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147
CHAPTER 12
The Northeastern Pacic White Shark
Shared Offshore Foraging Area (SOFA)
A First Examination and Description from Ship
Observations and Remote Sensing
Michael L. Domeier*
Marine Conservation Science Institute
Nicole Nasby-Lucas
Marine Conservation Science Institute
Daniel M. Palacios
University of Hawaii at Manoa and National Oceanic and Atmospheric Administration/
National Marine Fisheries Service/Southwest Fisheries Science Center
ABSTRACT
Previous studies have shown that adult White Sharks (Carcharodon carcharias) migrate from
aggregation sites near the coast to pelagic habitats situated between North America and Hawaii.
Studies using satellite-linked radio transmitting (SLRT) tags have allowed for a better spatial
description of this region while also delineating sex-specic offshore-habitat partitioning. Although
females roam widely in the pelagic habitat, males occupy a more dened region called the Shared
Offshore Foraging Area (SOFA). Here we report the rst direct observations of the SOFA, made
from a ship in June 2009, and compare these observations with oceanographic remote sensing data
to characterize the SOFA habitat. White sharks tagged with SLRT tags provided real-time tracking
positions to guide the research vessel toward offshore regions used by White Sharks. The timing of
the expedition coincided with a seasonal contraction of the SOFA. Ship observations in the region
where the sharks were detected revealed an absence of epipelagic sh and small cetaceans, but
Sperm Whales (Physeter macrocephalus) and three species of spawning squid (Architeuthis and
two species of Ommastrephid squids) were present. Oceanographic remote sensing data showed
the region to be an epipelagic cold spot, broadly characterized by downwelling conditions, reduced
* Corresponding author (ml.domeier@gmail.com).
148 GLOBAL PERSPECTIVES ON THE BIOLOGY AND LIFE HISTORY OF THE WHITE SHARK
horizontal motions or other dynamical processes, no major temperature fronts, and very low phy-
toplankton biomass. However, the presence of apex predators like White Sharks, Sperm Whales,
and squid suggests that the SOFA ecosystem supports a considerable mesopelagic biomass. Oceanic
hot spots are currently described primarily by epipelagic and surface observations; this study dem-
onstrates the need to incorporate mesopelagic observations into the characterization of hot and
coldspots.
INTRODUCTION
Pop-up satellite archival transmitting and satellite-linked radio transmitting (SLRT) tags have
revealed that adult White Sharks (Carcharodon carcharias) of the northeastern Pacic occupy an
entirely pelagic habitat for at least 3 months and as much as 15 months of the year (Boustany etal.,
2002; Weng etal., 2007; Domeier and Nasby-Lucas, 2008, 2011; Nasby-Lucas etal., 2009; Jorgensen
etal., 2010; Chapter 11, this book), raising many questions regarding the ecosystem that sustains them
during this time. Individual White Sharks from both central California and Guadalupe Island, Mexico,
migrate to the Shared Offshore Foraging Area (SOFA) centered between the Hawaiian Islands and Baja
California (Boustany etal., 2002; Weng etal., 2007; Domeier and Nasby-Lucas, 2008; Nasby-Lucas
etal., 2009; Jorgensen etal., 2010; Chapter 11, this book). Although the use of SLRT tags allowed for
the SOFA to be better dened spatially (Chapter 11, this book), our understanding of the ecosystem and
environmental characteristics of this seemingly vast open-ocean habitat is in its infancy.
The factors that motivate White Sharks to make these round-trip offshore migrations are
unknown, but hypotheses that propose foraging and/or mating have been suggested. The length of
time the sharks spend in the pelagic realm, coupled with very active vertical diving behavior (Nasby-
Lucas etal., 2009), suggests that the area is used for foraging (Domeier and Nasby-Lucas, 2008).
Alternatively, Jorgensen etal. (2010) proposed that the timing of the arrival of young-of-the-year
White Sharks into coastal nursery areas, together with the presumed length of gestation (Francis,
1996; Mollet etal., 2000), suggests that the SOFA may function primarily as a mating area. However,
evidence presented in this book demonstrated that males and females are spatially segregated while
offshore, with the SOFA being primarily occupied by males (Chapter 11, this book). This apparent
sexual segregation makes the offshore mating hypothesis unlikely (Chapter16, this book).
