Pinniped assessment in Point Reyes, California, 1983 to 1984

[From the U.S. Government Printing Office, www.gpo.gov]

NOAA Technical Memorandum
NOS MEMD 7

PINNIPED ASSESSMENT IN POINT REYES,
CALIFORNIA, 1983 TO 1984

Sarah G. Allen

Point Reyes Bird Observatory
4990 Shoreline Highway
Stinson Beach, CA 94970

Washington, D.C.
August 1987

UNITED STATEIS Natii cuN1i an* National Ocean Service
DEPARTMENT OF COMMERCE Ainespheic Admainisttat *
4*EN Q

NOAA TECHNICAL MEMORANDA

National Ocean Service Series

Marine and Estuarine Management Division

The National Ocean Service, through its Office of Ocean and Coastal Resource Management, conducts
natural resource management related research in its National Marine Sanctuaries and National Estuarine Reserve
Research System to provide data and information for natural resource managers and researchers. The National
Ocean Service also conducts research on and monitoring of site-specific marine and estuarine resources to
assess the impacts of human activities in its Sanctuaries and Research Reserves and provides the leadership
and expertise at the Federal level required to identify compatible and potentially conflicting multiple uses of
marine and estuarine resources while enhancing resource management decisionmaking policies.

The NOAA Technical Memoranda NOS MEMD subseries facilitates rapid distribution of material that may
be preliminary in nature and may be published in other referreed joumals at a later date.

MEMD 1 M.M. Littler, D.S. Littler and B.E. Lapointe. 1986. Baseline Studies of Herbivory and Eutrophication
on Dominant Reef Communities of Looe Key National Marine Sanctuary.

MEMD 2 M.M. Groom and N. Stone, Eds. 1987. Current Research Topics in the Marine Environment.

MEMD 3 C.E. Birkeland, R.H. Randall, R.C. Wass, B. Smith and S. Wilkens. 1987. Biological Resource
Assessment of the Fagatele Bay National Marine Sanctuary

MEMD 4 H. Huber. 1987. Reproduction in Northern Sea Lions on Southeast Farallon Island, 1973-1985.

MEMD 5 J.A. Bohnsack, D.E. Harper, D.B. McClellan, D.L. Sutherland, and M.W. White. 1987. Resource
Survey of Fishes within Looe Key National Marine Sanctuary.

MEMD 6 S.G. Allen, D.G. Ainley, L. Fancher, and D. Shuford. 1987. Movement Patterns of Harbor
Seals (Phoca vitulina) from the Drakes Estero Population, Califomia, 1985-86.

MEMO 7 S.G. Allen. 1987. Pinniped Assessment in Point Reyes, California, 1983 to 1984.

National Marine Sanctuary Program
Marine and Estuarine Management Division
Office of Ocean and Coastal Resource Management
National Ocean Service
National Oceanic and Atmospheric Administration
U.S. Department of Commerce

NOTICE

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products constitute endorsement or recommendation for their use.

REPORT TO
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
U.S. DEPARTMENT OF COMMERCE

NOAA TECHNICAL MEMORANDA SERIES NOS/MEMD

Pinniped Assessment in Point Reyes, Califronia, 1983 to 1984

Sarah G. Allen

August 1987

U.S. DEPARTMENT OF COMMERCE
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
NATIONAL OCEAN SERVICE
'OFFICE OF OCEAN AND COASTAL RESOURCE MANAGEMENT
MARINE AND ESTUARINE MANAGEMENT DIVISION
WASHINGTON, D.C.

REPORT TO
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
U.S. DEPARTMENT OF COMMERCE

NOAA TECHNICAL MEMORANDA SERIES NOS/MEMD

Pinniped Assessment in Point Reyes, California, 1983 to 1984

Sarah G. Allen

Point Reyes Bird Observatory, 4990 Shoreline Highway, Stinson
Beach, CA 94970

This work is the result of research sponsored by the U.S.
Department of Commerce, National Oceanic and Atmospheric
Administration, National Ocean Service, Office of Ocean and
Coastal Resource Management, Marine and Estuarine Management Division
Under Interagency Agreement Number NA-81-AA-H-CZ151

ABSTRACT

We surveyed three species of pinnipeds (harbor seals,

California sea lions, and northern sea lions) for a

second year in Point Reyes, California, from March 1983

through February 1984. Information gathered for both

years (1982-83, 1983-84) are compared. Harbor seals,

though present year round, were most abundant during the

breeding season; the maximum count for the season was

2449 including 527 pups. The majority of breeding seals

migrated to coastal locations rather than estuarine ones.

At Double Point the breeding population has expanded

three-fold since 1976; the annual rate of growth, though,

has not been constant. During the non-breeding season,

population numbers have remained stable. Sea lions also

were seasonally abundant in Point Reyes. northern sea

lion numbers peaked during the breeding season;

California sea lion numbers peaked during the southern

spring migration and the northern fall migration when

traveling to and from breeding grounds, and peaked again

in December during the herring run in Tomales Bay. A

significantly larger number of California sea lions,

composed of mostly immatures, was present in 1983-84 than

in 1982-83. The optimum time to census sea lions in

Point Reyes was between 1100 and 1600 hr when low tides

occurred mid day.

TABLE OF CONTENTS

Page

I List of Tables........................ 4

II List of Figures........................ 5

III Part A. Harbor Seals - Sarah G. Allen

Introduction. .......................6

Study Area and Methods. ..................7

Results . ..........................12

Discussion. ........................21

Summary. ..........................25

IV Part B. Sea Lions - Harriet R. Huber

Introduction. .......................26

Methods. ..........................27

Results. ..........................29

Discussion. ........................33

Summary. ..........................37

V Acknowledgements. ......................38

VI Literature Cited. ......................39

VII Tables .............................43

VIII Figures. ...........................62

IX Appendix. ..........................71

LIST OF TABLES

Table 1. Harbor seal counts for all sites in the Point Reyes region for
1983-84.

Table 2. The average number of harbor seals hauled out by season in
1983-84.

Table 3. Maximum number of harbor seal pups counted in the Point Reyes
region in 1982 and 1983.

Table 4. The hourly presence of harbor seals at primary locations in the
Point Reyes area in June 1983.

Table 5. Freeman-Tukey deviates for the deviation of the observed from the
expected for a log-linear model of independence of year, seal
location, and seal reproductive status.

Table 6. The average monthly number of harbor seals hauled out at Double
Point for each age class.

Table 7. The average percentage of sex and age classes of harbor seals at
Double Point during the breeding season, 1984.

Tabli 8. The yearly population growth rate at Double Point during the
breeding season from 1976 to 1984.

Table 9. The daily variability in the number of seals hauled out at Double
Point and Bolinas Lagoon during the breeding season, the molt, and
the end of molt.

Table 10. Summary of pupping success of known female harbor seals at Double
Point.

Table 11. Maximum counts of California sea lions at Point Reyes Headlands
1983-84.

Table 12. Maximum counts of California sea lions at Bodega Head, 1983-84.

Table 13. Maximum counts of northern sea lions at Point Reyes Headlands
1983-84.

Table 14. Hourly counts of California sea lions at Point Reyes Headlands,
1982-84.

Table 15. Hourly counts of northern sea lions at Point Reyes Headlands,
1982-84.

LIST OF FIGURES

Figure 1. Major pinniped haul-out locations in Point Reyes, California.

Figure 2. Maximum number of harbor seals by month in Point Reyes, 1983-84

Figure 3. Monthly mean number of harbor seals, 1982-84, at Tomales Bay.

Figure 4. Monthly mean number of harbor seals, 1982-84, at Tomales Point.

Figure 5. Monthly mean number of harbor seals, 1982-84, at Point Reyes
Headland.

Figure 6. Monthly mean number of harbor seals, 1982-84, at Drakes Estero.

Figure 7. Monthly mean number of harbor seals, 1982-84, at Duxbury Reef.

