t 

NOAA Technical Memorandum NMFS 

OCTOBER 1984 

HAWAIIAN MONK SEAL OBSERVATIONS 

ON FRENCH FRIGATE SHOALS, 1980 

Patricia A. Johnson 

Brian W. Johnson 

NO A A-TM-NMFS-SW FC-50 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Memorandum NMFS 

The National Oceanic andAtniosphericAdniinistration(NOAA), organized in 1970, has evolved intoan 

agency which establishes national policies and manages and conserves our oceanic, coastal, and atniospheric resources. An organizational elenient within NOM, the Office of Fisheries is responsible for 

fisheries policy and the direction of the National Marine Fisheries Service (NMFS). 

In addition to its fornial publications, the NMFS uses the NOAATechnical Menioranduni series to issue 

informal scientific and technical publications when complete fornial review and editorial processing’are 

not appropriate or feasible. Documents within’this series, however, reflect sound professional work and 

may be referenced in the formal scientific and technical literature. 

J 
NOAA Technical Memorandum NMFS 

Ths TM series is used lor documenlalion and timely communicaloon 01 preliminary resulh. lmterim repwb. M 

sDecial purme ontwmatim and have not recetved complete lormal review. edllorial conhd. or detailed eddtnp 

OCTOBER 1984 

HAWAIIAN MONK SEAL OBSERVATIONS 

ON FRENCH FRIGATE SHOALS, 1980 

Patricia A, Johnson 

Brian W. Johnson 

Aquatic Mammals Behavioral Research 

6843 SE Oakridge Dr, 

Gladstone, Oregon 97027 

Prepared for National Marine Fisheries Service 

Honolulu, Hawaii Contract 80-ABC-00 124 August 1984 

NOAA-TM-NMFS-SWFC-50 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige. Secretary 

National Oceanic and Atmospheric Administration 

John V. Byrne. Administrator 

National Marine Fisheries Service 

William G. Gordon, Asslstant Adminlstrator for Fisherlea 
PREFACE 

This report was prepared under Contract No. 80-ABC-00124 to the 

National Marine Fisheries Service by Patricia A. Johnson and Brian We 

Johnson. 

monk seal observational data collected during 1980 for the purpose of 

estimating the size of the French Frigate Shoals seal population. 

statements and findings in this report are those of the contractore and do 

not necessarily reflect the view of the National Marine Fisheries Service. 

