NOAA Technical Memorandum NMFS-AFSC-218

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

March 2011

by

M. E. Lander, D. S. Johnson, J. T. Sterling, T. S. Gelatt, and B. S. Fadely

Diving Behaviors and Movements

of Juvenile Steller Sea Lions

(Eumetopias jubatus) Captured in the

Central Aleutian Islands, April 2005
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service's Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The NMFS-NWFSC series is currently used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Lander, M. E., D. S. Johnson, J. T. Sterling, T. S. Gelatt, and

B. S. Fadely. 2011. Diving behaviors and movements of juvenile Steller

sea lions (Eumetopias jubatus) captured in the central Aleutian Islands,

April 2005. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-218,

41 p.

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
March 2011

NOAA Technical Memorandum NMFS-AFSC-218

by

 M. E. Lander, D. S. Johnson, J. T. Sterling, T. S. Gelatt, and,

B. S. Fadely

Diving Behaviors and Movements

of Juvenile Steller Sea Lions

(Eumetopias jubatus) Captured in the

Central Aleutian Islands, April 2005

Alaska Fisheries Science Center

7600 Sand Point Way N.E.

Seattle, WA 98115

www.afsc.noaa.gov

U.S. DEPARTMENT OF COMMERCE

Gary F. Locke, Secretary

National Oceanic and Atmospheric Administration

 Jane Lubchenco, Under Secretary and Administrator

National Marine Fisheries Service

Eric C. Schwaab, Assistant Administrator for Fisheries
This document is available to the public through: 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

www.ntis.gov 
iii 

ABSTRACT 

Population counts and pup production for Steller sea lions (Eumetopias jubatus) in the 

central Aleutian Islands (CAI) of the western distinct population segment (wDPS) continue to 

decline for unknown reasons. Due to paucity of telemetry data for this region, satellite-linked 

depth recorders were deployed on 16 juvenile Steller sea lions from 19 April to 2 May 2005 to 

gain a better understanding of their diving behaviors and habitat use. Overall, depths of dives (n 

= 89,993, x = 11.8 m, SD = 12.6, med = 8.0, and range = 5.0 to 255.0), durations of dives (n = 

155,620, x = 0.8 min, SD = 0.6, med = 0.5, and range = 0.5 to > 13.0), trip durations (n = 553, 

x = 14.0 hours, SD = 19.6, med = 10.7, and range = 0.3 to 280.0), and shore durations (n = 589, 

x = 10.5 hours, SD = 7.1, med = 10.7, and range = 1.0 to 58.7) were similar to findings for 

Steller sea lions previously tagged in the CAI. Diel behaviors, ontogenetic trends, and 

movements displayed by juvenile Steller sea lions also were similar to past accounts. Relative to 

data reported for Steller sea lions from the eastern DPS, however, trip durations of sea lions 

reported herein were longer, whereas depths of dives were shallower and durations of dives were 

shorter. 

A continuous-time correlated random walk model that was applied to the telemetry data 

was used to examine areas of predicted diving activity with respect to Steller sea lion designated 

critical habitat. Overall, the proportions of predicted locations associated with diving to > 4 m 

within zones of critical habitat appeared to reflect the proportions of Argos data well and results 

were similar to other reports. Additional models will be useful for examining sea lion 

movements and diving behaviors among regions and with respect to spatial management 

measures and environmental features. 
 
v 

 

CONTENTS 

ABSTRACT ................................................................................................................................... iii 

INTRODUCTION .......................................................................................................................... 1 

MATERIALS AND METHODS .................................................................................................... 2 

Diving Behaviors......................................................................................................................... 4 

Trip Durations ............................................................................................................................. 5 

Movements .................................................................................................................................. 5 

RESULTS ....................................................................................................................................... 7 

Diving Behaviors......................................................................................................................... 7 

Trip Durations ............................................................................................................................. 8 

Summary of Steller Sea Lion Movements .................................................................................. 8 

Individual Movement Models ................................................................................................... 10 

DISCUSSION ............................................................................................................................... 11 

ACKNOWLEDGMENTS ............................................................................................................ 15

CITATIONS ................................................................................................................................. 17 

INTRODUCTION 

From the late 1970s to the early 1990s, the endangered western distinct population 

segment (wDPS) of Steller sea lions (Eumetopias jubatus) in the United States declined to less 

than 75,000 animals, equating to a reduction of approximately 80% (Loughlin 1998, Calkins 

et al. 1999). Initially, a precipitous decline was observed during the 1970s in the eastern Aleutian 

Islands (Braham et al. 1980) and then it spread east to the central Gulf of Alaska and west to the 

central Aleutian Islands (CAI) during the late 1980s (Merrick et al. 1987). The rate of decline 

decreased during the 1990s (NRC 2003) and from a regional perspective, rates of decline were 

greater at the fringes of the wDPS’ geographical range than at the center (Fritz et al. 2008). 

Population trends, which are dependent on the temporal scale examined, have varied 

among sub-regions of the U.S. wDPS, including the eastern, central, and western Gulf of Alaska, 

and eastern, central, and western Aleutian Islands (including the eastern Bering Sea). Overall, the 

population of Steller sea lions has stabilized in many areas since 2002 (Sease and Gudmundson 

2002), but recent trends in the western Aleutian Islands (WAI) and western CAI have been 

negative, suggesting a stable or slight negative trend for the population as a whole (Fritz et al. 

2008). Over the past decade counts of non-pups in the CAI appeared to be stable for a brief 

period (i.e., 2000-2004; Fritz and Stinchcomb 2005, Lander et al. 2009), but recent trends 

indicate the population has since declined by 16% from 2004 to 2008 (Fritz et al. 2008). Within 

the CAI, however, there were different trends west and east of 178°W (Tanaga Island, Samalga 

Pass). West of this apparent boundary, counts continuously decreased from 2000 to 2008, 

whereas east of this boundary counts increased by 15% from 2000 to 2004, but then declined by 

17% through 2008 (Fritz et al. 2008). Similar to non-pups, 178°W also separates declining pup 
2 

numbers in the west (Delarof and Rat Islands) from stable or slightly increasing pup numbers in 

the east (Andreanof and Fox Islands). Overall, however, pup production in the CAI has declined 

at a rate of 1.6% per year since 1994 (DeMaster 2009) and 0.9% per year since 2000 (NMFS 

2010). 

Factors causing the decline or limiting the recovery of Steller sea lions in western Alaska 

are not well understood, but understanding the foraging behaviors and habitat requirements of 

animals from this area are necessary for assessing the effects of top-down and bottom-up forces 

on the population. This information is also critical for evaluating the efficacy of management and 

conservation efforts (NMFS 1992, NMFS 2000, NRC 2003), but unfortunately, telemetry data 

from these areas are limited (Loughlin et al. 2003, Fadely et al. 2005, Rehberg 2005, Call et al. 

