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The Northeastern Pacific White Shark Shared Offshore Foraging Area (SOFA): A First Examination and Description from Ship Observations and Remote Sensing

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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-specific offshore-habitat partitioning. Although females roam widely in the pelagic habitat, males occupy a more defined region called the Shared Offshore Foraging Area (SOFA). Here we report the first 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 fish 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 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 cold spots.
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147
CHAPTER 12
The Northeastern Pacic 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-specic offshore-habitat partitioning. Although
females roam widely in the pelagic habitat, males occupy a more dened 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
coldspots.
INTRODUCTION
Pop-up satellite archival transmitting and satellite-linked radio transmitting (SLRT) tags have
revealed that adult White Sharks (Carcharodon carcharias) of the northeastern Pacic occupy an
entirely pelagic habitat for at least 3 months and as much as 15 months of the year (Boustany etal.,
2002; Weng etal., 2007; Domeier and Nasby-Lucas, 2008, 2011; Nasby-Lucas etal., 2009; Jorgensen
etal., 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 etal., 2002; Weng etal., 2007; Domeier and Nasby-Lucas, 2008; Nasby-Lucas
etal., 2009; Jorgensen etal., 2010; Chapter 11, this book). Although the use of SLRT tags allowed for
the SOFA to be better dened 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 etal., 2009), suggests that the area is used for foraging (Domeier and Nasby-Lucas, 2008).
Alternatively, Jorgensen etal. (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 etal., 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 (Chapter16, 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 etal., 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 etal., 2009; Jorgensen etal., 2010). Furthermore, White Sharks in the SOFA
exhibit diel diving behavior, suggesting that these sharks may be exploiting the deep scattering layer
(Nasby-Lucas etal., 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 dened 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 etal., 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 signicantly
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 dened as the 50% density contour identied 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 specied 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 identied to species if possible. Floating marine debris were also
identied and quantied. 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 identication.
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
qualied 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 specic 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°
(~11km) 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
NOAAs Polar Operational Environmental Satellites; Imager on NOAAs 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° (~25km) 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 * (u2 + v2)], 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), unidentied
petrel (Ptetodroma sp.; n = 1), and an unidentied shearwater (Pufnus 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
unidentied 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
Figure12.2).
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 identiable 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), unidentied beaked whales (family Ziphiidae),
unidentied 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, unidentied 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 identication 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 Unidentied 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, unidentied 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 graycontour 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 unidentied 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 Pacic 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
EKE (cm2/s2) – June 2009
120°W
160°W 150°W 140°W 130°W 120°W
0.15
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–0.15
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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 Pacic 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 Ofeld 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 Ofce 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, andCLS.
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... Preferred prey for females in offshore waters is unknown. An expedition to the male focal area, the SOFA, found the presence of three species of spawning squid (Architeuthis sp. and Ommastrephes sp.) and sperm whales, but no small marine mammals, and very little other epipelagic life [22]. Mature females travel east/west over a much broader area than the males, so it is possible that the preferred offshore prey differs between males and females. ...
... White sharks have never been documented to prey on healthy, large cetaceans, and are probably too small to do so; however, it cannot be overlooked that adult white-shark migrations overlap with large cetacean migrations in many parts of the world. Sperm whales and white sharks coincide within the SOFA core [22], white sharks and calving humpback whales coincide in Hawaii [3] and the south Pacific [10], and white sharks coincide with northern right whales off the east coast of the USA [23]. The growing circumstantial evidence that white sharks migrate to regions with relatively high whale density suggests a foraging link; whether the sharks are actively predating or simply scavenging upon the whales (and/or calves) is not known. ...
... The seasonal constriction of the SOFA and the ROD-type diving pattern could be due to the pursuit of a seasonally available prey. An expedition to this region during the constriction identified the presence of three species of spawning squid and sperm whales [22], but again, the absence of behavioral observations deems it impractical to assign any cause to the ROD diving pattern. Diving patterns and mating systems aside, there are other strong arguments against the hypothesis that white sharks are mating during the offshore phase of their migratory pattern. ...
