9
months, and summer sea surface temperatures ranged from 3 to 7.5 °C,
much higher than today (McKay 2008).
Seasonally winter ice forces walrus to abandon
the Chukchi. They re-enter after the warmth of spring reduces sea ice cover.
Whether caused by CO2-driven global warming, observed natural changes in
atmospheric circulation due to the
Arctic Oscillation, or changes in the volume of
intruding waters associated with the Pacific Decadal Oscillation, the extent of
summer sea ice summer has fluctuated greatly over decades as seen in Figure 5
(from Jay 2012.)
 |
| Decadal Changs in Monthly Sea Ice Extent |
4.
Accessing Foraging Habitat
NOAA began their report card by arguing, “Sea ice
deterioration due to global climate change is thought to be the most pervasive
threat to ice-associated marine mammals in the Arctic, including walruses.” But
that threat has yet to be substantiated. The perceived threat to walruses is
solely based on a hypothesis that walruses “require” sea ice as a platform from
which they dive to suction clams, worms, etc. from the ocean floor. Based on
that belief, some researchers argue that declining sea ice denies access to
habitat and forces them to forage closer to their land haulouts. Expanding on
that assumption NOAA argues Arctic’s carrying capacity “must be in decline.”
But several lines of evidence clearly demonstrate
walruses do not “require” sea ice as a resting platform in order to hunt. A resting platform of sea ice is likely an
opportunistic and beneficial convenience - not a requirement. For example
after breeding a large proportion of male walruses abandon the sea ice and
migrate south to dwell in land haul outs in ice free waters along the Russian
and Alaskan coast (represented by red dots in Figure 3). From those traditional
land haulouts they embark on foraging trips that last for 4 to 10 days and
range as much as 130 kilometers away (Jay 2005). In addition
satellite radiotelemetry determined walruses throughout the Bering and Chukchi
spend over 80% of their time swimming, and the amount of time in the water was
the same whether walrus used sea ice or land for a resting platform. Swimming
at a relaxed speed of 10 km/hour, a walrus easily range over 200 km while
foraging along the way (Jay 2010, Udevitz 2009).
Some researchers suggest that the lack of
resting platforms of sea-ice will restrict walrus to hunting only along the
coast and hypothesizing they will more quickly deplete more limited accessible
resources. However the opposite scenario is more likely. Heavy sea ice
restricts hunting grounds and the most extreme example would occur if heavy ice
remained all summer in the Chukchi forcing herds to remain in the Bering Sea
throughout the year. Certainly the Bering Sea’s prey base would be rapidly
depleted. The migratory behavior of females and their calves into the shallow
waters of the Chukchi each summer is most likely a behavior that evolved to
reduce resource competition and exploit temporary access to rich foraging
habitat. With a greater reduction
of Chukchi summer ice, migrating herds can spread out and reduce localized
foraging pressure.
NOAA
Expert Opinion Claims Pacific Walrus have declined by 50%. Seriously?
Finally NOAA’s report card suggested that
“expert opinion” calculated a 50% decline in Pacific Walrus populations between
1980 and 2000. The experts did agree the population had decreased during the
early 1980s due to density-dependent effects when population abundance
increased and exceeded the region’s carrying capacity. But the expert consensus
ended there. Fay 1986 suggested after a relatively brief decline in the 80s,
population growth subsequently resumed. A growing population would be in
agreement with recent observations of increased marine productivity, greater
access to habitat due to decreased heavy ice, higher calves:cows ratios and
higher survival rates.
Estimating
walrus abundance is extremely difficult and all experts agree that abundance estimates have extremely wide
error bars and are totally unreliable. Russian and American biologists
jointly surveyed walrus populations in the autumn every 5 years between 1975
and 1990, but survey efforts were suspended because experts could not agree on
how to interpret limited data and the tremendous resulting uncertainty (Speckman
2010). The major problem revolves around estimating
how many walrus are in the water and escape detection. Furthermore due walrus
movements, it was impossible to replicate survey transects and constrain error
estimates. A repeated transect just one week later often resulted in observed
numbers differing by 2 or 3 orders of magnitude.
To circumvent survey uncertainties there have been attempts to model
abundance based on observed age structure of the population (Taylor 2015), and
those model results disagree with earlier calculations of a growing population.