The primary purpose of the contract was to summarize Hawaiian 

The 
TABU OF CONTENTS 

Page 

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

METHODS ............................................................... 3 

RESULTS AND DISCUSSION ................................................ 5 

Population Caunts ................................................ 5 

Distribution ..................................................... 8 

Total Atoll ................................................. 8 

Molt Survey Islands ......................................... 11 

Summary of Individual Islands ............................... 11 

Pupping .......................................................... 13 

Pup Production .............................................. 14 

Breeding: Female Dorsal Scars .................................... 17 

Molt ............................................................. 18 

Population Estimation ............................................ 18 

Calculation of Estimate .................................... 18 

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

Sex Ratio ........................................................ 22 

Comparative Data ............................................ 24 

Population Sex Ratio ........................................ 25 

Age Structure .................................................... 26 

Seasonal Distribution ....................................... 13 

SUMMARY ............................................................... 29 

ACKNWLEDGMENTS ....................................................... 30 

REFERENCES ............................................................ 31 

APPENDIXES 

A . Island Breakdown of Seals on Molt Surveys .................... 34 

B . Counts of Shark and Disappearing Islands ..................... 35 

C . Counts of Small Pups ......................................... 36 

D . Variation Between Atolls in the Pupping and 

Molt Season .................................................. 37 

E . Pup Production Estimate Based on 36-Day Interval 

Count ........................................................ 40 

F . Pup Production in 1977 and 1981 .............................. 43 

...-.. . 
G. Age/Sex Breakdown of Molting Seals Seen on all 

Molt Surveys ................................................. 45 

H. Age/Sex Breakdown of Count Data fox all Molt Surveys ......... 46 

LIST OF TABLES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

Monthly mean count data (with sample size) from French 

Frigate Shoals, 1980 ..........................................,..,. 6 

Total atoll surveys. Includes all dates when a count of 

Disappearing was made within 3 days of a molt survey count ....... 9 

Highest count for each year from 1975 through 1980 at French 

Frigate Shoals ................................................... 9 

Distribution of seals at French Frigate Shoals during 1980, 

including comparisons between the size of each island and the 

percentage of the population using the island for haul-out and 

for pupping ........................................................ 10 

Distribution of Hawaiian monk fieals on molt survey islands at 

French Frigate Shoals, 1980 ...................................... 12 

Estimate of 1980 pup production at French Frigate Shoals based 

on 40-day interval counts of attended pups ....................... 16 

Mean monthly number of seals sexed on all censuses including 

Gin and Little Gin Islands ............................................ 25 

Agefsex classification of molting seals seen on molt 

surveys .......................................................,....... 26 

A-1. Total number of seals, mothers with pups and weaned pups 

seen on molt surveys ............................................ 34 

B-1. Aerial and ground counts of seals on Shark and Disappearing 

Islands .......................................................o.oa 35 

C-1. Estimated births at French Frigate Shoals during 1980 based 

on size of pups ................................................. 36 

D-1. Pupping season dates for Kure (1964 and 19651, Laysan (1977 

to 19801, and French Frigate Shoals (1980) ...................... 37 

E-1. Estimated pup production on Laysan Island from 1977 to 1980 

based on counts of attended pups at 36-day intervals ............ 41 

F-1. Counts of attended pups and weaned pups with the source of 

the count for French Frigate Shoals, 1977 ....................... 43 

iii 
F-2. Counts of attended pups at French Frigate Shoals in 1981 ....e. 44 

G-1. Counts of male, female, and unsexed molting seals at French 

Frigate Shoals in 1980 e e . . . e . . e . e e . . . e e . . e . e . ..e 45 

H-1. Counts of Hawaiian monk eeals at French Frigate Shoals 

in 1980 .e . e e e e eo 0 e a a e 0 e 0 e .e ..e e e 6 0 *e e a 47 

LIST OF FIGURES 

2. Mean monthly counts at French Frigate Shoal8 in 1380 .........e e 7 

3. Patterns of u8e for three haul-out islands at French Frigate 

Shoals, 1980 '~~e..~eeee~ee~ee~.~~~~b~~meb~~~~~~e7 

4. Maximum monthly count of mother/pup pairs at French Frigate 

Shoals, 1980 e** e * e e 0 a 0 6 e 0 e b 6 6 a. e e a ..e a e b e 15 

5. Estimated number of births per month at French Frigate 

Shoals, 1980 8 6 e e a b 6 a 0 e e o e 4 a e e a a e e e s 8 e e 15 

6. Semi-monthly total of molting seals at French Frigate 

Shoals, 1980 e e e e e e e e e 0 e a e 6 e . e e e e i 19 

8. Sex ratio from French Frigate Shoals counte, excluding Shark 

and Disappearing, and corrected for female-with-pup bias .... .e 24 

10. 1omaature:adult ratio from counts at French Frigate 

Shoals, 1976 through 1980 ......e. De~.......o.~~~.~.~~~e~.D.~o~o 28 

Semi-monthly births at Laysan Island 1977-1980 and French 

Frigate Shoals, 1980 e...~e...~.~~~.~.~~m~.~m~~e.~~

38 

D-1. 

D-2. Mean semi-monthly mother/pup count, Laysan Island 1977-80 

and French Frigate Shoat8 ..~.~.:......~~..............L......L. 38 

D-4. Mean semi-monthly molting adult males, Laysan Island, 1978 

and French Frigate Shoals, 1980 . . . . . . e e. . e e . . . . . . 39 
ABSTRACT 

A non-disturbance method of estimating Hawaiian monk seal populations, 

developed and tented previously on Laysan Island, was tested at French 

Frigate Shoals (FFS) during 1980. This Molt-Summation technique counts 

molting seals seen at 8-day intervals (the number of days seals normally 

take to molt) from May through November (the molting season). 

429 molting seals were counted on all islands except Shark and 

Disappearing, where molting seals could not be counted regularly. 

the number of seals that could have molted on Shark and Disappearing 

Islands (extrapolated from the proportion of seals that used the two 

islands for haul-out) raises the estimate to 557 seals. 

born at FPS during 1980, resulting in a total population estimate of about 

660 seals. The mean total atoll count during 1980 was 226 seals, 

suggesting only one-third of the population is normally ashore. 

A total of 

Adding 

Over 100 pups were 

Although pups were born on eight islands within the atoll, over 90% 

were born on East, Round, and Whale-Skate. Both pupping and molt seasons 

were about 6 weeks later at FFS than at Kure or Laysan. The age structure 

of the FFS population was similar to Laysan, while the sex structure data 

suggested a nearly equal sex ratio, unlike other populations to the 

northwest where males may outnumber females 3:l. 

for correcting the female bias inherent in counts made during the pupping 

season when only a part of the population is sexed,) 

(A method is suggested 

V 
INTRODUCTIOI 

French Frigate Shoals (FFS) is located approximatciy 4.50 mi northwest 

of Oahu (Fig. 1). 

Hawaiian monk seal, Nonachus schauinslandi, prior to counts made in the 

1950'8 which reported fewer than 50 seals (Rice 1960). The number of eeale 

using the Shoals increased dramatically during the next 20 years with 274 

seals counted in 1975 (Johnson et al. 1982). Although counta have 

apparently stabilized, the present high numbers and the increase over 

recent years are in marked contrast to conditions at all other major 

breeding atolls, where seal numbers have shown large declinee during the 

same time period. Another difference in the FFS population is the ratio of 

males to females seen on most counts. 

that found at other major breeding locations, where males generally 

outnumber females. 

Little is known about the use of the atoll by the 

The sex ratio is nearer equal than 

The haul-out areas available to seals at FFS include sand islands with 

and without vegetation, periodically exposed coral reefs, and a rock 

outcropping (La Perouse Pinnacle). 

currente, the islands vary in size, and some occasionally disappear for 

days or months. 

AB sand shift8 with storms and 

The U.S. Coast: Guard (USCG) maintained a 20-man station on Tern Island 

(the largest of the sand islands at FFS) from the mid-1940's until 1979. 

The U.S. Fieh and Wildlife Service {FWS) assumed responeibility €or the 

facilities at Tern Island when the USCG decoaacsiseioned the Loraa station on 

30 June 1979. The FWS biologists and dependents currently maintain the 

structures as a research atation. 

Censuses were conducted during 1980 to test the usefulaess of a 

population estimation technique developed for the monk seal on Layean 

Island (Johnson and Johnson 1981a). 

"r(o1t Summation" technique (based on counte of molting seals) on a 

population aach as FFS was necessary to asses6 the appropriateness of.tbe 

technique to Hawaiian monk seale in general. 

and the amourat of infomation collected were restricted to the minimum 

necessary to test the population estimation methodology. Incidental to 

collection of information on molting seals, data on mortality, natality, 

distribution, etc., were recorded, when possible. Two researchers,.Susaa 

Schulraeiotcr ad Ruth fttner, were contracted t0 conduct the molt surveys. 

"he study was conducted under MPA/ESA Permit No. 258. 

Testing the applicability of this 

Visits to the various islaads 

French Frigate Shoals =ad Laysan Island differ in eeveral ways. 

French Frigate Shoal8 is a collection of small ielande, dispersing the 

available haul-out area; Laysaa is a single isfand, with the continuous 

beach and nearby barrier reef the only areas available for haul out. 

Couuata at hysan Islaad hdicate malee outnumber females by as much an 

3:1, whereas counts at PFS indicate a more equal sex ratio. Lastly, the 

Layean Ifsiand popuiatioza experienced a major die-off in 1978, with up to 

one third of the seals tither disappearing or known to have died (Johnson 

and Jobsoa 198lb). 'Ihe FFS popuiationr, after experiencing a dramatic 
2 
3 

population increase during the 1960's and early 1970'8, appears to have 

remained stable since 1Q75 (Johnson et al. 1982). 

This report summarizes the objectives, methods, and results of 

observations made at FFS during 1980. 

geography and history of the atoll, see Amerson (1971). 

on counts, behavior, mortality, tagged seal sightings, and the Tern Island 

population can be found in SchulmeiRter (1984). For comparative data from 

Laysan Island see Johnson and Johnson (1984). 