2007, Lander et al. 2009). To address this need, satellite transmitters were deployed on juvenile 

Steller sea lions in the CAI during the spring of 2005 as part of an on-going study by the 

National Marine Mammal Laboratory (NMML) and Alaska Department of Fish and Game 

(ADF&G) to compare sea lion habitat use and behavior between the wDPS and eastern DPS 

(eDPS). This report summarizes the diving behaviors, trip durations, and movements of those 

animals. Additionally, these data were examined with respect to Steller sea lion designated 

critical habitat. 

MATERIALS AND METHODS 

From April to May 2005, juvenile Steller sea lions were opportunistically captured using 

hoop nets on land or SCUBA methodologies as described in McAllister et al. (2001) at haul-out 

sites within the CAI. Satellite-linked depth recorders (SDR-T16, 13.5 x 4.5 x 3.7 cm, 330 g; 

Wildlife Computers Ltd., Redmond, WA) were attached to the dorsum of each animal using 5-
3 

minute epoxy (Devcon products, Riviera Beach, FL) while they were anesthetized following 

procedures of Heath et al. (1997). All transmitters were optimized to provide locations at sea and 

on land and to transmit three classes of messages including dive histograms, timelines, and status 

messages. All data were obtained through Service Argos, Inc., a satellite-based location and data 

collection system (Argos 1996) and decoded using Satpak software (Wildlife Computers Inc., 

Redmond, WA). For dive histograms, SDRs were programmed to summarize and store 

information for dive durations, maximum dive depths, and time at depth (TAD) into 14 bins, 

each of which contained counts for a given range of depth or duration (Merrick et al. 1994, 

Merrick and Loughlin 1997). Upper bounds of maximum duration histograms were 1, 2, 3, 4, 5, 

6, 7, 8, 9, 10, 11, 12, 13, and > 13 minutes. Upper bounds of maximum depth histograms were 4, 

6, 10, 20, 34, 50, 74, 100, 124, 150, 174, 200, 250, and > 250 m, whereas upper bounds of TAD 

histograms were 0, 4, 6, 10, 20, 34, 50, 74, 100, 124, 150, 174, 200, and > 200 m. Duration and 

depth histogram bins contained the number of dives that fell within the bin’s range, whereas the 

count within each TAD histogram bin represented the fraction of the 6-hour period that the 

animal spent in each depth range. Setting the upper bound of the first data bin to 0 for TAD bins 

allowed for calculating the percentage of time spent hauled out for each 6-hour period. Counts of 

dives were further accumulated into four 6-hour periods (period 0 = 13:00–18:59, period 1 = 

19:00–00:59, period 2 = 01:00–6:59, period 3 = 07:00–12:59; Greenwich Mean Time) per day, 

which were converted to local time (period 0 = 21:00–02:59, period 1 = 03:00–08:59, period 2 = 

09:00–14:59, and period 3 = 15:00–20:59). 

The SDRs, which were equipped with a saltwater switch to assess conductivity readings 

every 20 minutes, recorded whether the majority of those readings were “dry” or “wet.” These 

data were compiled into timeline messages detailing when the animals were dry (hauled out) or 
4 

wet (at sea) for 20-minute increments every 24 hours. Additionally, status messages provided 

information on the operating conditions of the SDR along with the maximum depth recorded for 

24-hour periods (Wildlife Computers 1997). 

Diving Behaviors 

Only dives exceeding 4 m in depth were considered a dive and mean (± 1 SD) and 

median dive depth and duration were calculated for each animal by summing counts of dives 

from the histograms and using the range midpoint of each bin as the depth or duration for all 

dives in that bin (Merrick et al. 1994, Merrick and Loughlin 1997). Furthermore, daily maximum 

dive depths obtained from the status messages were examined with respect to day of the year 

(also accounting for age) and corresponding percentage of the moon's visible illuminated disk for 

the CAI (Naval Oceanography Portal; http://www.usno.navy.mil/) using a two-step process. 

First, the presence/absence of maximum depth data was examined with respect to day of year 

and moon phase using generalized linear mixed models (binomial family; package lme4, R 

Development Core Team 2006). Secondly, for those days containing a maximum depth data 

point, the data were log transformed and also examined with respect to day of year and moon 

data using generalized linear mixed models (Gaussian family, package lme4). Individual sea lion 

was included as a random effect in all models and response variables were examined with 

respect to independent predictor variables, additive predictor variables, and full models. Akaike’s 

information criterion (AIC) was used for model selection. 
5 

Trip Durations 

Means (± 1 SD) and medians of trip and shore durations were calculated for each animal 

after extracting data (departure and arrival times at haulouts) from the timeline messages using 

the algorithm described in Call et al. (2007). 

Movements 

All daily locations from SDRs were filtered using a swim speed of 2 m/s with the 

algorithm described by McConnell et al. (1992) after deleting duplicate and Z locations. 

Timeline data, status messages, and dive data were used to determine if locations were on shore, 

at sea, or at sea with assumed diving activity. All locations associated with diving > 4 m were 

pooled among individuals, projected to an Albers equal-area conic projection defined for the 

state of Alaska, plotted, summarized, and examined within zones of designated critical habitat 

for Steller sea lions (50 CFR 226.202), including 0-3 nautical miles (nmi), 3-10 nmi, and 

10-20 nmi from the nearest major haulout or rookery and three large offshore foraging areas 

around Shelikof Strait, Bogoslof, and Seguam Pass (ArcMap 9.3, ESRI, Redlands, CA). To be 

consistent with previous analyses, locations within the 0-3 nmi and 3-10 nmi zones were pooled 

to form one 0-10 nmi zone. The GIS shape files used for the analysis (akland and 

Steller_10_20_Transit_Forage) are described in NMFS (2003). 

To further examine the movements of sea lions, the filtered data were processed with a 

continuous-time correlated random walk (CTCRW) model as described in Johnston et al. (2008). 

This model is incorporated into a state-space model framework with a Kalman filter and was 
6 

used to predict uniformly spaced animal locations for 20 minute intervals (Johnson et al. 2008). 

This model allowed for inclusion of measurement error in telemetry locations and parameter 

estimation using maximum likelihood (Johnson et al. 2008). In addition to the dry time covariate 

described in Johnson et al. (2008), the model was also generalized to account for the frequency 

of diving while at sea by allocating the number of dives reported for each 6 hour period to each 

20 minute interval defined as “wet” within that period. For periods reported as dry, but dive data 

were collected, the dry time covariate was assigned a value of 0.5 for all 20 minute intervals 

within that period. Because the CTCRW model performs poorly with missing covariate data, 

dive frequencies for all missing periods for each individual were predicted from a generalized 

additive model (GAM) that fit dive frequency as a function of day of year (with integrated 

smoothness estimation) and period (quasiPoisson family, R 2.4.1, R Development Core Team 

2006). Period of day was included as a predictor variable in the model because previous studies 

of juvenile Steller sea lions indicated most diving activity occurred during night when sea lions 

may have been foraging on vertically migrating prey (Loughlin et al. 2003, Fadely et al. 2005, 

Call et al. 2007, Lander et al. 2010). 