... Preferred prey for females in offshore waters is unknown. An expedition to the male focal area, the SOFA, found the presence of three species of spawning squid (Architeuthis sp. and Ommastrephes sp.) and sperm whales, but no small marine mammals, and very little other epipelagic life[22]. Mature females travel east/west over a much broader area than the males, so it is possible that the preferred offshore prey differs between males and females. ...
... White sharks have never been documented to prey on healthy, large cetaceans, and are probably too small to do so; however, it cannot be overlooked that adult white-shark migrations overlap with large cetacean migrations in many parts of the world. Sperm whales and white sharks coincide within the SOFA core[22], white sharks and calving humpback whales coincide in Hawaii[3]and the south Pacific[10], and white sharks coincide with northern right whales off the east coast of the USA[23]. The growing circumstantial evidence that white sharks migrate to regions with relatively high whale density suggests a foraging link; whether the sharks are actively predating or simply scavenging upon the whales (and/or calves) is not known. ...
... The seasonal constriction of the SOFA and the ROD-type diving pattern could be due to the pursuit of a seasonally available prey. An expedition to this region during the constriction identified the presence of three species of spawning squid and sperm whales[22], but again, the absence of behavioral observations deems it impractical to assign any cause to the ROD diving pattern. Diving patterns and mating systems aside, there are other strong arguments against the hypothesis that white sharks are mating during the offshore phase of their migratory pattern. ...
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Background Satellite tagging programs have provided detailed information about the migratory patterns of northeastern Pacific white sharks, revealing a seasonal migration between a vast offshore region and coastal aggregation sites. Although adult males undergo annual round-trip migrations, photo-identification programs have noted that sexually mature females may only visit coastal aggregation sites once every 2 years, a behavior that is presumably linked to an estimated 18-month gestation period. The whereabouts of females during their full 2-year migration were previously unknown, because of the limited battery capacity of satellite pop-up tags. Results Through the use of satellite-linked radio-telemetry tags with multi-year tracking capability, we describe the 2-year migratory pattern for four mature female white sharks tagged at Guadalupe Island, Mexico. The 2-year migration comprised four phases: 1) an Offshore Gestation Phase (which had an average duration of 15.5 months; 2) a Pupping Phase, which occurred along the Mexican coast between the months of April and August; 3) a Pre-Aggregation Phase (when the females were in transition between the Pupping Phase and Guadalupe Island; and 4) the Guadalupe Island Aggregation Phase, which began when the mature females arrived at Guadalupe Island between late September and early October. Conclusions Long-term satellite tracking of mature female white sharks highlighted the connectivity between a single presumed mating site at Guadalupe Island, and two widely separated pupping sites along the Mexican coast. The Offshore Gestation Phase provided evidence that the females remained offshore for up to 16 months during their 2-year migration cycle. The Pupping Phase along the Mexican coast coincided with the seasonal presence of young-of-the-year white sharks along the coast of North America, and with a presumed gestation period of 18 months, this placed mating between October and January, during the period when white sharks are known to be at Guadalupe Island. Tracking data during the time sharks were offshore showed that mature males and females are spatially segregated, except for their concurrent seasonal presence at Guadalupe Island. These discoveries provide important new details about the complete life history of northeastern Pacific white sharks while identifying crucial regions in which young-of-the-year, juveniles and adult females are most vulnerable.
... Most sensors used were onboard polar orbiting satellite platforms, delivering frequent global coverage (approximately every day) at spatial resolutions typically of the order of a few kilometers. One sensor onboard a geostationary orbiting satellite was used for SST retrieval (in combination with SST data from other polar orbiting satellites) (Domeier et al., 2012), the GOES (Geostationary Operational Environmental Satellite) Imager, a four-channel visible and infrared radiometer capable of imaging the western hemisphere every 30 min. In addition, two microwave sensors were used; the AMSR-E passive microwave radiometer was used for SST observations (n = 4) (Domeier et al., 2012) and the SeaWinds active microwave scatterometer provided wind data in one study (Wickham, 2011). ...