For a detailed description of the 

Additional data 

MEXHODS 

The primary data for this report cmc from contracted molt surveys 

conducted between May and December of 1980. To familiarize ourselves 

with conditions and personnel and to train the observers, the authors 

spent tt week at FFS in March of 1980. Brief visits were also made in 

September and November. Regular radio contact wag maintained with the 

contracted observers throughout the study. 

All areas available to seals could not be surveyed during the molt 

counts. Travel to Shark and Disappcnrinp rs1stntfP wne ~cncrnly not 

possible due to rough sea conditions and time constrajnte. Mirn conditions 

permitted, occasional visits were made by FWS and National Marine Fisheries 

Service (NMFS) personnel to both Disappearing and Shark Islands to count 

seals and look for molting animals. A few seals are known to visit La 

Perouse Pinnacle, incfi~ding the use of underwater "sleeping caves" (Taylor 

and Naftel 19781, and some have been observed hauled out on exposed coral 

reefs, but these areas were also excluded from molt counts. 

Counts of seals were made at 8-day intervals during the molting 

season, with occa8ional delays of up to 3 days. Data were generally 

collected by one of the contracted observers, but when possible, both 

observers participated in the molt surveys. Surveys were made by , 

observers traveling between islands in a Bouton whaler. Landings were made 

on the larger islands (Whale-Skate, East, Trig, Gin, and Little Gin) where 

animals were counted from shore. Counts of seals on the smaller islands 

(Bare, Mullet, Round, and the sand spits) were made from a boat offshore, 

Rough seas prohibited visits to Gin and Little Gin on five surveys. Atoll 

counts took 5 to 10 hours to complete, and usually started around 0900. 

Onshore counts allowed more complete collection of data on age-class, 

sex, molt, and pupping rather than counts made from offshore. Landing 

spots were carefully selected to avoid disturbance. 

for seal observations, and telephoto lenses for photographing seals. Care 

was taken to minimize disturbance to seals at all times. 

Binoculars were used 

In the course of other research, occasional visits were made to some 

islands between January and mid-May during which pup production and molting 

seals were noted. The contracted atoll surveys began in May, when the 

first seals were expected to begin molting. The initial molt surveys were 

done on 14 and 30 May, then at 8-day intervals, with the last survey 
4 

conducted on 1 December (data from 1 December have been included in the 

means for November unless otherwise noted.) 

Information collected on each animal included age, sex (when 

possible), haul-out location, and stage of molt. Tho animals were 

classified as follows. 

&g.--Animals were classified as either adult, subadult, juvenile, or 

pup, 

determination of animals older than pups. Because of the subjective nature 

of age classification, data from the juvenile and subadult age classes have 

usually been combined into a single "immature" age class. A description of 

the age classification system used can be found in Johnson and Johnson 

(1981a). 

Subjective assessment of length was the primary criterion for age 

&,--A clear view of the ventral surface was required,to determine 

eex. 

and previously identified oeals. 

The only exceptions were adults attending pups (assumed to be female) 

- Molt.--Seals were classified as pre-molt (old pelage generally showing 

green algal growth), molting (visibly shedding the hair), or post-molt 

(silver gray color) as described in Johnson and JohnGon (19RI.a). Pre-molt 

and post-molt seals wcre readily distinguishable by trained observers, t-lg~ 

color difference remaining distinct for sevcrnl monthn. The post-molt 

coloration was similar to the gray coat color of weened pups (also in new 

pelage after shedding the black natal coat) and it became increasingly 

difficult to distinguish between small post-molt juveniles and weaned pups 

a8 the season progressed. 

Data for estimating population size (using the Molt-Summation 

technique) were collccfed using methodology developed on Laysan Island 

(Johnson and Johneon 1981a). 

technique are: 

The assumptions of the Molt-Summation 

1. All monk seals molt once, and only once, each year. 

2. The shedding phase of the molt, when hair still attached to 

patches of the outer layers of epidermis is shed, can easily be recognized 

by trained observers. 

3. Molting seals remain hauled out throughout most of the shedding 

phase (data from Laysan Island indicate molting seala are ashore 

approximately 90% of the time). 

4. The average animal sloughs hair for 9 days. 

Based on these assumptions, an accurate estimate of the population can 

be obtained by summing the number of molting seals counted at 8-day 

intervals throughout the molting season. 

about 9 days and molting seals are ashore about 90% of the time, the 

molt estimate technique can be expected to overestimate the population size 

by roughly 5X if all molting seals ashore are counted. At FFS, the risk of 

Since the shedding phase lasts 
5 

disturbance to animals and the difficulty in censusing islands from 

offshore probably resulted in some molting seals being missed on counts. 

Therefore, it is unlikely the Molt-Summation technique would overestimate 

the population. 

Two additional factors affect the interpretation of the molt survey 

results. Due to the rotational system for FWS biologists at FFS, periods 

of overlap were infrequent for the two contracted observers. 

photographic inventory of well-identif ied seals to help calibrate the 

observers' size classifications and infrequent chances to compare ageing, 

criteria may have resulted in inconsistencies in age classif ication between 

observers. Secondly, some areas available to seals were not included in 

the molt survey censuses, thus limiting discussion of results to partial 

atoll rather than total atoll statements. 

The lack of a 

RESULTS AND DISCUSSIOB 

Population Counta 

Mean monthly counts for all islands are listed in Table.1. Data are 

taken from counts listed in Appendix A. 

including aerial counts, can be found in Schulmeister (1984). The mean 

number of seals counted each month on the molt survey islands, both 

including and excluding pups, are shown in Fig. 2. Including pups, the 

counts increased through July, then declined. When pups are excluded,,the 

mean monthly counts showed little change throughout the study period. 

Additional counts of some islands, 

The mean monthly counts (including pups) for the individual islands 

showed a variety of trends. The most dramatic differences are shown in 

Fig. 3. 

the total molt survey islands but Round and Trig Islands show divergent 

patterns. 

during the pupping season, while use of Trig (and to a lesser extent Tern 

Island) was low in the pupping season but increased during the latter part 

of the molting season. 