Whether or not mating is occurring offshore, it is accepted that the sharks must forage dur-
ing their prolonged pelagic residence (Domeier and Nasby-Lucas, 2008; Jorgensen etal., 2010). It
is not known what prey species form the diet of White Sharks in the SOFA, but archival tag data
from both Guadalupe Island and central California sharks show that White Sharks regularly dive
to great depths while in the SOFA, recording mean maximum daily swimming depths of 400–
500 m (Nasby-Lucas etal., 2009; Jorgensen etal., 2010). Furthermore, White Sharks in the SOFA
exhibit diel diving behavior, suggesting that these sharks may be exploiting the deep scattering layer
(Nasby-Lucas etal., 2009). Given the remote location, White Sharks have never been observed feed-
ing while in the SOFA.
The prolonged residence of adult White Sharks in the SOFA leads us to question whether the
SOFA may be an oceanic hot spot; hot spots are dened as regions of energetic and dynamic ocean-
ographic processes induced by winds, fronts, current instabilities, mesoscale eddies, or complex
topography that lead to enhanced biological productivity. Hot spots can have high sheries yields
and are known regions of apex predator aggregation (Palacios etal., 2006). Direct and indirect
measurements of the physical and biological parameters that persist in the SOFA are necessary to
properly describe the ecosystem. Biological productivity in the pelagic realm can be both tempo-
rally and spatially variable. Therefore, a detailed study of White Shark habitat in the offshore region
requires more precision with respect to the time and location that the sharks occupy while in this
region, precision that is afforded by the use of SLRT-tagged White Sharks.
149THE NORTHEASTERN PACIFIC WHITE SHARK SHARED OFFSHORE FORAGING AREA
The primary objective of this study was to describe the SOFA via remote sensing and direct
observations made from a research vessel. Analyses performed on location data from adult White
Sharks tted with SLRT tags indicated that adult male White Sharks occupy the same offshore region
each year, whereas females were found over a broader and more temporally and spatially unpredict-
able region (Chapter 11, this book). Furthermore, it has been noted that males occupy a signicantly
smaller pelagic space during the months of June and July, resulting in a predictable but temporary
constriction of the SOFA (Chapter 11, this book). The real-time, precise locations of the tagged
adult male White Sharks were used as a reference to guide the research vessel into this constricted
space during the month of June, allowing the rst direct examination of the SOFA environment. For
the purpose of this paper, the core of the SOFA is dened as the 50% density contour identied by
Domeier and Nasby-Lucas (Chapter 11, this book) for the June/July period of spatial constriction.
MATERIALS AND METHODS
Data from of eight SLRT (SPOT5; Wildlife Computers, Redmond, Washington) tagged males
(see Chapter 11, this book for deployment methods) were used as a reference before and after the
research expedition to the SOFA. Six of the eight males were tagged at Guadalupe Island in 2008
and 2009 (sharks 7M, 14M, 19M, 33M, 101M, and 102M)), and two were tagged at the Farallon
Islands in 2009 (sharks FI1M and FI2M). A research cruise was planned in the month of June 2009
to the northwestern region of the SOFA using near real-time position data from the tagged sharks
at the time of the cruise as a guide for the ship’s track. The research vessel departed San Diego on
June 8, 2009 and returned June 25, 2009 (Figure 12.1).
200 0 200 Kilometers
9
13
11
12
10
16
15 19 20 21
22
23
14
17–18
132°
25°
30°
35°
126° 120°
Figure 12.1 The ship’s actual track for the SOFA cruise in June 2009. Each number indicates the posi-
tion along the track of midday for the specied date in June 2009 and corresponds to marine
mammal observations along the ship’s tracks by date in Table 12.2. The gray contours rep-
resent the core utilization areas for sexually mature male White Sharks, with the smaller oval
being the 50% density contour for the months of June and July (Chapter 11, this book).
150 GLOBAL PERSPECTIVES ON THE BIOLOGY AND LIFE HISTORY OF THE WHITE SHARK
Visual Strip Transects of Biological Diversity within the SOFA
Strip transects were conducted, following the methods described by Olson et al. (2001).
Observations were made from the ying bridge, with eye level at 7 m above the waterline. In sum-
mary, all organisms that could be observed and counted, at or above the surface out to 300 m from
the vessel, were recorded and identied to species if possible. Floating marine debris were also
identied and quantied. Distance to the observed animal or object was estimated using a xed-
interval range nder (Heinemann, 1981), and binoculars were used to assist in species identication.