... One sensor onboard a geostationary orbiting satellite was used for SST retrieval (in combination with SST data from other polar orbiting satellites) (Domeier et al., 2012), the GOES (Geostationary Operational Environmental Satellite) Imager, a four-channel visible and infrared radiometer capable of imaging the western hemisphere every 30 min. In addition, two microwave sensors were used; the AMSR-E passive microwave radiometer was used for SST observations (n = 4) (Domeier et al., 2012) and the SeaWinds active microwave scatterometer provided wind data in one study (Wickham, 2011). ...
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Global elasmobranch populations have declined dramatically over the past 50 years, and continued research into the drivers of their habitats and distributions is vital for improved conservation and management. How environmental factors influence elasmobranch behavior, habitat use, and movement patterns is still relatively poorly understood, in part because of the scale over which many of these animals roam and the remote nature of the marine ecosystems they inhabit. In the last decade there has been an explosion of satellite remote sensing (SRS) technologies that can cover these vast spatial scales for the marine environment. Consequentially, SRS presents an opportunity to analyze important environmental drivers in elasmobranch ecology and to aid management decisions for the conservation of declining populations. A systematic literature review was undertaken to synthesize the current use of SRS environmental data in elasmobranch research. In addition, to facilitate the use of SRS in this field moving forward, we have compiled a list of popular SRS data sources and sensors for common environmental variables in marine science. Our review of 71 papers (55 published in the last 10 years) identified ten SRS-derived environmental variables that have been used in elasmobranch studies, from a range of satellite sensors and data sources. Sea surface temperature and ocean productivity were the most frequently used variables. Articles primarily analyzed variables individually or in pairs, with few studies looking at a suite of interacting variables. Here, we present a summary of the current state of knowledge on the application of SRS, current gaps and limitations, and discuss some of the potential future directions in which we envisage this field developing. Threatened elasmobranch populations inhabit some of the world's most remote marine ecosystems. With often global coverage, SRS presents an opportunity to analyze the important environmental drivers of elasmobranch ecology to aid management decisions for the conservation of declining and threatened populations.
... Oceanographic mechanisms supporting productivity in this ecosystem may therefore be fine-scale enough to be missed by the coarse spatial resolution of our analyses, or be occurring largely below the surface. This part of the subtropical gyre is also an important foraging area for many other animals, including white sharks, seabirds, whales, and cephalopods (Jorgensen et al., 2010;Costa et al., 2012;Domeier et al., 2012) and is a productive fishing ground for bigeye tuna (Choy et al., 2016). Additional sampling of the region, in particular subsurface measurements of biogeochemistry and lower trophic levels, could thus clearly improve our understanding of migration dynamics and foraging ecology of multiple species in the North Pacific. ...
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North Pacific albacore (Thunnus alalunga) is a commercially important tuna species known to undertake extensive migratory movements between nearshore waters of the California Current and offshore environments in the central Pacific. However, these migration behaviors are highly variable, with some individuals traveling thousands of kilometers within a season, and others largely resident in the southern California Current throughout the year. In this study, we use data from 33 archival-tagged albacore (released between 2003 and 2011) to examine the movements, physiology and ecology of tuna following different migratory pathways. We used direct measurements of body temperature and ambient water temperature from internal archival tags to estimate energy intake via the Heat Increment of Feeding (HIF), the increased internal heat production associated with digestion of a meal. Our results indicate that HIF was variable in space and time, but it was highest for individuals foraging in the offshore North Pacific Transition Zone and southern California Current during spring and summer, and lowest in the Transition Zone in fall. None of the migratory strategies examined appeared to confer consistently higher energetic benefits than the others. Fish remaining resident in the southern California Current year-round incurred lower migration costs, and could access favorable foraging conditions off Baja California in spring and summer. In contrast, fish which undertook longer migrations had much higher energetic costs during periods of faster transit times, but were able to reach highly productive foraging areas in the central and western Pacific. HIF was generally higher in larger fish, and when ambient temperatures were cooler, but was not strongly correlated with other environmental covariates. Our analyses offer new avenues for studying the physiology of wild tuna populations, and can complement diet and isotopic studies to further understanding of fish ecology.