All predicted locations that were generated with the CTCRW model were pooled among 

individuals. Predicted locations associated with diving to > 4 m as well as predicted locations 

associated with periods containing a dive frequency greater than the average frequency were also 

examined within zones of designated critical habitat for Steller sea lions outlined above (ArcMap 

9.3). To illustrate the full range of uncertainty in the individual movement models (due to 

location error), 20 tracks were sampled from the posterior distribution of 100 simulations of the 

fitted CTCRW models and plotted (R Development Core Team 2006). 
7 

RESULTS 

Satellite depth recorders were deployed on 16 juvenile (10.5 months at capture) Steller 

sea lions (n = 7 F, 9 M) from six locations within the CAI from 19 April to 2 May 2005 (Table 1, 

Fig. 1). Deployment periods lasted an average of 43 days (SD = 23, range = 8 to 90). 

Diving Behaviors 

Overall, depths of dives (n = 89,993) averaged 11.8 ± 12.6 m (med = 8.0) and ranged 

from 5.0 to 255.0 m (range of means = 5.4 to 15.9, SD = 3.0; Table 2), whereas durations of 

dives (n = 155,620) averaged 0.8 ± 0.6 minutes (med = 0.5) and ranged from 0.5 to > 13.0 

minutes (range of means = 0.6 to 1.0, SD = 0.1; Table 2). The majority of dives occurred during 

nocturnal hours (period 0, 21:00 – 2:59 local time; Fig. 2). Additionally, a greater percentage of 

time at depth occurred at night, whereas a greater percentage of time was spent hauled out during 

the day (period 2, 9:00-14:59; Fig. 3). 

Model selection indicated that day of year was the best covariate for predicting whether 

juvenile Steller sea lions displayed any diving activity (Table 3). In other words, juvenile sea 

lions had an increased probability of diving at least once a day over time (and with age). 

Additionally, maximum depth increased with day of year, but maximum dive depths also 

become shallower as a greater percentage of the moon was illuminated (Table 3). The latter 

inverse relationship appeared more apparent as sea lions became slightly older (Fig. 4). 
8 

Trip Durations 

Overall, pooled trip durations (n = 553) at sea ranged from 0.3 to 280.0 hours ( x = 14.0, 

med = 10.7, SD = 19.6), whereas shore durations (n = 589) ranged from 1.0 to 58.7 hours ( x = 

10.5, med = 10.7, SD = 7.1). From an individual perspective, mean trip durations ranged from 

7.0 to 35.9 hours and mean shore durations ranged from 8.7 to 14.5 hours (Table 4). Similar to 

the dive data, median values are also provided because the data were skewed (Table 4). 

Summary of Steller Sea Lion Movements 

Steller sea lions were captured at six different haul-out sites (Table 1). Two Steller sea 

lions (DBID 11246 and 11247) were captured and tagged at Silak Island. DBID 11246 remained 

at Silak Island for approximately 5 weeks before traveling around Chaika Rock to Ragged Point, 

Sharp Cape, and Kaga Point on Kagalaska Island. With the exception of a few sporadic 

locations, this animal remained on the continental shelf within the 100 m isobath. Unlike DBID 

11246, DBID 11247 remained around Silak Island for the duration of the deployment period. 

Only one Steller sea lion (DBID 11248) was captured and tagged at Little Tanaga Strait. 

That animal first moved to Oglala Point, Kagalaska Island for a couple of days before spending 

the rest of his time near Cape Azamis, Little Tanaga Island. 

Half of the Steller sea lions were captured and tagged at Lake Point, Adak Island and 

movements varied among individuals. Two animals (DBID 11250 and 11252) remained at Lake 

Point, one animal (DBID 11253) made multiple trips from Lake Point to many points of interest 

around the perimeter of Kanaga Island (Round Head, Ship Rock, Eddy Rock, and Capes 

Chlanak, Chunu, and Tusikand), and one animal (DBID 11262) swam over to Ship Rock, 
9 

Kanaga Island 3 days after being tagged to remain within the general vicinity of that area. The 

remaining four animals (DBID 11249, 11251, 11260, and 11261) tagged at Lake Point traveled 

to multiple islands and displayed some longer ranging movements. For example, DBID 11249 

remained near Lake Point and Cape Yakak for approximately 3 weeks before heading north to 

Eddy Island (between Argonne and Careful Points, Adak Island). He then proceeded to travel 

over the northernmost point of Adak Island (between Capes Kigua and Adagdak) and over to the 

northern area of Great Sitkin Island. He then made a brief trip south to Anagaksik Island, headed 

north to Asuksak Island, and west to Little Tanaga Island (Cape Lises), Kagalaska Island (Black 

Point), and Adak Island. DBID 11251 remained close to Lake Point for 2 weeks before traveling 

to northern Adak Island, spending substantial time at Capes Kiguga and Moffett. He then moved 

north to the eastern side of Great Sitkin Island (between Teapot Rock and Sulphur Point), spent a 

few days in Great Sitkin Pass, and then traveled to Tagalak and surrounding islands for the 

remainder of transmitter life (with the exception of a quick trip to western Atka Island). The 

remaining two sea lions (DBID 11260 and 11261) made trips into pelagic waters. DBID 11260 

traveled from Lake Point over northern Great Sitkin Island, proceeded south to swim the 

perimeter of Igitkin Island, before turning back to Great Sitkin Island. DBID 11260 then went on 

a 6-day trip to sea, approximately 200 km from Atkin Island and then spent the remainder of his 

time around western Atkin Island. DBID 11261 remained at Adak Island for almost 2 weeks 

before going to sea for 13 days, approximately 435 km north of Cape Adagdak, Adak Island, 

over the waters of Bowers Ridge. He then traveled back down around the southern end of 

Semisopochnoi Island before resting on Tanaga Island for a few days. This male sea lion then 

embarked on an 11-day trip to Buldir Island, looping widely north of Semisopochnoi Island and 

then swam south (bypassing Buldir Island) into waters south of the Near Islands, before turning 
10 

back to Buldir Island. He remained there for 3 days before taking a 2-day trip over to Shemya 

Island and remained around the Semichi Islands until signal cessation. 

Two Steller sea lions (DBID 11255 and 11256) were captured and tagged at Ship Rock, 

Kanaga Island. DBID 11255 primarily remained along the shoreline within ~ 8 km of Ship Rock, 

whereas DBID 11256 used areas similar to those of DBID 11253 around the perimeter of 

Kanaga Island. 

Two Steller sea lions (DBID 11257 and 11258) were captured and tagged at Kagalaska 

Island. DBID 11257 traveled from Kagalaska Island to Crone Island (south of Adak Island), 

before heading over to Capes Kagigikak and Yakak. DBID 11258 traveled to Quail Bay 

(southern Kagalska Island) and over to Little Tanaga (Cape Chisak) and Chisak Islands before 

settling at Lake Point, Adak Island. 

Lastly, a single Steller sea lion (DBID 11259) was captured and tagged at Semisopochnoi 

Island and remained near shore around the northern area of the island. 

Individual Movement Models 

A total of 5,233 locations from the 16 sea lions was obtained from Service Argos, Inc. 