Figure 8. Monthly mean number of harbor seals, 1982-84, at Bolinas Lagoon.

Figure 9. Monthly mean number of harbor seals, 1982-84, at Double Point.

Figure 10. Monthly mean number of California sea lions at Point Reyes
Headlands, 1982-84.

Figure 11. Monthly mean number of California sea lions at the Farallones,
1972-1984.

Figure 12. Monthly mean number of California sea lions at Bodega Rock,
1982-1984.

Figure 13. Monthly mean number of northern sea lions at the Farallones,
1972-1984.

Figure 14. Monthly mean number of northern sea lions at Point Reyes,
1982-1984.

PART A. HARBOR SEALS

Sarah G. Allen

INTRODUCTION

Throughout historical times, harbor seals, Phoca vitulina, have

resided at Point Reyes, California. Scammon (1874) was the first to record

their presence (1850's), but only in recent years have researchers

attempted to document the seasonal abundance of this species in the

California coastal zone (Carlisle and Alpin 1966 and 1971, Dohl et al.

1982, Frey and Alpin 1970, Hanan 1985, Mate 1977, and Miller 1983). The

results of these surveys, however, are insufficient for designing a

reliable management plan for harbor seals specific to the Point Reyes area.

With the more generalized state-wide emphasis of present information, we

lack insight into the peculiarities of this local population. In addition,

little information has been available on the reproductive rates of harbor

seals in the region. Incidental information on pinnipeds in Point Reyes

has been noted by Chan (1979) in reports on Areas of Special Biological

Significance (ASBS) and by Allen et al. (1985).

Our two-year survey, 1982-1984 was designed to provide comprehensive

information on abundance and seasonal use patterns of harbor seals in the

coastal zone of the Point Reyes area. In the first survey year, we refined

our census techniques by evaluating the tidal and diurnal differences in

seal haul-out behavior as well as identifying haul-out sites and the

significance of each. Data from the second survey year validated findings

on seasonal and spatial trends. We include in this report analyses of data

collected since 1976 at Double Point, the largest breeding site in the

region.

STUDY AREA AND METHODS

Study Area

The coastal zone of the Point Reyes/Farallon Islands National Marine

Sanctuary extends from Bodega Bay (380 30'N) south to Bolinas Bay (370

30'N) (Figure 1). Included are embayments such as Tomales Bay, Drakes

Estero, and Bolinas Lagoon. The Point Reyes National Seashore (PRNS), the

Golden Gate National Recreation Area (GGNRA), and the Marin County

Department of Parks and Recreation share boundaries with the Sanctuary over

segments of this coastline. In addition to the protection afforded by Park

and Sanctuary status, Bird Rock, Point Reyes Headland, and Double Point

were designated as Areas of Special Biological Significance (ASBS) by the

California Department of Fish and Game (CDFG) and the State Water Resources

Control Board.

Much of this coastline remained largely undeveloped even before

inclusion into PRNS and GGNRA during the 1960's and 1970's. An

agricultural character and the inaccessibility of much of the area afforded

protection from human disruption. Consequently, use of habitat by seals

has probably has not changed significantly over the past few decades.

The topographical diversity of this coastal zone contributed to the

broad range of substrates in seal habitat, including tidal mud flats,

offshore tidal ledges, and sandy beaches. Coastal locations included

Tomales Point, Point Reyes Headland, Double Point, and Duxbury Reef;

estuarine locations included Tomales Bay, Drakes Estero, and Bolinas Lagoon

(Figure 1).

Data Collection

We counted seals twice each month at all locations from March 1983

through February 1984. Censuses occurred simultaneously in the afternoon

during low to medium-low tides except on a few occasions when weather

conditions hindered human access to remote sites. Days when low to

medium-low tides occurred mid-day to early afternoon were chosen to

maximize counts (Ainley et al. 1977, Allen et al. 1985, Fancher 1979,

Stewart 1984). In addition, an all day census at primary locations was

conducted in June when seal numbers reach their annual maxima in the area

(Allen and ]Iuber 1983, Miller 1983). This all-day census was undertaken to

confirm that there were no diurnal and tidal differences in haul out

patterns between locations and to provide a maximum estimate of seals in

the Point Reyes region.

Whenever possible we classified seals in three categories based on size

and color: adults, subadults, and pups. Seals in the eastern Pacific are

purported to reach sexual maturity between three and six years of age (Bigg

1969). At locations other than Double Point, Drakes Estero, Point Reyes

Headland, and Tomales Point, distance from observer and the oblique angle

of view made it difficult to distinguish subadults. Pups were easily

identified at all locations during the breeding season because of their

bright coloration and diminutive size.

We counted seals on four to five consecutive days at Double Point

during the breeding season (March through June) and molting period (June

through August) in 1983 and 1984 in order to determine daily variability in

the haul out pattern.