Counts took place on only one side of the ship (whichever side had better visibility), from the bow
through a 90° arc that ended perpendicular to the vessel at observer’s position on the ying bridge
for 1 h. The exact position, bearing, and speed of the ship were recorded at the beginning and end
of each transect so that the total area of the surveyed strip could be calculated. If the bearing of the
ship was altered during a transect, that particular transect was discontinued. There were not enough
qualied personnel on the vessel to maintain continuous surveys; instead, such surveys were con-
ducted daily when time and weather permitted. All of the transects were conducted by the same
person (M. L. D.).
The counts of organisms and debris were converted to density (#/km2) by dividing by the area
covered during the 1-h transect. On a few occasions, a specic organism was encountered in such
large numbers that it was impossible to count; in these instances an entry saying “too many to be
counted” was entered to document the event.
Marine Mammal Surveys
Similar surveys were conducted for marine mammals, but in this case the surveys were con-
ducted to the horizon on both sides of the vessel. Whenever a marine mammal was sighted, the
course of the vessel was changed to approach, count, and identify the species. Marine mammals
were spotted both via active searching with gyro-stabilized binoculars and with the naked eye.
Searching occurred during all daylight hours by the ship’s crew on watch, and they alerted the
expedition leader (M. L. D.) of any sightings so that he could attempt to count and identify the
species. The methods were not rigorous enough to calculate densities. For example, larger ceta-
ceans could be spotted from a greater distance than small cetaceans so a precise search radius
could not be calculated. Thus, raw marine mammal counts provided a rough index of relative
abundance.
Environmental Characterization
The research vessel was not tted with oceanographic sampling gear, and therefore in situ envi-
ronmental data were not collected from the ship. Instead, we relied on remote sensing data to provide
a general description of the survey region, with the important caveat that satellites only measure the
near-surface properties of the ocean, and consequently, potentially important subsurface features
are not detected. We obtained monthly composites for June 2009 for various remote sensing prod-
ucts available through the Environmental Research Division’s Data Access Program (ERDDAP), a
data pass-through service hosted by the CoastWatch West Coast Node of the National Oceanic and
Atmospheric Administration (NOAA) (http://coastwatch.pfeg.noaa.gov/erddap/index.html).
The primary products obtained from ERDDAP were sea surface temperature (SST), phyto-
plankton chlorophyll-a concentration (CHL), and sea surface height deviation (SSH). SST is a 0.1°
(~11km) spatial-resolution product blending observations from several satellite platforms for optimal
coverage Moderate Resolution Imaging Spectroradiometer (MODIS), on the National Aeronautics
and Space Administration (NASA) Aqua satellite; Advanced Very High Resolution Radiometer on
151THE NORTHEASTERN PACIFIC WHITE SHARK SHARED OFFSHORE FORAGING AREA
NOAA’s Polar Operational Environmental Satellites; Imager on NOAA’s Geostationary Operational
Environmental Satellites; and Advanced Microwave Scanning Radiometer on Aqua. CHL is a 0.05°
(~5.5 km) spatial resolution product from MODIS/Aqua. Finally, SSH is a 0.25° (~25km) spatial
resolution product that merges observations from multiple satellite altimeters and that is provided by
the Archiving, Validation and Interpretation of Satellite Oceanographic data program and Collect
Localisation Satellites (CLS) in France.
SSH measures the ocean’s surface topography, from which geostrophic current vectors (u and
v for the zonal and meridional components, respectively) can be derived. A related product, geo-
strophic current anomaly (u′ and v′, respectively), which measures current deviations caused by
mesoscale processes like eddies, was also obtained in order to compute eddy kinetic energy [EKE;
where EKE = 0.5 * (u′2 + v′2)], a more direct description of mesoscale motions.
RESULTS
Strip Transect Results
Strip transects began on June 9, 2009, after the ship’s track had moved west of the continental
shelf. Twenty-two 1-h strip transects were performed along the ship’s track between June 9 and 22,
2009 (Figure 12.1). On June 17, high sea-state conditions caused the cessation of all research activi-
ties, preventing all but one transect from being sampled on the return voyage (June 22).
