NOAA Technical Memorandum NMFS-AFSC-77

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

August 1997

Field Studies of

Steller Sea Lions (Eumetopias jubatus)

at Marmot Island, Alaska

1979 Through 1994

by

K. Chumbley, J. Sease, M. Strick, and R. Towell
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 new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Chumbley, K., J. Sease, M. Strick, and R. Towell. 1997. Field studies 

of Steller sea lions (Eumetopias jubatus) at Marmot Island, Alaska, 

1979 through 1994. U. S. Dep. Commer., NOAA Tech. Memo. NMFSAFSC-77, 99 p.

 

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

the National Marine Fisheries Service, NOAA.
August 1997

NOAA Technical Memorandum NMFS-AFSC-77

Field Studies of

Steller Sea Lions (Eumetopias jubatus)

at Marmot Island, Alaska

1979 Through 1994

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries

by

K. Chumbley, J. Sease, M. Strick, and R. Towell

Alaska Fisheries Science Center

7600 Sand Point Way N.E., BIN C-15700

Seattle, WA 98115-0070
Illustration by Katherine Zecca

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iii

ABSTRACT

The Alaska Department of Fish and Game and the National Marine Fisheries Service

conducted field studies of Steller sea lions (Eumeropias jubatus) on Marmot Island, Alaska, from

1979 through 1994. Marmot Island is one of 15 trend sites and four trend rookeries used to

identify population trends in the central Gulf of Alaska. Prior to the 1970s Marmot Island was

one of the largest Steller sea lion rookeries in Alaska. Since the 1970s numbers of non-pup

(adults, sub-adults, and juvenile) sea lions observed on Marmot Island during the breeding season

declined dramatically: 87.1% since 1979. From 1976 to 1994, non-pups declined 76.9% at the

14 other trend sites and 79.1% at the three other trend rookeries in the central Gulf of Alaska.

The proportion of juvenile sea lions on Marmot Island also declined, from 15 to 35% of all nonpups during 1979 and 1983, respectively, to 5% or less during 1987 through 1994. The decline in

pup numbers were commensurate with those for non-pups. From 1979 to 1994, pup numbers

declined 88.1% at Marmot Island and 84.4% at the other three trend rookeries in the central Gulf

of Alaska. From 1991 to 1994, pup production declined by 50.1% at Marmot Island and by

40-50% at two of the other central Gulf rookeries. Since 1979, four rookery sites on Marmot

Island have either become haulouts or have been abandoned entirely.

Non-pup counts were made from 12 through 29 June on Marmot Island since counts

made during these dates were likely to be 90% or more of the maximum number of sea lions

counted during the breeding season. The hours of 1100 to 1400 ADT or 0900 to 1700 ADT

were optimal for observing 90% and 80%, respectively, of daily maximum counts. Optimal dates

for counting pups were 29 June through 9 July. Beach 3Z, a rookery beach occupied by relatively

few sea lions during the breeding season, was the preferred haul-out site from December through

March or April. How and when sea lions make the fall and spring transitions between breeding

season and non-breeding season distribution could not be determined.

During June and July of 1987 and 1988, 751 pups (390 females, 361 males) were branded

and tagged on Marmot Island. Through December 1994, 151 (20.1%: 78 females and 73 males)

of these animals were resighted on 204 occasions. Most resightings (116 of 204: 56.9%) were

from Marmot Island; an additional 33 resightings (16.2%) were from within a radius of about
iv

75 km. The resighting most distant from Marmot Island, approximately 1,700 km, was at Loretta

Island, British Columbia, Canada. All resightings except five were of live animals. The observed

numbers of resightings were significantly below the number expected to be alive (based on life

tables) at any given age. Nine branded females (2.3%) were observed with pups during 1993 or

1994: five were on Marmot Island and three were on the Sugarloaf Island rookery, about 75 km

north of Marmot Island. One female with a pup was seen during March 1994 on Latax Rocks,

approximately 70 km north of Marmot Island. It is not known on which rookery that pup was

born.
V

CONTENTS

Page

INTRODUCTION ...........................................................

Study Site .......................................................................

Protective Measures ..................................................................

Summary of Additional Studies ..............................................................

Study Objectives ............................................................................

METHODS .............................. . . . . . . . . . . . . . . . . . . . . . . . . . .

Land-based Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Breeding Season. . . . . . . . . . . . . . . . . . . . . . . . . . . .................

Non-Breeding Season........................................................................... 

Pup Counts....................................................................................... . . . . . . . . . . . . . . .

Aerial Surveys.................................................................................................... . . .

Resighting of Branded and Tagged Animals...................................................................

Data Analysis...................................................................................................... . .

RESULTS...........................................................................................

Abundance and Distribution During the Breeding Season.............................................

Decline in Abundance from 1979 through 1994...................................................... 

Seasonal Distribution Patterns .............................. ..................................................... 

Daily Distribution Patterns ....... ..........................................................................

Age and Sex Composition During the Breeding Season....................................................

Comparison of Aerial Survey and Cliff Counts....................................................... .

Observations During Non-Breeding Season.................................................................. .

Land-based Counts .............................................................................. .......... 

Aerial Surveys .................................................................................... . ...........

Distribution............................................................................................... . .. .

 1

. 2

3

4

7

8

8

8

9

9

10

10

. 11

1 4

1 4

1 5

1 6

1 7

18

21

. 22

. 22

22

23
vi

Resighting of Branded and Tagged Animals ................................................................ 24

DISCUSSION ............................................................. 25

Decline in Abundance ................................................... 25

Juvenile Survival in Relation to the Population Decline ......................... 28

Timing of the Breeding Season ................................................................................ . . 29

Differences in Distribution Between the Breeding Season and Non-breeding Season . . 30

Comparison of Aerial Survey and Cliff Counts .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1

Optimal Survey Dates and Times.......................................................................................... . . 33

Branded Animal Resights .... . . . . . . . . . . ............................................................... . . . . . . . 34

ACKNOWLEDGMENTS ....................................................................................................... 36

CITATIONS . . . . . . . . ................................................................................................................ 37
INTRODUCTION

An overall decline of about 70% in the number of Steller sea lions (Eumetopias jubatus)

has occurred throughout most of Alaska since the 1970s (Loughlin et al. 1992, Sease et al. 1993,

NMFS 1992, NMML 1995). On 26 November 1990, Steller sea lions were listed as a threatened

species under the U.S. Endangered Species Act (55 FR 49204). Data collected from surveys

conducted since 1990 indicate that the decline is continuing in the Gulf of Alaska and Aleutian

Islands (Merrick et al. 1991, Menick et al. 1992, Sease et al. 1993, NMML 1995). The Alaska

population census data were gathered by aerial and ship-based surveys except at Marmot Island,

where surveys were conducted from land. During the 1980s rookeries on Marmot and Sugarloaf

Islands were the largest with respect to pup production, producing approximately 40% of the

total number of pups born annually in the central Gulf of Alaska (Calkins and Pitcher 1982).

Marmot Island has been the site of land-based research on Steller sea lions since the

197Os, primarily as a cooperative effort between the Alaska Department of Fish and Game

(ADF&G) and the National Marine Fisheries Service (NMFS). Work conducted on the island

included:

1. Daily counts by age and sex class.

2. Hourly counts of age and sex classes performed weekly from dawn to dusk.

3. Resighting of branded and tagged animals.

4. Collecting of scats for food habits data.

5. Recording of marine mammal/fishery interactions.

6. Recording presence of other marine mammals and wildlife.

Earlier research efforts consisted primarily of aerial surveys conducted in 1957 (Mathisen

and Lopp 1963) and from 1965 to 1976 (Calkins and Pitcher 1982, ADF&G unpubl. data).

During the summers of 1975 and 1976, ADF&G branded 598 and 3,669 sea lion pups,

respectively. In 1979, ADF&G investigated population dynamics at Marmot Island under

contract to the Outer Continental Shelf Environmental Assessment Program (OCSEAP).

Although the purpose of this research was to assess the possible impact of pending offshore oil
2

and natural gas development in the Gulf of Alaska, it formed an important baseline for future

work on the island.

Study Site

Marmot Island is located 45 km northeast of Kodiak Island and approximately 5 km off

the easternmost shore of Afognak Island (Fig. 1). The Marmot Island rookery is defined as

58o14’N, 151o47’W to 58o10’N, 151o51’W (50 CFR 227.12). The island is 3800 hectares

with the highest elevation rising to 385 m. There were no permanent human residents on the

island during the years of this study. Fifty-one species of birds (Appendix A), five species of land

mammals, and nine species of marine mammals are found on the island or in its environs

(R. MacIntosh1, ADF&G2, and NMFS’) (Appendix B). Domestic cattle (Bos taurus) were

introduced to the island in the 1920s as were European boars (SUS scrofa) in 1985. Both species

became feral, although cattle have not been seen in more than 10 years. Vegetation consists

primarily of Sitka spruce (Picea sitkensis) interspersed with open meadows and alpine tundra

(Appendix C).

Marmot Island includes several Steller sea lion rookery and haul-out beaches. Rookeries

are sites where adult males defend territories, pups are born, and mating takes place. Haul-outs

are sites where sea lions predictably rest, but where few pups are born and mating typically does

not occur (Calkins and Pitcher 1982, Loughlin et al. 1984). On Marmot Island, rookery and haulout areas are located along on the southeastern side of the island (Fig. 2). Steller sea lion.

rookeries and haul-outs in Alaska often are located on isolated rocky islands or outcroppings. On

Marmot Island, however, the rookery beaches are typically composed of black sand and cobble

1R. Macintosh, National Marine Fisheries Service, P.O. Box 1638, Kodiak, AK 99615. Pers.

commun., September 1996.

2ADF&G, unpubl. data. Alaska Department of Fish and Game, 333 Raspberry Road,

Anchorage, AK 99518.

3NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point Way N.E.,

Seattle, WA 98115.
3

and are bordered by talus cliffs ranging in height from 50 m to over 300 m. In 1979, Aumiller and

Orth (ADF&G4

) described seven separate rookery and haul-out beaches on the island. Rookeries

and haulouts were considered distinct sites if they were geographically isolated from adjoining

beaches by natural barriers. Sea lion use of beaches has not remained constant over time; some

rookeries have become haulouts while others have been abandoned altogether. Figures 2 through

6 describe Beaches 1, 2, 3, 3Z, and 4, which were the primary observation sites in this study.

Protective Measures

In June 1990, the state of Alaska designated Marmot Island a Special Use Area

(ADL 225034) in order to minimize human disturbance of Steller sea lions. Activities prohibited

under the special use designation include the use of ground transportation, aircraft or boats,

access development, camping, introduction of domestic animals, permitting or leasing for

facilities, timber harvest, mining, and material sales. In addition to the state regulations, NMFS

enacted several protective measures pursuant to listing Steller sea lions as “threatened” under the

Endangered Species Act (55 FR 49204). With few exceptions, vessels are not authorized to

approach within 5.5 km of rookeries on Marmot Island and elsewhere in the Gulf of Alaska and

the Aleutian Islands (Fig. 1). On land, unauthorized persons may not approach within 2.4 km or

within sight of the Marmot Island rookeries. This ruling also prohibits the discharging of firearms

near Steller sea lions. On 23 January 1992, under the authority of the Magnuson Fishery

Conservation and Management Act, NMFS instituted year-round prohibition of trawl fisheries

within 18.5 km of Steller sea lion rookeries in the Gulf of Alaska and the Aleutian Islands,

including Marmot Island (57 FR 2683) (Fig. 7).