( x = 327 locations per individual, SD = 215, range = 77 to 757), 4,044 locations were retained 

after filtering the data ( x = 253, SD = 163, range = 60 to 581), and 2,839 locations were 

associated with diving to > 4 m ( x = 177, SD = 128, range = 12 to 429; Fig. 5). A total of 41,958 

predicted locations was generated using the CTCRW ( x = 2,622 locations per individual, SD = 

1,493, range = 502 to 6,232; Fig. 6), 26,878 of which were locations associated with diving to 

> 4 m ( x = 1,680, SD = 1,147, range = 241 to 4,388; Figs. 6 and 8), and 9,243 of which were 
11 

locations associated with periods during which the frequency of diving exceeded more than the 

average frequency ( x = 578, SD = 453, range = 88 to 1,613; Figs. 7 and 8). The CTCRW had to 

be modified (i.e., set to mimic Brownian Motion) for five individuals (DBID 11246, 11247, 

11250, 11252, and 11262), possibly due to limited data or the lack of directional persistence 

relative to the amount of data collected. 

Plotting all of the data sets with respect to designated critical habitat illustrated that only 

a slightly greater proportion of locations occurred farther from shore as the data became more 

detailed (i.e., ranging from filtered Argos locations to enhanced foraging locations; Table 5). 

Plots depicting the uncertainty of predicted data sets are illustrated in Figure 9. 

DISCUSSION 

Collectively, the data summarized for this report corroborated findings for Steller sea 

lions previously tagged in the CAI (Loughlin et al. 2003, Fadely et al. 2005, Rehberg 2005, Call 

et al. 2007, Rehberg and Burns 2008, Lander et al. 2010). Dive statistics, diel behaviors, 

ontogenetic trends, trip durations, and movements reported here were similar to past accounts 

despite the annual differences in data collection. With a few exceptions, dives conducted by 

juvenile Steller sea lions from the CAI were generally short and shallow; deeper diving occurred 

during nocturnal hours as did a greater proportion of diving activity (Loughlin et al. 2003, 

Rehberg and Burns 2008, Lander et al. 2010). Depths of daily maximum dives increased 

significantly with age (Pitcher et al. 2005), but this relationship was confounded by lunar 

illumination. 
12 

Daily maximum dives of Steller sea lions were examined with respect to lunar data 

because not only did they increase over time when plotted, but they appeared cyclical. Unlike 

other pinniped studies (Horning and Trillmich 1999, Lea et al. 2010), daily maximum depth was 

inversely related to lunar illumination. This was unexpected for a predator reputed for feeding on 

shallow, vertically migrating prey such as walleye pollock (Theragra chalcogramma), which 

tend to rise in the water column during the night (Sinclair et al. 1994). However, Atka mackerel 

(Pleurogrammus monopterygius), which comprise a large portion of the diet for sea lions from 

the CAI (Sinclair and Zeppelin 2002, Call and Loughlin 2005, Lander et al. 2009), display 

opposite behaviors. For example, Nichol and Somerton (2002) used archival tags to relate the 

diurnal vertical migration of Atka mackerel to light intensity and found a positive relationship. 

Additionally, Atka mackerel displayed surface directed vertical excursions only during diurnal 

hours and little to no vertical migration during night (Nichol and Somerton 2002). Hence, if the 

deepest of dives performed by Steller sea lions indicate when they are targeting Atka mackerel, it 

makes sense that they will be deeper as lunar illumination decreases (assuming little vertical 

migration occurs at night). 

For the duration of instrument deployment, sea lions exhibited both central place and 

multiple central place foraging (Raum-Suryan et al. 2004). Trip durations were relatively short, 

albeit a few males displayed some long-range movements (i.e., 11260, 11261). This was not 

surprising as branded animals from the CAI have been observed in the Commander Islands, 

Russia (NMFS 2008) and long-range movements of branded and tagged sea lions have been 

reported elsewhere (Merrick and Loughlin 1997, Loughlin et al. 2003, Raum-Suryan et al. 2002, 

Raum-Suryan et al. 2004). Relative to data collected for Steller sea lions tagged in the eDPS, trip 

durations of sea lions reported here were longer (Raum-Suryan et al. 2004, Pitcher et al. 2005, 
13 

Call et al. 2007), but dive depths and durations were shallower and shorter, respectively 

(Loughlin et al. 2003, Raum-Suryan et al. 2004, Pitcher et al. 2005). However, the data sets are 

not easily comparable due to a myriad of caveats, including annual, seasonal, and age related 

effects, differences in data collection and defining behaviors (e.g., depth considered a dive or 

distance considered a trip), and others discussed in Pitcher et al. (2005). 

After applying CTCRW models to the telemetry data, the proportions of predicted 

locations associated with diving to > 4 m within zones of designated critical habitat were similar 

to the proportions of Argos data (Table 5). Additionally, proportions in 0-10 nmi of critical 

habitat across datasets in Table 5 corroborated the CAI summer data reported in NMFS (2010), 

which was an updated analysis of the distribution of juvenile Steller sea lions at sea prepared for 

the Draft Groundfish Biological Opinion (NMFS 2003). However, proportions in the 10-20 

zones doubled that presented in NMFS (2010), whereas proportions outside of critical habitat 

were less than half of that presented in NMFS (2010). These differences were likely a result of 

different filtering techniques or sample sizes. 

The CTCRW models were advantageous for predicting locations at short temporal 

intervals, for retaining small-scale movements (Johnson et al. 2008), and for generating data that 

were less likely to be collected as a result of biases due to the transmission and reception of 

telemetry data (i.e., animal behavior; Fadely et al. 2005). Because the original satellite data 

served as the foundation for the CTCRW models, some of those biases were retained in the 

results. However, the models were still useful for elucidating general areas where a greater 

frequency of diving occurred. Employing CTCRW models to archived data sets collected from 

western areas of the wDPS will continue to be useful for examining areas of enhanced foraging 

activity and corresponding telemetry error with respect to critical habitat and other fishery 
14 

regulations. Given the contrasting sea lion demographics opposite of 178°W, additional models 

will also be useful for comparing regional differences within the wDPS. 

 As specified in the Revised Steller sea lion Recovery Plan (NMFS 2008), the documented 

variation in the rate of population decline among regions within the wDPS demonstrates the need 

to employ a recovery strategy that accounts for the spatial and temporal variation of essential 

habitat characteristics. Additionally, NMFS (2008) reiterated the importance of using telemetry 

studies to obtain refined information on sea lion foraging ecology and the effects of habitat 

features (i.e., bathymetry, continental shelf, and the spatial and temporal variability of essential 

oceanographic processes) on behavior. Upon visual inspection of the data it appeared that some 

of the animals utilized bathymetry, shelf gradients, and ridges and these observations warrant 

further investigation. In the future, movement models will be examined with respect to 

environmental covariates, which is not only necessary for understanding how sea lions respond 

to their environment, but ultimately needed before modeling movement as a function of those 

covariates. 
15 

ACKNOWLEDGMENTS 

Special thanks to Kate Call and Rod Towell of the National Marine Mammal Laboratory 

(NMML), Kimberly Beckman, Jamie King, Dennis McAllister, Ken Pitcher, and Greg Snedgen 

of the ADF&G, Bill Taylor (Wildlife Veterinary Services), Kathy Burek (Alaska Veterinary 

Pathology), Lisa Hoopes (University of Central Florida), and the crew of the MV Stimson for all 

of their support and assistance capturing sea lions. This report was improved with reviews by 

Carey Kuhn and Alex Zerbini (NMML) and James Lee (AFSC). This work was conducted under 

Federal Marine Mammal Permits 358-1564 and 782-1532. The use of trade, product, or firm 

names in this publication is for descriptive purposes only and does not imply endorsement by the 

U.S. Government. The findings and conclusions in the paper are those of the authors and do not 

necessarily represent the views of the National Marine Fisheries Service. 

