Individual gray whale use of coastal waters off northwest Washington during the feeding season 1984-2011: Implications for management

Abstract

Gray whales (Eschrichtius robustus) in northwest Washington were studied, with the aims to: (1) increase understanding of gray whale use of the study area; (2) document the annual and seasonal fluctuations in the numbers of whales utilising the area; and (3) assess the fidelity of whales to the study area within and between years. Together these goals establish a baseline of gray whale behaviour during summer and autumn in the region of the Makah Tribe's proposed whale hunt. From 1984 to 2011, a total of 225 unique gray whales were observed, with 49% being observed again in a future year. There was significant variability in observation rates of gray whales by month and year. During the feeding season, the observation rate increased to a peak in August in the north research segment in the Pacific Ocean and to a peak in October in research segments in the Strait of Juan de Fuca and in the southern research segment in the Pacific Ocean. Gray whales were most commonly observed at depths of 5-15m over rocky substrates and often near kelp forests, although the locations where they fed were dynamic by both month and year. Some whales habitually returned to northwest Washington, however the average whale in the study area was observed in only 31.6% (SE = 1.6%) of the possible years in which they could have been observed. Gray whales in the study area had an average minimum tenure (residency time) of 24.8 days out of a possible 183 days of the feeding season. A discovery curve analysis did not reach an asymptote over the 27 years of this study showing that there is no population closure to the research area. Based on these findings, it can be concluded that even though northwest Washington is an important feeding area, most Pacific Coast Feeding Group (PCFG) gray whales do not have strong fidelity to this one region within the IWC defined PCFG range. The findings presented in this paper provide a baseline for evaluating the impact of Makah hunting activities on the behaviour of PCFG whales that utilise the Makah's traditional hunting area once hunting activities resume.

Full text

Individual gray whale use of coastal waters off northwest
Washington during the feeding season 1984–2011:
Implications for management
JONATHAN J. SCORDINO1, MERRILL GOSHO2, PATRICK J. GEARIN2, ADRIANNE AKMAJIAN1, JOHN CALAMBOKIDIS3AND
NANCY WRIGHT4
Contact e-mail: jonathan.scordino@makah.com
ABSTRACT
Gray whales (Eschrichtius robustus) in northwest Washington were studied, with the aims to: (1) increase understanding of gray whale use of the
study area; (2) document the annual and seasonal fluctuations in the numbers of whales utilising the area; and (3) assess the fidelity of whales to
the study area within and between years. Together these goals establish a baseline of gray whale behaviour during summer and autumn in the region
of the Makah Tribe’s proposed whale hunt. From 1984 to 2011, a total of 225 unique gray whales were observed, with 49% being observed again
in a future year. There was significant variability in observation rates of gray whales by month and year. During the feeding season, the observation
rate increased to a peak in August in the north research segment in the Pacific Ocean and to a peak in October in research segments in the Strait of
Juan de Fuca and in the southern research segment in the Pacific Ocean. Gray whales were most commonly observed at depths of 5–15m over
rocky substrates and often near kelp forests, although the locations where they fed were dynamic by both month and year. Some whales habitually
returned to northwest Washington, however the average whale in the study area was observed in only 31.6% (SE = 1.6%) of the possible years in
which they could have been observed. Gray whales in the study area had an average minimum tenure (residency time) of 24.8 days out of a possible
183 days of the feeding season. A discovery curve analysis did not reach an asymptote over the 27 years of this study showing that there is no
population closure to the research area. Based on these findings, it can be concluded that even though northwest Washington is an important feeding
area, most Pacific Coast Feeding Group (PCFG) gray whales do not have strong fidelity to this one region within the IWC defined PCFG range.
The findings presented in this paper provide a baseline for evaluating the impact of Makah hunting activities on the behaviour of PCFG whales that
utilise the Makah’s traditional hunting area once hunting activities resume.
KEYWORDS: GRAY WHALE; PACIFIC OCEAN; FEEDING GROUND; MOVEMENTS; SITE FIDELITY; NORTHERN HEMISPHERE;
SURVEY–VESSEL
previous definitions of this group. This is primarily because
most photo-identification surveys have been focused on
41–52°N. Population estimates are therefore more reliable
for this range. There are few historic or projected future
catches of gray whales north of 52°N and south of the Bering
Sea, making the more narrowly defined range more
applicable to management (IWC, 2012). The abundance
estimate for the PCFG in 2012 was 209 whales
(Calambokidis et al., 2014).
Recent genetic studies have found small but statistically
significant differences in frequencies of mtDNA haplotypes
between samples collected from PCFG whales and other ENP
whales in other portions of their range (Frasier et al., 2011;
Lang et al., 2014). No statistically significant differences have
been found in the frequencies of nuclear DNA (D’Intino et
al., 2013; Lang et al., 2014). Despite the significant difference
in mtDNA haplotype frequency, PCFG and ENP whales had
similar haplotype diversity which suggests that immigration
into the PCFG could be occurring (Lang et al., 2014). The
results of a genetics simulations study (Lang et al., 2012) and
photo-identification work (Calambokidis et al., 2014) were
consistent with immigration from other portions of the
ENP range into the PCFG having a significant role in the
J. CETACEAN RES. MANAGE. 16: 57–69, 2017 57
INTRODUCTION
Most Eastern North Pacific (ENP) gray whales (Eschrichtius
robustus) migrate from wintering grounds in Baja California,
Mexico, to feeding grounds in the Bering, Chukchi and
Beaufort seas. A small subset of the ENP gray whale
population does not complete the migration to arctic feeding
grounds and instead spends the summer and autumn at
feeding grounds along the coast of the Pacific Ocean from
California through Southeast Alaska (Calambokidis et al.,
2002). This group of whales has been referred to by many
names since it was first studied in the 1970s and is currently
recognised as the Pacific Coast Feeding Group (PCFG) by
the International Whaling Commission (IWC, 2011) and the
US Government (Carretta et al., 2013). The IWC defines the
PCFG as gray whales seen in more than one year in the
months of June to November within the range of northern
California to northern British Columbia (41°N–52°N),
excluding gray whale sightings in Puget Sound, Washington
(IWC, 2012). The range is restricted to 52°N even though
PCFG whales are known to frequently occur as far north as
Kodiak Island, Alaska (Gosho et al., 2011) and have been
observed in the Beaufort Sea (Calambokidis et al., 2014).
The IWC-defined range of the PCFG is narrower than
1 Marine Mammal Program, Makah Fisheries Management, Makah Tribe, Neah Bay, Washington, USA.
2 National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic Atmospheric Administration,
Seattle, Washington, USA.
3 Cascadia Research Collective, Olympia, Washington, USA.
4 Olympic Coast National Marine Sanctuary, National Ocean Service, National Oceanic Atmospheric Administration, Port Angeles, Washington, USA.

