2/5/2011

Site fidelity among Grey Whales (Eschrichtius robustus) as determined by

photographic identification in Bahía Magdalena, Baja California Sur, Mexico

Margaret V. du Bray, Eduardo Najera-Hillman

Whitman College, Walla Walla, WA USA

School for Field Studies: Center for Coastal Studies, Puerto San Carlos, BCS,

Mexico

ABSTRACT: Eschrichtius robustus (grey whales) within Bahía Magdalena, Baja

California Sur, Mexico, are an economically and culturally important species. A

migratory species, they travel from their feeding grounds in Arctic waters to

winter and calve in Mexico. Bahía Magdalena is one of the notable areas where

grey whales are found during the winter. As has been done elsewhere,

photographic identification was performed by the School for Field Studies in

order to assess site fidelity and short-term movements of grey whales within the

bay. It was expected that whales would exhibit high site fidelity. Whales were

observed and photographed from pangas in the bay. The photographs were

organized into a photographic catalog. The catalog from the year 2011 was

compared to catalogs from the years 1998-1999, 2003, 2004, 2005, 2007, and

2009-2010. Whales were visually identified using markings including barnacles,

scars, and injuries. Two whales were resighted. One was initially sighted in 2003

and the other was initially sighted in 2004. No whales were resighted on different

days within 2011. The results of this study indicate that there is low site fidelity

among grey whales in Bahía Magdalena. More data is required to continue to

study this phenomenon. The study does demonstrate that photographic

identification studies should focus on the Santo Domingo Estuary, where whales

are more likely to surface. This allows for more comprehensive photographs.

Additionally, whales with distinct marks should be focused upon for photographs.

Finally, more research is necessary to examine short-term movement patterns

within the bay.

LITERATURE REVIEW

Sources which discussed the ecology and habitats of grey whales

(Eschrichtius robustus) were analyzed to understand patterns of populations in

Bahía Magdalena, Mexico. Other sources, which focused on photographic

identification, were examined in order to understand the context of prior research

relating to cetaceans. These sources were also helpful in developing a

methodology. Prior research was categorized four ways: ecology of grey whales,

techniques for photographic identification, social organization as determined by

photographic identification, and the use of photographic identification to

determine anthropogenic causes of scarring.

Ecology and Population Dynamics of Grey Whales within Bahía

Magdalena. Grey whales are a migratory species. They travel 20,000 km from

their feeding grounds in Alaska to the calving grounds in the Pacific waters near

Mexico. Bahía Magdalena, Baja California Sur, Mexico, is one area where grey

whales calve and mate from December to March. The bay is utilized differently

by different groups of whales; mothers with calves are more likely to be found in

protected areas, like the estuaries in the Santo Domingo channel. Single males

and females, both mature and immature, are more likely to be found in areas

within Magdalena and Almejas Bays. The three areas within the bay are

considered separate locations with different utilities (Perez-Cortez et al. 2004).

Photographic Identification: Techniques. Marine mammals have been

documented and identified using photographic identification since the mid-1970s.

Traditionally, cameras with a single-lens reflex and either black and white or color

film were used (Shane 1990). More recently, digital photography has replaced

traditional film photography (Meyer 2006). Most photographers involved in

photographic identification of marine mammals have used digital single-lens

reflex cameras with zoom lenses (Wursig and Jefferson 1990).

Identification strategies have included technological programs and visual

matches. Technological programs have become popular for image matching and

identification in marine species. The FinBase system is a notable example of

these programs. This program has matched images of individuals by matching

distinctive marks on fins (Adams 2006). Other researchers have used algorithms

and affine invariant grids and curves in order to match the markings and shape of

fins and flukes (Ranguelova et al. 2004, Gope 2005). Data has also been

generated by examining light and dark patches on flukes and fins. The data

generated by these methods has been entered into databases and was available

for comparison at later dates. Other research has been conducted without the

use of computer-based programs. In this case, photographs were sorted before

one clear picture of each individual was chosen for closer analysis. All

distinguishing marks of an individual were noted. The tables generated by this

initial cataloguing were then available to document resightings (Karczmarski

1998).

Social Organization and Population Dynamics as Determined by

Photographic Identification. The social organization of two populations of pilot

whales was studied through the use of photographic identification. Pilot whales

were identified through key features including fins and saddle patterns. Once the

photographs were catalogued, researchers examined them for site fidelity and

pod dynamics. The photographs suggested that pilot whales return to specific

locations seasonally, as many were seen in the same location year to year.

Photographs have indicated that pilot whales are likely to remain with their pod.