 

17 

CITATIONS 

Argos. 1996. User’s Manual, Satellite Based Data Collection and Location System. Service 

Argos Inc., Landover, MD, USA. 176 p. 

Braham, H. W., R. D. Everitt, and D. G. Rugh. 1980. Northern sea lion decline in the eastern 

Aleutian Islands. J. Wildl. Manage. 44:25-33. 

Calkins, D. G., D. C. McAllister, K. W. Pitcher, and G. W. Pendleton. 1999. Steller sea lion 

status and trend in Southeast Alaska: 1979-1997. Mar. Mammal Sci. 15:462-477. 

Call, K. A., B. S. Fadely, A. Greig, and M. J. Rehberg. 2007. At-sea and on-shore cycles of 

juvenile Steller sea lions (Eumetopias jubatus) derived from satellite dive recorders: A 

comparison between declining and increasing populations. Deep-Sea Res. Part II 54:298-

310. 

Call, K. A., and T. R. Loughlin. 2005. An ecological classification of Alaskan Steller sea lion 

(Eumetopias jubatus) rookeries: a tool for conservation/management. Fish. Oceanogr. 

14(Suppl. 1):212-222. 

DeMaster, D. 2009. Aerial Survey of Steller Sea Lions in Alaska, June-July 2009 and Update on 

the Status of the Western Stock in Alaska. AFSC memorandum available at: 

http://www.afsc.noaa.gov/nmml/species/species_steller.php. 

Fadely, B. S., B. W. Robson, J. T. Sterling, A. Greig, and K. A. Call. 2005. Immature Steller sea 

lion (Eumetopias jubatus) dive activity in relation to habitat features of the eastern 

Aleutian Islands. Fish. Oceanogr. 14(Suppl. 1):243-258. 

Fritz, L., M. Lynn, E. Kunisch, and K. Sweeney. 2008. Aerial, ship, and land-based surveys of 

Steller sea lions (Eumetopias jubatus) in Alaska, June and July 2005 and 2007. U.S. Dep. 

Commer., NOAA Tech Memo. NMFS-AFSC-183, 70 p. 
18 

Fritz, L. W., and C. Stinchcomb. 2005. Aerial, ship, and land-based surveys of Steller sea lions 

(Eumetopias jubatus) in the western stock in Alaska, June and July 2003 and 2004. U.S. 

Dep. Commer., NOAA Tech Memo. NMFS-AFSC-153, 56 p. 

Heath, R. B., R. DeLong, V. Jameson, D. Bradley, and T. Spraker. 1997. Isoflurane anesthesia in 

free ranging sea lion pups. J. Wildl. Dis. 33:206-210. 

Horning, M., and F. Trillmich. 1999. Lunar cycles in diel prey migrations exert a stronger effect 

on the diving of juveniles than adult Galápagos fur seals. Proc. R. Soc. Lond. B: 1127-1132. 

Johnson, D. S., J. M. London, M. Lea, and J. W. Durban. 2008. Continuous-time correlated 

random walk model for animal telemetry data. Ecology 89:1208-1215. 

Lander M. E., T. R. Loughlin, M. G. Logsdon, G. R. VanBlaricom, and B. S. Fadely. 2010. 

Foraging effort of juvenile Steller sea lions Eumetopias jubatus with respect to 

heterogeneity of sea surface temperature. Endanger. Species Res. 10:145-158. 

Lander, M. E., T. R. Loughlin, M. G. Logsdon, G. R. VanBlaricom, B. S. Fadely, and L. W. Fritz. 

2009. Regional differences in the spatial and temporal heterogeneity of oceanographic 

habitat used by Steller sea lions. Ecol. Appl. 19:1645-1659. 

Lea, M. A., D. Johnson, S. Melin, R. Ream, and T. Gelatt. 2010. Diving ontogeny and lunar 

responses in a highly migratory mammal, the northern fur seal (Callorhinus ursinus). Mar. 

Ecol. Prog. Ser. 419:233-247. 

Loughlin, T. R. 1998. The Steller sea lion: a declining species. Biosphere Conserv. 1:91-98. 

Loughlin, T. R., J. T. Sterling, R. L. Merrick, J. L. Sease, and A. E. York. 2003. Diving 

behaviors of immature Steller sea lions, Eumetopias jubatus. Fish. Bull., U.S. 101: 566–582. 
19 

McAllister, D. C., D. G. Calkins, and K. W. Pitcher. 2001. Underwater capture of juvenile Steller 

sea lions with scuba: a narrated video presentation. Pages 53-56 In Cold water diving for 

science. Alaska Sea Grant College Program, University of Alaska Fairbanks, USA. AK-SG01-06. 

McConnell, B. J., C. Chambers, and M. A. Fedak. 1992. Foraging ecology of southern elephant 

seals in relation to the bathymetry and productivity of the Southern Ocean. Antarct. Sci. 

4:393-398. 

Merrick, R. L., and T. R. Loughlin. 1997. Foraging behavior of adult female and young-of-theyear Steller sea lions in Alaskan waters. Can. J. Zool. 75: 776–786. 

Merrick, R. L., T. R. Loughlin, G. A. Antonelis, and R. Hill. 1994. Use of satellite-linked 

telemetry to study Steller sea lion and northern fur seal foraging. Polar Res. 13:105-114. 

Merrick, R. L., T. R. Loughlin, and D. G. Calkins. 1987. Decline in abundance of the northern 

sea lion, Eumetopias jubatus, in Alaska, 1956-86. Fish. Bull., U.S. 85:351-365. 

National Marine Fisheries Sevice (NMFS). 2010. Bering Sea and Aleutian Islands (BSAI) and 

Gulf of Alaska (GOA) Groundfish Fisheries Section 7 Consultation – Draft Biological 

Opinion. National Marine Fisheries Service, Alaska Region. 836 p. 

National Marine Fisheries Sevice (NMFS). 2008. Recovery Plan for the Steller Sea Lion 

(Eumetopias jubatus). Revision. National Marine Fisheries Service, Silver Spring, MD. 

325 p. 

National Marine Fisheries Sevice (NMFS). 2003. Addendum to the Endangered Species ActSection 7 Consultation, Biological Opinion and Incidental Take Statement of October 2001. 