Data Analysis

For analysis of seasonal trends, we divided the year into three

seasons: breeding (March through June), summer (July through October), and

winter (November through February). We examined seasonal means for the

region and for each site and used a t-test to compare the average abundance

for spring, summer and winter of 1982 with that of 1983. Age class

representation for subadults and pups was expressed as a percentage of the

total herd. Maximum counts of pups for the region were based on

simultaneous censuses in the event that females with pups might travel

between locations. To test whether the seasonal haul-out pattern was

different at coastal compared to estuarine locations during breeding and

non-breeding seasons (summer and winter seasons combined) in 1982 and 1983,

we made two 2 x 2 contingency tables. We used a log-linear model to

analyze the tables and then we used Freeman-Tukey deviates to see which

* ~~~cells did not fit the model (Fienberg 1981).

Examination of trends in abundance at Double Point included data

collected by Allen (unpublished data) from January 1976 to June 1984.

During that period seals were censused on 325 days with over 625 hours of

observation. Seasonal coverage was similar for all years except 1979 and

1980. Most censuses were confined to the hours 0700-1630 because the

remoteness of the area required three hours of hiking, round trip. We

estimated the increase in the number of seals at Double Point from 1976 to

1984 by dividing the seasonal mean of 1984 by that of 1976. The change in

abundance for each year was determined from the formula =Nt+

N
t
where N is the mean population size and t is the year (Caughley 1977).

We examined the representation of sex and age classes at Double Point

in spring 1984 to identify more accurately which animals accounted for this

annual peak. The period was divided into early (March to mid-April),

middle (mid-April to mid-May), and late (mid-Hay Lo June). Seals were

categorized as male, female, female with pup, subadult, and pup. We then

calculated the percent representation of each category by dividing the

number identified for each category by the total number of animals

classified. Since male and female adult seals are almost identical in

size, we were not able to sex all adult animals and did not attempt to sex

subadults.

The daily variability in the number of seals hauled out at Double Point

during the breeding season was compared with that of the molt period (late

June through July) and the end of molt (August) using the coefficient of
SD
variation CV - (Snedecor and Cochran 1967). Only counts from

1200-1400 hr and from 1-3 hr .fter low tide were used in the analysis. For

comparison, we calculated an analogous CV from data gathered at Bolinas

Lagoon by Allen (unpubi. data).

We were able to identify a number of individual females at Double Point

by scars and unusual spot patterns. For eight years we noted the

recurrence of many of these animals during successive breeding seasons

(Allen, unpubl. data). To verify ifhe accuracy of our ability to identify

individuals, we compared the presence of known females during consecutive

three-day periods during the 1977, 1983 and 1984 breeding seasons,

excluding days when excessive disturbance occurred. We calculated the

probability of sighting, P, by the formula:

N
P= Iand 3

1-3

where N I n is the number of females seen only on days one and three,

and N1- is the number seen on all three days. The average for all

three-day periods was used as the probability of sighting (P). Our

estimated average probability of sighting was 0.9 (n = 3, range 0.8-1.0).

The sample size of known individuals was small (7, 5, 6), but these animals

were easily distinguished within a herd composed of 400-700 animals. Since

our probability of sighting was within an acceptable range, we felt

confident in calculating the pupping frequency of known females and the

probability of pupping.

The pupping frequency (pf) of females was figured from the conditional

probabilities for successive samples of females in three-year sets using

the formula:

No. of same females in denominator seen w/pup in yr i + 1
pf =

Noo of females seen in yri

Known individual adult females identified from 1977 to 1979 represented set

I and from 1982 to 1984 represented set 2. We eliminated from our

tabilations two groups of known females: 1) females not seen all three

years (Siniff et al. 1977); and 2) those that did not have pups in year 1

-Cse they may not have been sexually mature then. We included these two

groups of females, however, when presenting a summary of pupping success.

The probability of pupping (X) was estimated from a binomial pupping model

(Siniff et al. 1977) with the equation Xp = _ --i ,where P. is years with
n
pup for female divided by total years female was present, and n = the
i
number of known females. Only known females present in three successive

years were included in the model. If a female was determined to be

pregnant by the size and shape of her abdomen, but was not seen attending a

pup later, she was included in the sample as having pupped.

RESULTS

Seasonal and Spatial Use Patterns

Regional

Harbor seals were present year round at all locations censused within

the Point Reyes area in 1983 and, as determined in the 1982 survey, the

numbers fluctuated seasonally with more seals hauled out in spring (x =

1653 ,, SE = 121.0, n = 9) and summer ( = 1270.1, SE = 210.6, n = 8) than

in winter (X = 1089.1, SE = 70l1, n = 8)(Table 2). Seasonal means in 1982

versus those in 1983 were not significantly different (spring: t = 1.225, p

> 0.1; summer: t = .3318, p > 0.1ol; winter: t = .7421, 0.2 > p > 0.1). The

highest counts for the region in 1983 occurred in May (2449) and July (2323)

(Figure 2). Tomales Point, Drakes Estero, and Double Point were the areas

of highest seal concentration contributing most to the total number of pups

(Tables 1 and 3). Pups were first identified at haul-out sites in late

March, and their numbers peaked during the first week of May for both years

with 566 in 1982 and 527 in 1983. Pups represented 24% of the total count

(2339) in 1982 and 22% (2449) in 1983 (Table 3). The mean percentage

representation of subadult seals at Tomales Point, Point Reyes Headland,

Drakes Estero, and Double Point was much the same for all seasons in 1983

(spring: = 18.0, SD = 7.0, n 8; summer: x = 17.4, SD = 3.0, n = 8;

winter: x = 15.0, SD = 4.4, n = 9). As was observed in the 1982 survey,

subadult representation declined in May 1983 (x = 8.5%) (173/1820, 79/1101).

The all day census conducted in June 1983 confirmed that more seals were

present at all haul-out sites mid-day, a couple of hours after low tide,

with only Tomales Bay being exceptional, but did not provide a maximum

estimate for the seal population in the Point Reyes region (Table 4). More

seals were counted in Tomales Bay early in the morning, but the numbers were

only slightly lower mid-day. Though mid-day yielded maximum numbers, many

seals remained at haul-out sites into mid-afternoon, despite rising tides.

Duxbury Reef could accomodate large numbers of seals until about four hours

after low tide when it was awash. Seals that hauled out on offshore rocks

at Bird Rock and Double Point shifted to higher ground as the tide rose and

consequently, even at five hours after low tide, many seals were hauled out.

At estuarine locations haul-out space was reduced slightly beginning a

couple of hours prior to high tide, and so a substantial number of seals

remained until late afternoon.

Coastal areas accomodated a large influx of seals during the breeding

season (x = 992.7, SE = 75.8, n = 9) in comparison to estuarine sites

(R-= 660.8, SE = 59.0, n = 9). During the non-breeding season the coastal

populations declined substantially (x = 618.3, SE = 83.1, n = 15), whereas

estuarine ones declined only slightly (x = 595.9, SE = 37.6, n = 15). The

log-linear model comparing coastal and estuarine locations during breeding

and non-breeding seasons for 1982 and 1983 revealed that none of the
2
variables were equal (X = 26.45, p < 0.001). The variable which least fit

the model was the figure for estuarine locations during the breeding season

in 1983 (Table 5). The estuarine pattern changed significantly in 1983 with

fewer seals recorded during the breeding season and more during the

non-breeding season compared to that of 1982. Thus, the coastal pattern was

similar though not identical for both years. These findings suggested that

more seals were migrating to coastal areas than to estuaries during the

breeding season.

The seasonal pattern for each haul-out site reflected this difference

between coastal and estuarine groups, and when examining each we can

identify where the deviation from the 1982 estuarine pattern took place.

Bodega Rock

Seals were seen hauled out on tidal reefs of this offshore sea stack.

We counted a maximim of 54 seals in February 1984. Pups were not seen in

