Spatial and Temporal Distribution, Haulout Use and Movement Patterns of Steller Sea Lions (Eumetopias Jubatus) in Northern California

SPATIAL AND TEMPORAL DISTRIBUTION, HAULOUT USE AND MOVEMENT PATTERNS OF STELLER SEA LIONS (EUMETOPIAS JUBATUS) IN NORTHERN CALIFORNIA.

Allison R. Fuller

A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment of the Requirements for the Degree Master of Science in Biology

Committee Membership Dr. Patricia D. Goley, Committee Chair Dr. Erik Jules, Committee Member Dr. Michael Mesler, Committee Member Dr. Jeffrey Black, Committee Member Dr. Michael Mesler, Graduate Coordinator

December, 2012

ABSTRACT

SPATIAL AND TEMPORAL DISTRIBUTION, HAULOUT USE AND MOVEMENT PATTERNS OF STELLER SEA LIONS (EUMETOPIAS JUBATUS) IN NORTHERN CALIFORNIA.

Allison R. Fuller

I describe the spatial and temporal distribution, abundance and habitat use of

Steller sea lions (Eumetopias jubatus) in northern California between 2006 and 2011 obtained through shore and at-sea surveys and by tracking branded individuals.

Understanding Steller sea lion habitat use is critical in designing and implementing near- shore management initiatives such as the Marine Life Protection Act (MPLA) initiative.

The MLPA initiative process began in northern California in 2009, affecting areas offshore of Mendocino, Humboldt and Del Norte counties. Between the Oregon border and Trinidad, California (Humboldt County) there is one rookery (Southwest Seal Rock) and eight non-breeding haulouts. Steller sea lions are more abundant on haulouts in northern California during the late spring and summer months than during the rest of the

year. When Steller sea lions are numerous in the area, their distribution is influenced by

age/sex class and breeding status. Adult males were seen more frequently on in-shore

haulouts in both Trinidad and Crescent City, CA in late spring/early summer suggesting that these haulouts serve as staging areas for breeding or near-breeding aged bulls (Otter

Rock mean = 7 ± 1, Sea Lion Rock mean = 4 ± 2, Castle Rock mean = 16 ± 5). Breeding

Steller sea lion abundance peaked at Southwest Seal Rock during the June and July pupping and breeding season (mean = 574 ± 38). Presence of pups peaked at haulouts in

Trinidad the late summer/early fall suggesting that these sites serve as “nurseries” for females and their dependent young (Otter Rock mean = 5 ± 2, Turtle Rocks mean = 6.3 ±

3). Steller sea lion pups were branded on Southwest Seal Rock in 2002 and 2004 by

Oregon Department of Fish and Wildlife (ODFW) and National Marine Mammal Lab

(NMML) as part of a larger population dynamics study. Females from these cohorts are now actively breeding in northern California, while fewer branded males have come back to the rookery during breeding season (49 females vs. 18 males). Resights of branded females were more common than males. Of the 62 branded animals that were seen in more than one year during the study period, 73% were female. Male Steller sea lions tended to be resighted farther from the natal site than females. Steller sea lions frequented many haulouts during a single year and females, in particular, showed fidelity to the northern California and southern Oregon near shore waters.

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ACKNOWLEDGEMENTS

I want to thank my major advisor Dr. Dawn Goley, for introducing me to the

exciting world of marine mammal biology. I have seen things, and studied animals that I

never thought I would have, and I’m extremely thankful for the opportunity. Thank you

to my graduate committee members, Dr. Erik Jules, Dr. Michael Mesler, Dr. Jeffrey

Black and Dr. Luke George. Your advice and comments were invaluable throughout the

entire process. Thank you to Aicha Ougzin, Carrie Hudson, Greg Hacker, Allison Lui,

Kellan Korcheck, Ashley Donnell, Brett Carrothers, Wiley Archibald and Janet Thibault

for assistance during the 2009-2011 offshore survey seasons. Special thanks to Janet

Thibault for passing on her knowledge to me, and teaching me so much during the 2009

survey season. Thank you to Gerry McChesney (US Fish and Wildlife Service) and Dr.

Rick Golightly (HSU) for assistance during the 2009 field season, as well as sparking my interest in the amazing world of seabirds. Thank you to all of the undergraduate MMERP

(Marine Mammal Education and Research Program) interns for assistance with Steller

sea lion shore surveys from 2006-2011, and for reminding me how exciting this field is

when I’ve been bogged down with work. Thanks to Steve Monk (HSU) for all of the

lessons in boat operation and maintenance – I learned so much from watching and

listening to you. Special thanks to Dr. Robert Van Kirk (HSU) for assistance with

statistical analyses. I want to especially thank Greg Hacker for reading hundreds of abstracts and thesis drafts and for listening for the last four years of graduate work –

you’re the best. Thanks to Wiley Archibald, Mary Beth Pacewicz, Cari Zourdos, Ashley

Donnell and Carrie Hudson for being fantastic lab mates (and honorary lab mates) – I’ll

be waiting for you all on the outside.

A huge amount of gratitude goes to the National Marine Mammal Lab (Pat

Gearin, Tom Gelatt and Bob Delong), Oregon Department of Fish and Wildlife (Robin

Brown, Bryan Wright and Susan Riemer), Kim Raum-Suryan, and Jonathan Scordino, for

sharing of select brand resights. This data added so much to my thesis, and was greatly

appreciated. Special thanks to Pat Gearin and Bryan Wright for offering advice and

answering numerous questions throughout the process – I appreciate all of your help.

Lastly I want to thank my wonderful family for their love and support.

Funding for this project was provided by the National Marine Mammal

Laboratory and Stuyvesant/Humboldt oil spill (1999) settlement. Travel funds to conferences were provided by the Humboldt State University presidential fund, and from

the California State University’s Council on Ocean Affairs, Science and Technology

(COAST) program. All offshore work was completed under National Marine Fisheries

Service permit no. 14097-01.

TABLE OF CONTENTS

ABSTRACT ...... ii ACKNOWLEDGEMENTS ...... iv LIST OF TABLES ...... vii LIST OF FIGURES ...... ix LIST AND ACRONYMS AND THEIR DEFINITIONS ...... xii INTRODUCTION ...... 1 MATERIALS AND METHODS ...... 10 Study Area ...... 10 Shore Surveys ...... 16 Offshore Surveys ...... 19 Analysis of Photographs...... 21 Multivariate Analysis ...... 26 Brand Analysis ...... 27 RESULTS ...... 29 Spatial and temporal distribution of Steller sea lions ...... 29 Haulout use and movement of branded Steller sea lions ...... 39 DISCUSSION ...... 51 Spatial and temporal distribution of Steller sea lions ...... 51 Haulout use and movement of branded Steller sea lions ...... 57 LITERATURE CITED ...... 63

LIST OF TABLES

Table 1. Steller sea lion pups branded at Oregon and California rookeries from 2001 – 2011. All brands have one to three numerical digits, and one letter – a Y for Southwest Seal Rock brands, and an R for Rogue Reef brands...... 12

Table 2. Number of shore-based surveys of Steller sea lion haulouts in per month from 2006-2011 ...... 18

Table 3. Number of boat surveys of Steller sea lion haulouts per month from 2006 to 2011...... 20

Table 4. Percentage of monthly average total Steller sea lions counted at Southwest Seal Rock, the rookery site...... 31

Table 5. “Scores” or “Correlation coefficients” generated from simple correspondence analysis. Scores were generated for the first two “correspondences” for each survey year – 2009-2011...... 33

Table 6. Total number of resighted male and female Steller sea lion brands by branding location for all years combined...... 41