population dynamics of the group. Given that there is
evidence both for the PCFG having open population
dynamics and evidence for matrilineal recruitment, there is
currently debate on whether or not the PCFG is a stock.
NOAA Fisheries used a panel of experts to evaluate whether
the PCFG is a stock; the panel could not agree whether the
PCFG is a stock for US domestic purposes but did agree that
more research is needed (Weller et al., 2013).
Interest in PCFG whales has been inspired by concern
regarding the possible impacts on the PCFG of the Makah
Tribe resuming their treaty protected right to hunt whales. In
1855, the Makah Tribe protected its whaling rights in the
Treaty of Neah Bay. In the 1920s, the Tribe voluntarily
suspended whale hunting due to the impacts of commercial
whaling on gray and humpback whale populations (Renker,
2012; Thompson, 2006). In 1994, when the gray whale was
removed from the US Endangered Species List, the Makah
Tribe informed the US Government of its intentions to
resume traditional whale hunting. The US Government has
obtained aboriginal whaling catch limits for the harvest of
gray whales from the IWC to be used by the Makah Tribe
since 1997. However, since that time the Makah Tribe has
only landed one gray whale due to domestic court cases and
regulatory processes suspending the hunt in 2000. The Tribe
has submitted a proposed management plan to the US
Government and the IWC for review. The management plan
restricts the hunt to the migratory season in the Pacific Ocean
portion of the Makah Usual and Accustomed (U&A) fishing
grounds to minimise the risk that a hunt takes a PCFG whale.
Nonetheless, it is recognised that the hunt may still take
PCFG whales, so the management plan also has a provision
to limit the number of PCFG whales landed through a
conservative calculation based on the abundance of PCFG
whales (IWC, 2013). The IWC evaluated the impact of
Makah hunting on PCFG population dynamics and found
that the Tribe’s proposed management plan meets the
conservation goals of the IWC of ensuring the PCFG will
remain above 60% of its carrying capacity over a 100-year
simulation (IWC, 2013).
Past studies have documented the behaviour of PCFG
whales throughout their entire range (Calambokidis et al.,
2002; 2010; 2012; 2014). This paper reports on the behaviour
of gray whales in the coastal waters of northwest Washington
during the summer and autumn feeding season. Data were
collected from 1984–2011 with the goals of: (1) increasing
our understanding of gray whale use of the study area; (2)
documenting the annual and seasonal fluctuations in the
numbers of whales utilising the area; and (3) assessing the
fidelity of whales observed within the study area within and
between years. Together these three goals establish a baseline
of gray whale behaviour in the region of the Makah Tribe’s
proposed whale hunt to evaluate (once the hunt is approved)
whether the hunt impacts gray whale behaviour in the
northwest Washington.
METHODS
Study area
Research effort was conducted along the northwest tip of
Washington State, USA (Fig. 1). Northwest Washington is
bounded by two bodies of water: the Strait of Juan de Fuca
to the north and the Pacific Ocean to the west. The rocky
shorelines are interspersed with sandy beaches, and rocky
underwater habitats dominated by forests of bull kelp
(Nereocystis luetkeana) and giant kelp (Macrocystis spp.) in
waters 5–15m deep. The waters of northwest Washington
have high biological productivity due to the confluence of
currents from the California Current and the drainage of
Puget Sound through the Strait of Juan de Fuca, and seasonal
winds causing upwellings (Marchetti et al., 2004). The study
area encompasses most of the nearshore habitat of the Makah
U&A and the entire area in which the Makah Tribe has
proposed for hunting gray whales (Makah Tribal Council,
2011).
Survey methodology
The northwest Washington survey area is too large to be
surveyed effectively in one day. One day of survey effort
covered the area to the east of Neah Bay along the shores of
the Strait of Juan de Fuca to Sekiu Point, approximately
25km from Neah Bay. The other survey day covered the area
west along the shores of the Strait of Juan de Fuca to Cape
Flattery and then south following the shoreline of the Pacific
Ocean to Sea Lion Rock (47°59.58’N, 124°43.45’W). The
total distance covered in the southbound leg is approximately
60km. Surveys for gray whales were generally conducted
within 1–2km of shore because gray whales feeding in
northwest Washington primarily congregate near shore.
Portions of the survey in the Pacific Ocean, particularly south
of Cape Alava, were conducted further from shore due to
poorly charted submerged rocks.
Survey effort was variable by year. The early years of
survey effort in northwest Washington were conducted
opportunistically with three years of surveys in the 1980s
(1984, 1986 and 1989) by Cascadia Research Collective
58 SCORDINO et al.: INDIVIDUAL GRAY WHALE USE OF COASTAL WATERS
Fig. 1. Map of the gray whale survey region in northwest Washington with
the focal survey area shown enclosed with a line. The numbered survey
segments are: (1) West Strait; (2) Neah Bay Entrance; (3) East Strait; (4)
North Ocean; and (5) South Ocean.