The haul-out pattern for Whale-Skate Island was similar to that of 

Round (and to a lesser extent East Island) was used primarily 
6 

Table 1.--Monthly mean count data (with sample size) from French Frigate 

Shoals, 1980. Count data are listed in Appendi 

Island 

- - 

Tern 17-3 15-2 15-2 14-3 14-4 26-4 18-4 20-4 27-4 18 

Whale-Skate 33-3 39-2 52-2 61-3 74-4 68-4 72-4 57-3 55-4 57 

29-4 21-4 18-4 33 

4-4 2-4 1-4 3 

26-3 16-2 12-2 17-3 18-4 26-4 29-4 42-3 50-4 26 . 

4 16-4 8-4 2-4 4-4 16 , 

-4 7-3 

6-2 R-2 16-2 -4* 9-3 6-3 5-1 8 

2-2 2-2 622 1-3 0-1 4 

136 132 191 98 180 161 175 

22-2 24-1 7-1 11-2 9-3 6-1 13-1 -- 31-1 15 

Disappearing 27-1 33-3 27-2 44-1 -I 25-1 40-1 -- 54-1 36 

To tal 185 189 225 257 -- 229 233 -- 250 226 
7 

N 225T il 

M 

B 

E 

R 

u 

M 

B 

E: 

R 

0 

t= 

I UL-11 I 11 

FIGIJRE 2 MEAH MOtdTHLY COlJNTS rlT 

IEl 1980. SOLID EARS flRE EIOEIPUP 

COUNTS, STRIPES IHCL-UUE PUPS. 

801- 

70-- WHALE-SKATE 

3 4 5 G 7 8 91811 

MONTH 

- 

FFS 

FIGURE 3 PQTTERNS OF USE FOR THREE 

HAUL-OUT ISLANDS AT FFS, 1988. 
8 

The authors participated in two aerial counts which included both 

Shark and Disappearing Islands. 

November, when ground counts of all molt survey islands (except Gin and 

Little Gin) and the aerial counts of Shark and Disappearing Islands 

resulted in a total seal count of 238. 

The higher of these counts was made on 18 

While only two aerial counts were made of seals on Shark and 

Disappearing by the authors, additional counts were made by NMFS, FWS, and 

other personnel (counts listed in Appendix B). 

atoll counts, including only surveys when a count of Disappearing Island 

was made withins3 days of a count of the molt survey islands. The 

highest total atoll count of 258 seals on 30 May includes a count of 

Disappearing on 2 June. 

the time when most seals were hauled out on the molt survey islands.) 

Table 2 presents total 

(No counts were made of Disappearing during July, 

The highest counts from 1975 through 1980 are listed in Table 3. They 

indicate the atoll population has remained relatively stable during the 

last few years. 

Distribution 

Total Atoll 

Seals regularly hauled out on some islands that were not visited in 

the course of the molt surveys. These areas include Shark, Disappearing, 

La Perouse Pinnacle, and exposed reefs. Of these areas, only Shark and 

Disappearing were known to have had enough use to affect the calculation of 

distribution patterns. 

Table 4 presents data on the relationship between island size and seal 

usage for the 12 commonly used sand islands. 

ashore using each area is calculated from the mean monthly count data 

(Table 1). These results suggest about 77% of the seals haul out on the 

areas regularly included in the molt surveys. 

hauled out on Whale-Skate, followed in descending order by Disappearing, 

East, and Trig. These four islands accounted for about two-thirds of the 

seals. The density of seals on three of the smaller islands, Round, Bare, 

and Shark, was much greater than that found on any other haul-out area. 

Mullet and Disappearing were also used by more seals than would be expected 

based on size. 

The percentage of the seals 

The largest number of seals 

Three islands accounted for 91% of the pups born at FFS. The greatest 

number of pups were born on East, followed by Round and Whale-Skate. On 

Whale-Skate the pupping activity was roughly proportional to size and total 

seal count. On both East and Round islands, a higher proportion of births 

occurred than would be expected based on size and total seal use. 

particular, it is surprising that so many births occurred on an island as 

small as Round (0.5 acres). At the other extreme, both Tern and Trig were 

well below the births that would be predicted based on size and total use. 

In 
9 

Table 2.--Total atoll surveys. (Includes all dates when a count of 

Disappearing was made within 3 days of a molt survey count. S = surface 

count, A = aerial count, 0 = offshore count, R = count made from roof of 

building on Tern island.) 

Mo 1 t s urvey 

Date No. Type 

3/05 154 A 

4/17 113 A 

4/28 151 S 

5/30 210 S 

8/27 190 S 

9/10 174 S 

11/18 153 S 

Disappearing Shark 

- 

Date No. Type Date No, Type To tal 

3/05 27 A 3/05 10 A 191 

4/17 23 A 4/17 24 A 160 

4/29 43 A 194 

6/02 44 S 5/30 4 R 258 

8/29 25 0 8/27 4 R 219 

9/08 40 A 9/10 13 A 227 

11/18 54 A 11/18 31 A 238 

-- -- 

Table 3.--Highest count for each year from 1975 through 1980 

at French Frigate Shoals. 

Year Month Count Source 

1975 * 27 4 Johnson et al. 1982 

1976 March 195 Johnson et al. 1982 

1977 April 223 Johnson et al. 1982 

1978 Augu e t 200 Coleman, FWS, unpublished data 

1979 241 Rauzon, FWS, unpublished data 

1980 fiY 258 Present study 

*The date of this count is not available in published 

accounte. 
10 

Table 4.--Distribution of seals at French Frigate Shoals during 1980, 

including comparisons between the size of each island and the percentage 

of the population using the island for haul-out and for pupping. 

Percent Percent PercenS Sealst 

Island area seals births acre 

1 2 

Tern 

Trig 

Whale-Skate 

East 

Round 

Mullet 

Gin 

Little Gin 

Spits 

Shark 

Disappearing 

~ Bare 

24.4 

13.8 

23.4 

15.7 

0.7 

0.6 

0.1 

4.5 

7.1 

? 

1.1 

8.6 

8 

12 

25 

15 

7 

1 

1 

3 

3 

2 

7 

16 

0 

1 

27 

34 

30 

0 

0 

1 

3 

0 

1 

3 

1.0 

2.6 

3.4 

2.9 

32.0 

7.5 

20.0 

2.5 

1.6 

? 