Furthermore, pilot whales were found in pods composed primarily of females and

sub-adult males (Shane 1990).

The western grey whale population has also been studied in order to

understand social organization and population composition. Because this

population is critically endangered, researchers have attempted to categorize the

numbers and the status of the population. A catalog of distinct features was

created based on photographs taken during monitoring sessions. The

photographs were then used to determine resightings and create a database in

which researchers could examine population dynamics in the future.

Researchers have suggested the need for continued research in order to monitor

the population dynamics (Yakovlev and Tyurneva 2003).

The Use of Photographic Identification to Determine Causes of

Anthropogenic Scarring. The western grey whale population is threatened by

whaling. Researchers speculate that the population is also threatened by its

interactions with vessels and entanglements in fishing gear. The body of the grey

whale was partitioned into twenty-one sections, and evidence of scars was

examined within each section. Scars were categorized as no scar, entanglement,

vessel collision, unknown scar, partially visible, or not visible scars. Among

western grey whales, the right side was more likely to show scarring than the left.

18.7% of grey whales were scarred due to fishing entanglements and 2.0% were

scarred due to vessel collisions. The researchers have suggested that continued

research is required due to inadequate information about the population.

Furthermore, they have suggested that more research must be carried out in

order to estimate the fatalities resulting from entanglements and collisions with

vessels; current data only demonstrates the number of whales that survive these

encounters (Bradford et al. 2009).

INTRODUCTION

Grey whales (Eschrichtius robustus) are a culturally and economically

significant species within Bahía Magdalena, Baja California Sur, Mexico (Dedina

2000). Grey whales are a migratory species; from Alaska, they travel 20,000 km

to Baja California Sur to mate and calve. Pregnant females often calve in Bahía

Magdalena and raise their calves in the sheltered waters. Previously an

endangered species, grey whales are now considered to be threatened; their

population numbers appear to be increasing (Perez-Cortez et al. 2004).

Grey whales are an economically viable species; where they were

previously hunted, now they provide income for locals involved in the tourism

industry. The increase in tourism within the Bay potentially threatens the grey

whales. Bahía Magdalena is also polluted by the effluent from the local sardine

cannery. These two issues are among the greatest immediate impacts affecting

the grey whale calving grounds in Bahía Magdalena (Dedina 2000).

Photographic identification is a widely used technique for understanding

population dynamics among other species. Research has examined group

relations and site fidelity among pilot whales (Shane 1990). Photographic

identification has also been used to assess anthropogenic impacts. Researchers

have also used photographic identification among the western grey whale

population in order to generate a database. This will allow future researchers to

monitor the size and status of the critically endangered population in Japan and

Russia (Yakovlev and Tyurneva 2003). Researchers have analyzed

anthropogenic effects on grey whales among the same population. Photographic

databases have allowed researchers to compare scars from fishing

entanglements and vessel collisions, and thereby estimate the numbers of

whales impacted by these interactions. It also estimated the extent to which this

is an ongoing problem (Bradford et al. 2009).

Photographic identification has been used in the Western grey whale

population to examine site fidelity. This study demonstrated that the grey whales

had high site fidelity, particularly related to their feeding ground (Weller et al.

1999, as cited in Swartz et al. 2006).

Within Bahía Magdalena, photographic identification has been used since

the 1960s. The research has yielded a significant photographic database that

allows researchers to recognize the whales sighted in the bay (Swartz, S. L. et al.

2006). Because the migration patterns of grey whales are so well-known, they

are a particularly viable species to study with photographic identification.

Observing grey whales in breeding areas is particularly useful due to the high

numbers of whales that visit calving grounds annually. Dorsal regions were

focused on due to their distinctive marks. Breeding patterns were examined in

several studies as a result of photographic identification (Jones 1990, Urban et

al. 2003).

Prior research has examined the phenology of whales in the bay, as well

as movements within the bay. This research also examined the areas (Boca,

Estuary, etc) in which specific populations might be found, and reproductive rates

(Urban et al. 2003). Studies focused in tandem on genetic distinctions within the

eastern grey whale population and the photographic identification that allowed

examination of interyear site fidelity. The study demonstrated that grey whales in

Bahía Magdalena had low interyear site fidelity, and that they were sighted

across differing spans of time. This research documents the difficulty of

identifying whales throughout their life, as they are born with very few marks and

add them as they age (Alter et al. 2009).

Photographic identification has evolved in the past decade. Whereas film

cameras (black and white and color) were used to document populations, digital

photography has become more prevalent (Shane 1990, Meyer 2006). Using

digital single-lens reflex cameras and zoom lenses, photographers have been

able to document populations of cetaceans (Wursig and Jefferson 1990).