In 1993, NMFS designated critical habitat for Steller sea lions in Alaska to include both

terrestrial and aquatic habitats (58 FR 45269). Terrestrial habitats include rookeries and haul-out

sites where more than 200 sea lions have been counted. Aquatic habitats include nearshore

waters around rookeries and haul-out sites. The boundaries of aquatic habitats are defined as the

4ADF&G, unpubl. rep. Alaska Department of Fish and Game, 333 Raspberry Road,

Anchorage, AK 99518.
4

mean low-water mark, traditional rafting sites where resting occurs in tightly packed groups (e.g.,

Bigg 1985) and foraging areas. While no definitive description of sea lion foraging habitat has

been developed (58 FR 45269) data from satellite telemetry studies indicate that the waters near

rookeries and haulouts are important foraging zones for females with pups during the breeding

season and yearlings during the non-breeding season (ADF&G5

, Merrick 1995). Critical habitat

designations also require that aircraft fly higher than 914 m above rookeries and major haulouts.

Summary of Additional Studies

Many other Steller sea lion research projects have been conducted on Marmot Island. The

following is a brief summary of these projects.

During the summer of 1980, Gisner (1985) conducted behavioral observations of adult

male Steller sea lions at the Beach 3 rookery on Marmot Island (Fig. 4) and compared the results

with observations from rookeries on Año Nuevo Island, California. Comparisons focused on

differences in territorial behavior, boundary displays, and reproductive behavior between sea lions

at the two sites.

In 1983, Merrick (1984) observed peaks in daily and hourly sea lion abundance trends at

Marmot Island beaches (Fig. 2). He determined the best dates and times for conducting aerial

surveys of the island to maximize total counts and pup counts. Additional research on the

behavior of female Steller sea lions was conducted in 1987. This focused on courtship displays,

maternal care, aggression, and differences in behavior between sites and time of day (Merrick

1987).

In 1984 and 1985, Lewis (1987) conducted studies of disturbance and pup mortality

during pup counts on Beach 4 (Fig. 6) in conjunction with age group composition counts.

Disturbance of the rookery during pup counts increased non-pup displacement, female aggression

and territoriality, pup separation and abandonment, and frequency of stampede in response to

5D. G. Calkins, ADF&G, unpubl. data. Alaska Department of Fish and Game, 333 Raspberry

Road, Anchorage, AK 99518.
5

natural events such as rock slides and low-flying bald eagles (Haliaeetus leucocephalus).

Trampling by adult sea lions during pup counts accounted for only 0.03% of pup mortalities.

In 1987 and 1988, Laughlin and Spraker (1989) tested the effectiveness of the drug

Telezo16 for immobilizing Steller sea lions. Drug dosages were determined relative to estimated

body mass, based on curvilinear and standard lengths. Loughlin and Spraker (1989)

recommended that Steller sea lions be injected with Telezol in or posterior to the shoulder region

to maximize immobilization response and to minimize accidental mortality. Activity patterns and

general behavior of injected and non-injected animals were monitored, by land-based observation

or remote telemetry for at least 2 weeks after injection. No behavioral differences were observed

between drugged and non-drugged animals 2 days after injection. Most behaved normally within

1 day of injection,

In 1987 and 1988, Laughlin and Merrick (1987) conducted counts of pups and non-pups

as well as branding, weighing and measuring of pups on Marmot Island. Return trips to the island

later in the season were made to assess the conditions of branded pups. Preliminary studies to

determine the effectiveness of Telezol as an anesthetic for sea lions and the feasibility of attaching

radio transmitters to drugged sea lions were conducted.

In June and July 1987 and 1988, Menick and Laughlin (in press) attached VHF radio

transmitters to 14 adult female sea lions to monitor their patterns of occupancy on the rookeries.

A VHF telemetry station on the bluff over Beaches 3Z and 4 (Fig. 6) recorded occupancy of the

14 sea lions. Average duration of trips to sea and stays on shore for eight of the 1988 females was

approximately 20 hours.

In 1989, Laughlin et al. (1990) conducted aerial surveys and pup counts on Marmot

Island to determine if the decline in abundance was continuing (NMFS’).

In 1990 and 1991, Loughlin et al. (1992) deployed satellite transmitters (PTT) to study

migration and foraging ecology of northern fur seals and Steller sea lions in Alaska. These studies

6Reference to trade names does not imply endorsement by the National Marine Fisheries

Service, NOAA.

7NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point Way NE,

Seattle, WA 98115.
6

were linked to their previous studies of interactions of pinnipeds with commercial fisheries. Data

on location, dive depths and durations, and water temperatures were collected.

In 1990 and 1991, Castellini et al. (1993) studied the blood chemistry and body condition

of Steller sea lion pups at Marmot Island. A series of blood indices that reflect hydration state,

blood oxygen transport, the metabolism of protein, and lipid and carbohydrate metabolism were

examined. These parameters are useful for detecting changes in health status. Animals were also

measured for blubber thickness. The resulting blood chemistries and body condition of newborn

pups at Marmot Island were within normal ranges for pinnipeds and had not changed compared

with the control animals examined over the past 22 years. Davis et al. (1993) used isotopelabeled water to estimate metabolic rates of pups. Williams et al. (1993) estimated energetic costs

of thermoregulation in pups based on measurements of blubber thickness, heat flow, and body

surface temperature.

During January 1990, Merrick and Miller (NMFS*) deployed a satellite-linked radio

transmitter on an adult female Steller. sea lion captured on Marmot Island to gather information on

sea lion movement and dive patterns. The animal was anaesthetized using Telezol, tagged on the

flippers, and fitted with a satellite transmitter (PTT) on the back and a VHF radio transmitter on

the head.

Since 1991, NMML has been collecting sea lion scats from Marmot Island for food habits

analyses. Because most of the rookery and haul-out beaches are inaccessible from land, scat

collections typically are done during pup counts. Although there are potential biases associated

with scat data analyses (Pitcher 1980, Harvey 1989, Harvey and Antonelis 1994) the advantage

of using fecal material rather than sampling stomach contents is that numerous samples can be

obtained with minimal disruption to the study animals. Basing prey identification on all recovered

bones and hard parts, not only on fish otoliths and cephalopod beaks, reduces sampling bias

(Merrick and Chumbley in press). In conjunction with National Marine Mammal Laboratory

(NMML) food habits research, hydroacoustic and trawl surveys of potential sea lion prey species

were conducted in the vicinity of Marmot Island during the summers (June-July) of 1992 through

8R. L. Merrick and R.V. Miller, NMFS, unpubl. data. National Marine Mammal Laboratory,

7600 Sand Point Way NE, Seattle, WA 98115.
7

1994 and the winters (November-March) of 1992 and 1993 (NMFS9). These surveys were

designed to assess the prey resources available to sea lions on the island.

During the summers of 1993 and 1994, Ono (1993) conducted behavioral studies at Beach

3Z (Fig. 6). Those studies focused on adult female feeding cycles and activity budgets, as well as

other population and behavioral parameters that may reflect nutritional state and health of the

animals. These data will be compared with similar data collected on Lowrie Island in Southeast

Alaska and Año Nuevo Island in California.

Study Objectives

This report presents the results of field work conducted at Marmot Island from 1979

through 1994,

Primary objectives of the Marmot Island research included:

1. Census Steller sea lions by age group and sex (non-pups, juveniles, and pups)’

during the breeding season.

2. Identify year-to-year trends in the numbers or composition of sea lions.

3. Describe seasonal and daily occupancy patterns.

4. Compare aerial survey counts to ground counts.

5. Identify optimal dates and hours for conducting aerial surveys and pup counts.

9R. L. Met-rick, NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point

Way NE, Seattle, WA 98115.
8

METHODS

Land-based Observation

Breeding Season

Counts and observations of Steller sea lions were made during the breeding season in

10 years from 1979 through 1994 (Table l), During the breeding season, count dates ranged

from early May through mid-July, Of the 669 daily counts of non-pups, 649 included composition

by age group and sex. There were also 647 counts of pups.

Daily or alternate day counts of sea lions were made at Beaches 1, 2, 3, and 4 during most

years. Daily counts at Beach 3Z and approximately weekly counts at Beaches 5, 6, and 7 began

in 1991.

Daily counts generally were made between 1000 and 1600 ADT in an effort to coincide

with peak abundance, although some counts were made as late as 1800 ADT (Withrow 1982).

Hourly counts were made at Beaches 3 and 4 on six occasions. These counts were made

each hour from dawn to dusk (0600 to 2300 ADT), weather permitting. Animals on the beach, as

well as those lying or walking in the surf zone were counted; animals free-swimming in the water

were not. Sea lions were tallied by the following age and sex classifications:

1. Territorial males - adult males (approximately age 8 years or older) actively

maintaining a territory on a rookery.

2. Other adult males - adult or subadult males (approximately ages 5 to 8 years) not

maintaining a territory on a rookery.

3. Adult females - (approximately age 4 years or older) based primarily on size, pelage

color and characteristics, -and frequently confirmed by the presence of a pup.

4. Juveniles - animals of either sex, smaller than adults but older than pups of the year

(ages 1 to 4 years), identified primarily by size, pelage color and characteristics,

and behavior. The number of suckling juveniles was also recorded.

a
5. Pups - live pups of the year.

6. Dead pups.

Observations were made from the edge of the cliffs overlooking each rookery or haul-out

site. More than one overlook was required at several beaches due to natural obstructions or the

length of the beach (Figs. 3-6). Counts were made using binoculars or variable-power spotting

scopes and recorded on hand tally counters (Table 1). Generally, counts by age group and sex

were made using binoculars while spotting scopes were used to look for branded and tagged

animals. Spotting scopes also were used at beaches where counting was done from great

distances (e.g., Beaches 6 and 7) especially for counting pups.

Because counts were made from cliff tops, fog and low-lying clouds were the greatest

potential obstacle to successful counts, especially at the higher observation posts (e.g., Beaches 4

through 7). Counts were partially or completely compromised by fog or clouds on about 20% of

all observation days in 1992 and 1994 and on 37% of the days in 1991. Weather was

exceptionally favorable during 1993 when only two counts (6%) at Beach 4 were missed during

33 days of observation.

Non-Breeding Season

Cliff counts outside of the breeding season were made during only one non-breeding

season, 18 November 1987 through 27 March 1988. Observers from ADF&G and NMFS made a

total of 89 composition counts of sea lions. Of those, 79 counts included only Beaches 1 through

4, and 10 counts included all beaches on the island.

Pup Counts

Between 1979 and 1994, ADF&G and NMFS conducted nine pup counts on all rookery

beaches at Marmot Island (Table 2). Counts took place in late June or early July, to maximize the

chance of counting newborn pups but to minimize the number of pups old enough to flee into the
10

water. These counts are sometimes referred to as “spook counts.” Because pups blend in with

the substrate and can hide behind rocks and in crevices, counts were made by walking through the

rookery rather than attempting to count from the cliffs above or from aerial photographs. To

perform pup counts, biologists landed on each rookery beach, typically by small boat or

helicopter. As the older sea lions vacated the rookery beaches, two or three biologists walked

along the beach and used hand counters to tally live and dead pups. The final count for each

beach was the mean of all individual counts. Final beach counts were summed to provide an

overall total for the island.

Aerial Surveys

The numbers of non-pups on Marmot Island during the breeding season have been

counted by aerial surveys during June in 11 years from 1957 through 1994 (Table 3). Aerial

surveys outside of the breeding season took place on 12 occasions (Table 3). Aerial surveys were

conducted from IS June to 16 July between 1000 and 1600 ADT to coincide with peak

abundance of non-pups on the beaches. Counts were made from oblique photographs (Braham

et al. 1980, Withrow 1982, Loughlin et al. 1990, Menick et al. 1991, Menick et al. 1992, Sease

et al. 1993). Most counts were generated from single overflights, although there were two flights

during a 6-day period in 1992 (Sease et al. 1993). These aerial survey techniques are not

appropriate for counting pups, primarily because pups are able to hide under cliffs, logs, and

rocks, blend in with the substrate, and are too small to locate in the photographs. In addition,

aerial surveys for non-pups frequently take place too early in the season to count peak numbers of

pups.

