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El
Nino, Krill, and Endangered Whales in the
Sanctuary
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There
is widespread agreement among scientists that
marine ecosystems are profoundly affected by global
climatic events. In the Pacific Ocean, climatic
events are natural phenomena, and they are known to
cause changes in both the short-term (5-7 year El
Niño events) and long-term (50-60 year
cold-to-warm water regime shifts). For example, the
1982-83 El Niño event caused declines in
nutrient upwelling, phytoplankton growth,
zooplankton, and larval fish productivity;
decreases in seabird and marine mammal abundance
and reproduction; and abrupt declines in commercial
fish landings in Monterey Bay. It is important to
point out that these "natural" global climate
events are probably our best opportunity to
understand the impacts of human-caused global
climate change such as global warming on the
Monterey Bay National Marine Sanctuary's marine
ecosystem.
The world's most
productive fisheries and marine mammal foraging
areas are located in coastal upwelling centers, and
are responsible for approximately 95 percent of the
annual global marine productivity. Monterey Bay is
one such center where during the spring in normal
years, northwest winds blow along the coast between
Año Nuevo and Davenport. These winds bring
cold, nutrient-rich water to the surface, which
feeds an explosive growth of phytoplankton,
providing the base of a food chain that ultimately
leads to dependably high concentrations of feeding
blue and humpback whales in the summer.
 For
the past three years we have been studying the
impacts of the 1997-98 El Niño on the links
between coastal upwelling, primary production,
krill production, and the distribution and
abundance of marine mammals and seabirds in the
Sanctuary upwelling system. Our data prior to the
1997-98 El Niño event established that in
normal years krill are the most abundant
phytoplankton grazers in the Monterey Bay upwelling
system. Most marine predators in the Bay (including
humans) are only one or two links in the food chain
away from krill, and krill is the primary prey of
seven of the ten most important commercial fishes
on the Central California coast. Because whales
cannot eat phytoplankton directly, krill form a key
food link for whales. Our research has shown that
over 95 percent of the diet of endangered blue and
fin whales consists of krill.
The recent 1997-98 El
Niño event provided us with the opportunity
to understand how short-term climate change affects
the upwelling ecosystem of the Monterey
Bay.
Preliminary analyses have
shown us:
- The recent El
Niño event led to remarkable declines in
coastal upwelling, phytoplankton growth, and
krill abundance in Monterey Bay. This is
consistent with what has been seen in past El
Niño events.
- Paradoxically, whale
populations in Monterey Bay during the summer of
1998 were the highest we have ever
recorded.
What could account for
this? During "normal" years a large proportion of
the whale population feeds on scattered schools of
krill many miles offshore on the edge of the
California Current. Dr. Francisco Chavez at the
Monterey Bay Aquarium Research Institute has
indicated that during this recent El Niño
event, offshore productivity was very low, and
these offshore krill swarms likely didn't develop.
We believe that the bulk of the whale population
moved into the coastal upwelling zone in search of
what little krill was available - these centers
became the only food source available. An
additional observation supports this hypothesis:
more fin whales were spotted in the Bay in the
summer of 1998 than had ever been seen before.
Normally, fin whales do most of their foraging
offshore. This species, too, likely came in search
of krill.
Our studies of the 1997-98
El Niño event have served to underline the
importance of coastal upwelling centers such as
Monterey Bay to marine productivity. Hopefully in
the not too distant future we can use our studies
to help predict the effects of global warming on
productivity in the Monterey Bay.
Donald A. Croll1, Baldo
Marinovic1, Scott Benson2
1University of California Santa Cruz
2Moss Landing Marine Laboratories
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Elephant
Seal
Populations
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Piedras
Blancas:
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Year
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Births*
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High
Count**
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1998
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1,650
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5,000
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1997
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1,200
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5,000
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* approximate number of births
** high count occurs during the spring
molt, and consists primarily of juveniles
and adult females (approximate
number)
Unpublished data,
provided by Brian Hatfield,
USGS, Piedras Blancas Field
Station
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Año
Nuevo:
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Year
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Births*
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High
Count**
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1998
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2,797
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4,588
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1997
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2,684
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5,358
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* estimated production (95% of all
females)
** high counts occurred in April of 1998
and February of 1997
Data provided by
Pat Morris and Guy Oliver,
University of California Santa
Cruz
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Pinniped
Research
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The
Sanctuary has one of the most diverse pinniped
communities in the world. Researchers continue to
study their population dynamics, foraging behavior,
and physiology. Most relevant this year is the
response of Sanctuary pinnipeds to the profound El
Niño event that occurred earlier in the
year.