1.983 (Table 1).

Tomales Bay

Seals hauled out predominantly on tidal sand bars extending from Toms

Point to Sand Point in 1983. They were seen infrequently at Hog Island.

Seasonal means revealed that numbers remained relatively stable throughout

the spring and summer months and were slightly higher in winter (Table 2).

The winter peak in 1983 was in contrast to a distinct decline in numbers in

the winter of 1982. Here is where the main divergence from the estuarine

model occurred. In 1983 both spring and summer numbers were markedly lower

than those in 1982 (Appendix I), possibly because of disturbance. Though

the frequency of disturbance was similar in 1982 and 1983 (1982: 16 of 26

censuses; 1983: 16 of 28 censuses), the level of human activity was much

greater in 1983 (Allen and Huber 1984). A maximum of 45 pups was counted in

May which is slightly lower than the figure in 1982 (58) and represents 16%

(45/275) of the population in Tomales Bay and 10% (45/527) of all pups

censused in the Point Reyes area. A graph of the average number of seals by

month, combining data for 1982 and 1983, displays the apparent decline in

attendance in early winter and again in June and July when visitor use in

the area is high (Figure 3). Seal numbers in January through March were

higher than for most other months. Herring, Clupea pallasii, spawn in

Tomales Bay at this time [a known prey item of seals in the area (Miller

1983)], and may be related to increased seal abundance.

Tomales Point

The largest concentrations of seals in the vicinity of Tomales Point

hauled out on Bird Rock, north tidal rocks and Driftwood Beach. The

seasonal haul-out patterns were nearly identical in 1982 and 1983 with most

seals recorded during the breeding season (Table 2). A graph of the average

number of seals present by month, combining data for 1982 and 1983

illustrates the rapid increase that occurs there in May, June and July, and

the equally rapid decline from August through February (Figure 4). Tomales

Point is one of the three most important breeding areas in the Point Reyes

region with pups representing 24% (122/514) of total seals censused at the

Point and 23% (120/527) of all pups censused in 1983.

Point Reyes Headland

Point Reyes Headland is a minor coastal haul-out area where seals were

scattered along offshore rocks and in pocket beaches around Split Rock and

Sea Lion Coves. Counts were highest during the breeding season (Table 2);

one pup was seen in June. In contrast to 1982, the mean count during winter

1983 was slightly larger than that of the summer. The combined data of 1982

and 1983 reveal an irregular pattern: small numbers of seals were present

during April and May, the peak of breeding, and again in winter, but were

most abundant just prior to and just after the breeding season (Figure 5).

Geographically, this point bisects the distance between two major coastal

haul-out sites, and may be frequented by animals moving to or from breeding

grounds. We often observed harbor seals sharing pocket beaches here with

northern elephant seals, Mirounga angustirostrus, and occasionally observed

them displaced by these larger seals.

Drakes Estero

Drakes Estero is one of the three largest breeding areas in the Point

Reyes area. Seals hauled out on virtually every sand bar far up into the

estero during the breeding season, and Limantour Spit was used primarily

then. The 1983 pattern resembled closely that of 1982 with high counts

during spring and summer and lower counts during winter (Table 2). A

maximum of 122 pups was counted in May 1983, accounting for 19% (122/656) of

the total breeding population there. Twenty-three percent (122/527) of all

pups in the Point Reyes area occurred at Drakes Estero in 1983. A graph of

the combined data from 1982 and 1983 reveals that seals were present in

large numbers year round in contrast to the two other most important

breeding areas, Tomales Point and Double Point (Figure 6).

Duxbury Reef

The majority of seals hauled out on an intertidal reef extending from

Bolinas Headland; we identified a secondary haul-out site in 1983 which was

another reef 1/2 mi further north at Bolinas Point. Duxbury Reef was the

only coastal site in 1983 where the seasonal mean number of seals was higher

in summer than in spring; the average in winter was similar to that in

spring (Table 2). The monthly pattern exhibited in Figure 7 displayed a

peak in September and October and a decline in July; numbers varied greatly,

however, within July. Few pups (<5) were observed in 1982 and 1983.

Bolinas Lagoon

Bolinas Lagoon is an estuarine habitat where seals haul out on tidal mud

flats bordering two islands, Kent and Pickleweed. In a previous study, Kent

Island was the preferred site for all seasons (Allen et al. 1985). In 1982

and 1983, however, Pickleweed Island was the preferred location. The

seasonal pattern in 1983 was nearly identical to that of 1982 with a summer

annual peak, rather than one in spring, and a much reduced number in winter

(Table 2). Bolinas Lagoon was not an important pupping ground; only 17 pups

were counted in May both of 1982 and 1983. Bolinas Lagoon, like Drakes

Estero, did not display the monthly extremes in seal numbers characteristic

of coastal colonies (Figure 8).

Double Point

The seasonal variation in the average number of seals at Double Point in

1983 followed the pattern recorded since 1976 with a large influx of animals

occuring in spring and then dispersing rapidly in summer and winter (Table 2).

Maximum numbers in 1982 and 1983 occurred during the months from April

through July; we observed fewer seals from September through January (Figure

9). The months August/September and February/March were transition periods

when numbers declined or increased, respectively. Counts during November

reached the annual low. Pups accounted for 32% (262/832) of all seals

censused at Double Point in May 1983 and 50% (262/527) of all pups censused

in the Point Reyes area (Table 3).

Since 1976, pups have been initially sighted each year in late March or

early April; the maximum pup count has occurred consistently during the

first two weeks of May. The May peak for all years coincided with the

annual peak for all age classes combined, but surprisingly more adult seals

hauled out in June (74%) and July (80%) than in May (59%). The peaks

coincided with the mating period and the onset of molt, respectively (Figure

9, Table 6). Females come into estrus after pups are weaned, and mating

apparently extends into August (Bigg 1969). We observed mating on four

occasions in late May and early June 1983 (Allen 1985). Seals at Double

Point molted from early June to early August.

The mean number of subadult seals was largest during the months flanking

the breeding season, February and March and June and July (Figure 9, Table

6). During May, the number of subadults declined only slightly, but their

proportion to all seals counted then was much lower than in other months.

The percent representation of subadults was highest in September, October,

and December (Table 6).

A closer examination of sex and age classes of the main herd at Double

Point during the breeding season in 1984 revealed distinct trends in the

representation of each category (Table 7). Early in the season females

(33%), males (30%), and subadults (27%) were equally abundant. At the height

of the season, though, the herd consisted primarily of females (38%),

particularly females with pups (33%), and pups (39%). Late in the season,

the herd also consisted mostly of females (38%) and pups (33%), but fewer

females were with pups and the percentage of subadults began to increase.

The representation of males remained low from April 17 through May 31.

A comparison of the mean number of seals counted during the 1976

breeding season (iR 195.2, SE = 17.6, n = 14, range = 112-320) with that of

1984 (R = 578.3, SE = 41.5, n = 22, range = 101-897) showed a three-fold

increase. The change in abundance for each year, however, was not linear

over this nine-year period (Table 8). For most years there was no change,

but in 1977 and 1982 seal numbers rose. The summer and winter seasonal means

for 1976 (summer: i = 165.7, SE = 35.7, n = 13; winter: _ = 123.8, SE =

34.0, n = 9) and 1977 (summer: x = 222.6, SE = 35.9, n = 21; winter: x =

106.8, SE = 22.1, n = 10) were not substantially different from those of

1983 (summer: R = 174.3, SE = 53.7, n = 14; winter: x = 215.8, SE = 32.2,

n = 15).

Daily Variability

The variability in the number of seals hauled out at Double Point over

successive days was greater during the breeding season than during the molt

(Table 9). The same was true for the herd in Bolinas Lagoon. At the end of

the molting period (August), the daily variability increased substantially

at Double Point, but in Dolinas Lagoon it remained the same. Disturbance

and inclement weather at Double Point are partially responsible for the