Resighting of Branded and Tagged Animals

Steller sea lion pups were branded and tagged on Beach 3 during 29 June to 1 July 1987,

and on Beach 3 and Beach 4 from 30 June to 1 July 1988 (Table 4). Sequential numbers were
11

branded on the right flank of each pup in 1987 (numbers 5l-401) and on the left flank in 1988

(numbers 401-800). Branding irons, with digits approximately 5 cm x 8 cm, were made from

1.0 cm rolled steel stock and heated in a propane-fueled forge (Merrick et al. 1996). Plastic

identification tags (Allflex medium cattle ear tags) embossed with the same number as the brand

were applied to both fore-flippers of each pup. The portion of the tag containing the

identification number is approximately 2.5 cm x 4 cm. During 1987, the first 49 pups received

tags but no brands. Most branded pups received a prophylactic injection of tetracycline (about

5 cc). One subadult male and 18 adult females were tagged (but not branded) during other

research on Marmot Island during 1987 and 1988. Other sea lions tagged on Marmot Island since

1988 include 4 adult females and 9 pups in 1990, 51 pups in 1993, and 21 pups in 1994.

Appendix D lists all sea lions branded and tagged on Marmot Island from 1987 through 1994.

Resight information on Marmot Island was gathered primarily during June and early July

in conjunction with the daily census of Beaches 1 through 4 and weekly census of Beaches

5 through 7. Although branded animals were detected during counting, additional daily

observation time was devoted solely to searching for branded or tagged animals, particularly

beginning in 1991. Resightings at other locations and during other times of the year were

opportunistic, reported by biologists from numerous state and federal agencies, and by the general

public.

Data Analysis

Analyses were restricted to composition counts made from 1000 to 1800 ADT

(corrections were made for 1979 and 1983 to account for local time zone changes). In 1991,

several counts of the non-territorial males at Beach 1 made after 1800 were included because

poor weather conditions greatly reduced the total number of counts. For many of the analyses,

count dates were converted to Day of Year (Appendix E).

A mean count was used in analyses whenever two or more counts were available within

the acceptable time window. This included multiple counts made by a single observer as well as
12

counts made by different observers. Whenever possible, means were calculated for each age and

sex group on each beach. For some days in 1979, morning and afternoon pup counts were

available for a single day with no specific time reference. These morning and afternoon counts

typically were made by different observers (L. Aumiller10). Accordingly, they were treated as

separate counts of pup abundance and a mean was used in the analyses. On days when hourly

counts were made at a given beach, the count between the hours 1000 to 1800 that included the

maximum number of non-pups was used for the daily count. The count for each age and sex

group From that time was used, whether or not each was the daily maximum (i.e., maximum

counts for each different age and sex group were not selected from different hourly counts).

Analyses of trends in overall abundance and composition by age group and sex at

rookeries focused on Beach 4. Beach 4 is one of the major rookeries containing animals on

Marmot Island and the only one observed consistently from 1979 through 1994. Therefore,

counts made at Beach 4 make up the longest and most continuous data set available for Marmot

Island from 1979 through 1994. The Beach 2 rookery was abandoned in 1985 and Beach 3

changed from a rookery to a haul-out after 1988. Regular counts of Beach 32, a relatively small

rookery, did not begin on a daily or weekly basis before 1991. Beach 7, a major rookery, was

rarely counted during the breeding season before 1991, and only about once per week during

199l-94. During the 1980s some of the work focused at particular beaches and counts for the

remaining beaches were not made on a daily basis, if at all.

Long-term trends in abundance of sea lions at Marmot Island during the breeding season

were examined using cliff counts of pups and non-pups, beach pup counts, and aerial surveys.

Two sets of analyses were derived from the cliff counts. The first used the maximum cliff count

during each year for each age and sex group separately or for non-pups as a whole (all four nonpup groups combined). The second focused on a 10-day period of peak abundance for each

group rather than on a single count per year. Ranges were selected by visually examining plots of

abundance over time. The ranges were 24 June to 4 July (days 175-185) for pups, 29 June to

9 July (days 180-190) for juveniles, and 14 June to 24 June (days 165-l 75) for all non-pups,

10L. Aumiller, Alaska Department of Fish and Game, 333 Raspberry Road, Anchorage, AK

99518, Pers. commun., December 1994
13

including juveniles. Ten-day means and standard errors were calculated for each age group and

each year. Beach counts of pups were made on a single visit to the rookery beaches in a given

year and typically were a mean of two or more individual counts. Aerial survey counts were made

for all non-pups, not for individual age or sex groups, on all rookery and haul-out beaches. A

single count was available for most aerial surveys from 1976 to 1994; a mean of two counts was

used for 1992. Aerial survey and beach pup counts were analyzed using simple linear regression

in the same manner as were the cliff counts.

Trends in abundance for pups, juveniles, and all non-pups combined (including juveniles)

were tested using three regression models. The first was simple linear regression of the natural

log of counts on year for the 1970s to 1994 and for 1,991 to 1994. Slopes of the regressions were

used as estimators of average annual rates of change. The second regression model (after Dennis

et al. 1991) used the mean counts and standard errors for the l0-day periods of peak abundance

for pups, juveniles, and all non-pups combined. The third was an iterative, or bootstrap, model

that randomly picked one data point from within the 10-day period for each year and fit a linear

regression. The final result for each age group was the mean of all outcomes from

1,000 repetitions.

Aerial survey and cliff counts of non-pups were compared by rookery beach to test for any

systematic over- or under-counting by method. Accordingly, the comparison of greatest interest

was between each aerial count and the cliff count made closest to it in time. Corresponding aerial

and cliff counts were available for five aerial surveys: 9 June 1985, 11 June 1991, 17 and 23 June

1992, and 12 June 1994. Paired counts were analyzed only if both the cliff and aerial counts were

made between 1100 and 1800 hours. Aerial survey photographs were re-examined to separate

counts by beach. The difference between cliff and aerial counts was analyzed by simple linear

regression of cliff counts on aerial counts. The resulting regression line was compared to the null

hypothesis that counts from the two methods should be the same (i.e., Ho: slope = 1 and

intercept = 0; H,: slope + 1 or intercept 0).

Assumptions about the days or hours of peak abundance at Marmot Island, as a guide for

selecting survey dates and times, were tested by plotting daily and hourly counts as a percentage

of the maximum count. Analyses included cliff counts for Beaches 1 through 4 combined, and
14

counts for Beaches 2, 3, and 4 separately. Date and time ranges were selected to include most of

the counts that were 1) 90% or more or 2) 80% or more of the maximum count.

The number of branded/tagged sea lions resighted was compared to the numbers expected

to be alive for each age class. Expected numbers were generated from the initial number of

branded/tagged pups and age-specific survival rates, adapted from Calkins and Pitcher (1982) and

York (1994). Animals with brands and tags are likely to be resighted more easily than animals

with tags only. Accordingly, except where noted, the results reported below refer to branded

animals, excluding those with tags only. Resightings from November 1987 through August 1989

also were excluded from the analyses, as there was a substantial effort to follow the survival of

pups branded in 1987 that was not repeated the following year.

RESULTS

Abundance and Distribution During the Breeding Season

The number and composition of sea lions varied between beaches, Beach 1, the

northernmost beach, was a haul out occupied by non-territorial, sub-adult and adult males during

all years of observation. Numbers of animals were as high as 1,400 from 1979 through the early

1980s (Table 5). Since 1991, there have been fewer than 100 males there. Beach 2 was a

rookery from 1979 through 1984 with 500-900 non-pups and about 100 pups. Beach 2 has been

vacant since 1985. Since 1991, there have been occasional observations of one or two sea lions.

Beaches 3 and 4 were rookery beaches of similar size from 1979 through 1987, with peak

numbers from 1,000 to 2,000 non-pups. During that time, pup production was slightly greater at

Beach 4 (l,000-1,800) than at Beach 3 (700-1,100). By 1991, Beach 3 had become a haulout.

From 1991 through 1994, fewer than 100 males and from 1 to 10 females and pups occurred on

Beach 3. From 1991 through 1994, Beach 4 was the largest rookery on Marmot Island, both in

numbers of non-pups (574-93 1) and in pup production (498-855).

The maximum number of non-pups on Beaches 1 through 4 during the breeding season, as

counted from cliffs, ranged from 6,391 in 1979 to 815 in 1994 (Table 5). Maximum counts for
15

the entire island (Beaches 1 through 7) range from 1,690 non-pups in 1991 to 1,161 in 1994,

Counts of non-pups for the entire island, from June aerial surveys, ranged from 9,862 in 1976 to

1,091 in 1994 (Table 3).

Total pup counts for all Marmot Island rookeries ranged from 6,741 pups in 1979 to 804

pups in 1994 (Table 2). The number of pups counted from the cliff tops at all rookery beaches

ranged from 1,244 in 1991 to 780 in 1994. Pup production on rookery Beaches 2, 3 and 4

combined, as estimated from cliff-top counts, ranged from 2,907 in 1979 to 552 in 1994

(Table 5).

Beaches 32, 5, 6, and 7 were observed weekly only since 1991. Prior to that time, counts

at these beaches were opportunistic and infrequent. Beach 7 was the largest, with from 348 to

586 and non-pups from 291 to 586 (Table5). pups From 1991 to 1994, peak numbers of sea

lions on Beach 3Z ranged from 63 to 217 non-pups and from 38 to 128 pups. Beaches 5 and 6

rarely were observed with more than 100 non-pups and 25 pups.

Decline in Abundance from 1979 through 1994

The number of non-pups declined significantly, based on simple linear regression, from the

late 1970s to 1994 for cliff counts at Beaches 1 through 4 combined (- 15.5% per year,

P < 0.001) and for all island aerial survey counts (- 12.7% per year, P < 0.001) (Fig. 8, Tables 3,

5). From 1991 to 1994 the decline in the number of non-pups also was significant for cliff counts

at Beaches 1 through 4 combined (- 14.6% per year, P = 0.037). Estimated annual rates of

decline were derived from regression lines (i.e., slopes of - 0.155, - 0.127, and - 14.6,

respectively). The decline in abundance from 1991 to 1994 was not significant for the aerial

surveys (P = 0.5) or for cliff counts from Beaches 1 to 7 combined (P = 0.09). See Table 6 for

detailed information on simple linear regressions.

Results from application of the Dennis et al. (199 1) regression method to 10-day mean

counts of non-pups at Beach 4 were not significant for a single-regression model for 1979 to 1994

(slope = - 6.9%, P = 0.153). Differences between slopes for 1979 to 1987 (- 3.2%) and 1991 to
16

1994 (- 23.2%) in a two-regression model were not significant (P = 0.113). The decline from

1979 to 1994 was significant (P < 0.025) using the iterative, or bootstrap, method (Table 7).

At Beach 4, the number ofjuvenile sea lions decreased dramatically after 1979 (Fig. 9).

During the 1990s from 10 to 40 juveniles were observed on any given day, almost an order of

magnitude lower than during 1979. During June, juveniles represented about 5% of all non-pups

at Beach 4 in 1987 through 1994, compared to 15 to 25% during 1979 (Fig. 10). At Beach 3, the

percentage ofjuveniles decreased from 15 to 35% in 1979 and 1983 to 10 to 15% in 1987. The

IO-day mean counts ofjuveniles at Beach 4 showed only marginal change from 1987 through

1994, but these means were significantly lower than the mean for 1979 (t-test, P < 0.01). The

regression model of Dennis et al. (1991) did not detect a significant decline over the period 1979

to 1994 (P > 0.28), but there were no data points for years between 1979 and 1987.