Different methods of analyzing the photographs have also been used; affine

invariant curves have been used to analyze tails and fins; other computer

programs have been used to match cetaceans within an already-generated

database (Ranguelova et al. 2004, Gope 2005, Adams 2006). Still other

researchers continue to visually match photographs (Karczmarski 1998).

The staff and students at the School for Field Studies’ Center for Coastal

Studies in Bahía Magdalena began documenting grey whale sightings using

photography in 1998. Photographs were taken in 1998, 1999, 2003, 2004, 2005,

2007, 2009, 2010, and 2011. The database generated by this documentation has

been used for several research projects in the past decade. Very little research

has examined the site fidelity among grey whales. While previous research has

demonstrated that different areas of the Bay are used by specific groups of

whales, no one has yet demonstrated that certain whales return each year to the

same areas of the bay.

This research used the existing photographic identification catalog

generated by past students and professors. This was combined with data

collected in the year 2011 to examine whether there is site fidelity among this

population of grey whales. Photographs from 2011 were categorized by location

within Bahía Magdalena in order to study short-term movement patterns. I

hypothesize that grey whales will show site fidelity within Bahía Magdalena. Due

to the challenges of photographing grey whales, it is unlikely that the

photographic catalog will demonstrate consistent, year-to-year site fidelity among

grey whales. If grey whales are matched across the database, this will be noted

as site fidelity. Additionally, I hypothesize that solitary whales will move between

the Boca and the main portion of the bay; mothers and calves will stay primarily

in the Estuary.

METHODS AND MATERIALS

Location and Temporality Grey whales were monitored and

photographed approximately once a week from the beginning of February until

the end of March annually. Monitoring was only carried out in favorable weather

conditions (Beaufort < 2). Whales were monitored by students and faculty from 8-

9m fiberglass pangas with 115 hp motors in several regions of Bahía Magdalena.

Bahía Magdalena is approximately 31 km long and 22 km wide. It is connected to

the Pacific Ocean by a 6 km mouth. Monitored areas included the Santo

Domingo Channel estuary, the main part of the bay, and the mouth of the bay.

The area was limited to regions between the coordinates 24°20’N-25°20’N and

111°30’W-112°10’W.

Figure 1. Map showing the range of grey whales and the study site located

within their winter breeding and calving grounds

Study Site Winter Breeding Grounds

Figure 2. Map showing the specific locations within Bahía Magdalena where

whales were monitored

Field Work Pangas slowly approached whales after a sighting. Fast

speeds were prevented to avoid disrupting the behavior of the whales. Surface

water temperature and depth were taken. A GPS waypoint position and longitude

and latitude were noted. The behavior and the number of individuals sighted

were also recorded. Photographs were taken using several cameras. These

cameras usually had a variable focal length which allowed whales to be

photographed at a distance and up-close. The dorsal region was a point of focus

due to notable characteristics in that region of the body. Behavioral pictures were

also taken, which showed other regions of the body. Multiple pictures of each

whale were taken and those with the best angle and clarity were entered into the

photographic database.

Data Analysis Photographs from the database were visually compared.

Two pictures were compared at a time. Markings including scars and injuries

were used as criteria for identifying individuals. Particular attention was paid to

markings along the back and knuckles of the whales, as these were most

commonly photographed. Images showing individuals with the same markings

were documented as a resighting of an individual. An individual was resighted

only if it was seen on a different day than that on which it was originally sighted.

The years of the sightings were recorded in a database. If an individual was not

previously in the database, it was considered a new sighting and was given a

number corresponding to the initial month, year, and date of the sighting.

Resightings of whales were noted in a database. The database was used

to examine the number of individuals which had been resighted, and at what

times. If whales were matched across years in the photographic catalog, it was

considered a resighting. The years in which the whale was not sighted were

considered to be years in which the whale might have been present, but was not

photographed or sighted.

RESULTS

The photographs from all whale-watching days in 2011 were sorted and

organized into a photographic catalog.

The total number of whales sighted and photographed in 2011 was 81.

Whales were not sighted or photographed more than once in 2011. Two mothers

with calves were sighted and photographed showing similar markings (Figures 3

and 4).

473 whales were sighted and photographed from 1998 to 2011, excepting

the years 2000, 2001, 2002, and 2006, when no photographs were taken or were

lost (Table 1). Out of a total of 473 whales photographed and catalogued from

1998 to 2011, only two were resighted (Table 3). Variance was measured to

understand the difference in the number of whale sightings and photographs

annually. Variance here demonstrates the numerical difference of whales

photographed year to year. There was a strong variance in the number of whales

sighted and photographed year to year (variance = 1908.8).