NMFS, Alaska Region, Protected Resources Division. 
20 

National Marine Fisheries Sevice (NMFS). 2000. Endangered Species Act-Section 7 consultation 

Biological Opinion and Incidental Take Statement on the authorization of the Bering Sea 

and Aleutian Islands groundfish fishery under the BSAI FMP and the authorization of the 

Gulf of Alaska groundfish fishery under the GOA FMP. Silver Spring, Maryland. 

National Marine Fisheries Sevice (NMFS). 1992. Recovery Plan for the Steller Sea Lion 

(Eumetopias jubatus). Prepared by the Steller Sea Lion Recovery Team for the National 

Marine Fisheries Service, Silver Spring, Maryland. 92 p. 

National Research Council (NRC). 2003. Decline of the Steller sea lion in Alaskan Waters: 

Untangling Food Webs and Fishing Nets. The National Academies Press, Washington, 

D.C., USA. 204 p. 

Nichol, D. G., and D. A. Somerton. 2002. Diurnal vertical migration of the Atka mackerel 

Pleurogrammus monopterygius as shown by archival tags. Mar. Ecol. Prog. Ser. 239:193-

207. 

Pitcher, K. W., M. J. Rehberg, G. W. Pendleton, K. L. Raum-Suryan, T. S. Gelatt, U. G. Swain, 

and M. F. Sigler. 2005. Ontogeny of dive performance in pup and juvenile Steller sea lions 

in Alaska. Can. J. Zool. 83:1214-1231. 

R Development Core Team. 2006. R: A language and environment for statistical computing. R 

Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL 

http://www.R-project.org

Raum-Suryan, K. L., K. W. Pitcher, D. G. Calkins, J. L. Sease, and T. R. Loughlin. 2002. 

Dispersal, rookery fidelity and metapopulation structure of Steller sea lions (Eumetopias 

jubatus) in an increasing and a decreasing population in Alaska. Mar. Mammal Sci. 18:746-

764. 
21 

Raum-Suryan, K. L., M. J. Rehberg, G. W. Pendleton, K. W. Pitcher, T. S. Gelatt. 2004. 

Development of dispersal, movement patterns, and haul-out use by pup and juvenile Steller 

sea lions (Eumetopias jubatus) in Alaska. Mar. Mammal Sci. 20:823-850. 

Rehberg, M. J. 2005. Pattern matters: changes in the organization of swimming and diving 

behavior by Steller sea lion juveniles in coastal Alaska waters. M.S. Thesis, University of 

Alaska, Anchorage, USA. 87 p. 

Rehberg, M. J., and J. M. Burns. 2008. Differences in diving and swimming behavior of pup and 

juvenile Steller sea lions (Eumetopias jubatus) in Alaska. Can. J. Zool. 86: 539-553. 

Sease, J. L., and C. J. Gudmundson. 2002. Aerial and land-based surveys of Steller sea lions 

(Eumetopias jubatus) from the western stock in Alaska, June and July 2001 and 2002. U.S. 

Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-131, 45 p. 

Sinclair, E., T. R. Loughlin, and W. Pearcy. 1994. Prey selection by northern fur seals 

(Callorhinus ursinus) in the eastern Bering Sea. Fish. Bull., U.S. 92:144-156. 

Sinclair, E. H., and T. K. Zeppelin. 2002. Seasonal and spatial differences in diet in the western 

stock of Steller sea lions. J. Mammal. 83:973-990. 

Wildlife Computers Ltd. 1997. Satellite-Linked Time-Depth Recorder Instruction Manual. 72 p. 

 
22 

Table 1.-- Capture location (including latitude and longitude) and data for 16 juvenile Steller sea 

lions (Eumetopias jubatus), as indicated by their identification (DBID). 

DBID Location Lat (°N) Long (°W) 

Date 

tagged 

Date last 

transmission Sex

11246 Silak I. 51.815 -176.246 4/19/2005 6/12/2005 F 

11247 Silak I. 51.815 -176.246 4/19/2005 5/11/2005 F 

11248 Little Tanaga Strait 51.819 -176.229 4/20/2005 5/14/2005 M

11249 Lake Point, Adak I. 51.625 -176.992 4/22/2005 6/12/2005 M

11250 Lake Point, Adak I. 51.625 -176.992 4/22/2005 5/21/2005 M

11251 Lake Point, Adak I. 51.625 -176.992 4/22/2005 6/25/2005 M

11252 Lake Point, Adak I. 51.625 -176.992 4/22/2005 5/11/2005 M

11253 Lake Point, Adak I. 51.625 -176.992 4/22/2005 6/17/2005 F 

11255 Ship Rock, Kanaga I. 51.778 -177.345 4/24/2005 5/7/2005 F 

11256 Ship Rock, Kanaga I. 51.778 -177.345 4/24/2005 7/1/2005 M

11257 Kagalaska I. 51.871 -176.310 4/25/2005 6/1/2005 M

11258 Kagalaska I. 51.871 -176.310 4/25/2005 6/28/2005 F 

11259 Semisopochnoi I. 51.963 -179.481 5/1/2005 5/9/2005 M

11260 Lake Point, Adak I. 51.625 -176.992 5/2/2005 7/31/2005 M

11261 Lake Point, Adak I. 51.625 -176.992 5/2/2005 6/21/2005 M

11262 Lake Point, Adak I. 51.625 -176.992 5/2/2005 6/5/2005 F 

 
23 

Table 2.-- Steller sea lion identification (DBID), number of dives (n), and mean, median, 

standard deviation (SD), and maximum (max) of dive depths (meters) and 

durations (minutes). Minimum dive depths (5 m) and durations (0.5 min) were 

equal to the midpoint of the first data bin. 

Depth (m) Duration (min) 

DBID n Mean Median SD Max n Mean Median SD Max

11246 10,342 10.4 8 7.9 62 12,981 0.8 0.5 0.6 5.5

11247 2,948 8.2 8 4.5 27 5,265 0.7 0.5 0.5 > 13 

11248 1,339 8.0 8 4.0 27 4,599 0.6 0.5 0.4 4.5

11249 8,056 10.3 8 7.2 162 13,009 0.9 0.5 0.7 > 13 

11250 1,439 8.5 8 4.6 27 2,725 0.6 0.5 0.3 2.5

11251 8,941 9.7 8 7.9 112 16,983 0.9 0.5 0.8 10.5

11252 1,544 8.9 8 4.8 27 3,236 0.6 0.5 0.3 4.5

11253 6,490 14.4 8 19.5 225 13,677 0.8 0.5 0.6 5.5

11255 548 6.4 5 2.3 15 1,046 0.6 0.5 0.3 2.5

11256 11,054 9.3 8 5.8 87 18,910 0.9 0.5 0.6 > 13 

11257 3,446 7.9 8 4.5 42 5,634 0.6 0.5 0.4 9.5

11258 5,357 13.7 15 9.2 112 8,238 1.0 0.5 0.8 4.5

11259 139 5.4 5 1.3 15 954 0.6 0.5 0.4 3.5

11260 17,776 15.9 8 19.5 187 25,669 0.8 0.5 0.7 4.5

11261 9,858 13.8 8 12.9 187 20,148 0.8 0.5 0.6 9.5

11262 716 8.3 8 4.2 27 2,546 0.6 0.5 0.2 3.5

 
24 

Table 3.-- Results for linear mixed effects models. For the first four binomial models dive 

presence (DP) was examined with respect to day of year (DOY) and lunar 

illumination (LI). For daily maximum dive depth (MD), only one model is presented 

for the Gaussian analyses because ΔAIC > 2 for the remaining models. Asterisks 

indicate significance (α = 0.05 or high Z-values). 