The number of pups declined significantly (simple linear regression, P < 0.001) from 1979

through 1994, for cliff counts of rookery Beaches 2 through 4 and for beach pup counts of all

rookery beaches (Fig. 11, Tables 2, 5, 6). Estimated annual rates of decline were 10.4% for cliff

counts and 15.3% for pup counts. From 1991 through 1994, estimated annual rates of decline

were 16.6% (P = 0.006) for combined cliff counts from Beaches 3, 3Z, and 4, 15.9% (p = 0.004)

for combined cliff counts of all rookeries (Beaches 3 to 7), and 23.4% (P = 0.028) for pup counts

of all rookery beaches. Using the regression model of Dennis et al. (1991) on mean cliff counts of

pups at Beach 4, numbers of pups declined by 8.6% per year (P = 0.056) from 1979 through

1994. A two-regression model suggested that rates of decline for 1979 to 1987 (5.0%) and 1991

to 1994 (26.8%) were different (P = 0.021). The iterative regression method also detected a

significant decline (7.5%) in pup numbers from 1979 to 1994 (P < 0.025) (Table 7).

Seasonal Distribution Patterns

In general, the number of non-pups on rookery beaches increased gradually during the

early part of the breeding season, reached a peak during mid-June, and then slowly declined. This

pattern was most apparent on Beaches 3 and 4, the larger rookery beaches (Fig. 12). There was

daily variability in the number of non-pups on rookery beaches. The coefficient of variation
17

(standard deviation divided by the mean) was 8 to 12% for non-pup counts at Beaches 3 and 4

during the peak period of abundance in most years. The coefficient of variation was 15 to 40%

for non-pup counts at Beach 2 during 1979, 1983, and 1984. Much of this variability was

smoothed by plotting 5-day maximum counts.

Annual variability also was apparent. For example, the number of non-pups on Beach 4

in 1979 was high early in the season on 9 May. Non-pup numbers continued to increase until

about 14 June (day 165), but the relative magnitude of the build-up was less than in other years

(Fig. 12). At Beach 2, numbers of non-pups increased throughout the breeding season during

1979, 1983, and 1984 and daily variability appeared greater than at other beaches. Beach 2 was

not used as a rookery after 1984.

The number of sea lions at Beach 7 (Fig. 13) appeared to continue building much later in

the season than at Beaches 3 and 4; however, this was based on very few observations. The

number of non-pups on Beach 3Z gradually increased to a peak in mid-season followed by a

gradual decline in 1993 when there were 120 to 220 non-pups on the beach. In 1991, 1992, and

1994, when there were fewer than 50 non-pups at Beach 3Z, occupancy generally increased over

the course of the observation period. During the last observations of 1992, in mid-July, the

number of non-pups on Beach 3Z increased sharply and the observer noted an apparent

immigration of sea lions from Beach 4.

The range of days when the greatest number of animals were hauled out was not constant

in all years, Generally, the window between 12 and 29 June (days 163-180) appeared to

maximize the chance of counts being at least 90% of the maximum counts (Fig. 14). This window

of opportunity was the same for Beaches 3 and 4 combined or for Beach 4 separately. Even

within this window, however, numerous individual counts fell below the 90% threshold. No

optimal window for maximizing counts was apparent for either Beach 2 or 3.

Daily Distribution Patterns

Attempts to identify an optimal daily window for counting non-pups were inconsistent,

Three dawn-to-dusk time series were available for Beach 3, all during 1987: 14 June, 18 June, and
18

8 July (Fig. 15). On 18 June and 8 July, counts were above 90% of the maximum counts from

about 1100 to 1700 ADT, and above 80% from 0900 ADT until after 1700 ADT. Counts on

14 June never dropped below 92%. Three time series were available for Beach 4. On 12 June

1991, the number of non-pups was 90% or more of the day’s maximum count from about 0900 to

1400 ADT. All counts were greater than 80% except at 1600 and 1800 ADT (79.7% and 77.9%,

respectively). On 21 June 1993, counts were greater than 90% only from about 1100 to 1300

ADT, and greater than 80% from 0639 to 1400 ADT. On 9 June 1992, however, counts were

above 90% intermittently from 0600 to 1800 ADT; none was below 80%.

Age and Sex Composition During the Breeding Season

Adult females -- Abundance curves for the number of adult females on rookery beaches during the

breeding season were similar to those for all non-pups: increasing gradually during the early part

of the breeding season, reaching a peak during mid-June, and then slowly declining. This

relationship is understandable because adult females accounted for 75-95% of all non-pups on the

rookery beaches during the breeding season.

There were approximately 15 to 20 adult females per territorial male at Beaches 3 and 4

from 1979 through 1988 (Fig. 16). The ratio dropped to 5 to 10 adult females per territorial male

at Beach 4 during 1991 to 1994.

Territorial males -- The number of territorial males generally followed a pattern similar to those

for adult females or for all non-pups. Territorial males appeared on the rookery beaches slightly

earlier in the season, the peak in abundance was less pronounced, and the decline in numbers took

place later. On Beach 4, the number of territorial males remained at or above 80% of the

maximum number observed each year during most days in June. During 1984 and 1985, the

number of territorial males increased substantially after 9 July, both on Beach 4 and on Beach 3.

No year-to-year trend was apparent in the numbers of territorial males. On Beach 4, for

example, there were approximately 65 to 90 territorial males present during the peak of breeding
19

from 1979 to 1993. Some of the lowest counts of territorial males on Beach 4 were from 1993

and 1994, whereas the highest counts were from 1992.

Juveniles -- For Beach 4, counts of juveniles were available primarily during 1979 and 1991

through 1994. Very few counts were available from Beach 4 during 1987 (5 days) and 1988

(4 days). For Beaches 2 and 3, juvenile counts also were available from 1979 and 1983, and for

Beach 3 from 1987. Observers did not attempt to differentiate juveniles from other non-pups

during 1984 and 1985 at any beaches (J. Lewis”).

Juveniles represented 20-50% of all non-pups early in the season at Beach 4 during 1979.

This dropped to about 15% by early June, then slowly increased to about 20% by early July

(Fig. 10). The proportion of juveniles was much lower during 1991 to 1994, but it still increased

during the season, from 2% to 5% in early June to only 4% to 8% by early July (Fig. 10). Those

within-season increases were significant in 1992 and 1993 (P < 0.001) and in 1994 (P = 0.024),

but not in 1979 (P = 0.23) or 1991 (P = 0.10). On Beach 3 the proportion ofjuveniles in the

population decreased significantly (P < 0.001) from 30% to 15% during 1983. No significant

increasing or decreasing trend in the number ofjuveniles was demonstrated by simple linear

regression during other years at Beaches 2 or 3. The proportion of juveniles on Beach 7 was

calculated for only four occasions each year from 1991 through 1994. Compared with the other

beaches, the proportion ofjuveniles was low (about 2.5% of non-pups) during 1991. About 5%

of non-pups were juveniles early each season during 1992 through 1994, but that number

increased to over 10% by July in 1992 and 1994.

Pups -- Birth of pups began on rookery beaches in mid- to late May (days 130-140). The number

of pups generally increased rapidly during most of June and leveled off in late June or early July

(days 180- 190). Median pupping dates were 10 to 13 June at Beach 4 (days 161 - 164: 1979-94),

11 to 15 June at Beach 3 (days 162-166: 1979-87), and 18 to 22 June at Beach 2 (days 168-173:

1979-83). On the smaller rookery beaches at Marmot Island (i.e., Beaches 2 and 32, with fewer

11J. Lewis, Alaska Department of Fish and Game, 802 3rd Street, Douglas, Alaska 99824.

Pers. commun., June 1991.
20

than 200 pups), however, the median pupping date typically was a week later: 19 to 23 June.

Phenology of pupping was similar at all rookeries, regardless of size, and during all years.

Characterizing pupping at Beach 7 was difficult due to infrequent counts, but timing appeared to

be comparable to other beaches in 1993 and 1994. However, in 1991 and 1992, perhaps earlier

by 10 to 14 days.

Extended series of cliff pup counts during mid- to late July were available only for 1984

and 1985. At Beaches 3 and 4, numbers of pups declined dramatically after 9 July during both

years (Fig. 17). The onset of the decline in 1984 coincided with pup counts, which were

conducted on 8 and 10 July at Beach 4 and on 10 July at all other rookery beaches (Lewis 1987).

At Beach 2 in 1984 however, numbers of pups increased for about 10 days after the pup count

before beginning. to decline. There were no pup counts in 1985. During 1994, there was no

apparent change in numbers of pups at Beach 4 after the pup count, which was conducted on

27 June. At Beach, 7, pup numbers appeared to increase after the pup count in 1994.

A decline in pup abundance may have begun at Beach 4 during mid-July 1992, a year with

no pup counts. Pups were observed swimming to Beach 3Z, where a concurrent increase in pup

numbers took place. The observer assumed these pups were immigrating from Beach 4, which is

located only a few hundred yards to the south (S. Stanford”). Unfortunately, observations ended

that year on 15 July, so the extent of this pup movement is not known.

The number of pups per adult female tended to increase linearly during the breeding

season. By early July, when very few new pups were being born, the ratio of pups to adult

females on Beach 4 ranged from 1.2 to 1.8. (Fig. 18). The ratio of pups to adult females was

consistently lower (from 0.5 to slightly over 1.0) at Beach 3, and lowest (between 0.2 and 0.4) at

Beach 2. No consistent difference was apparent between years at Beach 4 (Fig. 18). At Beaches

2 and 3, the number of pups per adult female appeared to decrease slightly from 1979 to 1983 and

again from 1983 to later years. A ratio of pups to females greater than unity can be explained by

adult females spending more time at sea as their pups grew older.

12S. Stanford, Alaska Department of Fish and Game, 333 Raspberry Road, Anchorage, Alaska

99501. Pers. commun., July 1992.

l
21

The number of pups per territorial male also increased linearly until early July at each of

the rookery beaches, The greatest number of pups per male (approximately 35) were observed

during 1979 at Beach 4 (Fig. 19). Pups per male declined consistently each year from 1979

through 1994, seldom more than 10 pups per male. Other rookery beaches had fewer pups per

male than Beach 4. Peak numbers at Beach 3 were approximately 10 to 15 pups per territorial

male from 1979 through 1987. The ratio of pups to territorial males was consistently lowest at

Beach 2, typically well below 10 pups per male.

Comparison of Aerial Survey and Cliff Counts

Fifteen paired counts were available for comparing aerial to cliff counts. The range in time

difference for the paired counts was between 43 minutes and 4.7 hours. On five occasions, the

cliff count was made prior to the aerial survey count and on 10 occasions the cliff count was made

later. The relative difference between the number of animals counted by the two methods ranged

from 2.5% to 67.6% (x = 21.8%). If the sign of the difference was retained (a negative value

when the cliff count was smaller), the range was from -67.6% to +24.6% (x = - 16.1%). Thus,

the cliff count averaged about 16% below the aerial survey count. Linear regression also

indicated that the cliff counts were consistently lower than the aerial counts, as the observed slope

of 0.781 (Fig. 20) was less than 1 (P < 0.001, R2= 0.996). By this method, the cliff counts

averaged only 78.1% as many animals as the aerial survey counts. The intercept was not different

from zero (t-test, P = 0.56). There was a direct relationship (simple linear regression, P = 0.040,

R

2

= 0.287) between the relative numerical difference in the counts and the time difference

between them (Fig. 21). That is, the earlier a cliff count was made in advance of the aerial count,

the lower it was.
22

Observations During Non-Breeding Season

Land-based Counts

Cliff counts were made on a regular basis from 18 November 1987 through 27 March

1988, in conjunction with other research. Observers were able to follow the progress of pups that

were branded and tagged during the previous June and July, assessing the survival of branded

pups and the integrity of brands as they healed and pups molted. Observers also made counts of

pups and .non-pups at each beach. These included 74 to 86 counts each at Beaches 1 through 4

and 9 to 10 counts at Beaches 5 through 7. All counts were dependent on weather conditions.