increased variation during the breeding season. Because of these

uncontrolled factors influencing the daily variability, we are not

completely confident with the results of these analyses.

Reproductive Rates

A summary of pupping success of known individual females is presented in

Table 10. The proportion of known females observed in a given year that had

pups was similar for all years. A small proportion of females were not

seen in successive years with the exception of 1984. A larger proportion of

females also did not bear pups in 1984. A total of 13 females (present all

three years) were observed with pups in 1977. Eleven of the females were

resighted with pups in the second year, yielding a pupping rate of 0.85

(11/13). The proportion of known females that pupped all three years for

this set was 0.77 (10/13). In the second set, a total of 11 females

(present all three years) were seen with pups and all of these were

resighted with pups in 1983. This yielded a pupping rate of 1.0 (11/11);

the proportion of females that pupped all three years was 9/11 for a rate of

0.82. Both three-year sets yielded a high probability that females with

pups in year 1 would have a pup in successive years. The probability of

pupping was 0.89 for set 1 and 0.92 for set 2.

DISCUSSION

The results of the 1982 survey in combination with those of 1983 provide

a much clearer understanding of harbor seal aggregations in Point Reyes. We

have identified when and where seals are seasonally abundant and when is the

optimum time to census. In 1982 we determined that diurnal and tidal

effects on seal haul-out behavior vary within an optimum range from mid-day

to late afternoon at low to medium tides depending upon the physical

attributes of each location. This was verified in the all day simultaneous

census in June, 1983. The diurnal pattern was similar to that of other

locations in California: Mowry Slough in San Francisco Bay (Fancher 1979),

Southeast Farallon Island (Ainley et al. 1977), Bolinas Lagoon (Allen et al.

1985), and San Miguel Island (Stewart 1984).

It is apparent that the Point Reyes area accomodates a large

harbor seal breeding population. Peak figures tabulated in May (2449) and

July (2323) 1983 and in May (2339) and June (2502) 1982 are comparable.

Population estimates by the California Department of Fish and Game (CDFG)

based on aerial surveys in April and June, 1982 and 1983 (Miller 1983; D.

Hanan 1985), are similar to our censuses for those months. The Point Reyes

harbor seal population during the breeding season represented 19% of the

total estimated California population, excluding the Channel Islands, in

1982 considered to be the largest concentration in the state (Miller 1983).

Preliminary analysis of the CDFG survey in 1983 confirms this estimate with

a state-wide figure of 9,010 animals in April and 10,763 in June, including

an estimated 1852 and 1985 seals, respectively, in Point Reyes (D. Hanan,

pers. comm.). Miller calculated an estimate of 1309 pups in California,

excluding the Channel Islands, in April 1982. The April 1983 pup count for

the state was 642 (D. Hanan pers. comm.). The respective pup estimates

calculated by CDFG for Point Reyes were 217 (10% of the total state pup

estimate) in 1982 and 157 (25% of the total pup estimate) in 1983. Nearly

three-quarters of pups censused by CDFG in Point Reyes in 1983 were at

Double Point. The representation of pups at Point Reyes to the state-wide

estimate is likely even greater because most pups are born in May rather

than April. Consequently, Point Reyes is perhaps even more important as a

breeding ground for harbor seals.

Coastal areas accomodated the major portion of migratory animals again

in 1983. There was no evidence that estuarine animals shifted to coastal

areas to breed. However, a subadult, male seal, rescued from Tomales Bay on

4 March 1984 by the California Marine Mammal Center and released the

following day at Point Reyes Headland with a rear flipper tag was identified

by us at Double Point on April 11 and 12, 1984 (L. Amaya, California Marine

Mammal Center, Fort Cronkhite, CA., pers. comm.). That the animal arrived

at a major coastal haul-out site rather than returning to an estuarine one

indicates that the animal was probably familiar with the area. Although

seals radio-tagged by Brown and Mate (1983) traveled locally between a

coastal haul-out site and estuarine ones, the majority of migrants in the

Point Reyes area likely travel from outlying areas. A comparison of aerial

surveys conducted by Dohl (1982) in May and January suggested a northward

movement of seals from this region to Sonoma and Mendocino Counties in

winter. Slater and Markowitz (1983) believed that adult seals dispersed

from San Mateo County haul-out sites during the breeding season.

The large influx of animals to coastal areas in Point Reyes during the

breeding season is composed primarily of adult seals. The absence of

subadult seals during the breeding season also has been documented in other

harbor seal populations (Naito and Konno 1979, Slater and Markowitz 1983).

Based on our analysis of herd composition at Double Point, adult females may

be the primary migrants to the region in April and May. "Nursery" herds in

harbor seals have been remarked upon by others (Brown and Mate 1983,

Knudtson 1975, Naito and Konno 1979, Slater and Markowitz 1983). In

addition, we have documented seasonal breeding site fidelity in females at

Double Point where several known females were resighted over successive

years. We did not gather information on the sex composition of the herd in

June at Double Point; we would expect, though, that males would represent an

increasingly larger proportion then because June is the mating season and

the onset of molt. The larger number of adult animals at Double Point in

June and July rather than MCay corroborates this. Thus there may actually be

two distinct waves of migrants to rookeries in coastal areas, the first one

consisting of mostly pregnant, adult females, and the second one mostly of

adult males.

There is little information available for determining whether seal

abundance has been increasing in the Point Reyes region. Earlier surveys

(Carlisle and Alpin 1966 and 1971, Mate 1977, Risebrough et al. 1978) and

data collected at Double Point indicates an increase during the breeding

season, but there is no indication that the resident population has changed

because summer and winter averages at Double Point have been about the same

since 1976. Nevertheless, the rate of expansion in seal numbers at Double

Point has not been constant. Instead, 1977 and 1982 are remarkable as years

when seal numbers rose substantially and then leveled out during the

intervening years. Why these increases occurred is not known.

SUMMARY

1. The optimum time during a day to census seals in Point Reyes is from

mid-day to late afternoon at low to medium tides depending upon the physical

attributes of each location.

2. Day to day variability in the number of seals at haul-out sites appears

to be less during the molt than during the breeding season. We feel a

minimum of three successive-day censuses are required for more reliable

estimates during the breeding season because of the unpredictable influences

of other factors such as human disturbance and extreme weather conditions.

3. Seals should be censused in the first two weeks of May, when pup

representation is highest in order to determine an index on the health of

the breeding population. A second census in late June or early July, when

more adult seals are present at haul-out sites to molt, would provide more

reliable estimates for the total population.

4. Annual censuses would provide data for determining trends in abundance.

Data at Double Point indicate that the growth rate is not constant.

5. Information on summer and winter movements of breeding animals would be

invaluable for any long-term management programs since the breeding

population in Point Reyes represents a sizeable proportion of the state

population and since these animals migrate from unknown areas. Radio-tagging

is the most reliable method for tracking-seal movements.

PART B. SEA LIONS

Harriet R. Huber

INTRODUCTION

A two-year survey of the California (Zalophus californianus) and

northern (Steller) sea lion (Eumetopias jubatus) populations in the Point

Reyes/Farallon Islands National Marine Sanctuary was initiated in March

1982. This survey was designed to determine the size of the Point Reyes

sea lion population, its breeding status, seasonal and diurnal fluctuations

in haul-out patterns, and how the Pacific herring (Clupea pallasi) run in

Tomales Bay affects sea lion numbers along the coast.

Historical information on the Point Reyes sea lion population is

sketchy, because identification of the two species was frequently confused

during the 1800's. However, both species were present at the Farallones and