18.8 

5.8 

'Area (acres) for each island taken from Amerson (19711, except 

for Tern Island. G. H. Balazs and W. G. Gilmartin (personal communication) 

recalculated the area of Tern to be 35 acres rather than 56.8 listed in 

Amerson (1971). For these calculations, the acreage of Tern was halved 

since about that much of the island is unavailable for haul-out. Area of 

all islands varies with season and year. 

*Seal numbers based on mean count from Table 1. 

3Birth numbers are based on mean estimate from the 40-day interval 

pup production estimate in Table 6. 
11 

Disappearing and Shark Islands also appear to have comparatively few pups 

but births could have been missed on these islands. 

Mo 1 t Su r ve y Is 1 and s 

The counts of seals on the molt survey islands were the only counts 

for which age/sex composition and number of molting seals could be 

determined. 

censuses, there were marked differences in the degree of use for the 

various haul-out locations. 

While seals were generally seen on all the islands during 

Table 5 presents data on usage of the molt survey islands. The 

islands most used for haul-out were Whale-Skate, East, and Trig. When pups 

and nursing females were excluded, the most used areas were Whale-Skate, 

Trig, and Tern. East Island was used by the most nursing mothers, followed 

by Round and Whale-Skate. 

pups. 

Tern and East the only other islands where molting seals were seen 

regularly. 

East was second to Whale-Skate in use by weaned 

Whale-Skate and Trig were used by 78% of the molting seals, with 

Absolute determination of the ageisex etructure WBR not possible for 

FFS due to observer differences in classifying seals (see Age Structure 

section). On any particular census, however, the biases which exist should 

affect all islands equally, allowing the islands to be ranked. The three 

areas with the highest percentage of males were the sand epits, Trig, and 

Tern. 

Mullet, Bare, and East. The highest percentage of adults was found on 

Round, East, Trig, and Little Gin. The highest percentage of immatures 

occurred on Mullet, the sand spits, Tern, and Bare. 

The four areas having the highest percentage of female8 were Round, 

Summary of Individual Islands 

The following summaries are based on data from Table 5 which excluded 

Shark and Disappearing. Brief summaries of the Limited data from tho8e two 

islands are included at the end of the section. 

- Tern.--Tern is the largest of the sand islands and is the only island 

with regular human habitation. 

seals due to man-made structures. Much of the beach crest is vegetated. 

With each year since the closing of the USCG facility, the number of 

eeals uaing Tern Island has increased (Schulmeister 1981). Tern Island 

wa8 used by about the same number of seals as Round Ieland but unlike the 

pattern seen at Round, seals used Tern throughout the study period with 

numbers increasing in the fall. 

pregnant females and weaned pups were frequently sighted. 

regularly by molting seals, particularly adult males. 

Part of the shoreline is unavailable to 

No pups were born oa Tern although 

Tern was used 
12 

Table 5.--Distribution of Hawaiian monk seale on the molt survey islands at 

French Frigate Shoals, 1980 (excludes Disappearing and Shark Islands). 

Molting We eeals anej 4 SubIeland count total PUPS Births 1 2 Mean 

Tern 

Trig 

Whale-Skate 

East 

Round 

Mu1 let 

Bare 

Gin 

Little Gin 

Spit s 

19 

27 

59 

33 

17 

3 

3 

8 

7 

4 

18 

24 

42 

15 

3 

2 

3 

7 

6 

4 

1.2 

2.1 

9.4 

8.4 

4.4 

0.6 

0.1 

1 .o 

0.5 

0.2 

0 

1 

25 

32 

28 

0 

0 

1 

3 

0 

3.7 

10.0 

15.0 

3.0 

0.0 

0.0 

0.1 

0.1 

0.3 

0.0 

'Numbers from Table 1, except all April counts and aerial counts are 

'Subtotal excludes parturient females and all pups. 

3Mean count of weaned pups, from Appendix A. 

4Mean of five 40-day estimates of pup production from pupping section 

'Mean number of molting seals seen on all molt surveys made between 14 

excluded. 

of report . 

May and 1 December. 

Trig.--Trig is vegetated over about half of its area. The mean count 

ranked Trig third in total usage. When sighting8 of parturient females and 

all pups are excluded from the counts, Trig became the second moet used 

haul-out area. 

average of two weaned pups were eeen on Trig; one pup was born on the 

island. 

Trig also ranked second in use by molting seals. An 

Whale-Skate.--The second largest of the islands, Whale-Skate is long 

and narrow with vegetation along the beach crest of much of the ieland. It 

wa8 used by the largest number of seale throughout the study period, and 

the largest number of molting animals. 

parturient females, and was used by large numbers of weaned pups. 

Whale-Skate ranked third in use by 

- East.--East island is the third largest island and is vegetated. It 

has been the focus of much of the green sea turtle, Chelonia mydas, 

reeearch done since 1972 (Balaze 1980). 

parturient femalee and near Whale-Skate in use by weaned pups. 

parturient females and all pups were excluded, East dropped from second to 

East ranked highest in use by 

When 
13 

fourth in seal usage. 

censuses. 

An average of three molting seals were seen during 

Round.--A small, circular island, Round has no vegetation. The island 

is surrounded by coral reefs and shallow water. 

used by parturient females, suckling, and weaned pups. Excluding parturient 

females and pups, the mean count for Round drops from 17 to 3 seals. Round 

ranked second to East as a rookery area, with an estimated 28 births. 

The island was primarily 

Gin and Little Gin.--Both Gin and Little Gin are unvegetated sand 

islands. Little Gin, the larger of the two, is the highest of the sand 

islands at FFS. 

15 seals. 

Gin apparently did not survive to weaning. 

weaned pups were seen on Gin and Little Gin. 

Counts were generally low, with a combined island mean of 

At least one pup was born on each island, but the pup born on 

Occasional molting seals and 

Bare, Mullet, and Sand Spits.--These small sand islands were used 

infrequently by seals and all were subject to tidal inundation, 

count for all areas combined was eight seals. 

pups were rarely seen hauled out on these small islands and no births were 

recorded. 

The mean 

Molting seals and weaned 

Shark.--Shark Island was visited on six of the molt surveys. Rough 

water prohibited close approach on most days. 

on Shark, 

One pup was known to be born 

Aerial and occasional ground counts ranged from 5 to 34 seals. 

-.--Because of the rough water normally around Disappearing 

and the distance from Tern, the only counts available from 1980 were aerial 

counts and infrequent visits from personnel on research vessels. 

three pups were born on Disappearing, and counts ranged from 23 to 54 

animal s. 