Day-to-day variability in counts was much greater during the non-breeding season than

during the breeding season, even when the data is smoothed by plotting using 5-day maximum

counts (Fig. 22). The total number of non-pups counted at all beaches ranged from 8 to 756.

Pup cliff counts for all beaches ranged from 4 to 981. For Beaches 1 through 4, counts ranged

from 7 to 873 for non-pups and 9 to 981 for pups. The numbers of sea lions on the beaches

appeared to be governed primarily by weather conditions, with the fewest number of animals on

the beach during stormy weather when water levels and surf were highest13. For the Beaches 1

through 4, which were surveyed on a regular basis, virtually all animals were observed on Beaches

3Z or 4. A total of 26 animals were seen on four occasions at Beach 3 and none were seen on

Beaches 1 or 2.

Aerial Surveys

Aerial surveys, at times other than the breeding season (June and early July), were

conducted on 12 occasions from July 1956 through December 1994 (Table 3). The largest

estimate of sea lions from an aerial survey made outside of the breeding season was 8,819 nonl3 L. Aumiller and C. Matt. 1988. Summary of data collected on Marmot Island, Alaska,

November 17, 1987 - March 28, 1988. Unpubl. summ., avail. National Marine Mammal

Laboratory, Alaska Fisheries Science Center, 7600 Sand Point Way N.E., Seattle WA 98115.
pups in late July 1986. At that time of year, pups could be differentiated from older animals and

excluded from the counts. Counts from the non-breeding season aerial surveys ranged from 114

in March 1993 to 6,790 in September 1957. These counts include all animals because pups had

molted into adult-colored pelage and were not discernable from juveniles.

Distribution

Redistribution of animals was observed twice from November 1987 to March 1988. Prior

to 5 December 1987, Beaches 3Z and 4 were usually occupied by several hundred sea lions each

(Fig. 22). From 5 December 1987 through 21 March 1988, however, the number of sea lions on

Beach 3Z increased while Beach 4 was virtually abandoned. Sea lions were observed at Beach 4

on only 7 occasions during the following 73 counts. Presumably, all or most of the Beach 4

animals moved to Beach 3Z during the non-breeding season. In fact, 45 branded pups moved

from Beach 4 to Beach 32 during late November and early December. From 22 to 24 March,

however, most of the sea lions on Beach 32 moved back to Beach 4, including 79 branded- pups.

Of the pups observed to change beaches, 23 made both moves, from Beach 4 to Beach 3Z in the

fall and back to Beach 4 in March.

For Beaches 5, 6, and 7, which were observed less frequently from November 1987 to

March 1988, sea lions appeared to use all three early in the observation period. After late

January, however, animals were seen only on Beach 5. Unfortunately, the low frequency of

counts makes it impossible to identify when this change in haul-out use took place.

Counts made from a skiff on 31 July 1993 also detected substantial redistribution of sea

lions along the Marmot Island beaches following the end of cliff counts in mid-July. No sea lions

were observed on Beach 3 where there had been 50 to 70 males in mid-July. The total number of

non-pups on Beach 3Z dropped from 150 or more to 40- 45. The number of sea lions on Beach 4

dropped from 400 non-pups to only 16-l8 males. Conversely, on Beach 5 the number of animals

increased from no more than 14 animals during June and July to 135 to 144 on 31 July. The 225

to 240 animals on Beach 7 were only marginally below the June to July counts. On 31 July, pups
24

were observed to be present but could not be counted on Beaches 3Z, 5, 6, and 7. No pups were

observed on Beach 4.

Aerial surveys during March 1993 and December 1994, as well as opportunistic

observations made during February 1993, March 1994, and November-December 1994 support

the supposition that Beach 3Z is a preferred haulout during the fall, winter, and early spring., On

those occasions, virtually all of the sea lions hauled out on Marmot Island were at Beach 3Z.

Resighting of Branded and Tagged Animals

Of 49 Steller sea lion pups tagged (and not branded) on Beach 3 in 1987, 3 1 (63.3%)

were females and 18 (36.7%) were males. An additional 751 pups were both branded and tagged

during 1987 and 1988: 390 (5 1.9%) females and 361 (48.1%) males (Table 4). Through

December 1994, 151 individual sea lions (20.1%: 78 females and 73 males) of the 751 branded

pups were resighted on 204 occasions. Of the 151 resighted animals, 114 (77.6%) have been

resighted only once, 19 (12.9%) have been resighted twice, 9 (6.1%) were seen three times, 3

(2.0%) were seen four times, and 1 each (0.7%) were resighted five and six times. Of the 49 pups

that were only tagged, only one female was resighted on a single occasion. Considering all

observations through December of 1994, there has been no apparent difference in the resighting

rate for branded males and females or for the 1987 and 1988 cohorts (x2, P > 0.05).

Branded sea lions were observed at 23 different locations through 1994 (Table 8). The

greatest number of resightings (116 of 204: 56.9%) were from Marmot Island; an additional

33 resightings (16.2%) were from the Kodiak Archipelago or Sugarloaf Island, within a radius of

about 75 km. The one female that was tagged without a brand was also resighted at Marmot

Island, The resighting most distant (approximately 1,700 km) from Marmot Island was made at

Loretta Island (53o45'N, 128o50’W), in the upper reaches of Douglas Channel, British Columbia,

Canada (P. Olesiuk14). Tags from 13 (6 females, 7 males) animals, branded/tagged as pups, were

14P. Olesiuk, Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, British

Columbia, Canada V9R 5K6. Pers. commun., July 1995.
recovered from the stomach of a killer whale found dead on the beach in Prince William Sound,

Alaska, and two animals were killed in gillnets. All other resight observations were of live

animals.

The greatest number of resightings occurred when animals were about 1 -year-old

(Fig. 23). Yearlings accounted for 72 of 187 (38.5%) or 71 of 186 (38.2%) resightings,

depending on whether the analysis included animals that were tagged but not branded. For males,

the frequency of resighting was low for 2- through 5-year-olds. Resighting generally was low for

females 2 or more years old; the greatest frequency of resighting (10 individuals) was for 7-yearolds from the 1987 cohort. The observed number of females and males was significantly below

the number of animals expected to be alive at any given age (x2, P 0) (Table 9).

By 1994, nine branded females were observed with pups. Two were seen with pups on

Marmot Island during June 1993 (one pup was later abandoned) and one was seen with her pup

on Latax Rocks, approximately 70 km from Marmot Island, in March 1994. During June 1994,

three branded females were observed with pups on Marmot Island and three were observed on the

rookery at Sugarloaf Island, approximately 75 km north of Marmot Island. The pup abandoned

on Marmot in 1993 and one of the 1994 Sugarloaf pups did not survive.

DISCUSSION

Decline in Abundance

The most striking result to come from the many years of observation at Marmot Island is

the overall decline in the number of Steller sea lions present during the breeding season. The

decline was consistent from the 1970s to 1994, both for non-pups and pups. The population

decline was not unique to Marmot Island, but rather reflected a trend that was observed from the

Gulf of Alaska westward. However, the decline in abundance was more severe at Marmot Island

than in the central Gulf of Alaska as a whole. From 1976 to 1994, the number of non-pups at

Marmot Island declined by 88.9%. By comparison, the decline in abundance was about 76.9%

(14,816-3,427) at the other 14 trend sites and 79.1% (9,617- 2,008) at the other three trend
26

rookeries (Sugarloaf, Chirikof, and Chowiet Islands). From 1991 to 1994, the decline in the

number of non-pups at Marmot Island ranged from 25% to 33%,, depending on whether aerial

surveys or cliff counts were compared. Based on aerial survey results, the decline from 1991 to

1994 was 28.8% for the other 14 trend sites and 30.2% for the other three trend rookeries in the

central Gulf of Alaska (NMFS15). From 1976 to 1994, estimated annual rates of decline were

12.8% at Marmot Island, 8.8% for the other trend sites, and 8.9% for the other trend rookeries.

The decline in pup production at Marmot Island was also comparable to those observed

for pups in the central Gulf of Alaska. From 1979 to 1994, the observed decline in pup numbers

was 88.1% at Marmot Island and 84.4% for Sugarloaf, Chirikof, and Chowiet Islands combined.

From 1991 to 1994, pup production declined by 50.1% at Marmot, 41.5% at Sugarloaf Island

(1990-94), and 48.6% at Chirikof Island (1991-94) (NMFS16). Reliable counts were not available

for Chowiet Island for 1990 or 1991,

The statistical significance of declines in the numbers of pups and non-pups at Marmot

Island, as well as the estimated annual rates of decline, varied among the regression methods. The

numbers of non-pups from 1979 to 1994 provide an example of this discrepancy. Simple linear

regression indicated similar annual rates of decline in counts from Beaches 1 through 4 (- 15.5%,

P < 0.001) and in aerial surveys (- 12.7%, P < 0.001). By the bootstrap method, the decline was

still significant, but the rate was lower (- 5.9%, P < 0.025). The Dennis et al. (1991) model did

not detect a significant decline (- 6.9%, P = 0.153). These differences arise from differences in

the data points used in the analyses as well as in the way the model analyzes those data.

The simple linear regressions used a single data point for each year from the aerial surveys,

beach pup counts, or the maximum cliff count. For any given count, an unknown proportion of

all animals that use the beach are not present. Although aerial surveys are timed to maximize the

likelihood of observing at least 90% of the maximum number of non-pups that use a particular

rookery beach, daily counts may vary by 30% or more. Reliance on maximum annual counts

15R. L. Merrick, NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point

Way N.E., Seattle, WA 98115.

16NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point Way N.E.,

Seattle, WA 98115.
27

assumes that after several weeks of daily observation the maximum count should approach the

actual number of animals that use the beach during a given year. The beach pup counts may be

less problematic. If they are conducted at the correct time, the number of pups that have already

left the beach or that have not been born should be negligible.

The Dennis et al. (1991) and iterative models, as applied to the Marmot Island data, avoid

the problems associated with single counts by using all available counts from a l0-day period.

Certainly, the selection of an interval is critical and a slight shift earlier or later in peak abundance

could affect the results. The Dennis model also incorporated adjustments for count variability as

well as for non-independence (i.e., the count in one year is not independent of the counts in

previous or successive years). The bootstrap model handles count variability and nonindependence by examining many solutions derived from data points randomly selected from all

observations.

Given these differences, it is not surprising that the different regression methods may yield

different results. Arguments could be made in favor for or against each method, but the important

conclusion is that each presents a similar general trend: Steller sea lions, both pups and non-pups,

have declined in number at Marmot Island from 1979 to 1994.

The one age/sex group that did not show any sign of a population decline at Marmot

Island was the territorial males, The number of territorial males on a particular rookery beach

appeared to be independent of population size. As the population of adult females decreased,

territorial males either had fewer females in their territories or more males held territories

containing no females. By the 1990s adult females and pups on Beach 4 were concentrated

primarily on the northern half of the rookery. A number of adult males continued to occupy

territories without females in the southern part of the rookery, however. The size and overall

distribution of individual males appeared to be quite similar for the males at either end of the

beach.
2 8

Juvenile Survival in Relation to the Population Decline

Juvenile Steller sea lions appear to have declined more precipitously than other groups,

both in absolute numbers and relative to the numbers of all non-pups. This drop in the proportion

ofjuveniles From 1979 to 1994 suggests either that unusually high numbers ofjuveniles were

observed at Marmot during 1979 and 1983 or that the number ofjuveniles has decreased from

1987 through 1994. Based on observations during 1981, Smith (1988) noted that the relative

numbers ofjuvenile sea lions were much greater on Marmot Island than on Sugarloaf Island,

approximately 75 km to the north Physiography is perhaps the most significant difference

between the rookery areas on the two islands. Smith (1988) suggested that the gently sloping,

wide beaches on Marmot Island created a more favorable habitat for juveniles than did the steepsided, rocky rookeries on Sugarloaf Island. If, in fact, Marmot Island has always been a preferred

site-for juvenile sea lions, then the 1979-83 counts would not be inordinately high. Thus, the

dramatic drop in observed numbers ofjuveniles at Marmot Island could suggest that their survival

rate has decreased since the late 1970s or early 1980s.