at Seal Rock in San Francisco, and so presumably they were present at the

Point Reyes Headlands as well. During the 1800's northern sea lions

apparently bred on the Farallones and California sea lions hauled out

in large numbers during the non-breeding season (Allen 1870, Scammon 1874,

Allen 1880). In the early twentieth century, mostly northern sea lions

occupied what is now Marine Sanctuary waters and only northern sea lions

bred there (Everman 1921, Starks 1921, Rowley 1929). California

Department of Fish and Game censuses of breeding sea lions along the

California coast between 1930 and 1970 (Bonnot 1937, Bonnot et al. 1938,

Bureau of Marine Fisheries 1947, Bonnot and Ripley 1948, Carlisle and Alpin

1966, 1971, Frey and Alpin 1970, Ripley et al. 1962) and other censuses

(Chan 1979, Dohl 1982, Mate 1977, BLM 1981) are summarized in Allen and

Huber 1983, as are the results of the first year of this study (March 1982

to February 1983). These articles describe fluctuations in numbers on the

mainland in recent years.

METHODS

We censused California and northern sea lions at the Point Reyes

Headlands (Figure 1) twice a month for the first year (March 1982-February

1983) and weekly during the second year (March 1983-February 1984). During

both breeding seasons we censused once a week, checking for evidence of

births. One census each month lasted from 0700 h to 1800 h to assess sea

lion haul-out patterns, to discover when maximum numbers haul out and to

determine how seasonal, diurnal and tidal changes affect each species.

Some censuses were incomplete because weather (fog, rain, high winds or

heat waves) impeded the count. We censused California sea lions at

Bodega Rock once a month during the first year and twice a month during the

second year. During the herring run in Tomales Bay (December to March)

we conducted censuses by boat of California sea lions in the water; nine

occurred during the first year and five during in the second year.

All counts of the Point Reyes Headlands were made from Sea Lion

Overlook with a 25X spotting scope. In August 1982, a hidden cove

containing up to 100 animals was found south of the main haul-out site; from

then on we censused regularly from the antenna emplacement north of Sea

Lion Overlook. Descriptions of animals with distinctive scars or marks

were recorded whenever seen. Weather and tidal conditions were also noted.

Whenever possible, we separated both sea lion species into five age and

sex classes: adult male, subadult male, female-size, immature, and pup.

Adult males were defined as full-grown males with completely developed

igital crests, sub-adult males were animals with the beginnings of a

. ,iti] crest, female-size were large immature animals of either sex

-i. nrtt evidence of sagital crest (this size also included adult females),

immratures were small animals of either sex (yearlings and 2 year olds) and

pup-. Tere pups of the year (May through December). These categories were

fairly e.asy to distinguish among northern sea lions and all animals of this

spcedi, described as female were indeed females. With California sea lions

almost all female-size animals were, in fact, immature males. If we assume

that sex ratios of animals hauled out at Point Reyes are similar to animals

hauled out at the Farallones, then the number of females changed from

virtually no females in the years prior to 1983 to a proportion of one

female to every three males in 1983-84 in the female-size and smaller

category. We compared mainland censuses with weekly sea lion censuses from

the Farallones during the same time period. Because of the difficulty in

separating age classes when counting thousands of animals, California sea

ioas on the Farallones were divided into only four age classes: male,

female-size, immature, and pup. Males were defined as any animal with a

.agital crest.

RESULTS

California sea lions

Major differences in the number of California sea lions present and the

seasonal variation in age/sex classes occurred in all three areas during

the second year of censusing (March 1983 to February 1984).

The peak number of animals was 763 on 5 August 1983 at the Point Reyes

Headlands (Table 11), 1530 on 31 October at Bodega Head (Table 12), and

5570 on 28 July at the Farallones. These counts are all two to three times

greater than peak numbers counted in the first year of the study. Up to

116 Zalophus (95% of them immatures) were counted at Double Point between

May and August 1983, another indication of increased numbers at Point

Reyes. N'o California sea lions had been seen at Double Point during

theprevious seven years (Allen, unpubl. data).

At Bodega Rock the two years were similar with peaks during the spring

and fall migration. Numbers during the second year, however, exhibited a

third peak coincident with the Tomales Bay herring run (Figure 10). At the

other two sites there was less similarity between years. The monthly mean

number of California sea lions was significantly larger during the second

year from May to August at Point Reyes (Mann-Whitney U-test p<0.05) and from

July to September at the Farallones (Mann-Whitney U-test p<0.025).

At Point Reyes and the Farallones, not only did the number of animals

change between the two years but so did the yearly pattern. In the first

year there were three peaks at Point Reyes: in March at the beginning of

the southward migration to the breeding rookeries, in early September

during the northward migration, and in late December during the herring run

in Tomales Bay (Figure 11). In 1983-84, there was one large peak from May

to August which began during the southward migration and lasted through the

period of the northward migration. This was followed by a much smaller peak

coinciding with the herring run in late December (Figure 11). At the

Farallones during 1982-83, there were two peaks, which corresponded to the

spring and fall migrations (Figure 12). In 1983-84, a peak persisted through

the breeding season when there is normally a decline in numbers (Figure

12), similar to the situation at Point Reyes Headlands.

In looking at the proportion of different age classes in the Point Reyes

Zalophus population during 1982-83, we found adult males present in large

numbers from Iarch through the first week of June, when numbers dropped

dramatically. Numbers remained low during the summer breeding season

except for a short peak in August. These peaks in the number of adult males

coincided with migration to and from southern rookeries and is the same

pattern we have found on the Farallones from 1972 to 1982. The pattern for

adult males in 1983-84 was quite different. The southward migration peak

began earlier (in March) and was essentially completed by mid-May. During

the summer of 1983 the actual number of adult male California sea lions was

three times larger than in 1982 but the proportion of adult males in the

population dropped significantly from about 20% in 1982 to 10% in 1983

(t-test, p<O.05)> This indicates that the increase in total numbers was

due to a tremendous influx of immature animals rather than an equal

increase in all age classes.

At the Farallones, where census results for adult and subadult males

were combined into a single category, the changes are not quite as clear.

The Farallon situation appears to be similar, however, for during the first

year the highest monthly mean number of males and the highest proportion of

males (over a third of the population) occurred during the same months, May

and October. This indicates that peak numbers were the result of males stopping

briefly at the Farallones during migration. In 1983-84, the highest

monthly means were in June, July, and August, when adult males comprised

only 12 to 14% of the population, again indicating that peak numbers in

the summer of 1983 were due to higher numbers of immature animals.

During censuses we noted the presence of up to 22 immature California

sea lions tagged on the Channel Islands. Ten of these were tagged at San

Miguel Island and 12 were tagged at San Nicolas Island.

Northern sea lions

The difference between 1983-84 and the previous year of study was not

as distinct with the northern sea lions as with the California sea lions.

The northern sea lion population is quite small at both Point Reyes and the

Farallones, and the numbers remained essentially the same for the two

years. The yearly patterns in both areas were similar: low numbers in

fall and winter with a peak during the breeding season (Figure 13, Figure

14). Maximum numbers reached 20 on 8 May at Point Reyes (Table 13) and 141

on 2 June at the Farallones in 1983-84. When comparing the monthly mean

numbers we found no significant differences between the two years in either

area (Mann-Whitney U-test, p>0.05).

Patterns in occurrence of the various age and sex classes differed

between years. At Point Reyes, in 1983 adult males arrived three weeks

later and remained six weeks longer than in 1982 whereas subadult males