... The use of pelagic preys as primary diet resource is not well documented in white sharks, but has not been disregarded as a potential feeding strategy (Cliff et al. 1989;Dewar et al. 2004;Weng et al. 2007;Domeier et al. 2012;Pethybridge et al. 2014). Previous research using SIA in adult white shark dermis and muscle tissues demonstrated that predation in offshore areas on pelagic prey (e.g., large tunas) is important in the shark's long-term diet, as well as pinnipeds from Guadalupe Island (Jaime-Rivera et al. 2013). ...
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White sharks (Carcharodon carcharias) are described as generalist predators, with a demonstrated ontogenetic dietary shift which occurs between subadult and adult life stages. Trophic ecology studies on white shark have been focused mainly on large and mature individuals, necessitating studies of young white shark trophic ecology to better understand their resource use. This study provides new insights into young white shark diet in the North eastern Pacific Ocean using stable isotope analysis in muscle tissues. We analyzed δ13C and δ15N values of young white shark muscle (n = 21) from Sebastián Vizcaino Bay (SBV) during 2015–2018. We found changes in prey composition across early [neonates, young-of-the-years (YOYs), juveniles] white shark life stages, with significant changes in isotopic composition throughout early ontogeny. Mixing model results indicate a high use of coastal areas for foraging, mainly for juvenile stages and the substantial contribution of pelagic preys (e.g., S. japonicus, Prionotus spp., Cynoscion spp., S. sagax, etc.) in YOYs, white shark diet also indicates an important role of offshore foraging. This change in isotopic composition likely represents the shift from the embryo’s typical maternally derived isotopic signature, incorporated in offshore foraging regions, to the postpartum isotopic composition incorporated by foraging neonates in inshore nursery habitats. This study provides relevant information regarding young white shark feeding preferences, reinforces the importance of coastal areas as critical habitat for the development and the successful foraging of this species, and also provides indirect insights on the feeding habits of the adult female of white sharks, which constitutes a baseline for further research.
... This diel vertical behavior is similar to previous observations of mako sharks [1,3,26] as well as a range of other pelagic sharks and teleosts [45,[76][77][78][79] and is typically associated with foraging in association with the deep-scattering layer. A previous study of the offshore environment in the ENP indicated that the region north of the North Equatorial Current and east of the Hawaiian Islands was a cold spot, relatively devoid of epipelagic life, but was observed to contain an abundance of mesopelagic squid species [80]. This is consistent with analyses showing a high abundance of jumbo squid in mako shark stomachs [9,14]. ...
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... Tagged sharks include both subadult and adult white sharks and all were resighted between one and 11 yrs post tagging with minimal impact to the dorsal fins. These tags provided multi-year tracking data with tracks as long as 7.4 yrs, resulting in multiple peer-reviewed publications with information on the life history of northeastern Pacific white sharks, data on the 2-yr migrations of mature females, and insights into the timing and location of mating, gestation, and pupping (Domeier and Nasby-Lucas 2012, Domeier et al. 2012a, Domeier et al. 2012b, Domeier and Nasby-Lucas 2013. ...
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... In all references to PTT tag numbers in the current study, the two digits to the right of the decimal point correspond with the abbreviated Julian calendar year in which the satellite-monitored movement was initiated. Great white sharks were tracked using similar technology deployed by different methods ( Domeier et al., 2012;Francis et al., 2012). In brief, SPOT5 PTT tags were affixed using 34 small plastic or stainless steel bolts in the apex of the dorsal fin of each temporarily restrained individual. ...