Table 7. Total male and female Steller sea lion resights per each survey season. Females were consistently resighted more than males...... 42

Table 8. Total number of unique Steller sea lion brand resights by branding location for each year of the study...... 43

Table 9. Resights of St. George Reef Steller sea lion brands from the 2002 cohort vs. the 2004 cohort...... 44 vii

Table 10. Steller sea lion resights of Rogue Reef brands each field season from 2006 to 2009...... 47

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LIST OF FIGURES

Figure 1. The geographic range of three Steller sea lion stocks: Eastern stock, Western stock and Asian stock. The Asian stock ranges west of the Commander Islands, to Russia, including the Kamchatka peninsula, the Kuril Islands, and the sea of Okhotsk. The Western stock ranges from the Commander Islands east to the Gulf of Alaska, including the Aleutian Islands. The Eastern stock ranges from the Gulf of Alaska south to Año Nuevo Island in California, including the United States west coast (Alaska Fisheries Science Center, NOAA)...... 3

Figure 2. Geographic locations of National Marine Mammal Lab’s and Oregon Department of Fish and Wildlife’s Steller sea lion branding efforts in California and Oregon. Branding took place at rookery sites on the Rogue Reef, Oregon, and on the St. George Reef, California...... 6

Figure 3. Steller sea lion haulout and rookery locations off of the coasts of Humboldt and Del Norte counties, CA...... 11

Figure 4. Steller sea lion shore site locations where counts and brand resight surveys were conducted – Patrick’s Point, Lost Whale Inn Rock and Otter Rock in Humboldt County ...... 17

Figure 5. Typical mature Steller sea lion bull, exhibiting large “mane,” thick neck, and powerful shoulder muscles...... 22

Figure 6. A female Steller sea lion next to her pup – highlighting the color and size difference of the pair...... 24

Figure 7. Extent of additional Steller sea lion brand resights provided by National Marine Mammal Lab and Oregon Department of Fish and Wildlife ...... 28

Figure 8. Temporal distribution of Steller sea lions from offshore and shore-based surveys. The solid line with markers represents the number of Steller sea lion seen per month during offshore surveys (2009-2011), while the plain solid line represents the same for shore surveys (2006-2011). Average monthly counts of Steller sea lions peaked from May to August –breeding and molting season. Error bars represent the standard deviation among the means for each month...... 30

Figure 9. Distribution and counts of Steller sea lion Bulls and Pups between March and October. Sites were grouped into “Trinidad Inshore” haulouts “Offshore haulouts”, “Turtle Rocks”, “Del Norte Inshore” haulouts, and “Rookery” (Southwest Seal Rock). Bulls are present early in the breeding season at non-breeding haulouts in addition to the rookery, while pups are present late in the season at non-breeding haulouts after an initial peak at the rookery (birth)...... 32

Figure 10. Simple correspondence analysis plot of Steller sea lion haulout use based on age and sex class, representing 2009 data. Each data point represents a “site/time” for a given age or sex class. Data points are plotted in a Euclidian space based on their values, and the relative similarity of their values to each other. When data points that separate from other data points within this space, it suggests that these points are different from the others. When data points are close to each other, it suggests that these points are similar to other nearby points...... 34

Figure 11. Simple correspondence analysis plot of Steller sea lion haulout use based on age and sex class, representing 2010 data. Each data point represents a “site/time” for a given age or sex class. Data points are plotted in a Euclidian space based on their values, and the relative similarity of their values to each other. When data points that separate from other data points within this space, it suggests that these points are different from the others. When data points are close to each other, it suggests that these points are similar to other nearby points...... 35

Figure 12. Simple correspondence analysis plot of Steller sea lion haulout use based on age and sex class, representing 2011 data. Each data point represents a “site/time” for a given age or sex class. Data points are plotted in a Euclidian space based on their values, and the relative similarity of their values to each other. When data points that separate from other data points within this space, it suggests that these points are different from

the others. When data points are close to each other, it suggests that these points are similar to other nearby points...... 36

Figure 13. Simple correspondence analysis plot of Steller sea lion haulout use based on age and sex class, representing 2009 – 2011 pooled data. Each data point represents a “site/time” for a given age or sex class. Data points are plotted in a Euclidian space based on their values, and the relative similarity of their values to each other. When data points that separate from other data points within this space, it suggests that these points are different from the others. When data points are close to each other, it suggests that these points are similar to other nearby points...... 38

Figure 14. Age of Steller sea lions that were branded in 2002 and 2004 at Southwest Seal Rock and the resight frequency of each age class. Resight frequency is represented as percent of total branded in each cohort...... 45 Figure 15. Yearly Steller sea lion resights - Rogue Reef brands from 2006 to 2011. Lines represent each brand cohort ...... 46

Figure 16. Movements of branded Steller sea lions between haulouts within a single season...... 49

Figure 17. Subadult bull compared to a mature bull. Above: Steller sea lion subadult bull at Sea Lion Rock in June – the bull was likely too small to hold territory at the rookery site (Southwest Seal Rock). Below: Steller sea lion bull at Otter Rock in June – the bull appeared to be large enough to hold territory...... 54

LIST AND ACRONYMS AND THEIR DEFINITIONS

AFSC Alaska Fisheries Science Center

BLM Bureau of Land Management

COAST Council on Ocean Affairs, Science and Technology

ESA Endangered Species Act

HSU Humboldt State University

MLPAI Marine Life Protection Act Initiative

MMPA Marine Mammal Protection Act

NMFS National Marine Fisheries Service

NMML National Marine Mammal Lab

NOAA National Oceanic Atmospheric Administration

ODFW Oregon Department of Fish and Wildlife

SWFSC Southwest Fisheries Science Center

USFWS United States Fish and Wildlife Service

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INTRODUCTION

Steller sea lions (Eumetopias jubatus) play a major role in marine ecosystems

throughout the North Pacific Ocean as top marine predators. The Steller sea lion is the

largest living member of the family Otariidae (which includes all sea lions and fur seals), and utilizes near shore and offshore habitats for foraging and coastal rocky habitat for

breeding (Pitcher and Calkins 1981). Steller sea lions are generalist central-place

foragers, foraging on a wide variety of prey species in both near shore and pelagic

habitats (Raum-Suryan et al. 2002, Womble and Sigler 2006, Trites and Calkins 2008,

Reimer et al. 2011). Steller sea lions breed and haul out on near shore haulouts and

rookeries along the Pacific Rim. “Haulouts” are used almost exclusively for rest and

thermoregulation, while “rookeries” are used for parturition and mating (Pitcher and

Calkins 1981).

As sexually dimorphic polygynous breeders, Steller sea lion males and females have

significantly different life histories. Female Steller sea lions become sexually mature at

three to four years of age while males are sexually mature at five to seven years of age.

Males, however, are not socially mature (capable of defending territory) until they are

over nine years old (Pitcher and Calkins 1981). Breeding male Steller sea lions defend

territories from other males, mate with multiple females and forage infrequently during

the breeding season (Mate 1973, Pitcher and Calkins 1981). Females give birth to a

single pup, and can nurse this pup for up to four years. Because of extended periods of

lactation, and the high energy demands of nursing pups, females periodically leave their

pups to forage locally soon after parturition (Merrick 1987, Higgins et al. 1988, Merrick

and Loughlin 1997, Trites and Porter 2002, Maniscalco et al. 2006, Burkanov et al.

2011). After the breeding season, female Steller sea lions and pups disperse together to

non-breeding haulouts. During the non-breeding season, males and females can disperse widely (Griswold, 1985, Raum-Suryan et al. 2002, Raum-Suryan et al. 2004, Scordino

2006).