At least 

Pupping 

Seasonal Distribution 

Pups were born on ei&..t islands during 1980; Round, East, Whale-Skate, 

Gin, Little Gin, Trig, Disappearing, and Shark. The first pup was born in 

early March, the last in October. The maximum number of mothers attending 

pups was 49, seen on 7 June. 

attended and weaned pups) was 71, also on 7 June. 

The maximum total pup count (including 

The pupping season can be described in two waysr by actual birthe, 

beginning with the first birth and ending with the last; or by counts of 

mother-pup pairs, beginning with the first birth and ending when the last 

pup is weaned. The peak of pupping and the midpoint of the pupping season 

will be later when based on counts of mother-pup pairs. 

The 1980 pupping season at FFS can best be described by counts of 

mothers attending pups because surveys were too infrequent to record actwl 
14 

births. 

attending pups, shows the peak of pupping occurred in June. Data are taken 

from incidental ground counts prior to May and from molt surveys after May. 

Figure 4, which presents the maximal monthly counts of mothers 

Although the actual number of births was not determined, the number of 

births per month can be estimated from data collected on the size of pups 

seen on each census. Whenever possible, attended pups were subjectively 

assigned a size, either small, medium, or large. Based on growth stages of 

pups on Laysan Island, a pup was called small for about a week, medium for 

20 to 24 days, and large, thereafter. One pup was present in early March 

on Round Island. By the end of March two more pups had been born, one on 

East, the other on Whale-Skate. By the end of April, there were an 

additional 24 births. 

from May through September estimated by the 8-day interval counts of small 

pups (see Appendix C). 

were extrapolated, resulting in at best a rough estimate of births per 

month at FFS. However, the shape of the curve is similar to that shown by 

counts of mother-pup pairs. 

that shown by count data, as expected. 

Figure 5 shows the births per month, with births 

Since pups were not sized on all surveys, some data 

The peak in May was about 1 month earlier than 

Appendix D compares pupping data from FFS with data from Kure and 

Laysan. 

days later than at other atolls to the northwest. 

The comparison shows the pupping season at FFS occurred about 45 

Pup Production 

It was not possible to count the total number of pups born, or the 

number born per island, as visits were infrequent and the pups could not be 

individually recognized. Pup production can be estimated using a technique 

first mentioned by Kenyon and Rice (1959). 

attended pups at intervals approximating the mean lactation period can 

provide an estimate of total pup production. 

data collected from 1977 through 1980 on Laysan Island, where the mean 

weaning age (36 days) and actual pup production were known. The data 

presented in Appendix E suggest that on Laysan, the method underestimated 

the number of births (by roughly 9%), but correctly estimated the pup 

recruitment (as defined by the number of pups surviving through weaning). 

The greater the mortality of pups prior to weaning, the greater the degree 

of underestimation of total births. 

They suggested that counting 

The technique was tested on 

Molt surveys at FFS were made every 8 days. Counts of pups during the 

surveys allowed five 40-day interval estimates. The 40-day interval was 

selected over a 32-day interval to err on the conservative side as mean 

weaning age was not known. Table 6 presents data showing the estimated 

number of pups born on Round, East, and Whale-Skate Islands to be between 

81 and 91. 

islands was nine (three pups each on Disappearing and Little Gin, one each 

on Shark, Gin, and Trig). The mean of the five series (85) added to the 

pups born on other islands gives an estimated pup production of 94. 

The minimum number of pups known to have been born on the other 
15 

MONTH 

FIGURE 4 MAXIMUM MONTHLY COUNT OF 

MOTHERlPUP PAIRS AT FFS, 1988. 

35- 

30- 

25- 

20- 

15-, 

C 

T 

H 

S 0. 

MONTH 

FIGURE 5 ESTIMATED NUMBER OF BIRTHS 

PER MONTH AT FRENCH FRIGATE, 1980. 
16 

Table 6.--Estimate of 1980 pup production at French Frigate Shoals 

based on 40-day interval counts of attended pups. 

Start WhaleSeries date Round East Skate Other Total 

1 3/03 30 33 22 9 94 

2 3/11 28 32 25 9 94 

3 3/19 29 34 28 9 100 

4 3/27 25 31 25 9 90 

5 4/04 27 31 26 9 93 

Mean 28 32 25 9 94 

While little data on lactation interval or pup survival are available 

for FFS, pups appear to be weaned at about the same size and stage of molt 

as at Laysan. 

prior to normal weaning. Assuming mothers at FFS nurse pups about 36 day8 

(for pups surviving until normal weaning), then using a 40-day interval 

will underestimate pup production by 10% (correcting for the pups that 

could have been born and weaned between counts). 

total pup estimate of 104. 

on Laysan, then a further correction of 9% should be made to account for 

births that would not be detected when using a 36-day interval. 

bring the FFS eetimate to 114 pups. 

if pup mortality is less than at Laysan, this estimate could be high.) 

At least five pups were known to have died or been abandoned 

Adding 10% of 94 gives a 

If mortality of pups on FFS is similar to that 

This would 

(If the mean weaning age is longer, or 

Two different approaches to determining pup production also indicate 

over 100 pups were born. 

Seasonal Distribution section estimated 104 pups. The second method 

extrapolates the ratio of maximum mother-pup count to total pup prodbction 

from Laysan Island to the FFS population. 

from 1977 through 1980 was 0.43. The yearly ratios were 0.43, 0.52, 0.41, 

and 0.39, respectively. Applying these ratios to the maximum mother-pup 

count of 49 at FFS results in an estimate of 94 to 126 pups, with 114 pups 

the mean. 

First, the small pup tally mentioned in the 

The mean ratio for Laysan Island 

The small pup results and the 40-day estimate can be compared to known 

pup production numbers using the 7 June survey data. 

71 pups were counted on the molt survey islands. An additional three 

attended pups were seen on Disappearing on 2 June, and one dead pup had 

been seen on Round Island earlier. Added together, the lowest number of 

pups that could have been born by 7 June was 75. On 7 June the small pup 

tally accounted for 74 pups, and the total for the 40-day series falling on 

that date was 75 pups. This close fit with the minimum number of pups 

known to have been born shows both estimates are reasonable but conaervative methods of assessing pup production. 