(CRC). Starting in 1992 surveys were conducted annually
by the National Marine Mammal Laboratory (NMML) and
CRC but effort was low and opportunistically conducted
during studies of other marine mammal species. After 1996,
surveys were standardised and were generally conducted on
a bi-weekly basis from June through November as weather
and ocean conditions allowed with NMML and the Makah
Tribe as the primary research groups. The objective was
to collect photo-identification of whales. Thus, if the
researchers had good reason to suspect that survey effort in
the Strait of Juan de Fuca would result in limited or no
photographs of gray whales, then effort was focused on the
Pacific Ocean and vice versa. The Pacific Ocean survey area
was generally surveyed monthly regardless of anticipated
opportunities to photograph gray whales because the surveys
were also used for monthly California and Steller sea lion
research. All research effort was conducted from small
vessels of 6–9m in length.
During surveys, observers periodically recorded time and
location and variables that could have influenced the
probability of sighting a whale such as cloud cover and
Beaufort sea state. When gray whales were sighted, their
location, depth and activities were recorded. Observers then
attempted to take photographs of the dorsal ridge along both
flanks as well as the flukes. Photographs were taken using
digital SLR cameras with a 70–300mm lens (35mm film
cameras were used prior to 2004). The lens magnification
allowed photo-documentation of unique colouration patterns
on the lateral sides and flukes of the whales (Darling, 1984).
The frame numbers from the photographs were recorded on
the field data sheet with the sighting information.
Photo-identification methodology
All gray whale photographs of suitable quality were
compared to a catalogue of gray whales previously seen in
the PCFG as described in Calambokidis et al. (2012) by
CRC. If a photographed whale was matched to a catalogued
whale then the catalogue number of the whale was recorded.
If a match could not be made, and the photograph was of
sufficient quality, then the photographed whale was assigned
a new catalogue number. All catalogue numbers of sighted
gray whales were recorded in a database along with attributes
of the sighting such as date, time, water depth, location and
whale behaviour.
Data exploration
The three primary goals of this research were: (1) to increase
understanding of gray whale use of the study area; (2) to
document seasonal and annual fluctuations in the numbers
of whales using the study area; and (3) to assess fidelity of
whales to the study area. The analyses conducted could be
interpreted as achieving one or more of these goals but for
the purpose of explaining each method, and why it was
conducted, each method is listed by research goal. For all
analyses observations of uniquely identified whales were
used instead of all gray whale observations to prevent
pseudo-replication. Research effort and data collection was
not consistent in all years (as described above) and as a result
some analyses could not use all collected data whereas others
could (Table 1).
To address the goal of increasing understanding of gray
whale use of the study area four analyses were conducted.
The first analysis was to characterise the depth range and
habitat types where gray whales were observed. The second
analysis was to document the occurrence of new whales in
the study area. The purpose of this analysis was to determine
the turnover of individuals in the study area. New whales
were simply defined as whales not previously observed in
the study area although they may have been observed within
the PCFG in the past. For each year the number of new
whales observed and the proportion of those that were
observed to ‘recruit’ into the study area and be observed
again in a subsequent year were determined. The third
analysis documented how many calves were observed and
calculated an estimate of proportion of newly observed
whales that were calves (see Calf Analysis below). The last
analysis determined if there is population closure to the study
area. Calambokidis et al. (2010) concluded that gray whales
who utilise northwest Washington have fidelity to a region
at least as large as Oregon to Southern Vancouver Island.
Despite the findings of Calambokidis et al. (2010), domestic
processes for evaluating the impact of the proposed Makah
whale hunt still question what the local area should be
for analysis. To evaluate closure discovery curves were
constructed both for all whales observed and for whales that
were observed to have some fidelity to the area and were
observed in more than one year.
Two analyses were used to document seasonal and annual
fluctuations of whales in the study area. In the first analysis
J. CETACEAN RES. MANAGE. 16: 57–69, 2017 59
Table 1
Years of data used and justification for each analysis.
Analysis Years of data used Justification
Depth 1984–2011 All depths recorded were used for the analysis.
Temporal and spatial distribution
of sightings
1996–2011 Data prior to 1996 was not used for analysis because effort was opportunistic in nature and could
not be quantified to research segment.
Mapping 2004–2011 We used 2004–11 only because during prior years whale locations were not recorded precisely
leading to challenges in interpreting maps.
Fidelity to research area 1984–2011 All data was used.
Minimum tenure 1996–2011 Survey effort was standardised for 1996–2011 in all years but 2004 with effort throughout the
summer and fall feeding season.
Occurrence of new whales 1996–2011 All years were used in the analysis. Some of the analysis focused on 1996–2011 to ensure that new
whales were not whales that commonly use the study area but had not been ‘discovered’ yet.
Photo analysis of new whales 2004–2011 The analysis was performed at Makah Fisheries and only photographs after 2004 were available for
analysis.
Population closure in study area 1984–2011 All data was used.