They suggested populations continued to decline from 1980 to 2000, but admit their
results after 2003 were equivocal. They also acknowledged that information
provided by age structure data cannot mitigate uncertainties in the population
size, admitting the absolute size of the Pacific walrus population will “continue to be speculative until accurate
empirical estimation of the population size becomes feasible”
Thus experts would likely agree that NOAA’s claim of a 50% reduction
due to “expert opinion” is likewise speculative and rather meaningless. NOAA
failed to express that extreme uncertainty and failed to report the tremendous
wide range in abundance estimates. For example in the most recent survey (Speckman
2010) of wintering walrus in the Bering Sea,
researchers used heat detectors calibrated by high-resolution photographic
evidence to estimate abundance. Unfortunately swimming walruses were
undetectable. For the region surveyed, they estimated 129,000 walrus that would
support a estimated 50% decline. However their 95% confidence ranged from
55,000 to 507,000 walrus. Furthermore due to time and weather constraints, the
survey covered less than 50% of the Bering Sea habitat known to contain walrus.
A complete survey may well have increased the estimate to well over 200,000
individuals. A midrange estimate would be similar to peak estimates of the
1980s, and high-end estimates would support hypotheses of a growing population
in the Pacific; a growth that
parallels observed growth in the Atlantic walrus.
Curiouser and curiouser, NOAA cited McCracken
2014 who used Speckman’s knowingly biased
underestimate of 129,000 to suggest the increasing ratio of calves per cow
supported a declining walrus population.
Biologically such an assertion contradicts density-dependent mechanisms.
Increased reproduction increases a population, unless survival rates
drastically declined, but rates had increased.
 |
| McCracken 2014 Hypothesized Correlation between Calves:Cows ratio and Population Abundance |
McCracken 2014 argued that calves:cows ratios
are inversely correlated with population abundance as illustrated in Figure
4. However that correlation is
partly speculative and unsupported and depends on using Speckman’s unrealistic
estimate of half the population. No one disagrees that overhunting reduced the
population in the 1950s so that more food became available for the survivors
stimulating walruses to increase reproductive output as evidenced by high
calves:cows ratios; a high ratio that approached the theoretical maximum.
Density increased as walruses recovered from overhunting (and increasing sea
ice was coincidentally recovering from its minimal in the late 1930s) so that
the carrying capacity declined and walrus responded with declining calves:cows
ratios that bottomed out in the 1980s. But the consensus on any population
trends stops in the 1980s.
McCracken 2014 acknowledged that the validity of
their inverse correlation is totally dependent upon the assumption that 300,000
walrus was the maximum population that could be sustained by the region.
However they did not explore the possibility that the carrying capacity could
possibly increase due to less sea ice and higher marine productivity. So they
assumed that any observations of higher calves:cows ratios that would normally
indicate a growing population, were only possible if the population had
declined by such an extent that more food again became available.
The only dynamic that could have possibly offset
increased ocean productivity and cause a population decline in an era of
regulated hunting, and conservation efforts that are now protecting haulouts,
was a strictly hypothetical dynamic that less sea ice prevents access to
foraging habitat and was reducing the Arctic’s carrying capacity. But all
reported evidence discussed above contradicts that hypothesis and McCracken’s
suggestion the population had declined by 50% is untenable.
NOAAs claim that the “carrying capacity is almost certainly declining because
of sea ice declines” is advocated by USGS and US Fish and Wildlife researchers
who believe that CO2 warming and declining sea ice must be bad. That belief is
advocated in the opening paragraphs of nearly every publication. Wedded to that
belief their interpretations ignore robust evidence suggesting less has been
beneficial. So one must wonder how politicized those agencies have become and
if political pressure has biased their publications. Researchers in those
agencies likewise ignored
their own observations that it was cycles of thick springtime ice in the Beaufort Sea
that caused declines in ringed seals and polar bear body condition. Instead
without evidence, they only advocated that reduced summer ice, consistent with
CO2 warming, has negatively impacted polar bear populations and walrus Such
unsupported biased interpretations are most likely the result of the
politicization of science, and I fear this decade will be viewed as the darkest
days of environmental science.