The low return rate of branded sea lions also suggests low juvenile survival during recent

years. For any given age group and sex, the number of branded animals that have been resighted

was about an order of magnitude lower than the number expected to be alive, as estimated by

age-specific survival rates (Table 8). Given the strong tendency of adult female sea lions to return

to their natal rookery (Gentry 1970, Calkins and Pitcher 1982), however, most surviving females

would be expected to return to Marmot Island as they recruit into the breeding population.

Female Steller sea lions reach sexual maturity between 3 and 6 years of age (Calkins and Pitcher

1982). Females branded as pups on Marmot could have returned to breed for the first time in

1990 or 1991. By 1994,6 and 7 years after branding, almost all surviving females should have

been sexually mature. The expected number of resighted 6-year-old females was 140 to 150, but

through 1993 and 1994 only 10 of these animals were resighted.

The success for resighting branded or tagged animals is determined largely by observation

effort. Since 1991, that effort has been uniform and extensive at Marmot Island only during the

breeding season. Two of the 8 branded females observed with pups during June 1994 were
29

resighted on Sugarloaf Island, where there has been little observer effort since 1987-88.

Presumably, the number of resighted branded females would have been greater with increased

observer effort. Unless the number of branded/tagged females returning to rookeries is observed

to increase substantially during 1995 or 1996, it would appear that recruitment into the breeding

population is low.

In comparison, 380 California sea lion (Zalophus californianus) pups were branded on

San Miguel Island, California, in 1987 (95 females, 111 males) and 1988 (85 females, 89 males).

Since 1990, the proportion of the branded females that were resighted each year on San Miguel

has been 5 to 10 times greater” than for the corresponding age groups of Steller females resighted

at Marmot Island. The San Miguel Island and Marmot Island brand-resight work were for

different, albeit closely related species, and took place on extremely different habitats separated by

about 24 degrees of latitude. In addition, resight effort was not the same at the two islands and

certain behaviors at San Miguel Island may enhance resighting ability (animals frequently travel

from inland sites to the water to escape the afternoon heat, thus providing a convenient

opportunity for a well-situated observer to search for brands18). Despite these differences,

however, the extreme disparity between the observed numbers of females on the two islands

suggests a much lower survival of juvenile sea lions at Marmot Island.

Timing of the Breeding Season

Timing of the breeding season for Steller sea lions is uniform throughout their range. This

includes rookeries as geographically dissimilar as Año Nuevo Island off northern California

(Evermann and Hanna 1925, Orr and Poulter 1965, Gentry 1970) several rookeries in British

Columbia, Canada (Pike and Maxwell 1958), the Gulf of Alaska (Calkins and Pitcher 1982), and

the Pribilof Islands in the Bering Sea (Scheffer 1945). Peak numbers of adult and juvenile sea

17R. DeLong and S. Melin, unpubl. data. National Marine Mammal Laboratory, 7600 Sand

Point Way N.E., Seattle, WA 98115.

18S. Melin National Marine Mammal Laboratory, 7600 Sand Point Way N.E., Seattle, WA

98115. Pers. commun., October 1995.
30

lions on the rookery typically occur during late June and early July at Marmot Island, as well as at

Año Nuevo Island (Gentry 1970) and at Ugamak Island in the eastern Aleutian Islands (Menick

et al. 1988). The increases, peaks, and declines in the number of territorial males and adult

females on Marmot Island’s rookery (Beaches 3 and 4: Figs. 12 and 24) are simultaneous and

parallel to those at Año Nuevo Island (Gentry 1970).

The range of dates for viable births, from mid-May to mid-July, also is uniform for

Marmot Island, for Alaska in general (Calkins and Pitcher 1982), for Rogue Reef in Oregon

(Merrick 1987) and for Año Nuevo Island (Gentry 1970). Slightly shorter seasons are described

for the Pribilof Islands (23 May to 20 June: Scheffer 1945), Fish (also called Lewis or Wooded)

Island, approximately 340 km northeast of Marmot Island (25-28 May to 29 June- 1 July:

Sandegren 1970), and British Columbia (late May through late June or early July: Pike and

Maxwell 1958). From 1979 through 1994, the median pupping date for the Marmot Island

rookery (Beaches 3 and 4) was from 10 to 15 June. Dates within the same range were observed

at Fish Island in 1967/68 (13- 16 June: Sandegren 1970), at Ugamak Island in 1977/78 and

1985/86 (12-15 June: Withrow 1982, Merrick 1987, Merrick et al. 1988) at Cape St. James,

British Columbia in the 1970s (14 June: Edie 1977, cited in Menick 1987), and at Año Nuevo

Island in 1968 (approximately 14 June: Gentry 1970).

Differences in Distribution Between the Breeding Season and Non-breeding Season

Beaches 4 and 7 have been the major rookeries on Marmot Island since 1991. Beaches 2

and 3 were also important rookeries prior to the mid-1980s. Beach 3Z, a small rookery during

the breeding season, appears to be the primary haul-out beach during winter and early spring.

Virtually all sea lions observed hauled out on the island during November through March have

been on Beach 3Z.

There appears to be a variable transition period between distribution during the breeding

and non-breeding seasons. In 1992, immigration of adult females and pups to Beach 3Z was

observed beginning on 12 July. Presumably these sea lions arrived from Beach 4, which may have

signaled the onset of the seasonal redistribution in that year. In 1993, observers detected no
31

appreciable movement away from Beach 4 to Beach 3Z by 9 July when observations ended for the

season. A l-day visit on 3 1 July, however, revealed that a substantial redistribution had occurred

sometime during the previous 3 weeks. The number of sea lions on Beach 7 remained essentially

unchanged, but other rookeries were almost completely abandoned. More than 100 sea lions were

on Beach 5, a beach used by few sea lions during the summer. By March 1994, the next time the

island was visited, virtually all sea lions observed were on Beach 3Z. In 1987, the only year with

continuous non-breeding season observations, the shift from Beach 4 to Beach 3Z took place

during a l-or 2-day period around 5 December.

The transition back to breeding season distribution in the spring may be equally variable.

In 1988, after spending most of the non-breeding season on Beach 3Z, most sea lions abruptly

moved to Beach 4 From 24 to 28 March. Observations ended at that time, so we do not know if

that marked the redistribution of sea lions from one beach to the other or merely marked the onset

of a transition period characterized by large-scale movements. As late as 20 March in 1993 and

15 March in 1994, almost all sea lions were still located on Marmot Island on Beach 3Z.

Certainly by May the animals began shifting back to a breeding season distribution, as numbers of

territorial males increased on rookeries. The variable number of adult males and juveniles

observed in 1979 during the last half of May suggests that animals are returning to the rookery

beaches at that time but may not be remaining there for long periods of time. Stability of the

rookery beaches probably does not occur until the adult females begin to return in significant

numbers in June to give birth to their pups.

Comparison of Aerial Survey and Cliff Counts

Our results led us to reject the null hypothesis that cliff counts and aerial survey counts at

Marmot Island yield the same results. In particular, cliff counts were systematically lower than

aerial counts by 16% to 22%. Numbers of non-pups on rookery beaches tend to build during the

day and earlier counts might be expected to be lower. However, all aerial and cliff counts were

made during peak hours when higher numbers of animals are likely to be present on the beach.

Even cliff counts that were made later in the day were lower than aerial counts.
32

There are several possible explanations for this observed difference: 1) aerial survey

counts overestimated the number of animals on the beach; 2) cliff counts under-estimated the

number of animals on the beach; 3) both counts were accurate but the number of animals changed

between counts; 4) some combination of the above. Counters use a variety of cues to interpret

aerial photographs. The head, flipper, or rump of a single sea lion conceivably could be

interpreted as parts of two or more animals, particularly if there are many animals on a beach,

animals are densely packed, and the photographic image is small. Such conditions may occur with

photographs of the largest rookery beaches on Marmot Island (i.e., Beaches 4 and 7). During

cliff counts, some animals certainly are obscured from view, as most beaches have some areas that

are difficult or impossible to see from the observation sites above. Even though some animals

may haul out high on the beach, particularly during cool weather, systematically missing 20% of

the animals on a beach in this manner is unlikely. Alternatively, observers may just tend to undercount the number of animals on the beach.

Withrow (1982) compared ground counts of Steller sea lions with aerial survey counts

from photographs taken at Ugamak Island during 1977 and 1978. and found no significant

difference between them. Count data from Ugamak Island were less problematic than those from

Marmot Island. At Ugamak Island, ground counts were made within 15 to 30 minutes of the

aerial survey. Typically, the ground observer waited in position and started counting immediately

after the aircraft passed overhead and observers could walk between outlooks in a few minutes

(D. Withrow19). ‘Under these circumstances there probably was little or no change in the number

of sea lions counted by the two methods. Because of the distances between the different beaches

on Marmot Island, a complete census requires 6 hours or more, guaranteeing a large time

difference and increasing the likelihood that the number of animals on the beach changed between

aerial and cliff counts. In addition, the view of beaches on Ugamak Island was unobstructed,

leaving almost no blind spots for counters. The appropriate controls for analyzing the Marmot

Island data, namely knowing exactly how many animals were available for either count or how

much change occurred between counts, are unavailable.

19D. Withrow, National Marine Mammal Laboratory, 7600 Sand Point Way, N.E., Seattle,

WA 98115. Pers. commun., October 1995.
33

Optimal Survey Dates and Times

Based on his observations at Ugamak Island (54o12.5’ N, 164o50.0’ W) in the eastern

Aleutian Islands during 1977 and 1978, Withrow (1982) determined that aerial surveys conducted

between 18 June to I6 July should maximize the likelihood that at least 90% of the animals will be

hauled out. Similarly, Menick (1987) identified the optimal survey window as 18 June through

7 July using observations at Rogue Reef, Oregon (1982), Marmot Island Beach 3 (1983) and

Ugamak Island (1986 and 1987). Our observations at Marmot Island from 1979 through 1994,

suggest that the optimal dates are from 12 to 29 June. A slightly wider survey window, 10 June

to 4-5 July (days 161 to 185- 186) probably would yield satisfactory counts in most years.

Survey dates after 9 July are unsatisfactory.

Identification of a specific hour window for surveys is less straightforward, possibly

because of the limited number of observations. The three dawn-to-dusk count series at Beach 3

suggest that surveys should be conducted from 1100 to 1700 ADT (0900-1500 “local sun time”;

i.e., when the sun is directly overhead at 1200) to maximize the likelihood that a survey count will

be within 90% of the daily maximum. Survey times could be expanded to 0900-2 100 ADT if the

threshold is reduced to 80% of the maximum. The three series of dawn-to-dusk observations

from Beach 4 suggest a more narrow window to include 90% of the daily maximum: 1000- 1300

ADT. The likelihood of observing at least 80% of the daily maximum was high almost all day at

Beach 4, but it may drop after about 1400 ADT.