all sightings were divided into five research segments
(Fig. 1). The five research segments were: (1) East Strait
(Sekiu Point to Third Beach); (2) Neah Bay Entrance (Third
Beach to Waadah Island); (3) West Strait (Waadah Island to
Tatoosh Island); (4) North Ocean (Tatoosh Island to Cape
Alava); and (5) South Ocean (Cape Alava to Sea Lion Rock).
The number of sightings were divided by the number of
surveys in the research segment and the length of the
research segment in km to standardise the number whales
observed per segment for comparison purposes, hereafter
this standardised sighting rate will be referred to as
‘observation rate’. Observation rates were compared by
month and year within each research segment using
ANOVA. The second analysis used was mapping and is
described in more detail below. The purpose of these
analyses was to provide a baseline of habitat use behaviour
in the area.
To evaluate gray whale fidelity to the study area, two
analyses on different temporal scales were used. Fidelity was
evaluated on an annual basis by analysing sighting histories
of individual whales to determine the proportion of individuals
that were observed in a subsequent year after being first
observed. The average percent of years whales were observed
in the study area was determined by dividing the number of
years each whale was seen in the study area by the number of
possible years it could have been observed in the study area.
Fidelity was also evaluated within each feeding season by
calculating the average ‘minimum residency time’ for each
identified individual by year. For this analysis, minimum
residency time was defined as the number of days between the
first and last day a whale was seen during the June through
November survey time period. The residency time estimate is
a minimum because it was possible that a whale was present
before the first day (or after the last day) it was sighted during
a given year. This estimate may also overestimate residency
time because whales could have left the survey area for some
unknown length of time between the first and last sighting of
the year. Minimum residency time calculations are sensitive
to the number of days of survey effort within a year and the
temporal distribution of surveys within the survey season.
Calambokidis et al. (2014) noted that whales observed in the
PCFG range during the summer can generally be described as
‘transient’ whales who are only observed in one year and then
not observed in the future and ‘PCFG whales’ who show some
level of fidelity to the IWC defined PCFG range. Fidelity
analyses were conducted both for all whales including
transients and for whales that have been seen in more than one
year. This analysis was conducted to determine a baseline of
gray whale fidelity to the area where hunts were planned.
Mapping
To analyse trends in monthly and annual gray whale use of
northwest Washington coastal water, the number of photo-
identifications made during a whale survey were mapped
onto a grid of 1km2cells that were aggregated into one of
five regions: (1) East Strait; (2) Neah Bay Entrance; (3) West
Strait; (4) North Ocean; and (5) South Ocean. Each of these
regions extended 2km offshore except the South Ocean
which extended 3km, and according to the survey protocol,
any survey effort in one of these regions was counted as a
full day of effort.
To develop spatial statistics for the survey effort, latitude/
longitude coordinates from whale sightings were spatially
joined to the 1km2grid in ArcGIS 10.1 and exported to MS
Excel where total whale counts per 1km2grid cell were
divided by the survey effort from the same monthly or yearly
period to determine sighting density of whales corrected for
effort. The sighting densities for each grid cell were re-
imported to ArcGIS and plotted as estimates of areal use by
gray whales. The grid cells with whale sighting density less
than 0.1 were ranked as ‘Rare’; cells with sighting density
greater than 0.1 but less than 0.3 were ranked as ‘Seldom’;
cells with sighting densities greater than 0.3 but less than 0.6
were ‘Common’; and cells with sighting density greater
than 0.6 were ranked as ‘Very Common’. This coding was
standardised for monthly and annual maps.
The objective of mapping was to document what areas
within the larger study area were most important to gray
whales and to document how use of those sites changed by
month and year.
Calf analysis
During the surveys a whale was recorded as a calf if it was
in close association with a much larger individual and
appeared to be less than 8m in length. It is possible that
calves weaned prior to when they were first observed in the
study area as cow-calf pairs in the PCFG have been observed
separated as early as the beginning of July (Calambokidis et
al., 2012). To make an estimate of what proportion of new
whales observed in the study area are calves, photographs
were analysed following methods developed by Bradford
et al. (2011). The analysis was limited to new whales in the
study area that were also seen in the PCFG for the first time
in that year. Only whales with suitable photo-quality of the
60 SCORDINO et al.: INDIVIDUAL GRAY WHALE USE OF COASTAL WATERS
Table 2
Number of gray whale dedicated surveys tallied by year for each segment
of research area and total opportunistic surveys by year.
East
Strait
West
Strait
North
Ocean
South
Ocean
Neah Bay
entrance
Opportunistic
surveys
1984 – – – – – 3
1986 – – – – – 10
1989 – – – – – 2
1992 – – – – – 2
1993 – – – – – 5
1994 – – – – – 7
1995 – – – – – 5
1996 13 32 23 7 40 5
1997* 22 54 38 14 63 6
1998 28 37 29 13 55 4
1999 14 23 17 15 30 1
2000 13 19 13 8 26 4
2001 12 15 15 10 28 1
2002 10 12 8 6 21 0
2003 15 19 15 8 27 0
2004 4 2 1 1 6 0
2005 11 17 14 6 21 1
2006 15 22 15 9 30 0
2007 13 19 11 8 27 1
2008 25 19 10 5 35 3
2009 23 22 12 7 32 0
2010 18 28 22 14 40 0
2011 11 29 24 18 35 1
Total 247 369 267 149 516 81
*20 surveys were conducted during effort to monitor the Makah setnet
fishery. All of these surveys transited the West Strait and into the
Northern Ocean research segment.