Model and predictor variables (fixed effects) Estimate SE Z-value P 

DP ~ DOY (AIC=266.3) 

DOY* 0.04913 0.01172 4.193 2.75e-05

DP ~ LI (AIC=288.2) 

LI -0.004954 0.004671 -1.061 0.289

DP ~ DOY + LI (AIC=267.8) 

DOY* 0.048091 0.011660 4.125 3.7e-05

LI -0.003550 0.004756 -0.746 0.4554

DP ~ DOY + LI + DOY:LI (AIC=267.2) 

DOY 0.0211257 0.0190496 1.109 0.267

LI -0.0674502 0.0409183 -1.648 0.099

DOY:LI 0.0004956 0.0003156 1.571 0.116

MD ~ DOY + LI (AIC=141.3) 

DOY* 0.0078889 0.0007393 10.671 

LI* -0.0020580 0.0003567 -5.769 

 
25 

Table 4.-- Steller sea lion identification (DBID); number of trips (n); and mean, median, standard 

deviation (SD), minimum (min), and maximum (max) amount of time on shore and at sea 

(hours). 

 Time on shore (hour) Time at sea (hour) 

DBID n Mean Median SD Min Max n Mean Median SD Min Max 

11246 51 8.7 8.0 4.9 1.3 22.3 51 15.2 15.7 8.7 0.3 42.7

11247 19 9.7 10.7 7.3 1.0 26.7 18 17.7 13.2 16.6 0.3 66.7

11248 23 14.5 10.7 13.8 2.3 58.7 22 11.0 9.2 7.3 2.7 37.3

11249 36 9.8 8.0 5.9 2.3 26.7 33 12.6 10.7 7.9 2.7 45.3

11250 24 10.8 9.3 7.4 1.0 26.7 23 9.5 8.0 5.6 0.3 26.7

11251 61 9.3 8.0 5.4 1.0 24.0 58 13.7 13.0 7.3 0.3 34.7

11252 23 9.0 8.0 5.2 2.3 18.3 21 9.5 10.7 3.5 2.7 16.0

11253 43 11.8 10.7 6.7 2.7 32.0 37 16.7 13.0 14.1 2.7 77.3

11255 14 10.8 9.3 8.3 2.3 29.3 14 9.6 8.0 8.0 2.7 29.3

11256 51 11.4 10.7 8.3 1.3 40.0 52 15.6 10.7 16.2 0.3 74.7

11257 39 9.8 8.0 6.3 1.0 24.0 37 10.3 8.0 7.1 0.3 29.3

11258 55 10.1 8.0 5.3 2.3 21.3 47 10.5 10.3 4.5 2.7 24.0

11259 9 8.9 10.7 6.0 1.0 18.7 8 11.0 6.7 12.2 0.3 39.7

11260 74 11.7 10.7 7.0 1.3 37.3 71 17.1 10.7 21.5 0.3 160.0

11261 26 10.6 12.0 5.0 1.3 21.3 23 35.9 10.7 74.1 0.3 280.0

11262 41 10.3 10.7 9.9 1.0 38.3 38 7.0 6.5 4.8 0.3 21.0
26 

Table 5.-- Percentages of Argos locations associated with diving to > 4 m (Fig. 5), predicted 

locations associated with diving to > 4 m generated from CTCRW models (Fig. 6), 

and predicted locations associated with periods during which the frequency of dives 

exceeded the average dive frequency (Fig. 7) in zones of designated critical habitat. 

Sample sizes in parentheses denote number of Steller sea lions. 

Critical Habitat Zone 

Argos Locations 

Diving > 4 m 

(n = 16) 

Predicted Locations 

Diving > 4 m 

(n = 16) 

Predicted Locations > 

ave. dive frequency 

(n = 16) 

0 – 10 nmi 68.30 69.49 65.37 

10 – 20 nmi 23.71 23.69 26.21 

Foraging Areas (> 20 nmi) 0.04 0.00 0.00 

> 20 nmi 7.96 6.82 8.42 
Figure 1.-- Capture locations ( ) for 

in the central Aleutian Isl

 

27 

16 juvenile Steller sea lions (Eumetopias jubatus)

ands, Alaska. 

 
28 

A) 

B) 

Figure 2.-- Percentage of dives in duration bins (A; n = 155,620 dives) and depth bins (B; n = 

89,993 dives). Minimum depth considered a dive was > 4 m. Data are parsed into four 

6-hour periods (local time) as indicated in the legend. 

0

5

10

15

20

25

30

35

40

0-11-22-33-44-55-66-77-88-9

9-10

10-1111-12

12-13

>13

% Dives

Duration range (min)

period 0, 21:00-2:59

period 1, 3:00-8:59

period 2, 9:00-14:59

period 3, 15:00-20:59

0

2

4

6

8

10

12

14

16

18

20

4-6

6-10

10-2020-3434-5050-74

74-100

100-124124-150150-174174-200200-250

> 250

% Dives

Depth range (m)

period 0, 21:00-2:59

period 1, 3:00-8:59

period 2, 9:00-14:59

period 3, 15:00-20:59
29 

A) 

B) 

C) 

Figure 3.-- Percentage of counts in each duration (n = 155,620 counts; A) and depth (B; n = 

155,503 counts) bin for each period of the day (local time). Percentage of time spent 

at depth (TAD) and percentage of time spent hauled out (HO) are also provided for 

each period of the day (C; n = 635, 967 counts). All data bins are presented.

0

20

40

60

80

0-11-22-33-44-55-66-77-88-9

9-10

10-1111-1212-13

>13

% dives / period

Duration range (min)

period 0, 21:00-2:59

period 1, 3:00-8:59

period 2, 9:00-14:59

period 3, 15:00-20:59

0

20

40

60

80

2-44-6

6-10

10-2020-3434-5050-74

74-100

100-124124-150150-174174-200200-250

> 250

% dives / period

Depth range (m)

period 0, 21:00-2:59

period 1, 3:00-8:59

period 2, 9:00-14:59

period 3, 15:00-20:59

0

20

40

60

80

HO

2-44-6

6-10

10-2020-3434-5050-74

74-100

100-124124-150150-174174-200

>200

% TAD / period

Depth range (m)

period 0, 21:00-2:59

period 1, 3:00-8:59

period 2, 9:00-14:59

period 3, 15:00-20:59
30 

Figure 4.-- Average daily maximum depths (m) of Steller sea lions (n = 16; primary axis) and percentage of the moon's visible 

illuminated disk (secondary axis) plotted with respect to day of year. Note the x-axis is compressed over time as transmissions cease for individuals.