Seabirds encountered during strip surveys included Leach’s Storm Petrel (Oceanodroma
leucorhoa; n = 60), Laysan Albatross (Phoebastria immutabilis; n = 1), Black-Footed Albatross
(Phoebastria nigripes; n = 2), Red-Tailed Tropicbird (Phaethon rubricauda; n = 3), unidentied
petrel (Ptetodroma sp.; n = 1), and an unidentied shearwater (Pufnus sp.; n = 1). Combined
seabird densities ranged from 0 to 8.4/km2 and were highest near the continental shelf. Eleven
of the twenty-two strip transects encountered no seabirds of any kind. Leach’s Storm Petrel was
the most abundant species observed, but only one individual was seen west of 127.3°W longitude.
Seabirds were very sparse in the core of the SOFA, with only two Red-Tailed Tropicbirds and one
unidentied petrel counted during strip transects. However, several Black-Footed Albatross (n = 8)
were seen within the SOFA during times when strip transects were not underway (Table 12.1 and
Figure12.2).
Flying Fish densities were rarely above 0.0, but small peaks were found at 120°, 127°, and
132°W longitude. Between 122.7° and 123.3°W longitude, Velella velella (By-The-Wind-Sailor)
were encountered in such high numbers that they were impossible to count. A small debris eld
(debris density = 0.5/km2) was observed at approximately 123°W longitude, and a much larger
debris eld (peak density = 3.63/km2) was encountered between 131° and 135°W longitude (Table
12.1 and Figure 12.2). The most abundant identiable objects in these elds were plastic shing
oats, but bits of rope, wood, and other plastics were also observed.
Marine Mammal Surveys
Short-Beaked Common Dolphin (Delphinus delphis), Striped Dolphin (Stenella coeruleoalba),
Pantropical Spotted Dolphin (Stenella attenuata), unidentied beaked whales (family Ziphiidae),
unidentied large rorqual (Balaenoptera sp.), Risso’s Dolphin (Grampus griseus), and Sperm
Whales (Physeter macrocephalus) were observed (Table 12.2 and Figure 12.3). With the excep-
tion of Risso’s Dolphin (near 130°W), no small cetaceans were found west of about 127°W. The
only cetaceans found in the core SOFA region were Sperm Whales. Note that only animals at the
surface were used to estimate numbers, and no allowance was made for those members of the pod
underwater.
152 GLOBAL PERSPECTIVES ON THE BIOLOGY AND LIFE HISTORY OF THE WHITE SHARK
Table 12.1 Observations of Seabirds, Flying Fish, Hydrozoans, and Floating Debris in Density per Square Kilometer from Visual
Transects
Transect Date Start Time Distance (km) LSP BFA LA SW P TB FF V FD
1 6/9/2009 7:10 14.1 2.12 0 0.24 0 0 0.24 0 0 0
2 6/9/2009 11:46 14.2 8.44 0 0 0 0 0 0.23 0 0.23
3 6/10/2009 7:57 15.2 0.44 0 0 0 0 0 0 TNC 0
4 6/10/2009 8:59 16.3 0 0 0 0 0 0 0 TNC 0
5 6/10/2009 11:30 14.2 0 0 0 0 0 0 0 TNC 0.47
6 6/10/2009 15:15 15.6 0 0 0 0 0 0 0 0 0
7 6/11/2009 8:00 14.5 0.46 0 0 0 0 0 0 0 0
8 6/11/2009 12:45 7.0 2.38 0 0 0.48 0 0 0 0 0
9 6/11/2009 16:34 13.6 1.23 0 0 0 0 0 0.74 0 0
10 6/12/2009 8:15 13.7 0 0.24 0 0 0 0 0 0 0
11 6/12/2009 14:05 14.1 0 0 0 0 0 0 0 0 0
12 6/12/2009 16:00 14.5 0 0 0 0 0 0 0 0 0
13 6/12/2009 19:12 14.6 0 0 0 0 0 0 0 0 0
14 6/13/2009 9:15 15.3 0.22 0 0 0 0 0 0.66 0 0.87
15 6/13/2009 11:00 14.6 0 0.23 0 0 0 0 0.23 0 1.14
16 6/13/2009 14:18 13.7 0 0 0 0 0 0 0.24 0 1.22
17 6/14/2009 12:35 11.9 0 0 0 0 0.28 0 0 0 3.63
18 6/15/2009 9:45 15.9 0 0 0 0 0 0.42 0 0 0
19 6/15/2009 13:28 15.0 0 0 0 0 0 0 0 0 0
20 6/16/2009 8:30 12.3 0 0 0 0 0 0 0 0 0.27
21 6/16/2009 12:17 11.5 0 0 0 0 0 0 0 0 0
22 6/22/2009 13:00 12.4 0 0 0 0 0 0 0 0 0
LSP, Leach’s Storm Petrel; BFA, Black-Footed Albatross; LA, Laysan Albatross; SW, shearwater; P, unidentied petrel; TB, tropicbird; FF, Flying Fish;
V, Velella velella; FD, oating debris; TNC, too numerous to count.