head and postcranial region were used for the analysis.
Whales with evidence of only recently attached barnacles,
no old barnacle scars, and white pigmentation mottling the
postcranial region were recorded as calves (Bradford et al.,
2011). The goal of this analysis was to determine how
important northwest Washington was as a site for cow-calf
pairs and for recently weaned calves.
RESULTS
Effort to photographically identify gray whales in northwest
Washington was conducted between 1984 and 2011. From
1996–2011, surveys were conducted on a more dedicated
and rigorous basis resulting in 516 surveys in the research
area. Survey effort was greatest from 1996–1998 and 2008–
11 (Table 2). By month, effort during dedicated surveys was
greatest in the late summer and early autumn (Table 3). The
majority of field effort during the autumn was conducted
within the Strait of Juan de Fuca due to weather conditions
in the Pacific Ocean and the distribution of gray whales.
Research effort resulted in the collection of photographs
from 225 gray whales that could be identified as unique
individuals during the months of June through November
from 1984 through 2011.
Gray whales were most often observed in water 5–15m
deep, often associated with either kelp forests or emergent
offshore rocks (Fig. 2). Sightings of gray whales in waters
greater than 20m or less than 5m were rare and were not
associated with any obvious habitat type (Fig. 2).
Temporal and spatial distributions of sightings
Gray whale distribution in the Strait of Juan de Fuca
(hereafter Strait) varied widely by month and year. Gray
whale use of feeding sites in the West Strait and East Strait
J. CETACEAN RES. MANAGE. 16: 57–69, 2017 61
Table 3
Number of surveys tallied by month for each segment of research area
during gray whale dedicated survey effort from 1996 through 2011.
East Strait
West Strait North Ocean
South Ocean
Neah Bay
entrance
Jun. 29 50 40 26 64
Jul. 43 78 59 34 99
Aug. 40 98 69 31 120
Sep. 56 79 57 31 114
Oct. 51 41 27 19 78
Nov. 28 23 15 8 41
Total 247 369 267 149 516
%
Fig. 2. Histogram of the count of gray whale identifications by depth binned
in 5m increments.
Fig. 3. Average observation rates in the three research segments in the Strait
of Juan de Fuca by month for the years 1996 to 2011. Error bars are two
times the SE.
Fig. 4. Average observation rates in the three research segments of the Strait of Juan de Fuca by year with months of the
feeding season, June to November, pooled. Error bars are 2 times standard error. * 2004 had much lower effort than other
years of the study.

research segments increased through the summer and early
autumn until use peaked in October (Fig. 3). The average
observation rate varied significantly between months in both
the West Strait (ANOVA, df = 368, p< 0.001) and the East
Strait (ANOVA, df = 246, p= 0.004) as the observation rate
increased from June to a peak in October. At the entrance to
Neah Bay, no significant differences in observation rate by
month were detected (ANOVA, df = 515, p = 0.73).
Significant differences in observation rate by year were
observed in the Strait of Juan de Fuca in all three research
segments (ANOVA: West Strait, df = 325, p< 0.001; Neah
Bay, df = 514, p< 0.001; East Strait, df = 249, p< 0.001)
(Fig. 4). From 1996 to 2003 (particularly 2000–03) and from
2010 through 2011, there were low observation rates in all
three of the research segments (Fig. 4). In contrast, the time
period 2004–09 had higher observation rates (Fig. 4).
Gray whale distribution in the Pacific Ocean (hereafter
Ocean) also varied by month and year. Within the North
Ocean survey area (Cape Flattery to Cape Alava), the
observation rate varied significantly by month (ANOVA,
df = 266, p= 0.001), peaking in August and with lows in
June and November (Fig. 5). In the South Ocean research
segment (Cape Alava to Sea Lion Rock), there were no
significant differences in observation rate by month
(ANOVA, df = 148, p= 0.34).
Similar to the Strait, significant year to year variability in
observation rate was observed in both ocean survey segments
(ANOVA: North Ocean, df = 266, p< 0.001; South Ocean,
df = 148, p< 0.001) (Fig. 6). Years of high and low
observation rates were not the same years as observed for
the Strait (Fig. 4, Fig. 6). Like the Strait survey areas, the
Ocean research segments had low observation rates during
the early years of the time series from 1996 to 2001.
Opposite the Strait, the observation rate increased in 2001
through 2003 and was also high in 2010 and 2011. The years
with greatest observation rates were 2005–11. The South
Ocean showed more year to year variability than the North
Ocean.
Maps were made using the average number of whales
identified per km2of research area to examine finer scale
trends in gray whale distributions in northwest Washington
by month and year. Trends observed in whale densities by
month reaffirm our findings that the number of gray whales
identified per survey increased to greatest densities and
greatest spatial coverage in September and October in the
Strait and in August and September in the North Ocean
(Fig. 7). Some sites were consistently used both in the Strait
and in the Ocean each month; whale densities at these sites
increased through the summer and into autumn in the Strait
62 SCORDINO et al.: INDIVIDUAL GRAY WHALE USE OF COASTAL WATERS
Fig. 5. Average observation rates in the two research segments of the Pacific
Ocean by month for the years 1996 to 2011, error bars are two times
standard error.
Fig. 6. Average observation rates in the two research segments of the Pacific Ocean by year for the months of the feeding
season, June to November. Error bars are two times standard error. *No surveys were conducted in the ocean in 2004.