Steller sea lions range from Russia (including the Kamchatka Peninsula, the Kuril

Islands and the Sea of Okhotsk), east to the Gulf of Alaska (including the Commander

and Aleutian Islands) and south to Año Nuevo Island in California, including the United

States west coast (Figure 1). Currently, there are three genetic stocks of Steller sea lions:

the Eastern stock, the Western stock, and the Asian stock. The Eastern and Western

stocks were recognized in the late nineties while the Asian stock was recognized more

recently based on new genetic evidence (Baker et al. 2005, Bickham et al. 1996).

All marine mammals, including Steller sea lions, have been protected under the

Marine Mammal Protection Act (MMPA) since 1972 (National Marine Fisheries Service

2006). While many marine mammal populations have recovered from overexploitation

prior to the enactment of the MMPA, some Steller sea lion stocks have not. The Western

stock of Steller sea lions (which also includes the Asian stock) suffered an 80%

population decline in the late 1970’s and early 1980’s (Bickham et al. 1996, Baker et al.

2005, Holmes et al. 2007). This decline was characterized by a decline in the number of

non-pup Steller sea lions, especially juveniles (Holmes et al. 2007). This decline led to

the listing of Steller sea lions as “threatened” under the Endangered Species Act (ESA) in

1990 (U.S. Federal Register 1990). The Western stock’s numbers continued to decrease by about 5% every year through the 1990’s, which caused the Western stock specifically to be upgraded to “endangered” in 1997 (U.S. Federal Register 1997, Loughlin and York

1999, Sease et al. 2001). Stock assessments through the 2000’s indicate that the decline

has ended and that numbers have stabilized – though this trend varies between sites

across the vast Western stock range and between rookery and haulout sites (Fritz et al.

2008). The Eastern stock of Steller sea lions did not suffer a population crash, but was

also listed as “threatened” in 1990 by the ESA (Figure 1) (Federal Register 1990).

However, the stock continues to thrive and will likely be delisted in the near future

(NMML pers. com.).

Several aspects of the ecology of the Western stock have been studied in an effort to pinpoint the cause of the decline – focusing largely on reproduction, habitat use, movement patterns, predation and foraging ecology. However, no definitive cause or combination of causes has fully explained the decline. Complimentary studies of the

Eastern stock have been implemented to compare a thriving population to a declining

one. Two monitoring programs have been implemented in the California and Oregon portion of Eastern stock’s range to monitor population size and describe the population

dynamics along the entire west coast of the United States. National Oceanic and

Atmospheric Administration’s (NOAA) Southwest Fisheries Science Center (SWFSC)

has conducted aerial count surveys during peak breeding season when Steller sea lions

are most numerous (Mark Lowry pers. com.). National Marine Mammal Lab (NMML)

and Oregon Department of Fish and Wildlife (ODFW) have implemented a branding

resight program in Oregon and California in order to track animals of known age and sex

to study the population dynamics of the Eastern stock for comparison to the Western

stock.

As a part of the branding resight study, Steller sea lion pups were branded at the St.

George Reef in California, and at the Rogue Reef in Oregon (Figure 2) (Table 1). Each

sea lion was branded with one to three consecutive numbers followed by either a Y

(California) or an R (Oregon) (Table 1). Resightings of these branded sea lions

throughout the range enabled ODFW and NMML to study vital rates in order to explain

the population dynamics of the Oregon and California populations. Humboldt State

University’s Marine Mammal Education and Research Program (MMERP) became

involved with this effort in 2006 – conducting surveys of local Steller sea lion haulouts

and rookeries to resight branded sea lions. This work has contributed to the species-

based conservation efforts at the population-level, and has also provided the opportunity

to study the ecology of Steller sea lions that live and breed in northern California. Other

exclusively local studies have focused on the distribution of Steller sea lions in northern

California – including brand resight and seasonal distribution studies (Griswold 1985,

Scordino 2006), and fine scale haulout-specific behavioral studies (Stack 1979).

Generally, Steller sea lions are present in California and Oregon from April to

October, and are absent (or present in much smaller numbers) during the rest of the year

(Mate 1973, Sullivan 1980). Though local haulouts and rookeries have been identified in

previous studies, fine scale habitat use patterns have not been described for Steller sea

lions that breed and haulout in northern California - especially during non-breeding months - making it difficult to accurately identify the “critical habitat” that should be conserved (Stack 1979, Sullivan 1980, Griswold 1985, Scordino 2006). Identifying the manner by which Steller sea lions utilize local habitats in the context of their natural history will help identify and conserve these critical habitats. In addition to informing larger population-level issues, it is becoming increasingly important to understand the fine-scale habitat requirements of Steller sea lions in light of recent local habitat conservation and management concerns.

In California, the Marine Life Protection Act (MLPA) Initiative process began in the

“North Coast region” (Mendocino County to Del Norte County) in 2009. The MLPA

Initiative’s goal is to conserve marine species by protecting associated habitats from disturbance by commercial and recreational activities. As threatened animals that utilize local habitats, Steller sea lions were identified as a “species likely to benefit” from

protection based on their ecology and natural history during the breeding season.

Habitat-based conservation efforts, like the MLPA, have become favorable, especially when considering a wide-ranging, highly mobile species like the Steller sea lion, which faces complex challenges involving prey disturbances, predation and other unknown

factors in a portion of its range (Holmes et al. 2007, Horning and Mellish 2012). In order

to effectively conserve habitat for a species like the Steller sea lion, the complex seasonal

haulout use patterns (including differential patterns of different age and sex classes) must

be identified and managed appropriately.

There were two objectives in this study. My first objective was to describe local

seasonal haulout patterns of Steller sea lions at haulouts and rookeries in northern

California with a goal of describing variation in behaviors of different age and sex

classes. I examined differences in these patterns in both breeding season and non-

breeding season. I identified key local haulout sites that play important roles in the life

history of Steller sea lions. Placing this information in the context of known behavioral

and foraging ecology of the species painted a more complete picture of local Steller sea

lion biology. My second objective was to determine haulout use patterns and movements

of branded male and female Steller sea lions. To complement coast-wide brand resight

efforts, I examined male and female habitat use, with an emphasis on year-round

attendance patterns and dispersal of branded Steller sea lions from their natal site, to nearby haulouts, and distant haulouts throughout the extent of their range.

This study introduces a new protocol and a more focused, long-term description of

Steller sea lions’ use of northern California’s inshore and offshore haulouts and the role that each plays in the life history of the Steller sea lion. My study complements the coast wide approaches of brand resights and aerial surveys with new targeted approaches that

describe the near and offshore habitat requirements of Steller sea lion in northern

California.

MATERIALS AND METHODS

Study Area

My study area encompassed approximately 90 km of northern California coastline

from Trinidad, Humboldt County (41º 3.380, 124º 8.771) to Crescent City, Del Norte

County (41º 50.260, 124º 22.532). Study sites in northern California included one

rookery and eight haulouts (Figure 3). All near shore and offshore islands with consistent

Steller sea lion attendance were considered as study sites. These study sites are also used

by California sea lions (Zalophus californianus), seabirds and shorebirds periodically.

All of the sites are part of the Bureau of Land Management’s (BLM) California Coastal

National Monument (CCNM) system, except for Castle Rock, which is a National

Wildlife Refuge managed by the United States Fish and Wildlife Service. Apart from

their geographic locations, each study site has unique features which may contribute to

when and how frequently it is used by Steller sea lions.