153THE NORTHEASTERN PACIFIC WHITE SHARK SHARED OFFSHORE FORAGING AREA
Anecdotal Observations in the SOFA
On June 14, the dorsal n of a shark was spotted at the surface (26.4°N 134.8°W) in the SOFA
core. A maximum of 10 cm of n broke the surface with a at-calm sea state, as the shark repeat-
edly surfaced and submerged, allowing it to be tracked visually at intervals for 60 min. The tip of
the caudal n was never visible, and the body of the shark was not seen well enough to estimate its
length. The shape and color of the dorsal n were consistent with that of a White Shark, but without
more visual evidence, it was impossible to assign any species-level identication to this sighting.
Attempts to attract and catch the shark using bait failed.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
2021
22
200 0 200 Kilometers
132°
25°
30°
35°
126° 120°
Figure 12.2 The ship’s actual track for the SOFA cruise in June 2009. The thick blue segments indicate 1-h
strip transects and are labeled by transect number. The gray contours represent the core utiliza-
tion area for sexually mature males, with the smaller oval being the 50% density contour for adult
male White Sharks for the months of June and July (Chapter 11, this book).
Table 12.2 Marine Mammal Sightings
DateaSpecies Number Latitude
(°N) Longitude
(°W)
6/9/2009 Delphinus delphis 29 30.9 119.9
6/10/2009 Stenella attenuata 15 30.3 123.4
6/10/2009 Balaenoptera sp. 3 30.2 124.3
6/11/2009 Delphinus delphis 100 29.5 127.5
6/11/2009 Unidentied beaked whale 4 28.4 129.8
6/11/2009 Stenella delphis 100 28.3 129.8
6/11/2009 Delphinus delphis 40 28.3 129.9
6/12/2009 Grampus griseus 50 28.1 130.4
6/14/2009 Physeter macrocephalus 35 26.0 135.5
6/15/2009 Physeter macrocephalus 20 25.2 136.4
6/15/2009 Physeter macrocephalus 20 25.1 136.5
a Dates correspond to midday locations from Figure 12.2.
154 GLOBAL PERSPECTIVES ON THE BIOLOGY AND LIFE HISTORY OF THE WHITE SHARK
The ship was in the June/July core region of the SOFA (Chapter 11, this book) from June 14 to
17. Although the ship was underway almost continuously, a sea anchor was deployed in the vicinity
of the rst encountered pod of Sperm Whales (June 14), and the ship was allowed to drift overnight.
Lights were deployed during the nighttime drifts, which attracted two species of Ommastrephid
squid (Red Squid [Ommastrephes bartramii] and Purpleback Flying Squid [Sthenoteuthis oualani-
ensis]) (Figure 12.4); for both species, males were running ripe, and females were gravid. On the
48.4
3.5
3
2.5
2
1.5
# per km2
1
0.5
0
Seabirds Debris Flying fish
119.2
119.9
122.7
Common Dolphin
Large Baleen Whale
Striped/Common Dolphin
Beaked whales
Sperm Whales
and squid
Risso’s Dolphin
Unid. shark
Velella velella
122.9
123.3
124.2
125.2
126.3
127.2
127.3
129.4
129.8
130.4
131.0
132.2
132.5
132.8
134.8
135.1
135.6
135.7
SOFA core
Figure 12.3 Sightings and concentrations of seabirds, Flying Fish, and debris along this ship’s track (longitude).