J. CETACEAN RES. MANAGE. 16: 57–69, 2017 63
Fig. 7. Sighting density of gray whales identified per km2in northwest Washington per day of research effort in 2004
to 2011 by month: (a) June; (b) July; (c) August; (d) September; (e) October; and (f) November. Grid cells with
sighting densities of less than 0.1 whales were ranked as ‘Rare’, cells with sighting density greater than 0.1 and
less than 0.3 whales were ranked as ‘Seldom’, cells with sighting densities greater than 0.3 and less than 0.6 whales
were ranked as “Common” and cells with sighting densities greater than 0.6 whales were ranked as ‘Very Common’.

and increased until late summer/early autumn in the Ocean
(Fig. 7). A review of nautical charts and knowledge of
the area show that sites with high use were generally
characterised by rocky bottoms and large kelp forests,
whereas sites with low use were characterised by sandy
bottoms. The maps do show sightings of whales in areas of
sandy bottoms, however these sightings were primarily of
whales that were presumed to be travelling or resting. The
greater distance from shore of gray whale distributions in the
ocean as compared to the Strait was likely due to the gradual
slope of the bottom in the ocean as compared to the steep
drop off in the Strait.
Maps of the yearly distribution of whales display greater
variability in gray whale site use, where whales appeared to
use some areas frequently for a number of years and then
subsequently either abandon those areas or use them
intermittently (Fig. 8). This phenomenon can be observed by
examining the area just east of the Neah Bay research
segment. From 2006 to 2009, high densities of whales were
observed in this area and then were not observed using the
site at all in 2010 and only rarely in 2011. Other areas
appeared to be used intensively for one year and then not
used again. This can be seen most easily by looking at the
southern border of the South Ocean research segment and
noting the changes in gray whale sighting density through
the years.
Fidelity to the research area
Fidelity to the research area was examined by comparing the
number of individual whales that returned to the northwest
Washington research area after the first year observed and
estimating how long individual whales used the research area
within a given year. Some gray whales were observed to use
the waters of northwest Washington consistently after they
were first observed. Sixteen percent of whales were observed
in six or more years in the study area, although not
necessarily in consecutive years. Roughly half (51%) of the
whales identified in this study were only observed in the area
during one year (Fig. 9). The average whale was observed
in 2.48 years (SE = 0.14). Removing the individuals that
were only observed in one year, the average whale was seen
in 4.01 years (SE = 0.20). Whales first observed in 2010 or
earlier were observed in an average of 31.6% (SE = 1.6%)
of possible years after they were first observed (number of
years observed divided by total number of possible years to
be observed for each whale); removing whales only seen in
one year increased the average percentage to 38.7% (SE =
1.9%) of possible years. Among the whales that were first
identified prior to 2010 and therefore have more than one
year in which they could have been resighted, only two
whales were seen in all possible years after the first
observation; these whales were seen in every year after being
first observed in 2004 and 2006, respectively.
The length of time a whale used the study area during the
feeding season was estimated by calculating minimum
tenure, in this case the minimum number of days an
individual whale resided in the research area assumed to be
equal to the difference in time between the date of first and
last observation. The average minimum tenure calculated for
whales observed in the northwest Washington research area
64 SCORDINO et al.: INDIVIDUAL GRAY WHALE USE OF COASTAL WATERS
Fig. 8. Sighting density of gray whales identified per km2in northwest
Washington per day of research effort in the feeding season, June through
November by year: (a) 2005; (b) 2006; (c) 2007; (d) 2008; (e) 2009; (f)
2010; and (g) 2011. Grid cells with densities of less than 0.1 whales were
ranked as ‘Rare’, cells with sighting density greater than 0.1 and less than
0.3 whales were ranked as ‘Seldom’, cells with sighting densities greater
than 0.3 and less than 0.6 whales were ranked as ‘Common’ and cells
with sighting densities greater than 0.6 whales were ranked as ‘Very
Common’. No map was provided for 2004 because data collection lacked
spatial and temporal resolution.

was 24.8 days (range 1 to 151 days) out of a possible 183
days in the June to November feeding season. A large degree
of variability in minimum tenure by year was observed in
the research area (ANOVA, df = 493, p< 0.01) (Fig. 10).
No evidence was found that the number of years a whale
has been observed in northwest Washington affected average
minimum tenure during the study (ANOVA, df = 202,
p= 0.62) (Fig. 11). However, it was found that average
minimum tenure was a good predictor of whether a whale
would be seen in the following year. Whales seen in year Y
and in the following year (Y+1) had an average minimum
tenure of 28.3 days, which was significantly greater than
whales seen in year Ybut not year Y+1 (19 days; Two-sample
t-test, df = 506, p= 0.002).
Occurrence of new whales
From 1996 through to 2011, an average of 10.8 new whales
were observed per year (SE = 1.8) in the northwest
Washington study area. From 1996 through 2010 (excluding
2011 to allow a year for recruitment), an average of 5.6
new whales per year (SE = 1.1) were observed again in a
future year. The number of new whales observed was not
consistent between years. High numbers of new whales
(> 15) were observed in 1993, 1995, 1998, 2001, 2006 and
2008 (Table 4). It is possible that the high numbers of new
whales observed in 1993 and 1995 were not actually new
whales to the research area; rather it is likely that some of
these whales regularly used the area but had not been seen
previously due to low research effort in the early years of the
study. In a time series of population estimates, Calambokidis
et al. (2014) found a large increase in PCFG gray whale
abundance in the late 1990s and early 2000s that they
postulated was caused, at least in part, by immigration from
J. CETACEAN RES. MANAGE. 16: 57–69, 2017 65
Fig. 9. Count of unique whales observed by the number of years a whale
was observed.
Fig. 10. Average minimum tenure (residency time) computed as the number of days between the first and last sighting of an
individual in a given year. *2004 had lower total survey effort and lower temporal coverage of survey effort than other
years, and the estimate of minimum tenure is likely underestimated.
Fig. 11. Average minimum tenure of whales in days compared to the number
of years they have been observed in northwest Washington.