arrived earlier and stayed into November. This was three months longer than

in 1982, a "normal" year. Immature animals, seen throughout the

year in 1982, disappeared in 1983 after the end of August. Adult females

were present the entire year (Table 13). These changes at Point Reyes

Headlands reflect similar changes on the Farallones.

Two adult females, one adult male, and one subadult male northern sea

lion recognizable by distinctive scars were seen on both Point Reyes and

the Farallones.-

All day watches

Regardless of season, the sea lions exhibited a strong diurnal haul-out

pattern, with low counts morning and evening and a sustained peak from 1100

h to 1600 h (Table 14, Table 15). Two other factors affected numbers at

Point Reyes as well: tidal and weather conditions. Lower numbers occurred

when the haul-out area was reduced by high tides or large swells, as well

as on calm hot days when sea lions frequently went into the water.

No pupping or breeding was observed in either species in 1983-84 at Pt.

Reyes.

Tomales Bay

During the winter herring run we censused California sea lions in

Tomales Bay five times. A peak number of 37 Zalophus were seen on 20

January 1983. Few Zalophus were seen on other censuses. Five percent of

all animals seen in December 1983 and January 1984 were adult males

compared to 20% in the previous year.

DISCUSS ION

It was fortunate that this study took place between 1982-1984, for we

were able to document some dramatic changes in the sea lion populations

within the Point Reyes/Farallon Islands National Marine Sanctuary. The

changes, which we attribute to the effects of warm waters associated with

El Nino, include a remarkable three-fold increase in the California sea

lion population and a shift in the haul out pattern of age and sex classes

in both species.

The warmer than usual water temperature measured at the Farallones

(PRBO, unpublished) and throughout the northeast Pacific altered the

distribution of fish species and reduced numbers and breeding success of

marine birds and mammals in California (Heath and Francis 1983, DeLong

pers. comm., Stewart pers. comm., PRBO unpubl.). Both California and

northern sea lions are at the edge of their breeding ranges in the Point

Reyes/Farallon Islands National Marine Sanctuary, therefore any unfavorable

perturbation to food supply such as occurred during El Ni'ino, may have

significant effect on local populations. California sea lions breed

primarily south of Point Conception with major rookeries at San Miguel and

San Nicolas Islands, California, and the islands off Baia California,

Mexico; major breeding areas of northern sea lions are on the Aleutian and

Pribilof Islands in Alaska (Scheffer 1958). Both species have small

breeding colonies on the Farallon Islands where up to 27 northern and up to

3 California sea lion pups have been born each year since 1974 (Huber et

al. 1985). Ten northern sea lion pups and 3 Zalophus pups were born in

1983 on the Farallones. No cows of either species gave birth on the

mainland in 1982 or 1983.

California sea lions

The population of California sea lions has increased throughout its

range in the last 50 years; since 1960 the increase has been about 5% each

year in California (DeMaster et al. 1982). In the past, only adult and

subadult males migrated north, while adult females and juveniles

remained near the southern rookeries (Bartholmew 1967)> A change in

migration pattern was first noted at the Farallones in 1978 when large

numbers of immature sea lions began to haul out in the fall. By 1981 the

population at the Farallones had tripled. Ainley et al. (1981) proposed

that the increase in numbers and in the proportion of immatures at the

Farallones was due primarily to changes in the availability of Pacific

whiting (Merluccius productus), a primary prey species, near the islands.

The availability of whiting to sea lions increased dramatically when the

foreign whiting fishery, which was competing directly with sea lions, was

eliminated by the imposition of the 200 mile fishing limit in 1977.

Unfortunately we do not have comparative censuses for the mainland sea lion

population to see if similar changes occurred there.

Changes in the Farallon California sea lion population from 1972 to

1984 are summarized in Figure 12. Prior to 1978 there was only one

peak (in the spring) at the Farallones. Between 1978 and 1981 the number

of Zalophus on the Farallones grew by 15 to 20% each year, a much higher

rate than the rest of the state. This growth which was due primarily to

immature animals created a second peak (in the fall). The remarkable

increase that occurred during the 1983 breeding season was unprecedented,

although the numbers for the rest of the 1983 were within normal ranges.

Most of the summer increase in both areas was due to large numbers of one

to four year old animals, the number of adult males increased to double the

number seen the previous year.

The population at Point Reyes (Figure 11) reflected the same trend that

we saw on the Farallones 1982-84. During this time, Heath and Francis

(1983) reported reduced numbers of breeding animals at the Channel

Islands. Apparently many adult Zalophus remained in central California

rather than migrating to southern rookeries during the El Nino summer of

1983. We do not know for certain why so many immature sea lions

congregated at the Farallones and Point Reyes, but we can speculate that it

was likely the result of an altered distribution of prey.

High numbers of California sea lions seen at Bodega Head and Point

Reyes Headland during the 1983-84 winter were probably attracted to the

herring spawn in Tomales Bay. That this peak was not recorded at Bodega

Head in December 1982 (Figure 10) is probably due to the large winter

swells which reduced available haul-out area during censuses.

Northern sea lions

At Point Reyes, little change in the numbers of northern sea lions

occurred between 1982-83 and 1983-84 despite great changes in the marine

environment during the second year. The population on the mainland is

quite small and as a result it was difficult to discover what effects, if

any, El Nino had. In 1983-84, peak numbers of animals occurred in May,

before the breeding season, whereas in 1982-83 the peak occurred in August,

after the breeding season. Numbers during the rest of the year were

similar (Figure 13).

The mortality of northern sea lion pups born on the Farallones was

higher in 1983 than at any time in the last 10 years but that may be

related more to a problem of premature pupping in Eumetopias (Huber et al

1984) than to the effects of El Nino. Although numbers during the

breeding season in 1982-83 were higher than in 1983-84 (Figure 14), neither

year was significantly different from the monthly means during 1972-81

(t-test p>0.05).

In fall 1983 the absence of immature northern sea lions and the

extended attendance of subadult males at both coastal and off-shore sites

may possibly be related to the El Nino conditions and their effect on prey

availability.

We suspect that sea lion populations within the Sanctuary will return

to pre-1983 numbers and age-class ratios after the widespread residual

effects of El Nino recede.

SUMM4ARY

1. The California sea lion population hauling out at mainland sites in the

Point Reyes/Farallon Islands 'National Marine Sanctuary is comprised

primarily of migrating animals. Numbers peaked at 338 in 1982-83 and at

1530 in 1983-84 at the Point Reyes Headlands. The northern sea lion

population reached a maximum of 20 animals at Point Reyes. There is some

interchange of animals between the Farallon and Point Reyes populations.

2. Neither species gave birth nor bred at Point Reyes from 1982-84. On

the Farallones up to three California sea lion pups and up to 27 northern

sea lion pups have been born each year since 1974.

3. Peak numbers of Zalophus occurred during the southern spring

migration and northern fall migration to and from breeding rookeries in

southern California and Mexico. The population peak of Eumetopias occurred

during the summer breeding season.

4. Maximum numbers of both species hauled out between 1100 h to 1600 h.

Where high tides and large swells decreased the haul out area, the highest

numbers were counted when low tides occurred at mid-day. Numbers decreased

on hot, calm days when many animals went into the water.

5. A peak in California sea lions on the coast in December corresponded

to the herring run in Tomales Bay. A winter peak was not observed at the

Farallones.

6. Numbers of California sea lions within the Sanctuary were greatly

inflated during 1983-84, due to an influx of immature animals. This was

probably related to the warm waters of El Nino; "normal" numbers are

probably closer to the results of censuses in 1982-83.

ACKNOWLEDGEMENTS

This study was made possible under the auspices of the Sanctuary

Programs Office of the National Oceanic and Atmospheric Administration, the