1009080706050403020100 0

80604020

140120100

110

115

120

125

130

135

140

145

150

155

160

165

170

175

181

189

200

208

% Lunar Illumination

Ave of daily max depths (m)

Day of Year

depth moon
31 

Figure 5.-- Locations (n = 4,044) of 16 juvenile Steller sea lions after filtering the raw 

diagnostic data and plotted with respect to designated critical habitat depicted 

in gray (0-3 nmi, 3-10 nmi, 10-20 nmi, and foraging areas > 20 nmi from 

haulouts and rookeries). Note that locations associated with diving to > 4 m 

(n = 2,839) produce a similar plot. 
32 

 

Figure 6.-- Predicted locations (n = 41,958) that were generated with the CTCRW model, pooled 

among individuals (n = 16 Steller sea lions), and plotted with respect to designated 

critical habitat depicted in gray (0-3 nmi, 3-10 nmi, 10-20 nmi, and foraging areas 

> 20 nmi from haulouts and rookeries). Note the CTCRW models do not account for 

land. Additionally, predicted locations associated with diving to > 4 m (n = 26,878) 

produce a similar plot. 
33 

Figure 7.-- Predicted locations (n = 9,243) associated with periods during which the frequency of 

dives for each individual (n = 16 sea lions) exceeded the average dive frequency. 

Locations are plotted with respect to designated critical habitat (0-3 nmi, 3-10 nmi, 

10-20 nmi, and foraging areas > 20 nmi from haulouts and rookeries).
Figure 8.-- Predicted locations associ

model for 16 individual S

map. Predicted locations a

exceeded the average dive

are plotted with respect to

3-10 nmi, 10-20 nmi, and

Scales of plots differ amo

34 

iated with diving to > 4 m (●) generated with the 

Steller sea lions as indicated by their DBID on the 

associated with periods during which the frequenc

e frequency (●) overlay all predicted locations. Lo

o designated critical habitat depicted in gray (0-3 n

d foraging areas > 20 nmi from haulouts and rooke

ong individuals (projection: NAD83 Albers). 

CTCRW 

top of each 

cy of dives 

ocations 

nmi, 

eries). 
Figure 8.-- Continued. 

35 
Figure 8.-- Continued. 

36 
Figure 8.-- Continued. 

37 
Figure 9.--Illustrations of the varianc

sampled from the posterior

DBID is indicated on top o

data were not projected as 

38 

ce associated with the predicted tracks (i.e., 20 trac

r distribution) for 16 juvenile Steller sea lions. Ind

of each map and axes differ among individuals. N

they were for Figures 5-8. 

cks 

dividual 

Note the 
Figure 9.-- Continued. 

39 
Figure 9.-- Continued. 

40 
Figure 9.-- Continued. 

41 

RECENT TECHNICAL MEMORANDUMS

Copies of this and other NOAA Technical Memorandums are available from the

National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167

(web site: www.ntis.gov). Paper and electronic (.pdf) copies vary in price. 

AFSC217 LAZRUS, H. M., J. A. SEPEZ, R. G. FELTHOVEN, and J. C. LEE. 2011. Post-rationalization

restructuring of commercial crew member opportunities in Bering Sea and Aleutian Island crab

fisheries, 62 p. NTIS number pending.

216 CHILTON, E. A., C. E. ARMISTEAD, and R. J. FOY. 2011. The 2010 eastern Bering Sea continental

shelf bottom trawl survey: Results for commercial crab species, 101 p. NTIS number pending.

215 VON SZALAY, P. G., C. N. ROOPER, N. W. RARING, and M. H. MARTIN. 2011. Data Report: 2010

Aleutian Islands bottom trawl survey, 153 p. NTIS number pending.

214 LEW, D. K., J. LEE, and D. M. LARSON. 2010. Saltwater sportfishing in Alaska: A summary and

description of the Alaska saltwater sportfishing economic survey, 2007, 229 p. NTIS number pending.

213 CAHALAN, J. A., B. M. LEAMAN, G. H. WILLIAMS, B. H. MASON, and W. A. KARP. 2010. Bycatch

characterization in the Pacific halibut fishery: A field test of electronic monitoring technology, 66 p.

NTIS number pending.

212 KELLY, B. P., J. L. BENGTSON, P. L. BOVENG, M. F. CAMERON, S. P. DAHLE, 

J. K. JANSEN, E. A. LOGERWELL, J. E. OVERLAND, C. L. SABINE, G. T. WARING, and J. M.

WILDER 2010. Status review of the ringed seal (Phoca hispida), 250 p. NTIS number pending.

211 CAMERON, M. F., J. L. BENGTSON, P. L. BOVENG, J. K. JANSEN, B. P. KELLY, 

S. P. DAHLE, E. A. LOGERWELL, J. E. OVERLAND, C. L. SABINE, G. T. WARING, and J. M.

WILDER. 2010. Status review of the bearded seal (Erignathus barbatus), 246 p. NTIS number

pending.

210 JOHNSON, S. W., J. F. THEDINGA, A. D. NEFF, and C. A. HOFFMAN. 2010. Fish fauna in

nearshore waters of a barrier island in the western Beaufort Sea, Alaska, 28 p. NTIS No. PB2011-

102346. .

209 RONE, B. K., A. B. DOUGLAS, A. N. ZERBINI, L. MORSE, A. MARTINEZ, P. J. CLAPHAM, and J.

CALAMBOKIDIS. 2010. Results from the April 2009 Gulf of Alaska line transect survey (GOALS) in the

Navy training exercise area, 39 p. NTIS No. ADA522221.

208 VON SZALAY, P. G., N. W. RARING, F. R. SHAW, M. E. WILKINS, and M. H. MARTIN. 2010. Data

Report: 2009 Gulf of Alaska bottom trawl survey, 245 p. NTIS No. PB2011102345.

207 PUNT, A. E., and P. R. WADE. 2010. Population status of the eastern North Pacific stock of gray

whales in 2009, 43 p. NTIS No. PB2011102344.

206 ALLEN, B. M., and R. P. ANGLISS. 2010. Alaska marine mammal stock assessments, 2009, 276 p.

NTIS No. PB2010-107408.

205 CAHALAN, J., J. MONDRAGON, and J. GASPER. 2010. Catch sampling and estimation in the

Federal groundfish fisheries off Alaska, 42 p. NTIS No. PB2010-105918.

204 LAUTH, R. R. 2010. Results of the 2009 eastern Bering Sea continental shelf bottom trawl survey of

groundfish and invertebrate resources, 228 p. NTIS No. PB2010-113178.

203 LAAKE, J., A. PUNT, R. HOBBS, M. FERGUSON, D. RUGH, and J. BREIWICK. 2009. Re-analysis of

gray whale southbound migration surveys 1967-2006, 55 p. NTIS No. PB2010-103939.