Positions of marine mammal sightings and anecdotal observations are also indicated. Blue shad-
ing indicates the region where Velella velella was sighted, and the red shading indicates the 50%
density contour for adult male White Sharks for the months of June and July (Chapter 11, this book).
14M
33M
7M
Flying Squid
Giant Squid
Sperm Whales
Shark fin
Ship’s track
50 0 50 Kilometers
136°
25°
27°
134° 132°
Figure 12.4 Sperm Whale, Flying Squid, Giant Squid, unidentied shark n, and SLRT-tagged sharks detected
between June 14 and 19, 2009. The upper gray contour is the xed-kernel 50% density contour
indicating the major focal area of sexually mature male White Sharks during the months of June
and July, and the lower graycontour is the xed-kernel 50% density contour for all offshore loca-
tion data from SLRT-tagged sexually mature males (Chapter 11, this book).
155THE NORTHEASTERN PACIFIC WHITE SHARK SHARED OFFSHORE FORAGING AREA
morning of June 14, a freshly dead Giant Squid (Architeuthis dux) was found oating at the surface
near the rst Sperm Whale pod sighting. The Giant Squid was missing all but the bases of its arms
and tentacles, as well as its eyes. Dissection revealed it to be a running-ripe male. Sperm Whales
were again sighted on June 15 (Figure 12.4). From June 17 to 18, the ship returned to the region
where the shark n was originally sighted, making more observations while drifting for 24 h. SLRT
tags on sharks 7M, 14M, and 33M all reported positions, between June 14 and 19, 2009, in close
proximity to the ship’s track while in the SOFA core, also placing the White Sharks in close spatial
and temporal proximity to both Sperm Whales, squid, and the unidentied shark (Figure 12.4).
Environmental Description
Based on the satellite remote sensing observations for June 2009, oceanographic conditions at
the SOFA were characterized by SSTs that were intermediate between the cold, upwelled waters
typical off the North American coast and the warm waters around Hawaii and to the south (Figure
12.5a), but no major temperature gradient or front occurred within this region. In contrast to the
very high CHL concentrations typical of the coastal upwelling ecosystem off the North American
coast, the SOFA occurred in an area with very low phytoplankton abundance, characteristic of the
oligotrophic North Pacic Gyre (Figure 12.5b). SSH throughout much of this region was generally
below the mean sea level in June 2009, and at the SOFA it was punctuated by a few cyclonic (i.e.,
downwelling) mesoscale eddies (Figure 12.6a). In contrast to the high EKE values off the North
30°N
25°N
20°N
15°N
25°N
30°N
20°N
15°N
160°W 150°W 140°W 130°W
SST (°C) – June 2009
CHL (mg m–1) – June 2009
120°W
160°W 150°W 140°W 130°W 120°W
28
26
24
22
20
18
16
3
(a)
(b)
1
0.5
0.1
0.05
Figure 12.5 Monthly satellite composites of SST (a) and CHL (b) for the month of June 2009 in the region of
the SOFA. The upper gray contour is the xed-kernel 50% density contour indicating the major
focal area of sexually mature male White Sharks during the months of June and July, and the
lower gray contour is the xed-kernel 50% density contour for all offshore location data from
SLRT-tagged sexually mature males (Chapter 11, this book). The ship’s track is indicated as a
black line. Red circles represent Sperm Whale sightings, and the white circle with black edge is
the location where the dead Giant Squid was found.
156 GLOBAL PERSPECTIVES ON THE BIOLOGY AND LIFE HISTORY OF THE WHITE SHARK
American coast, near the Hawaiian islands, and along a latitudinal band centered at about 17°N,
EKE at the SOFA was very low (Figure 12.6b).
DISCUSSION
Contrary to our expectation that the SOFA may occur within an oceanographic hot spot, the
region was broadly characterized by downwelling conditions, reduced horizontal motions, no major
temperature fronts, and very low phytoplankton biomass. Very stable water columns, a strong ther-
mocline, and depauperate conditions at the surface are typical of these regions because they have
a tightly coupled production cycle from primary to tertiary producers, resulting in negligible accu-
mulation of surplus biomass (Longhurst, 2007). However, the remote sensing data used in this
characterization cannot detect potentially important subsurface features or dynamic processes in
these regions. Therefore, although the SOFA may appear as a “cold spot,” relatively devoid of epi-
pelagic life, the presence of apex predators like White Sharks, Sperm Whales, and squid indicates
that the SOFA ecosystem supports considerable mesopelagic biomass. This suggests that in oligo-
trophic regions where there is a strong coupling between production and consumption, in situ and
water column observations may be necessary in addition to remotely sensed measurements to more
completely describe these ecosystems. Certainly more measurements of the mesopelagic faunal
composition and habitat characteristics within the SOFA are needed.