On 7 June a total of 
17 

In conclusion, the best estimates indicate about 114 pups were born at 

FFS in 1980, with about 104 surviving through weaning. Data from 1977 and 

1981 indicate over 100 pups were born in each of those years (Appendix F), 

suggesting that the pup production at FFS in 1980 was not unusual. 

Breeding: Female Dorsal Scars 

In 1978 a breeding encounter was observed about 1 km off Laysan Island 

(Johnson and Johnson 198lb). Numerous males encircled an adult female and 

Some males repeatedly bit the back of the female causing extensive injury. 

The lesion exposed blubber and muscle, and probably resulted in the death 

of the female. 

(W. G. Gilmartin, personal communication). 

A similar incident was observed again at Laysan in 1982 

Although other breeding encounters have been observed which involved 

only one male and did not result in injury to the female (Johnson and 

Johnson 1981b; Schulmeister 19841, adult females with extensive scars 

along the dorsal midline have been observed at all major hauling areas. 

This raises the possibility that breeding related injuries to adult females 

are not uncommon and may occur primarily when the encounters involve more 

than one male. 

One test of this theory is to compare the percentage of females with 

dorsal scars at Laysan and at FFS. 

adult females 3:l (Johnson and Johnson 1981a), the probability of multi-male 

breeding encounters should be greater than at FFS where the sex ratio is 

nearly equal (see Sex Ratio section). Comparing the frequency of dorsal 

scars from animals aeen on ground counts would probably be biased as 

conditions for viewing animals are different at Laysan and FFS. The 

presence of a sample of seals individually recognizable by natural marks at 

both haul-out locations provides a less biased basis for comparison. 

At Laysan, where adult males outnumber 

Based on photographs and sketches made primarily by Susan Schulmeister 

and Ruth Ittner from 1979 through 1981, 52 adult females with individually 

recognizable natural marks were identified at FFS (S. Schulmeister, 

personal communication). Of these, only six (12%) had the distinct dorsal 

midline scars which might have resulted from a breeding injury. 

On Laysan, where a much more intensive effort was made to identify all 

seals, 96 adult females were recognizable as distinct individuals over the 

4 years of the study. 

of tags or minor marks. 

comparable to those used for identification at FFS, 26 (35%) had distinct 

dorsal midline scars. 

Of these, 21 were recognizable only on the basis 

Of the remaining 75 females with natural marks 

Chi-square analysis indicated the dorsal scarring rate observed at 

FFS was significantly lower than that seen at Laysan (X2 9.96, pC0.005). 

These data suggest that when the sex ratio becomes skewed in favor of 

adult males, the frequency of multi-male breeding encounters may increase, 

resulting in an increase in potentially fatal injuries to adult females. 
This would lead to maintaining or increasing the disparate sex ratio to the 

detriment of the population. 

extent of this problem. 

Further research is needed to ascertain the 

Molt 

Molt surveys were conducted between 14 May and 1 December. Molting 

seals were regularly seen during all of these months. Between 1 January 

and 30 April, 13 trips were made to Whale-Skate, Trig, and/or East Islands 

and daily observations were made at Tern Island. During these months, only 

two molting seals were seen, an unsexed juvenile on Tern (2 January) and an 

unsexed adult on East (9 April) indicating molting seals were rare before 

the start of the nolt surveys. (Counts of molting seals are listed in 

Appendix G,) Molting seals were seen on all islands, but animals molting 

on Shark or Disappearing are not included in the following calculations, 

Figure 6 presents the number of molting seals seen on molt survey 

counts. 

peak occurring in October. 

the various age/sex classes. 

longer than for the other age/sex classes, and the peak, in August (or July 

if estimated numbers from Table 7 are used), occurred earlier than the peak 

of the other age/sex classes. 

molted in August and September. 

The peak of molting activity for the adult males was the latest, occurring 

in October. 

The majority of seals molted between July and November with the 

Figure 7 shows the molting season differed for 

The molting season for adult females was 

The greatest number of immature females 

The immature male peak was in September. 

Although the reliability of breaking down the immature age class into 

subadult and juvenile is questionable, it should be noted that all but one 

of the immature seals molting after September were classed as juvenile 

size. 

These data agree closely with data from Laysan which show the long 

molting season for adult females (apparently due to the prolonged pupping 

season), the short and late molting period for adult males (presumably not 

beginning until after the breeding season ends), and the late molt for many 

yearlings, Compared to Laysan, the molting season at FFS appears to occur 

about 6 weeks later (Appendix D). 

Population Estimation 

Calculation of Estimate 

Based on the 8-day interval counts of molting seals, a total of 426 

animals (excluding pups) molted between 10 March and 1 December in 1980. 

In addition, one molting seal was seen on Tern Island in January and two 

were seen on Tern in mid-December. This total of 429 seals is clearly a 

conservative estimate of the number of seals using the molt survey island6 

for several reasons. 
19 

5 G 7 8 9 10 - 1’1 - MONTH 

FIGURE 6 SEMIMONTHLY TOTAL OF MOLTING 

SEALS AT FRENCH FRIGATE, 1980. 

ADM 

15.- 

0 A L - 

4 5 G 7 8 9 1011 

MONTH FIGURE 7 MONTHLY TOTAL OF MOLTING 

SEALS BY ACE CLASS, FROM 8-DAY 

COUNTS. FRENCH FRIGATE, 1980. 
1. Some molters may have been 

surveys in mid-May. 

2. The molting season had not 

20 

missed before the start of the molt 

ended when the last molt survey was 

conducted (12 molting seals were seen on 1 December). 

3. Gin and Little Gin were not visited during five of the molt 

surveys, thus seals molting on those islands would have been missed. 

4. Some molting seals, particularly those just beginning or ending 

the molt, could have been missed on islands censused from offshore. 

Adding in the estimated pup recruitment (births minus pre-weaning 

mortality) of 104 gives an estimate of 533 seals using the molt survey 

islands. Because Shark and Disappearing were excluded, this is a partial 

rather than a total atoll estimate. 

Although seals were known to molt on both Shark and Disappearing 

during 1980, no counts of the actual number of molting seals were 

available. 

was obtained on 1 August 1981 when one of the authors (P. A. Johnson) 

visited all islands at FFS. 

were on Shark and Disappearing, suggesting the importance of the two 

islands as molting areas. 