Based on his observations in 1977 and 1978, Withrow (1982) determined that the optimal

hours for aerial surveys at Ugamak Island are 1000-1800 BST (Bering Standard Time). In 1977

and 1978, BST coincided with local sun time. Using counts at Ugamak Island from 1986 and

1987, Merrick et al. (1988) identified the hours of 1000-2000 AST (Alaska Standard Time) as the

best time to conduct an aerial survey. Because of the Alaska-wide, 2-hour time-zone shift in

October 1983, 1000-2000 AST in 1986 and 1987 corresponded to 0800-1800 BST or local sun

time, in 1977 and 1978. Thus, during our observations, the optimal window for counting sea

lions on Marmot Island occurred two or more hours earlier on Marmot Island than on Ugamak,

according to “local sun time.”
3 4

Met-rick (1984, 1987) noted the lack of a well-defined daily peak in occupancy on Marmot

Island Beach 3 during 1983. At that time, it appeared that a tidal effect obscured the hauling

pattern typical of other rookeries, as a mid-day high tide restricted beach space and reduced the

area available for sea lions to haul out. However, it is difficult to build a convincing argument

that tides played a significant role in shaping daily hauling patterns on Beach 4 during 1991 and

1992. By 1991, only about one-half of Beach 4 was occupied by sea lions. Even during stormy

conditions there appeared to be ample beach area for animals to haul out. At this time, there is no

clear explanation for the lack of a clearly defined daily haul-out pattern on Marmot Island.

The optimal time for pup counts on Marmot Island was between 29 June and 9 July.

Performing pup counts a week or 10 days earlier likely would not diminish the count results

severely, but there is some evidence to suggest that pup numbers could decline precipitously after

9 July. Unfortunately, the number of late-season counts was too small to verify the extent of this

decline.

Branded Animal Resights

The number of resights of branded or tagged animals is a function of observation effort.

For Steller sea lions at Marmot Island and elsewhere in Alaska, that effort has not been uniform

temporally or geographically. There was considerable resighting effort for branded/tagged pups

on Marmot Island from November 1987 through March 1988. There was no significant

difference in mortality between branded and unbranded pups20. During the summers of 1988,

1989, and 1990, however, resighting effort at Marmot Island and other locations came largely

from opportunistic observations made during other research. Concerted effort to resight

branded/tagged animals has taken place on Marmot Island during the breeding season each year

since 1991. There was similar effort on Sugarloaf Island during the breeding seasons for 1994

and 1995. Observers at other locations and during other times of year continued to be

opportunistic.

20NMFS, unpubl. data. National Marine Mammal Laboratory, 7600 Sand Point Way N.E.,

Seattle, WA 98115.
35

Another complication with the resighting of marked animals is the potential confusion with

animals marked at other locations. Three sea lions observed on four occasions in southern British

Columbia, Canada, may have been marked at Marmot Island, but probably were Steller sea lions

tagged at rookeries in Oregon, Those three Oregon animals were marked with different color

tags and were not branded*‘. Potential confusion arises, however, because tag color can change

as tags weather (i.e., white tags may appear yellow or blue tags may appear green) and brands

may not be visible.

21R. Brown Oregon Department of Fish and Wildlife, Marine Region, Marine Science Drive,

Bldg. No. 3, Newport, OR 97365. Pers. commun., July 1995.
36

ACKNOWLEDGEMENTS

We would like to thank L. Aumiller, G. Orth, J. Lewis, C. Matt, W. Cunningham, and S.

Stanford from the Alaska Department of Fish and Game; L. Ferm, R. Merrick, C. Hutchinson, M.

Strick, and J. Cesarone from the National Marine Mammal Laboratory; K. Ono from University

of California Santa Cruz; L. Gerber from University of Washington; and. volunteers P. Lewis, L.

Taylor and J. Waite who participated in this study. R. Menick (NMFS), T. Laughlin (NMFS), D.

Calkins (ADF&G) and J. Lewis (ADF&G) participated in the design of the field studies. Pup

branding work in 1987-1988 was directed by T. Loughlin (NMFS). P. Anderson, R. Otto, R.

Macintosh, N. Terrell, and others at the National Marine Fisheries Service Kodiak Laboratory

provided invaluable logistical support. R. Macintosh at National Marine Fisheries Service Kodiak

Laboratory provided a comprehensive list of bird species on the island. D. Prokopowich and K.

Brennan of the Commercial Fisheries Division, Alaska Department of Fish and Game, Kodiak,

Alaska, provided much appreciated radio contact and logistical support. H. Reed and T. Walters

of Maritime Helicopters, M. Machulsky and H. Downs of Alaska Helicopter, and various pilots

of U.S. Coast Guard, Kodiak, Alaska, provided air transport of personnel and field gear to and

from Marmot Island. P. Dyson of Kodiak provided valuable and reliable weather information.

This work was authorized under Marine Mammal Protection Act permits 598 and 809. H. Huber

(NMFS), D. Withrow (NMFS), T. Laughlin (NMFS), R. Merrick (NMFS), and H. Braham

(NMFS) provided critical review of this manuscript. K. Zecca provided the front cover

illustration. Finally, we thank our friends and families for their continued support.
37

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Orr, R.T. and T.C. Poulter. 1967. Some observations on reproduction, growth, and social

behavior in the Steller sea lion. Proc. Calif. Acad. Sci., Series 4, 35: 193-226.

Orr, R.T., and T.C. Poulter. 1965. The pinniped population of Ano Nuevo Island, California.

Proc. Calif. Acad. Sci., Series 4, 32:377-404.

Perlov, A.S., L.A. Popov, and D.G. Calkins. 1982. Daily population dynamics and some

behavioral features of Steller sea lion bachelor rookeries on Marmot Island, AK.,

P. 137-143, In V.A. Zemskii, V.I. Krylov (ed.), Morskie Miekopitayushchie Sbnornik

Nauchnykb Trudov. M.Izd. VNIRO. 165 p.

Pike, G.C., and B.E. Maxwell. 1958. The abundance and distribution of the northern sea lion

(Eumetopias jubata) on the coast of British Columbia. J. Fish. Res. Board Can., 15:5-17.

Pitcher, K.W. 1980. Stomach contents and feces as indicators of harbor seal, (Phoca vitulina)

foods in the Gulf of Alaska. Fish. Bull., U.S. 78(3):797-798.

Sandegren, F.E. 1970. Breeding and maternal behavior of the Steller sea lion (Eumetopias

jubata) in Alaska. M.S. Thesis, Univ. Alaska, Fairbanks, AK., 138 p.

Scheffer, V.B. 1945. Growth and behavior of young sea lions. J. Mammal. 26:390-392.

Sease, J.L., J.P. Lewis, D.C. McAllister, R.L. Merrick, and SM. Mello. 1993. Aerial and shipbased surveys of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, the Gulf of

Alaska, and Aleutian Islands during June and July 1992. U.S. Dep. of Commer., NOAA

Tech. Memo. NMFS F/NWC-17, 57 p.

Smith, L.N. 1988. The influence of rookery terrain on population structure, territorial behavior,

and breeding success of Steller sea lions in the Gulf of Alaska. M.S. Thesis, Univ. of

Alaska., Fairbanks, AK. 100 p.
41

Williams, T.M., R. W. Davis, M.A. Castellini, T.R. Loughlin, D.G. Calkins, and J.L. Sease. 1993.

The relationship between body condition and thermoregulatory costs in Steller sea lion

pups. Abstract. P. 17, In Proceedings of the Tenth Biennial Conference on the Biology of

Marine Mammals, November 11 - 15, 1993, Galveston, TX.

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WA., 102 p.

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10(1):38-51.
42

Table l.--Range of dates, total number of counts, number of composition counts (by

age/sex classes) for non-pups, and number of pup counts made during the

breeding season by observation from cliff tops at five rookery beaches on

Marmot Island, Alaska, 1979-94.
43

Table 1 .--Continued.

1

 Sources: I-ADF&G, unpubl. data; 2-NMML, unpubl. data.

2

 Composition counts for territorial males and pups only.
44

Table 2.--Counts of Steller sea lion pups on Marmot Island, Alaska, 1979-94.

*Sources: I-ADF&G, unpubl. data; 2-Laughlin et al. 1990;

3-Merrick et al. 1992; 4-NMFS, unpubl. data.
45

Table 3.--Numbers of Steller sea lions on Marmot Island, Alaska, counted from aerial

photographs, 1957-94. Counts for May though July are of non-pups only;

counts for September through March include pups.
46

Table 3 .--Continued.

‘Sources: 1-Mathisen and Lopp 1963; 2-Calkins and Pitcher 1982;

3-ADF&G, unpubl. data; 4-NMFS, unpubl. data.; 5-Lewis 1987;

6-Calkins and Goodwin 1988; 7-Laughlin et al. 1990; 8-Menick

et al. 1991; 9-Merrick al. 1992; l0-Sease et al. 1993.
47

Table 4.--Steller sea lion pups marked with sequentially numbered flipper tags and hot

brands at Marmot Island, Alaska, during 29 June to 1 July 1987, and 30 June to

1 July 1988. Flipper tags were applied to the posterior margin of both foreflippers of each pup; hot brands were on the right (1987) or left (1988) flank.

1

 Tag/brand number 045 was not used.

2

 Two pups were tagged and branded with number 401.
48

Table 5.--Maximum counts of Steller sea lion non-pups and pups counted from cliff-top

observation posts overlooking rookery and haul-out beaches on Marmot Island,

Alaska, during the breeding season., 1979-94.

‘Only approximate numbers available for Beach 2 in 1985.

‘Pups were observed immigrating from Beach 4 on 12- 15 July. During the

4-day period the number of pups increased from 17 to 66.
49

Table 6.--Statistics for linear regressions of the natural log (In) of counts on year for

aerial survey counts of non-pups and beach counts of pups for the entire island

and for cliff counts of non-pups and pups for Beaches 1-4 and Beaches l-7,

combined. The slope estimates the annual rate of decline during the interval.
50

Table 7.--Statistics for the Dennis (after Dermis et al. 1991) and iterative (bootstrap) models for

cliff counts of pup, juvenile, and all non-pup Steller sea lions at Beach 4, Marmot

Island, Alaska. Type of model, interval (years), number of data points (n: one point per

year), slope, standard error (SE), and probability value (P) are listed below.
51

Table 8.--Location, approximate distance from Marmot Island, and number (n) of

resightings of Steller sea lions branded as pups on Marmot Island, Alaska, in

1987 and 1988. Multiple resightings are included for individual sea lions from

different years or from different locations in the same year.

1Does not include the resight of one female that was tagged but not branded.

2

Tags recovered from the stomach of a beach-cast killer whale. Tags from 14

individual sea lions were recovered; 13 were positively identified as animals

tagged on Marmot Island.

3Animals killed in gillnets.

4Animal released alive from gillnet, location not reported.
52

Table 9.--The number of Steller sea lions branded and tagged as pups on Marmot Island

during 1987 and 1988 expected to be alive and the number observed at given

ages. Expected numbers (Exp.) were generated from the initial number of

branded or tagged pups and age-specific survival rates (SW-V.) adapted from

CaIkins and Pitcher (1982) and York (1994). Observed numbers of animals

(Obs.) were those resighted at all locations, excluding those for which age of

death is unknown. One resighted female was tagged but not branded.

a

a

54

Figure 2

Source: Alaska Dept. Fish and Game, 1979.