Previous data calculated the number of whales sighted per year. This was

compared with the number of whales per year as calculated in 2011 (Table 2).

The body region which was used for photographic identification was

recorded by year. Until 2005, the right side was exclusively photographed. In

2009 and 2010, more flukes were recorded than in previous years. In 2011, right

and left sides were photographed (Table 5).

The number of photographs taken this year was compared with the

number of photographs used from each site. The Boca de Bahía Magdalena had

the highest number of used photographs. The Estuary had the second most used

photos (Table 4).

Figure 3. Mother and calf showing similar white markings

Figure 4. Mother and calf showing similar white markings Table 1. The number of whales sighted as demonstrated by the photographic catalog Database by Year

1998-1999 2003 2004 2005 2007 2009-

2010 2011

# Whales sighted 53 160 56 46 42 32 81

Table 2. Previous data showing the number of whales identified, including resightings

Year Days of Effort

Useful Photos Individuals Re-

sightings 1998 1 4 1 -

1999 7 60 54 2

2004 12 78 64 -

2005 8 102 48 21 2007 6 108 70 -

2009 4 17 14 1

2010 4 32 25 -

2011 17 110 81 -

Table 3. The number of whales resighted, including the dates initially sighted and resighted, and the photos used to identify them

SFS ID # Photo #

initial sighting

SFS ID # resighting

Photo # Resighting

Date Initially Sighted

Date Resighted

SFS270 l103a3b

IMG 2537, IMG 2538, IMG 2539, IMG 2541, white spot calf, white spot cow and calf,

white spot cow right

side

February-03

February-11

SFS093 l304a8, l304a19b SFS233 IMG 0349 February-

04 February-

11

Table 4. The number of photos taken per three sites, the number used, and the percentages

Location Number

of Photos Taken

Number of Photos

Used Ratio

Estuary 429 80 0.18

Main Bay 255 27 0.1

Boca 9 3 0.33

Table 5. Showing which body region, by year, was used for identification

Body Region

# Whales 98-99

# Whales 2003

# Whales 2004

# Whales 2005

# Whales 2007

# Whales 2009-2010

# Whales 2011

Right Back 53 158 57 43 34 7 45

Left Back 0 2 0 5 8 12 36

Fluke 0 0 0 0 0 13 0

DISCUSSION

Conclusions from Hypotheses The hypothesis that whales would show

site fidelity in Bahía Magdalena was partially supported. The results indicate that

very few whales return to Bahía Magdalena across the years. Furthermore, the

whale resightings occurred across a large time span (6-7 years). It was expected

that whales would be resighted within a short time span. That they were not

further indicates low site fidelity. Prior research found that interyear site fidelity

existed among grey whales, but that the proportion of those resighted was very

low and was found across a long time span (Alter et al. 2009).

Because whales were only sighted and photographed once over the

season (they were not resighted on different days within 2011), short-term

movement patterns cannot be determined. Future research should continue to

examine whether whales are returning annually to Bahía Magdalena, and focus

on their movement patterns within Bahía Magdalena.

Data Analysis The high variance in the number of whales seen year to

year indicates the strong differences in the number of whales seen between

years. Some years have as few as 32 whales, while others had as many as 160.

The difference in numbers makes it difficult to compare the whales. If even

numbers of whales were photographed across the years, it would suggest that

there was a greater potential for the same whales to return to Bahía Magdalena.

Because the data fluctuates so greatly, however, it is difficult to say that the

same whales return.

Previous data collected and analyzed by past student Laura Conner was

compared to data that was analyzed in 2011. There were discrepancies between

the number of whales that were counted by Conner and by the current

researchers. This can be accounted for because several whales within previous

databases were found to be labeled as different whales. These whales, however,

were identified as being the same. Additionally, because the photographs were

organized into a catalog prior to 2011, there may have been some organizational

mistakes. These two situations account for the variance in the number of

individuals identified in older databases between previous research and current

research.

The percentage of used pictures by location initially indicates that future

researchers should focus their attention on the Boca de Bahía Magdalena.

However, the percentage is drawn from a very small sample. Only nine pictures

were taken within the Boca, out of which, three were used. Future researchers

should focus their attentions on the Estuary. The greatest number of pictures was

taken there (429). Because whales are closely grouped in the Estuary, there is

the greatest likelihood that multiple regions of the body can be photographed.