The rookery site – Southwest Seal Rock (41º 48.808, 124º 21.119) – lies

approximately ten kilometers west of Crescent City along the St. George Reef. The

approximately 8,240 – m2 island lies up to 15 m above mean high tide, and has haulout

access on all but the northeast point. The southwest point of the rock has a gently sloping

gulch with increased haulout space. The west-facing side of the island has a large pool,

which is used by Steller sea lions when the rock is heavily attended.

Figure 3. Steller sea lion haulout and rookery locations off of the coasts of Humboldt and Del Norte counties, CA.

Year Branding Site Brands 2001 Rogue Reef, OR 1R – 180R 2002 St. George Reef, CA Y1 – 140Y 2003 Rogue Reef, OR 181R – 370R 2004 St. George Reef, CA 141Y – 291Y 2005 Rogue Reef, OR 371R – 470R 2007 Rogue Reef, OR 471R – 663R 2009 Rogue Reef, OR 664R – 863R 2011 Rogue Reef, OR 864R - 999R/292Y-

There are two other haulout sites in Crescent City – St. George Lighthouse and Castle

Rock. St. George Lighthouse (41º 50.233, 124º 22.558) is a decommissioned lighthouse built in the late 19th century, approximately 13 km west of Crescent City along the St.

George Reef. The 44 - m tall lighthouse sits atop a concrete/granite foundation of which

only the lowest platform is accessible to the sea lions. The approximately 6,500 m2

island on which the lighthouse was built has a gradual slope on nearly all sides, and at

only about 20 m above sea level, is readily accessible to sea lions.

Castle Rock (41º45.713, 124º 14.935) is a National Wildlife Refuge, approximately 2 km offshore of Crescent City. Castle Rock, which is about six hectares in size, is steep- sided and used primarily by breeding seabirds (Common Murres (Uria aalge), Brandt’s

Cormorants (Phalacrocorax penicillatus), Western Gulls (Larus occidentalis) and Tufted

Puffins (Fratercula cirrhata)) in the summertime. However, the rock is surrounded by many smaller, low-lying peripheral rocks (adding up to about 14,000 m2 of area), which

are used by multiple seal and sea lion species year-round. These peripheral rocks are

highly tidally-influenced.

One haulout site near the Klamath River (41º 34.255, 124º 6.212) mouth is located 25

km south of Crescent City. This site consists of a rocky beach and several small near

shore rocks. The Klamath River mouth is an active fishing area for the area’s Yurok

Tribe, and sea lions are known to forage outside of the mouth and in the river as well

(Pers. Obs.).

Redding Rock (also known as “Reading” Rock) (41º 20.405, 124º 10.703) is a

haulout site located eight km off of Freshwater Lagoon, which is approximately 47 km

south of Crescent City. While this rock is part of the BLM’s CCNM, it is co-managed by the Yurok Tribe, to whom the island holds special cultural and historical importance.

Redding Rock has an area of 1,700 – m2, and a height of 31 m. This steep-sided rock is

actively used as an aid to navigation (ATON). This rock is also a seabird rookery in the

summer, accommodating Common Murres, Brandt’s Cormorants and Western Gulls, as

well as several non-breeding species, such as Brown Pelicans (Pelecanus occidentalis)

and Heerman’s Gulls (Larus heermanni). While Redding Rock is one of the tallest of the

study sites, sea lions regularly haulout at the very top of the rock – and have been seen

lying next to the base of the lighthouse (Pers. Obs.). The east face of the rock provides

almost all of the pinniped haulout space, while the west face is a sheer cliff with several

ledges on which Common Murres nest. Steller sea lions are largely limited to the

intertidal area on the south, east and northeast sides of the rock, though they are

sometimes spotted higher on the rock (Pers. obs.).

The remaining four haulout sites are located in Trinidad, Humboldt County, including

Turtle Rocks, Patrick’s Point, Otter Rock and Sea Lion Rock. Turtle Rocks (41º 7.931,

124º 11.033) consist of a pair of rocks approximately two km offshore of Patrick’s Point

State Park. The two rocks take up about 2,280 m2 of area, with the more southern rock

being less susceptible to tidal influences than the more northern rock due to its height.

However, both rocks are relatively low-lying (between three and 11 m above sea level

depending on the tide), and can be submerged or nearly submerged by large waves.

North Turtle Rock is accessible to sea lions on all sides, while South Turtle Rock is

accessible to sea lions only on the north-facing side and is sheer on the south-facing side.

Directly inshore of Turtle Rocks is a group of haulouts near Patrick’s Point State

Park. This area includes several small (less than 2,000 m2) inshore rocks around

Palmer’s Point – which are heavily tidally-influenced - as well as a larger rock (5,550 m2)

below Lost Whale Inn (41º7.425, 124º 9.801), a bed and breakfast in Trinidad. Lost

Whale Inn Rock is about 25 m tall, but haulout space is limited to a large, low-lying

platform on the east-facing side that is almost completely protected from waves.

Approximately 1300 m south of Lost Whale Inn Rock is Otter Rock (41º 6.445,

124º10.003), which is about 200 m from shore. Otter Rock, also known as “Ship Rock,”

is a 9,400 – m2 site made up of one main rock, and two smaller peripheral rocks – each

with several low-lying platform areas. Sea lions haulout primarily on the west-facing

side and the southern tip of the rock, though the east-facing side (albeit very steep) is

occasionally used. The rock is about 20 m in height, but sea lions typically don’t use the

upper 40% or so of the rock. Sea lions haul out on the peripheral rocks when attendance

at the main rock is high.

The final haulout, Sea Lion Rock (41º 5.698, 124º 9.978), is a relatively small rock

(5,510 m2) located approximately 600 m from shore. The rock is fairly steep, but is

accessible on all but the east-facing side. Sea Lion Rock lies nearby a complex of rocks

including Green Rock, White Rock and Puffin Rock, which are too steep on all sides to

be used for pinniped haulouts. Unlike these other rocks, however, Sea Lion Rock isn’t

used as a seabird rookery.

Shore Surveys

Humboldt State’s Marine Mammal Education and Research Program (MMERP)

has conducted shore surveys at select, accessible Steller sea lion haulout sites along the

coast from 2006 to 2011 (Table 2). Shore surveys took place two to four times a month

depending on weather and personnel availability at three near shore survey locations:

Otter Rock, Lost Whale Inn Rock and Palmer’s Point (Figure 4). At each site, photos

were taken of the haulout with a digital SLR camera (Nikon or Canon) equipped with a

70-300 mm lens, or by “digiscoping” with a point and shoot camera through a spotting

scope. Rough counts of Steller sea lions and California sea lions were recorded in the

field with the aid of a spotting scope. All branded sea lions were photographed and

documented.

Figure 4. Steller sea lion shore site locations where counts and brand resight surveys were conducted – Patrick’s Point, Lost Whale Inn Rock and Otter Rock in Humboldt County

Table 2. Number of shore-based surveys of Steller sea lion haulouts in per month from 2006-2011

Year Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 2006 0 0 0 0 0 0 0 0 0 4 3 2 2007 2 5 6 6 5 6 4 3 4 3 2 3 2008 1 3 5 6 5 8 5 4 5 2 0 0 2009 1 3 4 3 4 3 2 2 4 3 2 1 2010 1 2 2 3 3 2 2 0 0 2 1 2 2011 0 2 3 1 3 2 3 2 1 0 0 0

Offshore Surveys

Throughout the study period (2006 to 2011), surveys were conducted at the

rookery (Southwest Seal Rock) and surrounding haulouts in Crescent City, including St.