Source: Alaska Dept. Fish and Game, 1979
Source: Alaska Dept. Fish and Game, 1979


Figure 8.--Number of non-pup Steller sea lions counted on Marmot Island, Alaska, during

aerial surveys (1976 to 1994), maximum counts from cliff-tops for Beaches 1

through 7 combined (1991 to 1994), and maximum counts from cliff-tops for

Beaches l through 4 combined (1979 to 1994). Each maximum count represents

the greatest number of non-pups counted on a single day during a particular year.
Figure 9.--Number of juvenile Steller sea lions counted on Beach 4, Marmot Island, Alaska,

during the breeding season: 1979 to 1994. Data points represent maximum counts

during 5-day intervals.
Figure l0.--Proportion of juvenile Steller sea lions, relative to the total number of non-pups,

counted on Beach 4, Marmot Island, Alaska, during the breeding season: 1979 to

1994. Data points represent maximum counts during 5-day intervals.
63

Figure 11 .--Number of Steller sea lion pups counted on Marmot Island, Alaska, during spook

counts of all rookery beaches (1979 to 1994), maximum counts from cliff-tops for

Beaches 1 to 7 combined (1991 to 1994), and maximum counts from cliff-tops for

Beaches 1 to 4 combined (1979 to 1994). Each maximum count represents the

greatest number of pups counted on a single day during a particular year.
64

Figure 12.--Numbers of non-pup Steller sea lions counted during the breeding season on

rookeries at (A) Beach 3 during 1979 to 1987 and (B) Beach 4 during 1979 to

1994, Marmot Island, Alaska. Data points represent maximum counts during

5-day intervals. Since 1987, sea lions have used Beach 3 as a haulout and very

few pups have been born there.
65

Figure 13.--Number of non-pup Steller sea lions counted on Beach 7, Marmot Island, Alaska,

during the breeding season: 1987 to 1994. Counts were conducted about once per

week during each year.
66

Figure 14.--Number of non-pup Steller sea lions for daily counts on Beaches 3 and 4 combined

during 1979 to 1985 and on Beach 4 during 1991 and 1992, plotted as a proportion

of the maximum count during that year. The horizontal dotted line represents 90%

of the maximum count, vertical dashed lines represent 12 and 29 June (days 163

and 180, respectively).
67

Figure 15.--Number of non-pup Steller sea lions for hourly counts (A) on Beach 3 during 1987

and (B) on Beach 4 during 1991 and 1992, plotted as a proportion of the maximum

count during that day.
68

Figure 16.--Number of adult female Steller sea lions per territorial male on Beach 4, Marmot

Island, Alaska, during the breeding season: 1979 to 1994. Each plotted point is

the maximum number observed during a 5-day interval.
Figure 17.--Number of Steller sea lion pups counted (A) on Beach 3 from 1979 through 1987

and (B) on Beach 4 from 1979 through 1994. Data points represent maximum

counts during 5-day intervals.
Figure 18.--Number of Steller sea lion pups per adult female on Beach 4, Marmot Island,

Alaska: 1979 to 1994. Data points represent maximum counts during 5-day

intervals.
71

Figure lg.--Number of Steller sea lion pups per territorial male on Beach 4, Marmot Island,

Alaska: 1979 to 1994. Each plotted point is the maximum number observed

during a 5-day interval.
72

Figure 20.--Comparison of the number of non-pups counted from aerial survey photographs

and from the cliff count made closest in time. Each point represents an individual

rookery or haul-out beach for a particular aerial survey (e.g., Beach 3 - 1985

Beach 7 - 1994). The, solid line represents perfect concordance between the count

methods (slope = 1.0). The dotted line represents the regression of cliff counts on

aerial counts (slope = 0.789).
73

Figure 21 .--The relative difference between numbers of non-pups from cliff counts and fromaerial survey photographs, as a function of the time difference between the two

counts. A negative time means the cliff count was made before the aerial survey;

a negative difference means the cliff count was lower than the aerial survey.
Figure 22.--Numbers of Steller sea lion pups (black bars) and non-pups (white bars) counted

(A) on Beach 3Z and (B) on Beach 4, Marmot Island, Alaska, during November

1987 through March 1988. Each bar represents the maximum numbers observed

during a 5-day interval.
Figure 23.--Numbers of female (black bars) and male (gray bars) Steller sea lions branded and

tagged as pups on Marmot Island, Alaska, during (A) 1987 and (B) 1988 resighted

one to seven years after branding. Resightings are from all locations. Resightings

of the 1988 cohort during June 1995 are included. These data must be interpreted

with caution as resighting effort was not uniform during all years.
76

Figure 24.--Total number of non-pup Steller sea lions counted on rookery Beaches 3 and 4,

Marmot Island, Alaska, during the breeding season: 1979 to 1994. Data points

represent maximum counts during 5-day intervals. Counts for 1979 through 1987

, include both beaches, counts for 1988 through 1994 (after Beach 3 was abandoned

as a rookery) are for Beach 4 only.
77

Appendix A.--Avian species sited at Marmot Island, 1979 through 1994.

Red-throated Loon

Common Loon

Homed Grebe

Red-necked Grebe

Sooty Shearwater

Pelagic Cormorant

Red-faced Cormorant

Green-winged Teal

Mallard

American Wigeon

scaup sp.

Harlequin Duck

Oldsquaw

Black Scoter

White-winged Scoter

goldeneye sp.

Bald Eagle

Sharp-shinned Hawk

Northern Goshawk

Peregrine Falcon

Gyrfalcon

Willow Ptarmigan

Rock Ptarinigan

Black Oystercatcher

yellowlegs sp.

Surfbird

Western Sandpiper

Common Snipe

Red-necked Phalarope

Mew Gull

Herring Gull

Glaucous-winged Gull

Black-legged Kittiwake

Pigeon Guillemot

Marbled Murrelet

Tufted Puffin

Homed Puffin

Short-eared Owl

Belted Kingfisher

Gavia stellata

Gavia immer

Podiceps auritus

Podiceps grisegena

Puffimus griseus

Phalacrocorax pelagicus

Phalacrocorax urile

Anas crecca

Anas platyrhynchus

Anas americana

Aythya sp.

Histrionicus histrionicus

Clangula hyemalis

Melanitta nigra

Melanitta fusca

Bucephala sp.

Haliaeetus leucocephalus

Accipiter striatus

Accipiter gentilis

Falco peregrinus

Falco rusticolus

Lagopus lagopus

Lagopus mutus

Haematopus bachmani

Tringa sp.

Aphriza virgata

Calidris mauri

Gallinago gallinago

Phalaropus lobatus

Larus canus

Larus argentatus

Larus glaucescens

Rissa tridactyla

Cepphus columba

Brachyramphus marmoratus

Fratercula cirrhata

Fratercula comiculata

Asio flammeus

Cetyle alcyon
Appendix A.--Continued

a

78

a

Downy Woodpecker

Three-toed Woodpecker

Tree Swallow

Violet-green Swallow

Bank Swallow

Black-billed Magpie

Northwestern Crow

Common Raven

Black-capped Chickadee

Brown Creeper

Winter Wren

American Dipper

Golden-crowned Kinglet

Gray-cheeked Thrush

Hermit Thrush

American Robin

Varied Thrush

American Pipit

Yellow Warbler

Yellow-rumped Warbler

Wilson’s Warbler

Savannah Sparrow

Fox Sparrow

Song Sparrow

Golden-crowned Sparrow

Dark-eyed Junco

Gray-crowned Rosy Finch

Pine Grosbeak

Red Crossbill

White-winged Crossbill

Picoides pubescens

Picoides tridactylus

Tachycineta bicolor

Tachyciteta thalassina

Riparia riparia

Pica pica

Corvus caurinus

Corvus corax

Par-us atricapillus

Certhia americana

Troglodytes troglodytes

Cinclus mexicanus

Regulus satrapa

Catharus minimus

Catharus guttatus

Turdus migratorius

Ixoreus naevius

Anthus rubescens

Dendroica petechia

Dendroica coronata

Wilsonia pusilla

Passerculus sandwichensis

Passerella iliaca

Melospiza melodia

Zonotrichia atricapilla

Junco hyemalis

Leucoslicte tephrocotis

Pinicola enucleator

Loxia curvirostra

Loxia leucoplera

a

Source: Compiled by R. McIntosh, NMFS Kodiak Laboratory, Kodiak, Alaska
79

Appendix B.--Mammal Species (relative abundance) at Marmot Island 1979 through 1994

Abundance catagories: A = abundant

C = common

U = uncommon

R = rare 

Terrestrial:

River otter (Lutra canadensis) U

Red fox (Vulpes fulva) U

Arctic ground squirrel (Spermophilus undulatus) A

Sitka black-tailed deer (Rama lemionus) U

Feral cattle (Bos sp.) R

Wild boar (Sus scrofa) C

Snowshoe hare (Lepus americanus) C

Marine:

Sea otter (Enhydra lutris) A

Steller sea lion (Eumetopias jubatus) A

Harbor seal (Phoca vitulina) A

Gray whale (Eschrichtius robustus) U

Killer whale (Orcinus orca) R

Humpback whale (Megaptera novaeangliae) R

Minke whale (Balaenoptera acutorostrata) R

Dall’s porpoise (Phocoenoides dalli) R

Harbor porpoise (Phocoena phocoena) R
80

Appendix C.--Plats identified on Marmot Island, 1979 through 1994

Sitka Spruce

Salmonberry

Cow Parsnip

Devil’s Club

Northern Marsh Violet

Yellow Violet

Wild Flag

Northern Yarrow

Red-berried Elder

Western Buttercup

Marsh Marigold

 Kamchatka Dandelion

Alpine Shooting Star

Beach Cinquefoil

Villons Cinquefoil

Marsh Fivefinger

Silverweed

Kamchatka Lily

Wild Geranium

Oak Fern

Dwarf Cornel

Trailing Raspberry

Nagoonbeny

Narcissus-flowered Anemone

Roseroot

Bog Cranberry

Highbush Cranberry

Butterwort

Large-leaved Avens

Oeder’s Lousewort

Weasel Snout

Alpine Bearberry

Kinnikinnik

Alpine Azalea

Siberian Phlox

Seacoast Agelica

Seabeach Sandwort

Siberian Spring Beauty

One-flowered Wintergreen 

Alaska Heather

Picea sitchensis

Rubus spectabilis

Heracleum lanatum

Echinopanax horridum

Viola espisila

Viola glabella

Iris setosa

Achilles borealis

Sam bucus racemosa

Ranunculus occidentalis

Caltha palustris

Taraxacum kamtschaticum

Dodecatheon frigidum

Potentilla pacifica

Potentilla villosa

Potentilla palustris

Potentilla anserina

Fritillaria camschatcensis

Geranium erianthum

Dryopteris linnaena

Cornus suecica

Rubus pedatus

Rubus stellatus

Anemone narcissiflora

Sedum rosea

Oxycoccus microcarpus

Viburum edule

Pinguicula vulgaris

Geum macrophyllum

Pedicularis oederi

Lugotis glauca

Arctostaphylos alpina

Arctostaphylos uva-ursi

Loiseleura procumbens

Phlox sibirica

Angelica lucida

Honckenya peploides

Claytonia sibirica

Moneses unrflora

Cassiope stelleriana
81

Appendix C.--Continued.

Yellow Paintbrush

Labrador Tea

Nootka Lupine

Beach Pea

Dwarf Fireweed

False Hellebore

Brook Saxifiage

Leather-leafed Saxifiage

Pink Daisy

Yellow Monkey Flower

Groundsel

Amica

Castilleja unalaschensis

Ledum palustre decumbens

Lupinus nootkatensis

Luthyrus maritimus

Epilobium latifolium

Viride eschscholtzii

Saxifraga punctata

Leptarrhena pyrolifolia

Erigeron peregrinus

Mimulus gutlatus

Senecio atropurpureus

Arnica latifolia

Source: Alaska Department of Fish and Game, 1979.
82

Appendix D.--Steller sea lions marked with flipper tags or brands on Marmot Island, Alaska,

during 1987 through 1994, including the color of flipper tags, sex, age, weight

(kg), standard length (cm), and date of marking. Brands, on the left or right flank,

are the same number as on the flipper tags. Attachments of radio transmitters

(VHF) or satellite- linked, platform terminal transmitters (PTT) are noted as

comments. Tags from animals denoted as “dead, <1992” were found in the

stomach of a beach-cast killer whale in 1992. All are presumed dead, but the date

of death is unknown
















99

Appendix E.--Dates and corresponding Day of the Year used in analyses. Day of the

year was the same for leap years and non-leap years.
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