Additionally, prior research has indicated that mothers with calves breathe much

more often than single adult whales. As a result, it is likely that mothers and

calves spend more time on the surface (Rodriguez de la Gala-Hernandez et al.

2008). This allows them to be photographed more frequently and amplifies the

importance of continuing to study the Estuary. This area is likely to provide

researchers with comprehensive photographs for identification.

Prior research has largely focused on female grey whales within Bahía

Magdalena. Due to their proximity to calves, they are inherently able to be

identified as female (Jones 1990). Females are also focused upon in order to

understand changes in breeding cycles and the impact on the population size

(Swartz et al. 2006, Jones 1990). This practice should be continued due to the

relative ease with which females and calves can be photographed.

The Estuary is also the most useful place to take pictures because, in the

other two regions of the bay, the whales are more likely to fluke. Whales in their

wintering grounds are less likely to fluke than they are when they migrate. As a

result, fluke photographs do not allow a large number of comparisons (Jones

1990). Additionally, fluke photographs may make it more difficult to examine the

short-term movement patterns of the whales. If a whale fluke is photographically

captured in one region of the bay, but the body is captured in another, no visual

match can be made. The 2009-2010 photographs included a number of fluke

pictures. While more fluke pictures might allow photographic identification, the

current data, which focused more on the back and knuckles, does not allow that.

Some research indicates that flukes are generally not helpful for identification

(Jones 1990). As a result, the main part of the bay and the Boca, where whales

were most likely to fluke, should be not be the focus for photographic

identification purposes.

In 2011, researchers begin traveling to the estuary, which allowed them to

intensely focus on photographing the sides of whales. Future research should

continue to focus on photographing both sides of the whale, so that

comprehensive photographic identification can be carried out. While past years

have primarily focused on the right side of whales, capturing the left side as well

as the right will lead to a more holistic understanding of which whales return, and

how their markings are changing. Prior research has demonstrated that

photographing the whales from multiple angles is more comprehensive. It allows

researchers to better visualize marking patterns, and as a result, makes re-

identification simpler. Additionally, this practice prevents counting one individual

as two (Jones1990).

The number of whales photographed in past years must be viewed with

some skepticism. Due to the poor photographic quality, particularly in the year

2003, it is very difficult to match whales across the year. While ten whales had

markings distinctive enough to be matched across the year, the majority of the

photographs were too poor to match, and as a result, the number of whales from

2003 is likely an overestimation.

Research Concerns and Recommendations There are several reasons

that might undermine the quality of the conclusions of this research. Visual

identification is challenging when different types of technology are used. The

earliest photographs were taken with film cameras and were scanned into the

photographic catalog. Photographic quality was lost during scanning, which

makes it challenging to compare whales from earlier years.

Photographs were also taken from multiple directions and angles. It is

conceivable that photographs were taken of the same whale, but either from

different sides or different angles. Without photographs of both sides of the

whale’s body, it is difficult to match the two sides of the whale. As a result, some

photographs may be of the same whale, but are not counted as a resighting

because the photographs were of different sides and were unable to be matched.

A better method of counting and photographing whales might reduce the

variability in the number of pictures taken, and would allow photography of all

sides of the whales. If one panga in the group was dedicated to recording the

number of whales and the position, and another boat photographed, it would

allow the photographer to get multiple angles of the same whale while others

recorded.

Cameras with built in GPS would also aid in this process. By looking at

specific GPS coordinates, the location of the whale could easily be recorded, but

could also distinguish one whale from another. This would reduce the number of

pictures that had to be visually matched along with the possibility for mistakes.

Additionally, when whales lack distinct marks, such as injuries, scars,

large white patches, or large groups of barnacles, it is difficult to make a

comparison. Many whales are covered in grey dapples. Without extremely high

resolution and matching software, these marks do not provide enough data to

make a positive identification.

When paired with visual identification, matching software, such as a

variation on that which is used for dolphin databases, would provide the most

conclusive data regarding the site fidelity of grey whales in Bahía Magdalena

(Adams 2006). The matching software would be more effective than the human

eye at detecting patterns in markings (particularly for those whales without

distinct marks). Innovative software has begun to examine whether the knuckles

of whales are an identifying feature. Some software matches have been made

using the area under the knuckles as a feature (Nutch 2006). If implemented with

grey whales in Bahía Magdalena, this might further the identification process.

While software has not yet been implemented in this way, it is conceivable

that, with the correct algorithm, aging software could be used for grey whales.

Because their markings change as they get older, it is difficult to look at a picture

of a young whale and extrapolate what it would look like as a mature adult. If

aging software were properly manipulated, it might create an estimation of what

the adult whale would look like.

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