California sea lion,
Zalophus californianus.
California sea lions are the most common pinnipeds
in the Sanctuary, and their numbers continue to
increase. Possibly in response to El Niño,
we observed more sea lions (3,000-8,000) at
Año Nuevo Island than ever before. We also
observed a dramatic increase in the number of pups
born there. Typically, a small number are born
every year (about twelve), but this year there were
at least 160 pups, eighty of which were alive
several weeks after birth.
Northern sea lion,
Eumatopias jubatus.
Año Nuevo Island is the southern limit of
this species' breeding range. The population has
been in decline over most of its range. During July
the National Marine Fisheries Service conducted an
aerial survey of the Island and counted forty-two
adult males, 137 adult females and/or juveniles,
and 186 pups. These data indicate a continuing
decline in pup production of about 6 percent a year
(209 pups in 1997). At least six adult female sea
lions were observed with salmon flashers
(attractants attached to fishing hooks) hanging
from their mouths.
Harbor seal, Phoca
vitulina.
Work by Moss Landing Marine Laboratories (MLML)
researchers on the foraging behavior and population
dynamics indicates that the local population is
healthy and growing steadily, with a large increase
in the number of seals and pups using Elkhorn
Slough. Seals from throughout the Sanctuary appear
to forage offshore at the edges of the Monterey
canyon breaks, and have an extremely diverse diet,
consisting mainly of non-commercial prey species.
Investigators from UCSC, the Monterey Bay Aquarium
Research Institute, and MLML, using acoustic
tracking, underwater video, and molecular DNA
techniques, have demonstrated behavioral and
acoustic differences between seals in Monterey and
Elkhorn Slough, and have also revealed that animals
move between these areas. Research has revealed
that although young pups can dive at birth they are
not physiologically mature until at least one year
of age. This past year many of the pups born were
underweight and still had their neonatal pelage,
which suggests that younger age classes were
negatively impacted by the El Niño event.
Aerial survey and tracking work has indicated that
once weaned, pups are highly mobile and can move
out of the Sanctuary.
 Northern
elephant seal, Mirounga
angustirostris.
UCSC researchers have shown that females forage
across a wide area of the northeastern Pacific,
from Central California to Alaska and west five
degrees across the International Date Line, diving
nearly continuously to mean depths in the range of
400-700 m. Given their deep diving and spatial
distribution, we would expect El Niño events
to have less impact on northern elephant seals than
other more coastal pinnipeds. We tested the
response of elephant seals to the 1998 El
Niño by deploying a combination of
ARGOS-linked satellite tags and time-depth
recorders. During 1998 rates of mass gain were the
lowest ever measured (0.29 ± 0.36 kg/day),
with one female losing mass at a rate of 0.44
kg/day. In both the 1982-83 and 1997-98 El
Niño events, female seals appeared to
compensate for low foraging success by increasing
trip duration. In 1998, females spent more time at
sea, but they went to the same general locations.
However, the diving depths and the patterning of
the dives were different (Figure 1). This
demonstrates the strong effect of the 1998 El
Niño event on the foraging behavior of
elephant seals. We also studied the impact of the
1998 El Niño event on elephant seals during
the breeding season. Births in 1998 (2,893) were
similar to those of other years; however, pup
mortality on the Island was the third highest ever
measured, due to the high storm surf that
accompanied El Niño.
Daniel P. Costa, Dan
Crocker, Pat Morris, Jen Burns, and Burney
LeBoeuf
University of California Santa Cruz
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Gray
Whale Calf
Census Data*
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Year
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Calves
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Est.
% of total
pop.
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1998**
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1,316
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1997
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1,439
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6.5
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1996
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1,141
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5.1
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1995
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601
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2.6
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1994
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1,000
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4.5
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*Preliminary
results; data gathered from shore-based
sighting surveys of northbound migrating
gray whale calves passing Piedras
Blancas.
**Estimate
Please note:
these results are preliminary and still
unpublished; they are not to be cited
without the permission of the
author.
Provided by Wayne
Perryman
Southwest Fisheries Science Center
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