George Lighthouse, and Castle Rock. Each year, five to six surveys were conducted during peak breeding season – June through August. After 2007, the survey area was expanded to include haulouts south of Crescent City, including Redding Rock and haulouts in Trinidad. In 2009 and 2011, surveys were conducted outside of the breeding season as a complement to surveys during the breeding season. Breeding season surveys

in 2009 were supplemented by surveys conducted jointly by US Fish and Wildlife

Service (USFWS) and Humboldt State University (HSU), as part of a Common Murre

restoration feasibility study at Redding Rock (Table 3).

Offshore Steller sea lion surveys were conducted using a 20-foot (6.1 m) rigid

hull inflatable Zodiac Hurricane. Haulouts and rookeries were approached from

downwind at a distance of about 30 meters in order to avoid startling and flushing sea

lions. Each rock was photographed using either a Nikon D70S or a Canon (40D or 7D) at

several different scales (50-300 mm zoom) and angles for subsequent analysis. Branded

Steller sea lions were photographed and presence of any associated pups was recorded.

Table 3. Number of boat surveys of Steller sea lion haulouts per month from 2006 to 2011

Year Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 2006 0 0 0 0 0 0 3 2 1 0 0 0 2007 0 0 0 0 0 2 2 2 1 0 0 0 2008 0 0 0 0 0 3 1 1 0 0 0 0 2009 0 0 3 3 7 11 5 0 4 1 0 1 2010 0 0 0 0 1 1 5 3 0 0 0 0 2011 0 1 0 1 2 9 3 6 6 2 1 2

Analysis of Photographs

To describe seasonal haulout patterns of Steller sea lions at haulouts and rookeries

in northern California from 2009 to 2011, I analyzed digital photographs of rookeries and

haulouts using ImagePro (2009, Media Cybernetics Inc.) and Image J (2010-2011,

National Institute of Health) (Thibault et al. 2010). I identified each sea lion to species

(Steller sea lion vs. California sea lion) and then identified the age/sex class of each

individual Steller sea lion. To distinguish between the two species, I used the following

criteria: adult California sea lions (predominately males in northern California) are easily

differentiated from Steller sea lions, as their pelage is much darker brown in color, and as

they have a pronounced “forehead” due to a large sagittal crest. Juveniles of the two

species are more difficult to differentiate especially by pelage color, but juvenile

California sea lions tend to have more pointed snouts and more of a “forehead” than

juvenile Steller sea lions. Juvenile California sea lions are also much smaller than

juvenile Steller sea lion of the same age. To differentiate between 1) Adult Male or

“Bull,” 2) Subadult Male/Adult Female, 3) Juvenile, 4) Yearling, 5) Pup and 6)

Unknown, I used the following criteria: Adult males/Bulls had obvious secondary sexual

characteristics attributed to males such as size nearly double that of adult females, broad

shoulders and a large “mane” (Figure 5). The subadult male/adult female class was

categorized by large, broad shoulders, but lacked an obvious mane. Steller sea lions

categorized as juveniles were half the size to three-quarter the size of adult animals, and

lacked the characteristic flattened facial features of yearlings and pups. Steller sea lions

Figure 5. Typical mature Steller sea lion bull, exhibiting large “mane,” thick neck, and powerful shoulder muscles.

categorized as yearlings were less than half the size of adult females, and exhibited a

flattened facial appearance characteristic of young animals. Finally, Steller sea lions

categorized as pups were most easily identified by their dark brown pelage, compared to

the characteristic blonde coloration of the species (Figure 6). Animals that I was unable

to identify were classified as “unknown,” typically because the sea lion’s position or the

photo quality made it difficult for me to identify the sea lion to species. Since several of these designations depend on relative size comparisons, it is easier to differentiate the classes when there are many sea lions present on the rocks. However, when there are few sea lions for size comparison, familiarity with the rocks themselves, as well as referring to photos with many sea lions at the same rock was useful.

After identifying each sea lion by species and age/sex class, I marked or “dotted” each individual on the digital image. Image Pro or Image J tallied these “dots” into different categories resulting in counts for each category for each survey, as well as providing numbers for regional counts across the study range. All photos that were

“dotted” were saved as screenshots, and archived for future reference. This counting method reduced human error that can come from in-field counting, and is a common method used in determining the abundance of pinnipeds from aerial photographs.

Typical dotting procedure involves photos being “dotted” manually using a light box or slide projector, paper and a pen (Westlake et al. 1997, Lowry 1999, Snyder et al.. 2001).

Figure 6. A female Steller sea lion next to her pup – highlighting the color and size difference of the pair.

The software method, however, is used frequently in California sea bird studies and has promise for pinniped studies as well (Capitolo et al. 2011, Thibault et al. 2010). Studies have found that surveying pinnipeds from the air increases the precision and accuracy of counts due to lack of obstructions in the aerial view compared to ground counts (counts from a shore-based vantage point), and the fact that sea lions move when they are counted in real-time (Westlake et al. 1997, Lowry 1999, Snyder et al.. 2001). While the aerial view may enable a less obstructed view of some areas on haulouts, there are others that are more easily seen from the water. Consistent protocol for all surveys is critical to assessing attendance of pinnipeds on these haulouts.

The majority of the haulouts in this study were too far from shore for ground counts, aerial surveys were prohibitively expensive, and in-field counts were unreliable due to ocean conditions and sea lion movement on the rocks. The photographs analyzed in this study were not from an aerial point of view, so obstructions (crevices, cliffs, etc.) may have influenced the counts. In 2009, in-field counts ranged from 1% different to

71% (mean = 24%) than software-assisted counts, showing the range of variability depending on conditions on the boat on a given survey day. Using this boat-based method allowed for frequent, consistent surveying of every site in my study area which would have been impossible with costly aerial surveying.

Multivariate Analysis

I used program R to conduct a simple correspondence analysis in order to

visualize differences in spatial and temporal distribution of different age and sex classes

(Venables and Ripley 2002, R Development Core Team 2010). This descriptive method

takes a complicated dataset, and creates a visual display that highlights underlying

patterns within a dataset. I ran an analysis on data from each year individually (2009-

2011), as well as for all pooled data across the three years. Monthly averages of numbers

of sea lions present were calculated for each class, site and year. For the pooled analysis,

these averages were averaged across all three years. Each of these averages was

considered as a “site/time” point (i.e., Turtle Rocks, June 2009). Simple correspondence

analysis plotted all of these “site/times” in relation to the five age/sex classes on two

axes. “Scores” or “Correspondence coefficients” were generated for each axis, and

indicated the relative strength of the correspondences represented on each axis. A

relatively high “correspondence” indicated that a Steller sea lion class had a notable

relationship with nearby site/times, and this was largely indicated by the proximity of

each point to other points in the plot. Though this analysis did provide these “scores,”

correspondence analysis was designed to be an exploratory, descriptive method, and did

not carry any statistical significance. Future references to these “correspondences” will

be described as “associations” or “relationships” for ease of understanding.

Brand Analysis

I described the temporal and spatial distribution of branded Steller sea lions by

tracking resights of the branded animals of known age and sex from 2006 to 2011.

Branded Steller sea lions were classified into two categories: those that were seen only

once during the six years of study, and those that were seen more than once. Branded sea

lions resighted once could only be considered as a single data point – including spatial

and temporal data. Branded sea lions resighted more than once were analyzed for

haulout use over time. Sea lions that were resighted more than twice were included in

further analysis regarding movement throughout the entire Eastern stock range -

including resight data from Alaska to Año Nuevo Island, California. These data were

provided by NMML, and included resights from ODFW, as well as biologists from Año

Nuevo Island, the Farallon Islands, Oregon, Washington, Alaska and Canada (Figure 7).

Differences in movement patterns of males and females or different age classes were

documented.