National Park Service, the Marin County Department of Parks and Recreation,

the Point Reyes Bird Observatory, and D. Miller. F. and R. Allen, C.

Connors, C. Cutler, C. Depkin, J. Evens, L. Fry, C. Poulsen, S. Peaslee, A.

Rovetta, D. Shuford, B. Stewart, S. Trivelpiece, and J. Young all spent

long hours in the field, often under adverse weather conditions, collecting

the information on which this report is based. D. Miller and D. Hanan of

the California Department of Fish and Game, generously offered advice and

information from CDFG aerial surveys. L. Amaya and M. Webber of the

California Marine Mammal Center kindly provided us with information on the

recovery and release of harbor seals in the region. D. DeMaster and C.

Ribic gave guidance and assistance in the analysis of data from Double

Point. E. Tuomi and S. Goldhaber greatly assisted in the preparation of

this manuscript. Finally we are most grateful to D. Ainley of the Point

Reyes Bird Obsevatory, and P. Gogan and G. Fellers of the Point

Reyes/Farallon Islands National Marine Sanctuary for advice and

encouragement. This is Point Reyes Bird Observatory Contribution number

283.

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Table 1. Harbor seal counts for all sites in the Point Reyes region for 1983-84. Census days during which disturbance

occurred are noted with an asterisk. Numbers following a slash indicate pups.

LOCATION

Bodega Tomales Hog Bird Tomales Point Drakes Limant. Double Duxbury Bolinas Total
DATE Rock Bay Island Rock Point Reyes Estero Spit Point Reef Lagoon Pups Totals

1983
March 9 146 54 123 123 92 363 0 273 99 64 1337
25 148* 25* 162/1 252 179 414 0 404 41 76 1 1701
31 47
April 7 12 202/2* 0* 102/1 165 71 209* 0 313/22 101 67/1 26 1242
21 30 189/11* 0 164/13 196/14 92/1 334/19 0 634/128 67 65/3 189 1771
2/3 142 56 104*
9/10 148/3* 0 163/1 120 322* 0 387/33
16/17 105/3* 0 55/7* 168/4* 0 250/65
21 595/144*
23/24 189/18 485/36* 0 634/107*
30/1 193/29* 623/167
May 6 275/45 0 229/42 285/78 25 461/104 141/8 820/241 116 97/17 527 2449
20 169/34* 0 161/48 171/48 fog 218/62* fog 551/157 122/3 70/10 362 1462
7/8 156/24* 207/38* 480/102* 176/20 716/226*
12 25
14/15 89/19* 159/48* 370/90 122/16 267/118*
21/22 16 152/5* 204/38 249/71* 238/25* 567/173*
28/29 148/23* 161/17* 83/7* 362/28 335
June 3 84/2* 0 137/12 70/16 69/1 71/3 340/14 463/48 166/3 67/3 102 1467
16 93/2* 0 229/6* 74/2 50 354/8 150/10 455/103 100/2* 95/2* 135 1600
30 -- - 269/14 122/3 74/1 270/3 350 438/91 85/3 136 115 1894
4/5 69/3* 345/6
17 15
18/19 583/20
25/26 158* 132/13
30 44

Bodega Tomales Hog Bird Tomales Point Drakes Limant. Double Duxbury Bolinas Total
DATE Rock Bay island Rock Point Reyes Estero Spit Point Reef Lagoon Pups Totals

1983 (cont'd)
July 5 74 0 336 255 68 516 115 747 61 151 2323
18 93 0 315 265 45 422 150 316 118 174 1898
16/17 89* 215
19 50
22 410
30/31 305* 250 353
Aug 1 22 54* 0 232 131 60 324 207 301 138 122 1591
15 168 0 fog fog fog 362 0 51 fog 80 661
29/30 241 0 33 74 35 310 63 13 0 102 871
6/7 215
13/14 268* 77*
17 30
27/28 213 41* 380
31 2
Sept 9 -- -- 19 84 16 240 0 155 92 54 660
19 134 0 fog 81 46 298 45 50 270 70 994
3/4
6 21
18 14*
24/25 26* 252* 74
Oct 3 113 0 48 167 65 322 0 34 .220 102 1071
17 122 0 38 47 58 137 0 33 254 85 774
15/16 32
22/23 15 95* 60*
29/30 35 141 40
Nov 2 93 0* 51 15 113 415 0 0 235 107 1029
16 136 0 64 163 84 198 48 1 87 74 855
5/6 49
15 47
26/27 246* 59
29 31

Bodega Tomales Hog Bird Tomales Point Drakes Limant. Double Duxbury Bolinas Total
DATE Rock Bay Island Rock Point Reyes Estero Spit Point Reef Lagoon Pups Totals
m ret none mmmmmmmm mmmmmmmmm mn mminmmmmm mmmhnmmmmmmmiiqm mm Nmmmm mmmmmmrflmmmmmmuiimmmliqmmmmm mmmm m mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm mmm mmmm mmmmwimp mm mmm m mm 1
1983 (cont'd)
Dec 1 -- -- 30 67 5 243 15 136 79 46 621
15 135 0 46 143 fog 248 24 244 100 38 978
29 150 0 46 59 fog 250 25 283* 104 38 955
3/4 48 142
17/18 118*
20 11
27 49
28 348*
31 71* 368 0 281
1984
Jan 12 105* 250 63 129 29 313 0 267 45 2 1203
26 226* 0 50 100 70 321 0 285* 76 26 1154
14/15 56*
17 57
21/22
23 35
28/29 387/1* 0 32* 1
31 66
Feb 10 195 0 78 192 83 363 13 395 106 73 1498
24 202 0 60 93 34 286 0 237 91 38 1041
3 206
8 100
11/12 188*
16 54
18/19
23 331 0
25/26 63 250* 303
28 41
Mar 17 195 0
25 100 0

Table 2. The average number of harbor seals hauled out by season during censuses in the

Point Reyes area in 1983-84; x is the mean number of seals, SE is the standard

error, and n is the sample size. Tomales Bay includes Hog Island, Tomales Point

includes Bird Rock, and Drakes Estero includes Limantour Estero.

rn mm mm irn mm m mmmmnmmnrra TI~ mm in mm m m in mmmminmin m mm in inmm mmmmm mm mm in mmm mmin mmm mm mm m mm mmmin min mmm mmmm In111 Ill 711Th n lni m nmnin I

LOCATION

Tomales Tomales Point Drakes Double Duxbury Bolinas All
Bay Point Reyes Estero Point Reef Lagoon Sites
mm~ mm m mmmn~ mmNITT nm nn mm mm mm n inmmmnmT 11Th mmm mm mm mmmmm mm mm mmii inmuum mm in in miii mm TnMn n innnnnnminini in 711 WTh mii i iimi i 1 11 11NTT1iATHNnTh ii n mii mmuiininT T1 T ilThni

Breeding
x 155.7 337.1 81.5 420.2 501.9 99.7 81.9 1653.4
SE 12.3 31.6 15.9 34.3 32.8 11.7 8.0 121.0
n 16 9 8 17 30 9 9 9
range 84-275 207-514 25-179 168-656 104-832 41-166 64-136 1230-2449

Summer
x 138.7 265.6 49.1 393.1 174.3 144.1 100.0 1270.1
SE 19.9 77.4 6.2 41.0 53.7 34.0 12.4 210.6
n 12 8 8 14 14 8 10 8
range 54-268 81-591 16-68 181-631 13-747 61-270 54-174 661-2323

Winter
x 193.5 161.0 64.1 304.6 215.8 101.2 49.1 1089.1
SE 84.0 21.9 10.6 16.1 32.2 17.7 11.0 70.1
n 11 9 10 14 15 9 9 8
range 93-355 66-270 5-113 206-415 0-395 44-235 2-107 855-1498

Table 3. Maximum number of harbor seal pups counted at each haul-out site

by month in 1982 and 1983.

LOCATION

Tomales Tomales Point Drakes Double Bolinas
Date Bay Point Reyes Estero Point Lagoon

1982
April 22 19 1 101 262 0
May 58 135 19 170 263 17
June 23 54 18 60 90 4

1983
April 11 29 1 36 186 3
May 45 120 0 122 262 17
June 2 28 1 18 103. 3

Table 4, The hourly presence of harbor seals at primary locations in the Point Reyes area

on June 16, 1983. Low tide was -.7' at 1032 hr, and high tide was 5.2' at 1803

hr. An asterisk (*) indicates disturbance.

HOUR
i nmmmii n mm i mm mmm in n mm i miimin in mm imn mnmi irn in inmm ininmim mnin in ininin m m in in nn mm mm i in mm mm in i
LOCATION 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800

in m nmm mn mm mini inw l tn i mm m minm inrm mmmninin n immni Tn in n T i n ininn in n mmmm inm i nnn in mm n in n ininnnirnmian imm

Tomales Bay 91 93 77* 72* 64 81 82 85 77 70 -- --

Bird Rock 133 169 72* 108 173 146 200 234 212 159 148 165

Drakes Estero 151 274 343 370 430 504 491 332 316 218 39 30

Double Point 275 318 325 330 348 375 408 434 455 426 397 212

Duxbury Reef 84 93 95 100 82 54 95 14 0 0 0 0

Bolinas Lagoon 51 65 76 88 91 95 86 87 80 59 43 11

TOTALS 785 1012 988 1068 1188 1255 1362 1186 1140 932 627 418

.mi. mm.n.mimn.n mm. mm mm mmm.mmm.im.mmiin.min imi mimmimmm nnni.................. m im mmmmi7n mm mm rm in i

Table 5. Freeman-Tukey deviates (FT) for the deviation of the observed from

the expected for a log-linear model of independence of year, seal

location, and seal reproductive status. The numbers given are the

total number of seals counted for each zone during each season.

Coastal Estuary

1982
Breeding 9299 7213
F-T -1.67 1.93
Non-breeding 7957 7592
F-T 1.83 -1.85

1983
Breeding 8934 5947
F-T 1.73 -2.09*
Non-Breeding 9275 8938
F-T -1.68 1.73

*F-T deviate is significant at = 0.05.

Table 6. The average monthly number of harbor seals hauled out at Double Point from 1976 to 1984

for adults, subadults, and all age classes combined. Only those censuses when immatures

were distinguished were included in the sample; x is the mean number of seals, SE is the

standard error, and n is the sample size.

in mm mmm mmmm mm mmmmnmmmmm mmmnmrmnmmmmmmm mmmm mm in n inminininmmm inmin in il inrin inninrmm in inininin mm mmin mm ini

MONTII

J F M A M J J A S 0 N D

n 13 15 25 51 52 28 20 15 12 12 9 16

All Age Classes
x 128.2 252.2 239.0 372.8 517.9 413.3 397.2 143.6 123.3 82.2 32.7 151.9
SE 26.4 25.4 16.7 25.8 24.4 36.4 29.3 17.2 21.5 21.1 5.2 27.0

Adults
x 99.5 204.9 191.9 241.5 304.7 304.3 317.2 97.6 76.7 50.2 22.7 110.5
SE 21.9 21.9 12.7 16.0 16.3 29.6 24.7 15.1 16.9 14.8 5.4 22.3

Subadults
x 22.8 41.8 41.5 36.0 36.0 52.5 40.6 19.3 31.4 17.3 4.6 31.6
SE 7.4 6.8 5.4 4.2 3.2 8.8 6.6 3.6 6.4 7.8 1.3 7.0

% Subadult to Total
17.8 16.6 17.4 9.7 7.0 12.7 10.2 13.4 25.5 21.1 14.1 20.8

% Adult to Total
77.6 81.3 80.3 64.8 58.8 73.6 79.9 68.0 62.2 61.1 69.4 72.8

.m.....m...m..lm.................nl................n. ..nlwnlTH.rdTHTT.edt rm bT..w.wnlttwlvwbw.n, pllTRRWT.lT.w.lwR.llt...lU.t.tjlll. .......i...............

Table 7. The average percentage of sex and age classes of harbor seals at

Double Point during the early, middle, and late periods of

the breeding season, 1984; x is the mean percent of each class,

SD is the standard deviation, and n is the sample size.