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... Uppskattningar av biomassan mesopelagiska bläckfiskar i världshaven rör sig mellan 150-300 miljoner ton Boyle (2002). Cuviers näbbval har en hög populationstäthet i området mellan Hawaii och Nordamerika samt Centralamerika (Ferguson et al. 2006) och Domeier et al. (2012) rapporterar om flockar på 50-100-tal av Rissos delfin, sadeldelfin och andra delfiner av släktet Stenella. Carlisie et al. (2012) kunde med isotopsammansättning visa att predation sker oceaniskt. ...
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Pop-up satellite archival tags (PSATs) were used to study the migration patterns and habitat preference of 56 white sharks tagged off Guadalupe Island, Mexico, between 2000 and 2008. Nine tags were recovered, providing 1021 d of high resolution (2 min) archival data. Two individual sharks were tagged in consecutive years, providing 2 yr of tracking data for each individual. White sharks were found to make long-range, seasonal migrations from Guadalupe Island to an offshore pelagic habitat, sometimes traveling as far west as the Hawaiian Islands. The pelagic region inhabited by Guadalupe Island white sharks corresponds with that reported for sharks tagged off central California; thus we have termed it the Shared Offshore Foraging Area (SOFA). Sharks spent at least 5 mo off Guadalupe Island before beginning their migration around 15 February on average (earliest 21 December, latest 5 May). They traveled through a migration corridor in an average time of 16 d at an average speed of 3.2 km h(-1) and remained in the SOFA for an average duration of 140 d. Males and females began their offshore migrations around the same time and traveled to the same area, but males were found to return to Guadalupe Island on average around 22 July (earliest 15 July, latest 30 July), while females remained in the SOFA into early autumn. Diving profiles of sharks in the SOFA strongly suggest feeding behavior; however, the targeted prey species are unknown at this time.
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This book presents an in-depth discussion of the biological and ecological geography of the oceans. It synthesizes locally restricted studies of the ocean to generate a global geography of the vast marine world. Based on patterns of algal ecology, the book divides the ocean into four primary compartments, which are then subdivided into secondary compartments. *Includes color insert of the latest in satellite imagery showing the world's oceans, their similarities and differences *Revised and updated to reflect the latest in oceanographic research *Ideal for anyone interested in understanding ocean ecology -- accessible and informative.
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OVERVIEW Segregation of the sexes within a species is a widespread behavioural phenomenon in both terrestrial and aquatic animals. In the marine realm, sexual segregation is exhibited by many taxa including whales, seals, seabirds and fish. Of the latter group, sharks may be particularly appropriate model animals to test theories on the mechanisms underlying sexual segregation, because sexual segregation is a general characteristic of shark populations, with both sexually dimorphic and monomorphic species being well represented among the approximately 400 extant species (Springer, 1967; Compagno, 1999). The reproductive modes of sharks are diverse ranging from egg-laying (oviparity) to placental live-bearing (viviparity) (Wourms & Demski, 1993). Among sexually dimorphic, viviparous shark species it is generally the female that is larger than the male, whilst in some oviparous species males are larger than females. Sexually monomorphic species also occur. Therefore, sharks possess a number of characteristics that make them an interesting alternative to terrestrial animal models for investigating the causes of sexual segregation. In this chapter the prevalence and nature of sexual segregation in sharks is described and the relationship with reproductive modes is explored. Hypotheses suggested to account for sexual segregation in sharks are examined with respect to new field and laboratory behaviour studies of males and females of a monomorphic species, the lesser spotted dogfish ( Scyliorhinus canicula ). The chapter concludes by drawing together the main points from all shark studies to date, and suggests future directions for research in this area. © Cambridge University Press 2005 and Cambridge University Press, 2009.
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Book
This book presents an in-depth discussion of the biological and ecological geography of the oceans. It synthesizes locally restricted studies of the ocean to generate a global geography of the vast marine world. Based on patterns of algal ecology, the book divides the ocean into four primary compartments, which are then subdivided into secondary compartments. *Includes color insert of the latest in satellite imagery showing the world's oceans, their similarities and differences *Revised and updated to reflect the latest in oceanographic research *Ideal for anyone interested in understanding ocean ecology -- accessible and informative.