Figure 7. Extent of additional Steller sea lion brand resights provided by National Marine Mammal Lab and Oregon Department of Fish and Wildlife

RESULTS

Spatial and temporal distribution of Steller sea lions

Steller sea lions were most numerous on haulouts in northern California during

the breeding season (May to August) and less common during the rest of the year (Figure

8). Attendance patterns observed from offshore surveys were similar to those observed

from more limited shore surveys (Figure 8). Although the peak in overall Steller sea lion

presence occurred during peak breeding season, the timing of peaks differed for

individual sites throughout the region. Counts were consistently highest at Southwest

Seal Rock year to year, with totals at the rookery ranging from 55%-71% of the total

regional counts at the peak of breeding season in July (Table 4). Counts at Trinidad

haulouts (Otter Rock and Turtle Rocks) peaked in late May/early June. The timing of

peaks in Steller sea lion presence at different haulouts can be explained in part by the

proportion of different age and sex classes present at the haulouts. Counts of bulls peaked at non-breeding haulouts along the entire northern California coast early in the

breeding season. Counts of pups first peaked at the rookery, then at non-breeding

haulouts late in the breeding season after dispersing from the rookery (Figure 9).

When haulout site, age class, sex class and survey year were considered together,

pups and bulls were distinguished separately from other age/sex classes consistently over

all three survey years, 2009-2011 (Table 5) (Figures 10-12). Across all three survey

years, Subadult Male/Adult Females, Juveniles, and Yearlings were not clearly

1000 900 800 SSL

700 of 600 500 Offshore Surveys number 400 Shore Surveys 300 Average 200 100 0

Table 4. Percentage of monthly average total Steller sea lions counted at Southwest Seal Rock, the rookery site.

Survey month 2009 2010 2011 June 27% 55% 25% July 55% 71% 62% August n/a 60% 59%

20 Bulls

15 Trinidad Inshore SSL

of Offshore Haulouts 10 Turtle Rocks

Number Del Norte Inshore 5 Rookery 0

200 180 160 140 Pups 120 Trinidad Inshore SSL

of 100 Offshore Haulouts 80 Turtle Rocks 60

Number Del Norte Inshore 40 20 Rookery 0

Score for Correspondence Score for Correspondence YEAR [1] [2] 2009 0.5692421 0.3669104

2010 0.5077080 0.3210067

2011 0.5338969 0.4029768 2009-2011 0.5462797 0.3501053

distinguished by site/times (Figures 10-12). Rather, these three groups were clumped

together in the middle of the plots, overlapping on most of the same site/time points,

suggesting that their relationships with the different site/times were similar. Results were

consistent over all three years, so pooling the data across all years was appropriate.

In the pooled analysis, pups were associated with Southwest Seal Rock (July,

August, September, October and November), Point St. George Lighthouse (August,

September and October), Castle Rock (October), Klamath River Mouth (October),

Redding Rock (September and October), Turtle Rocks (September) and Otter Rock

(September and October) (Figure 13). Bulls were clearly associated with Southwest Seal

Rock (May), Castle Rock (May, June and July), Patrick’s Point (May and June), Lost

Whale Inn (April and June) and Sea Lion Rock (July) (Figure 13).

Haulout use and movement of branded Steller sea lions

During this study, 190 branded Steller sea lions were resighted: 22 in 2006, 64 in

2007, 86 in 2008, 78 in 2009, 47 in 2010 and 66 in 2011. Significantly more branded female Steller sea lions (116) were resighted than branded males (74) (X2 = 6.202, P =

0.0128, DF = 1) (Table 6 and 7). Of the 190 total resights, 115 were branded at St.

George Reef, and 75 were branded at the Rogue Reef. It is worth noting that 291 Steller

sea lions were branded at St. George Reef while over 1000 Steller sea lions have been

branded at the Rogue Reef. Consistently more St. George Reef sea lions have been

resighted (proportionately, and in raw numbers) than Rogue Reef sea lions year to year

(Table 9).

More St. George Reef brands were resighted from the 2004 cohort than the 2002

cohort (66 and 49, respectively). Progressively more 2004 brands were resighted in

relation to 2002 brands from 2006 to 2010 (Table 8, Figure 14). In 2011, this trend ended

when three more 2002 brands were resighted than 2004 brands (Table 8).

Of the Rogue Reef resights, 44 were female (59%) and 31 were male (41%). The

2003 cohort has been resighted most frequently. Brands from the 2003 cohort made up

the largest portion of Rogue Reef resights from 2006 to 2010, but not in 2011, when

brands from the 2007 cohort were more numerous (Figure 15, Table 10). Two patterns in

the distribution of branded Rogue Reef brands emerged – at Castle Rock and St. George

Reef. Castle Rock was attended by only male Rogue Reef brands. St. George Reef was

attended by two times more female Rogue Reef branded sea lions than males.

Table 6. Total number of resighted male and female Steller sea lion brands by branding location for all years combined.

Brand Location Male Female

St. George Reef, CA 43 (37%) 72 (63%)

Rogue Reef, OR 31 (41%) 44 (59%)

Table 7. Total male and female Steller sea lion resights per each survey season. Females were consistently resighted more than males.

2006 2007 2008 2009 2010 2011

Males 5 22 33 28 11 16

Females 17 42 53 50 36 50

Table 8. Total number of unique Steller sea lion brand resights by branding location for each year of the study.

2006 2007 2008 2009 2010 2011

St. George 20 45 66 52 29 45 Reef

Rogue 2 19 20 26 18 21 Reef

Table 9. Resights of St. George Reef Steller sea lion brands from the 2002 cohort vs. the 2004 cohort.

2002 2004 Ratio of 2002/2004

2006 13 9 1.4444 2007 30 29 1.0344 2008 40 46 0.8695 2009 19 33 0.5757 2010 8 21 0.3809

2011 24 21 1.1429

20 resighted

15 2002 Cohort

10 2004 Cohort individuals

% 5

0 23456789 Age (years)

12 2001 cohort 10 resights

2003 cohort of

8 2005 cohort 6 2007 cohort

Number 4 2009 cohort 2 2011 cohort 0 2006 2007 2008 2009 2010 2011 Survey Year

Figure 15. Yearly Steller sea lion resights - Rogue Reef brands from 2006 to 2011. Lines represent each brand cohort

Table 10. Steller sea lion resights of Rogue Reef brands each field season from 2006 to 2009

2006 2007 2008 2009 2010 2011 2001 cohort 1 3 3 2 1 1 2003 cohort 1 12 15 13 7 5 2005 cohort 0 4 2 6 3 3 2007 cohort 0 0 5 1 7 2009 cohort 0 6 4 2011 cohort 1

Steller sea lions tended to return to the rookery site, however, this tendency varied

between males and females. Of the 115 resights of St. George Reef brands, 49 of 72

females (68%) resighted were seen at least once at the rookery (Southwest Seal Rock)

during breeding season. Thirty of these females were conclusively seen with pups.

Eighteen of 42 males (43%) resighted were seen at least once at the rookery (when they

were of breeding age) during breeding season. Two of these “males,” 95Y and 208Y,

have female characteristics, suggesting that they may have been misidentified as males

during branding.

Steller sea lions are wide-ranging animals, as was evident throughout my study

period. Branded Steller sea lions tended to use several haulout sites within a season

(Figure 16). Eighteen branded sea lions moved between St. George Lighthouse and

Southwest Seal Rock– 13 females and five males. Five branded sea lions moved between

either St. George Lighthouse or Southwest Seal Rock and the Klamath River mouth – four females and one male. Seven branded sea lions moved between St. George Reef and

Castle Rock – three females and four males. Fourteen branded sea lions moved between

Crescent City (St. George Reef and/or Castle Rock) and Trinidad – 10 females and four males. Twelve branded sea lions moved between Crescent City and Redding Rock – 10 females and two males.