northern feeding grounds during the 1999/2000 mortality
event (Gulland et al., 2005). Based on the findings of
Calambokidis et al. (2014) a large increase in the number of
new whales observed and of new whales observed in a future
year during the time period of 1998–2002 was to be
expected. Instead, the average number of new whales
observed from 1998–2002 was lower than the 1996–2010
average, with 9.2 new whales (SE = 4.3) of which 4.3 whales
(SE = 1.5) were seen in a future year. The percentage on
average of new whales observed from 1998–2002 that were
seen in a future year (44.3%, SE = 18.4%) was also lower
than the 1996–2010 average.
Calf analysis
There were seven mother-calf pairs observed during surveys
(Table 5), showing that some of the new whales observed in
this study were internally recruited. One mother, CRC 67,
was observed with three calves: a suspected calf (CRC 169)
in 1995 and a confirmed calf in both 2004 (CRC 819) and
2011 (CRC 1350). Four other females were each observed
with one calf (Table 5).
Some new whales were first observed later in the year (i.e.
autumn) than when calves become independent of their
mothers (Bradford et al., 2011; Calambokidis et al., 2012).
To determine the proportion of new whales which are
actually calves digital photographs taken between 2004
and 2011 were analysed. Only new whales for which
photographs had already been obtained from the first year
they were seen in the entire PCFG (i.e. not just the first year
seen in northwest Washington) were analysed. Twenty one
photographs of new whales for which the first year they were
sighted in northwest Washington was also the first year they
were sighted in the PCFG were available. Of those, 18
photographs showed the head and post-cranial region clearly
in order to be able assess if they were calves. Of the 18
whales evaluated, 4 (22%) were either confirmed calves
(CRC 819 and CRC 1350) or were most likely calves (CRC
1047 and CRC 1054) and the other 14, based primarily on
observation of old barnacle scars, were not calves of that
year. CRC 1047 and CRC 1054 were both first observed in
2008.
The occurrence of calves in northwest Washington shows
that the site is used by cow-calf pairs and recently weaned
calves. The number of calves observed during the study were
low suggesting that the site is not a very important for cow-
calf pairs for the PCFG as a whole although it does appear
important for CRC 67.
Population closure in the study area
If population closure exists within the study area (no
immigration or emigration), one would expect that over the
17 years of research effort that all of the whales in the
‘population’ would have been photographed and identified
and the best fit line would approach a horizontal asymptote.
To test if there is closure a discovery curve was plotted with
the number of new whales observed for 1984 through 2011
and the number of whales observed in more than one year
for 1984 through 2010 (Fig. 12). The function best fitting the
discovery curve was linear for all new whales (y= 9.15x–
66 SCORDINO et al.: INDIVIDUAL GRAY WHALE USE OF COASTAL WATERS
Table 4
This table shows the sighting history of whales by the first year they were observed (row). Column totals report the number of uniquely identified whales
from each cohort in each feeding season. The first value in each row is the number of new whales observed for that year.
Year 1984
1986 1989
1992
1993 1994 1995
1996
1997 1998
1999
2000 2001 2002
2003
2004 2005
2006
2007
2008
2009
2010
2011
1984 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1986 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0
1989 4 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0
1992 2 0 1 1 2 2 0 1 0 0 0 0 1 1 1 0 0 0 0 1
1993 21 4 4 4 4 10 4 1 3 1 3 1 4 4 2 6 5 1 2
1994 5 2 0 1 1 0 0 1 1 1 0 0 1 1 1 0 1 0
1995 15 5 7 2 1 0 2 0 0 0 3 2 2 3 1 0 0
1996 8 4 3 2 1 1 0 1 1 1 4 0 3 4 1 2
1997 8 1 1 0 1 0 1 1 2 1 1 1 1 0 0
1998 17 1 1 1 0 0 0 0 2 1 2 0 1 0
1999 1 0 0 0 0 0 0 0 0 0 0 0 0
2000 11 6 3 2 0 2 5 1 5 3 4 3
2001 16 2 2 1 0 1 0 1 1 0 0
2002 1 1 1 1 1 0 1 1 1 1
2003 11 3 2 3 0 1 1 2 1
2004 12 7 7 3 7 5 3 5
2005 10 4 2 3 2 1 1
2006 20 5 10 7 4 6
2007 2 1 2 0 1
2008 29 11 3 3
2009 11 1 1
2010 4 1
2011 11
Total
2 4 4 2 21 10 22 19 27 35 11 14 32 8 22 21 33 56 20 74 56 27 39
%
Table 5
All known mother-calf pairs observed in northwest Washington from
1984–2011 with whales only suspected to be calves noted with an
asterisk.
Mother Calf Dates observed together
105 104 09/07/94
43 107 09/07/94 to 04/08/94
67 169* 19/07/95 to 23/07/95
596 595 26/06/01
216 860* 26/07/03 to 28/07/03
67 819 27/08/04
67 1350 23/06/11 to 01/09/11
&