30°N
25°N
20°N
15°N
25°N
30°N
20°N
15°N
160°W 150°W 140°W 130°W
SST (cm) – June 2009
EKE (cm2/s2) – June 2009
120°W
160°W 150°W 140°W 130°W 120°W
0.15
0.1
0.05
–0.05
–0.1
–0.15
0
>500
500
300
200
75
<50
(a)
(b)
Figure 12.6 Monthly satellite composites of SSH (a) and EKE (b) for the month of June 2009 in the region of
the SOFA. In both images the geostrophic current anomalies are shown as black vectors. The
upper gray contour is the xed-kernel 50% density contour indicating the major focal area of sex-
ually mature male White Sharks during the months of June and July, and the lower gray contour
is the xed-kernel 50% density contour for all offshore location data from SLRT-tagged sexually
mature males (Chapter 11, this book). The ship’s track is indicated as a black line. Red circles
represent Sperm Whale sightings, and the white circle with black edge is the location where the
dead Giant Squid was found.
157THE NORTHEASTERN PACIFIC WHITE SHARK SHARED OFFSHORE FORAGING AREA
Sperm Whales and three species of spawning squid were found within the core of the SOFA.
Red Squid in the North Pacic are known to undertake extensive migrations from subarctic to
subtropical waters to spawn in winter and summer (Bower and Ichii, 2005), whereas Purpleback
Flying Squid are believed to continuously reside and spawn in subtropical waters (Nesis, 1993). It is
possible that a spawning aggregation of squid, predictable in time and space, is driving the seasonal
constriction of the SOFA and subsequent concentration of White Sharks. It is unclear why such
an event would attract only male White Sharks, although sexual segregation in sharks is common
(Sims, 2005; Wearmouth and Sims, 2008).
It was previously thought that adult White Sharks feed largely on marine mammals (Tricas
and McCosker, 1984; Casey and Pratt, 1985; Klimley, 1985), whereas juveniles feed primarily
on invertebrates, demersal teleosts, and elasmobranchs. The absence of small cetaceans and pin-
nipeds observations during our SOFA expedition, coupled with the fact that White Sharks remain
in the SOFA for extended periods, suggests that White Sharks may rely upon nonmammal prey
during this portion of their annual life cycle. White sharks may be directly preying upon squid
while in the SOFA or preying upon other species that feed on squid. In previous studies, pelagic
cephalopod species have been shown to be an important part of the diet for other shark species
(Smale and Cliff, 1998; Chapter 4, this book), although the stable isotope signature has been found
to drop off for large White Sharks (Chapter 3, this book). Even though no small cetaceans were
observed in the SOFA, it remains possible that species such as Pygmy Sperm Whales (family
Kogiidae) and Risso’s Dolphin occur in low abundance but provide some predation opportunities
for White Sharks.
ACKNOWLEDGMENTS
We gratefully acknowledge the nancial support and eldwork of Chris Fischer, the Guy
Harvey Ocean Foundation, and the Ofeld Family Foundation. We also thank B. McBride and the
crew of M/V Ocean for their assistance in this project. We thank O. Sosa-Nishizaki, F. Galván-
Magaña, and M. Hoyos-Padilla for assistance in obtaining Mexican permits. Research was con-
ducted in accordance with permits through Secretaría de Medio Ambiente y Recursos Naturales,
Comisión Nacional de Áreas Naturales Protegidas, California Department of Fish and Game,
and NOAA Ofce of National Marine Sanctuaries Program. D. M. P. was supported by funding
from the Gordon and Betty Moore Foundation and from the NASA Applied Sciences Program,
Earth Science Division, through a grant provided by Research Announcement NNH07ZDA001N,
Research Opportunities in Space and Earth Sciences (2007), Program Element A.20: Decision
Support through Earth Science Research Results. Environmental satellite data were provided cour-
tesy of NOAA, CoastWatch, NASA, andCLS.
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