As of 2011, 73 branded Steller sea lions have been resighted in multiple seasons

(three or more years). Of these, 53 are female (73%), and 20 are male (27%). Additional data supplied by National Marine Mammal Lab revealed some patterns in these branded

Figure 16. Movements of branded Steller sea lions between haulouts within a single season.

Steller sea lion attendance from Central California to Alaska. Four locations were only

used by male branded Steller sea lions: Alaska, Cape Mendocino (California), the

Farallon Islands (California), and Año Nuevo Island (California). Four locations seemed

to be male “dominated,” though females were present there as well: Washington, British

Columbia, Cascade Head (Oregon), and Cape Arago (Oregon). One location was only

used by female branded Steller sea lions: Orford Reef (Oregon). The only branded

Steller sea lions that were never resighted outside of Northern California were females.

One location seemed to be female “dominated”: Rogue Reef (Oregon). The three

remaining locations – Columbia River (Oregon), Sea Lion Caves (Oregon), and Sea Lion

Gulch (California) – had relatively equal presence of males and females.

DISCUSSION

Spatial and temporal distribution of Steller sea lions

Steller sea lions are most numerous in northern California during the peak of breeding

season (June-July). My findings on the seasonal attendance and distribution patterns of

Steller sea lions in northern California are similar to attendance patterns in Alaska and

Oregon (Pitcher and Calkins, 1981, Sease and York 2003, Scordino 2006). The timing of

breeding overlaps for all regions (May to July), and attendance of sea lions on haulouts is

higher during these months than the rest of the year in most areas (Pitcher and Calkins,

1981, Scordino 2006, Sease and York 2003).

Steller sea lions must haulout on rookeries to breed and give birth. The described

increase in attendance is largely explained by a return of breeding animals to the area –

particularly to Southwest Seal Rock, the rookery. For example, in 2011, attendance at

Southwest Seal Rock increased 97% from May to July from 18 sea lions to 648 sea lions.

This pattern is consistent throughout the Steller sea lion range with approximately 50-

70% of total non-pup counts coming from rookery sites (Calkins et al 1999, Holmes et al

2007, Sease and York 2003, Sullivan 1980).

Surveys that were conducted outside of the breeding season revealed the ways in

which Steller sea lions depended on non-breeding haulouts. Different age and sex classes

utilized these haulouts in different ways. Southwest Seal Rock plays an important role in

the life history of northern California’s Steller sea lions, in that it supports the majority of

the local population during breeding months. Rookeries are critical habitat for Steller sea

lions as they support parturition, pup-rearing, and breeding – as well as provide refuge for a new generation of Steller sea lions. At least 720 pups were born at Southwest Seal

Rock from 2009 to 2011.

Adult males typically “staged” at non-breeding haulout sites before the breeding season, and then moved to Southwest Seal Rock in May. May was the month with the highest bull attendance at the rookery. An interesting pattern in my data was that counts of Steller sea lions at two Trinidad haulouts (Otter Rock and Turtle Rocks) peaked in late

May and early June unlike elsewhere in the study range (July). This suggests that the sea lions present at these rocks may have been of breeding age, and subsequently travelled north to the rookery in July.

Although Southwest Seal Rock supports a large portion of the local Steller sea lion population during the breeding season, multivariate analysis revealed that several other non-breeding haulouts were significant to Steller sea lion bulls and pups (and almost certainly their mothers) outside of the breeding season. Patterns in yearling, juvenile and subadult males/adult female Steller sea lions were not clear in the analysis. Running a follow-up simple correspondence analysis without the bull and pup data resulted in very low correspondence scores, thus did not resolve the clumping of these remaining age classes. I see two possible explanations for this pattern. Since these classes are more difficult to identify than pups and bulls, numbers may have been affected by my

misidentifying of some of them. Otherwise, these three age classes may utilize habitats similarly, explaining the overlap.

Steller sea lion females and pups are typically only present at Southwest Seal Rock in large numbers through August. Steller sea lion pups are especially prone to mortality or morbidity, though survival rates vary across the species’ range (Maniscalo et al 2002,

Kaplan et al 2008). Steller sea lion females and their pups are known to travel to non- rookery haulouts at the end of breeding season in other parts of their range (Raum-Suryan et al 2004, Scordino 2006), suggesting that “nursery sites” may increase the probability of survival of new pups by providing a safer alternative to the crowded rookery site or less intraspecific foraging competition (Trites and Calkins 2008).

Adult male bulls used seven non-breeding haulouts prior to the breeding season as staging areas for large breeding-aged bulls, or as “bachelor” haulouts for non-breeding

bulls. These types of haulouts are commonly used by Steller sea lions and other otariid

species (Gales et al 1992, Hernandez-Camacho et al 2008, Trites and Calkins 2008,

Merrick 1987, Robertson et al 2008). Bachelor haulouts are usually used by males that

are too old, not socially mature enough, or not large enough to hold territories (Trites and

Calkins 2008). In this study, distinguishing breeding-aged bulls from bachelors was

difficult as most were not branded, thus their ages were unknown. Some bulls appeared

to be large enough, and had large enough “manes” to be capable of holding territory and

some were definitely subadult, pre-breeding-age bulls (Figure 17).

Like other regions, Steller sea lion haulout selection in California likely took

place thousands of years ago, when pressures on survival and reproduction may have

been similar to present day pressures (Ban and Trites 2007). The key factors in habitat

selection in pinnipeds are likely proximity to foraging grounds, accessibility to the site at

different tidal levels, and to a lesser extent, thermoregulation (Mate 1973, Ban and Trites

2003, Stevens and Boness 2003, Gonzalez-Suarez and Gerber 2008). The haulouts

associated with bulls and pups meet these criteria to varying extents.

While none of the sites favored by bulls and pups had significant cover from heat

stress, this factor is likely not an important factor in haulout selection in northern

California. Lost Whale Inn Rock, Redding Rock and St. George Lighthouse do,

however, provide geographic cover from west winds and swells on parts of the islands.

All eight sites are accessible at all tide levels, except for some of the smaller peripheral

rocks around Castle Rock that are covered in high tides. However Redding Rock and St.

George Lighthouse are the only favored sites that have large and sufficient habitat

available in the event of very high swells.

Available nearby foraging habitat is another likely factor in habitat selection. Steller

sea lions around the St. George reef forage on a variety of different prey species,

including (in order of prevalence in scat) Pacific hake (Merluccius productus), Pacific

salmon (Oncorhynchus spp.), Pacific sardine (Sardinops sagax), clupeid species

(Clupeidae), rockfish (Sebastes spp.) and skates (Rajidae) – suggesting that foraging nearby the rookery is sufficient (Reimer et al 2011). There haven’t been any foraging

studies in the southern portion of my study area, but the habitats nearby the more

southern haulouts (including Sea Lion Rock, Lost Whale Inn Rock, Otter Rock, Turtle

Rocks and Redding Rock) are known fishing hotspots – especially for rockfish (Sebastes

spp.) (California Department of Fish and Game 2010, 2011).

Steller sea lions have a diverse diet, and there is some evidence that male and female diets may differ significantly - possibly due to differences in energy requirements or physiological limitations between sexes (Trites and Calkins 2008, Reimer et al 2011).

This kind of intersexual foraging habitat partitioning is fairly common for other pinniped

species, and may explain the fact that adult males in my study were using different

habitats at different times of the year than females (Campagna et al 2001, Page et al

2006). Though prey demographics may be different across the study area, it is likely that

the favored haulouts in the southern end of the range offer foraging habitat nearby, though more research is needed to confirm this.