18,193, r2= 0.95) and whales observed in more than one year
(y= 5.07x–10,076, r2= 0.97), suggesting that closure is not
occurring for the northwest Washington survey area.
DISCUSSION
Temporal and spatial distribution of whales
There was large annual variability in the numbers of whales
identified per survey in all research segments and large
amounts of inter-year and intra-year variability in where
whales were observed. Observation of variability is similar
to Darling et al. (1998) who concluded that year-to-year
variability in timing, prey type and feeding location is the
key feature of gray whale observations from the central coast
of Vancouver Island. Gray whale researchers of the PCFG
have noted that the whales are commonly observed to exhibit
benthic feeding behaviours (Avery and Hawkinson, 1992;
Darling et al., 1998; Dunham and Duffas, 2001; Kvitek and
Oliver, 1986; Oliver et al., 1984). However, in the present
study mud plumes were rarely observed, suggesting that
benthic feeding is uncommon in the northwest Washington
area. Within the dynamic nature of site use it was found that
more whales were observed per day of survey effort in the
autumn in both the Strait of Juan de Fuca and the South
Ocean research segment, whereas in the North Ocean
research segment peak use was late summer. Also, the vast
majority of gray whales were observed in waters between 5
and 15m of depth. This depth range coincides with the
primary depth range of the mysid shrimp (small epibenthic
and planktonic crustaceans of the family mysidae, suborder
pericarida) (Nelson et al., 2009). The primary mysid species
consumed by gray whales off Vancouver Island were
Holmesimysis sculpta, Acanthomysis pseudomaropsis and
A. anassa californiensis (Murrison et al., 1984; Darling
et al., 1998; Dunham and Duffus, 2002; Feyrer and Duffas,
2011) and they are also likely to be the primary prey species
in northwest Washington. Feyrer and Duffus (2011) found
that average mysid density was significantly correlated with
the average number of whales in the survey area near
Vancouver Island. We hypothesise that shifting mysid
density and fluctuations in abundance caused the observed
variability in gray whale counts in northwest Washington
since most of the gray whale sightings occurred in optimal
mysid habitat. Systematically monitoring prey at sites
commonly used in northwest Washington would allow
testing of this hypotheses on prey preference and specifically
the influence of mysid abundance on whale distributions.
A consistent pattern observed through the years was lower
observation rates in June compared to later in summer and
autumn. This fits with the movements of migrating gray
whales which generally reach Arctic feeding grounds from
May to June (Swartz et al., 2006). To date, there have been
three publications on the movements of six satellite tagged
PCFG whales, each of which had active tags between April
and June; of these six whales, four were observed to migrate
steadily north into southeast Alaska before their transmitters
stopped transmitting (Calambokidis et al., 2014; Ford et al.,
2013; Mate et al., 2010). Given that 66% (4 out of 6) of the
PCFG whales with documented spring movement patterns
travelled north of the PCFG area, it is quite possible that other
whales that feed in the PCFG also feed further north in the
spring and early summer before returning south to the PCFG
area later in the summer and autumn. It should be noted that
the migratory behaviour of four of the six individuals may not
be representative of all PCFG whales, as the three tags applied
by Ford et al. (2013) targeted whales presumed to be migrating
past Vancouver Island and one tag applied to a PCFG whale
by Calambokidis et al. (2014) targeted a feeding whale.
Occurrence of new whales in northwest Washington
From 1996 to 2011, an average of 10.8 new whales were
observed each year, of which 5.6 were observed in a future
year. Many of the whales that were new to the northwest
Washington study area had been seen previously in another
research area of the PCFG. For whales that were
photographed in northwest Washington during the first year
they were seen in the PCFG, analysis of photographs using
techniques described by Bradford et al. (2011) found that
22% of the whales were calves. Thus 78% of the new whales
observed in our research area and to the PCFG were either
born in a previous year in the PCFG and were not observed,
or were non-calves who emigrated from another feeding area
into the PCFG.
An analysis of the time series of population estimates of
PCFG whales shows a large increase in the number of whales
in the PCFG from 1998 through 2002 concurrent with the
timing of the 1999 gray whale mortality event (Calambokidis
et al., 2014). Somewhat surprisingly, a smaller average of
new whales (9.2) was observed from 1998 to 2002. The
lower number of new whales observed in that time period
could have been a result of poorer feeding conditions in
Washington compared to later years in the data series. Of the
new whales observed during those five years, a smaller
portion was observed again in a subsequent year (44.3%)
than the average for the whole data series. Based on the
calculated population increase of the overall PCFG, we
would have expected the average proportion of new whales
and new whales seen in more than one year to be much
greater from 1998 to 2002 than was observed in this study.
J. CETACEAN RES. MANAGE. 16: 57–69, 2017 67
Fig. 12. Plot of the cumulative number of whales observed during the
duration of this project for all whales (black dots) and whales observed
in greater than one year (grey squares).

CONCLUSION
Northwest Washington is a small but important region within
the summer and autumn feeding range of PCFG gray whales.
Individual gray whale use of this region is variable, with
some individuals observed regularly whereas most do not
show strong site fidelity to this region. This study allowed
examination of trends in site use over multiple decades
within northwest Washington and it was found that rocky
habitat in the 5–15m depth range is very important to gray
whales and that gray whale use of these habitats is dynamic
by year. The impacts of the Makah gray whale hunt are a
debated issue, thus it is hoped that the baseline of gray whale
behaviour provided here can be used to help evaluate if there
are discernible effects on PCFG whale behaviour in the
proposed hunt area when hunting resumes.
ACKNOWLEDGEMENTS
Field work by the Makah Tribe was funded by the Species
Recovery Grant to Tribes Program and the Bureau of Indian
Affairs. Field work by the National Marine Mammal
Laboratory was funded by NOAAs Northwest Regional
Office. We would like to thank the many people who have
contributed to data collection during the many years of this
project. We would especially like to thank Nate Pamplin who
was the primary investigator for the Makah Tribe from 2004–
06. Matching of identification photographs at Cascadia was
led by Amber Klimek and Alie Perez. Research was
conducted under permits 540–1502, 540–1811 and 16111 to
John Calambokidis and permits 782–1438, 782–1719 and
14245 to the National Marine Mammal Laboratory.
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