Many different factors influence Steller sea lion habitat use at any given time, and

that they are using many different habitats throughout their lives. The MLPA in the

California North Coast region provides protection for a portion of this habitat - the rookery site (Southwest Seal Rock) - with a special closure, which will protect the rock from disturbance out to 300 m. I have shown that the rookery supports a large percentage of the local Steller sea lion population during breeding season, which arguably justifies these protective measures. Additionally, non-breeding haulouts appear to play an important part in the life history of Steller sea lions. I showed that select non-breeding

haulouts may play a role in the breeding success of Steller sea lion males by providing

nearby foraging grounds, and that they also may affect the survival probability of Steller

sea lion pups. Identifying non-breeding haulouts as additional critical habitat will inform

future local management efforts, and may help to more completely support the recovery

of a threatened population.

Haulout use and movement of branded Steller sea lions

The availability of branded Steller sea lions allowed me to track the local habitat use of animals of known age and sex. Differences in the habitat use of these animals reflected the reproductive biology and natural history of males and females. Branded females were resighted more frequently and consistently year after year than males.

Additionally, more females were seen at the rookery than males. Females reach sexual maturity earlier than males and females do not disperse as far as males from their natal site once they reach sexual maturity (Pitcher and Calkins 1981, Raum-Suryan et al. 2002,

Scordino 2006). Dispersal distance – or the distance a sea lion travels away from its natal

site - increases with age (Raum-Suryan et al. 2002, Briggs 2005, Scordino 2006). Male and female dispersal patterns diverge at about three years of age, as males continue to

expand their range, and female ranges contract toward natal rookeries during breeding

months (Raum-Suryan et al. 2002, Raum-Suryan et al. 2004, Scordino 2006, Trites et al.

2006).

Of the St. George Reef brands that were resighted, more were from the 2004

cohort than the 2002 cohort. This disparity was the most pronounced in 2009 and 2010

(Table 10, Figure 13). By 2011, the number of Steller sea lions from both cohorts was

closer, without a significant change in survey protocol. Age-specific dispersal patterns

don’t explain this observation, as the 2002 cohort’s range should have been decreasing in

size by 2009 as the sea lions most certainly reached breeding age (Raum-Suryan et al.

2002, Raum-Suryan et al. 2004, Scordino 2006, Trites et al. 2006). It seems unlikely that

a mortality event occurred that affected only the 2002 cohort, especially since resights of the cohort rebounded in 2011. Detrimental changes in ocean conditions in 2009 and

2010 may have had an impact on the population.

Beginning in May of 2009, the California coast experienced strong negative

upwelling – an El Niño event - that persisted throughout the summer (Bjorkstedt et al

2010, Melin et al 2010). The anomalous ocean conditions in 2009 and 2010 resulted in a

reduction of forage fish, which resulted in a large die-off of various seabirds. Brown

pelicans (Pelecanus occidentalis) were seen in high numbers outside of their ranges, both

north and inland – likely following prey sources (Nevins et al 2010). During the same

season, California sea lions breeding in southern California suffered an 80% mortality of

the 2009 pup cohort, and record numbers of weaned pups stranded along the California

coast (Melin et al 2010). El Niño ocean conditions have been shown to have several

effects on sea lions, including: lower attendance at breeding grounds, less efficient

foraging, increased pup mortality, increased stranding of weaned pups, and reduced

fecundity (Feldkamp et al 1991, Francis and Heath 1991, Heath et al 1991, Huber 1991).

El Niño conditions in Northern California in 2009-2010 likely placed the same

pressures on Steller sea lions as described for California sea lions. With a change in prey distribution or prey abundance nearby, Steller sea lions likely had to travel farther away or dive deeper than usual to find sufficient food. Changes in foraging behavior in response to patchy prey availability may account for some of the differences in attendance that were observed between the 2002 and 2004 cohort. While females with pups are tied to the rookery site, they must utilize the ocean habitat around the rookery in order to support their pups nutritionally. Trip duration is likely driven by increasing energy requirements of growing pups, weaning stage of pups, prey availability, female condition, female foraging ability and the status of the population (Merrick 1987, Higgins et al. 1988, Merrick and Loughlin 1997, Trites and Porter 2002, Maniscalco et al. 2006,

Burkanov et al. 2011). Older female Steller sea lions tend to forage more efficiently

than less-experienced females and “efficient” foraging may be different during an El

Niño year than a typical year (Burkanov et al. 2011). It is possible that sea lions from the

2002 cohort were more experienced both in foraging and pup rearing, and chose a

different foraging strategy than the younger animals in the 2004 cohort, causing them to

leave the area. Steller sea lions tend to adjust haulout use with seasonal availability of

prey, so a significant change in prey distribution could also have a significant effect on

the distribution of Steller sea lions (Womble and Sigler 2006, Womble et al. 2009).

While St. George Reef brands of both cohorts made up the majority of the

resights, sea lions that were branded on the Rogue Reef rookery in southern Oregon were

also resighted, albeit far less frequently than the local animals. Steller sea lions tend to

disperse north rather than south in general, meaning that Rogue Reef sea lions would be

expected to haulout north of their rookery rather than south to California (Scordino

2006). However, California seemed to play a significant role in the life history of at least

a portion of the large population, as Rogue Reef brands were resighted here fairly

consistently. Only male Rogue Reef Steller sea lions were resighted at Castle Rock.

Castle Rock was identified as a non-breeding haulout that associated with bulls, so it

makes sense that it could serve the same purpose for non-breeding males from elsewhere

in the region.

Southwest Seal Rock and the St. George Lighthouse appeared to play a role in the

life history of Rogue Reef females, as 34 brands were resighted between those two sites.

While Steller sea lion females typically exhibit natal site fidelity, it is uncommon, but not

impossible for females to breed at nearby rookeries - and this occurrence may be density-

dependent (Raum-Suryan et al 2004). The Rogue Reef’s rookery sites are larger and

more populous than Southwest Seal Rock, which may have led to the displacement of

some breeding-aged females. The 2003 cohort was the most resighted in California of

the six total cohorts, and was also the most resighted at the rookery.

While Steller sea lions are present in high numbers along Northern California

coast during the breeding months, and utilize local resources, the animals are much less

abundant or absent for the fall and winter months. During breeding season, Steller sea

lions are using the entire local study area – swimming from the southern-most survey

sites to the northernmost frequently (Figure 13). During the non-breeding season, Steller sea lions have even more extensive dispersals, as branded Steller sea lions have been resighted as far north as Alaska, and as far south as Central California. As expected, male

Steller sea lions dispersed farther from their natal site more frequently than females

(Scordino 2006). Females were less likely to travel as far as Alaska, British Columbia

and Washington – instead, they favored non-breeding haulouts in Oregon and California.

Females consistently spent time at non-rookery sites in California and Oregon for large

portions of their lives. Sea Lion Caves in particular has been suggested as an important

nursery site in past studies, and features significant cover and protection from the

elements (Scordino 2006). These sites must play a role in female Steller sea lion life

history, likely offering nearby foraging habitat, or protection from inclement weather or

predation.

The collaborative brand resight efforts in this study showed that Steller sea lions

are very mobile animals that utilize a wide range, and a variety of different habitats

throughout their lives. While tracking branded individuals allows for interpretation of local haulout use, without incorporating information from a larger collaborative study with NMML and ODFW, these data may have been misinterpreted. Steller sea lions

from the St. George Reef use local habitat in a complex manner, but outside of Northern

California, the story becomes even more complex and interesting. Continued

collaboration with NMML and ODFW will enable researchers in northern California to

resolve these issues in the years to come.

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