One indication of the use of these two areas by molting seals 

Of the 21 molting seals seen on that date, 43% 

A rough estimate of the number of seals which molted on Shark and 

Disappearing during 1980 can be calculated based on the mean percentage of 

seals using those areas for haul out from Table 4. 

the seals ashore hauled out on Shark or Disappearing. 

were used by proportionately the same number of molting seals, then the 429 

seals counted on molt surveys represent only 77% of a total non-pup 

population of 557 seals. 

results in a total population estimate of 661 monk seals. 

An average of 23% of 

If these islands 

Adding the estimated pup recruitment of 104 

One method of testing whether the estimate of 557 seals is reasonable 

compares the population-estimate/mean-count ratio from FFS with those from 

other studies. 

the March through September period gives a ratio of 2.28 for Laysan during 

1980 (mean count = 118, population estimate = 2691, and a ratio from Stone 

(1984) for Lisianski of 2.19 (mean count = 98, population estimate = 215). 

The ratio for FFS was 2.46 (mean count = 226, population estimate = 557). 

Using the average of the monthly mean non-pup counts from 

Factors such as differences in population age/sex structure and the 

timing of the molt and pupping seasons complicate comparisons. Comparison 

with other atolls indicate, however, that the non-pup estimate of 557 could 

be too high for the FFS population. 

and Laysan are applicable to the FFS population, then the mean count of 226 

would suggest a total non-pup population of 495 to 515 animals.) 

(Assuming the ratios from Lisianski 

In conclusion, the 8-day molt counts indicate at least 429 seals 

molted (excluding pups). 

and Disappearing Islands for haul out, an estimate for the total atoll 

Extrapolating from the ratio of seals using Shark 
21 

population of monk seals at FFS becomes 557 animals (or about 660 seals 

including pups). 

Lisianski indicate this number could be slightly high. 

The ratio of estimate to mean count from Laysan and 

Discussion 

The major objective of this study was to test the feasibility of using 

molt data to estimate the size of the FFS population. 

preliminary nature of the project and the need to keep disturbance to a 

minimum, we were unable to adequately test all assumptions of the estimate. 

Specifically: 

Because of the 

1. A necessary assumption of the molt estimate is that seals shed 

hair for about 9 days and spend approximately 90% of the time hauled out 

(as at Laysan). 

not able to collect any data on percent of time ashore for seals at FFS and 

did not get molt duration for more than a few seals (see Schulmeister 

1984). If a significant difference in molt duration were found, the molt 

estimation methodology would need to be altered. Molt duration data are 

hard to collect as seals can freely move between haul-out areas at FFS. If 

duration of molt data for other areas, such as Necker, Nihoa or Kure, were 

found to be the same as Laysan, then it is likely that FFS seals follow the 

same pattern. 

While this seems likely, it needs to be tested. We were 

2. In the present study some molting seals were undoubtedly missed 

as counts were not made throughout the year, and it was sometimes hard to 

see molting seals on the islands which were censused from offshore. 

seals were missed, the 8-day molt estimate would be low. While the 

observers did not feel this was a major problem, in the future it could be 

measured by observation of the small islands for long enough time periods 

to ascertain the degree to which molting seals were missed on censuses, and 

by counts made in January and December. 

If 

3. The percentage of the seals molting on Shark and Disappearing was 

unknown. As mentioned previously, Shark and Disappearing could not be 

visited regularly. 

season in future years, data collected on the number of molting seals could 

confirm or modify our assumption that roughly equal numbers use these 

islands to molt as used the molt survey islands. 

If these islands could be visited during the molting 

In conclusion, this study has demonstrated that surface counts can be 

made at regular intervals throughout most of the year at FFS and that 

molting seals are readily distinguishable by trained observers. With care, 

censuses can be conducted which cause little disturbance yet yield valuable 

data. The aspects of the methodology which were not fully tested during 

1980 would not be too difficult to test in the course of other monk seal 

observation which will undoubtedly be made on the FFS population in future 

years. 

population is directly comparable to the Laysan population of monk seals, 

the value of the molt estimate from 1980 will be improved. 

With increased information on the degree to which the FFS 
22 

It appears the molt estimation technique is feasible for FFS and makes 

crucial information on population size available to aid in monitoring 

change and making decisions concerning use of the atoll. 

Sex Ratio 

There are problems in using data from ground counts to determine the 

sex ratio of any Hawaiian monk seal population. 

1980 data from FFS as well. Three sources of error include: a large 

proportion of the seals ashore were not sexed during surveys; an unknown 

proportion of seals were not ashore for counts; and, all areas available 

for haul out were not visited during counts. 

introduces bias into determination of the sex ratio. 

These problems affect the 

Each of these problems 

ani 

of 

1. Unsexed seals. The time constraints and risk of disturbance to 

.mal8 during censuses made sexing difficult. 

the adults and 57% of the immature seals were not sexed.) Of the 

(During 1980 censuses, 50% 

animals sexed on censuses, the sex ratio may not be representative of the 

seals ashore. For example, it is possible that males are slightly easier 

to sex from a distance than females, due to the visibility of the penile 

opening and hair ridge lacking in females. 

A more obvious bias exists during the pupping season. All adults 

accompanied by black pups are routinely sexed as female without the 

prerequisite ventral view required when sexing other animals. The effect 

of this bias can be seen by looking at a hypothetical adult population made 

up of 50 males and 50 females, 25 of which are accompanied by black pups. 

Two counts are made. On the first count all animals are sexed, resulting 

in a 1:l sex ratio. On the second survey conditions are such that the 

probability of sexing each individual seal is only 20%, except all adults 

accompanied by pups are still sexed as female. 

show that the second count, where not all of the seals were sexed, will be 

strongly biased toward females. 

The results of these counts 

Females 

Ma1e:Female 

Males Alone w/Pup Total Unsexed sex ratio 

Count 1 50 (25) (25) 50 0 1:l 

Count 2 10 (5) (25) 30 60 1:3 

In theory, this bias can be corrected by estimating how many of the 

mothers would have been sexed as female by the normal method of sexing 

animals, based on the ratio of sexed adults to total adults. 
23 

A/B = X/M 

or 

X = (MA)/B 

where : 

A = total adults sexed (excluding mothers) 

B = total adults (excluding mothers) 

M = females with pups (mothers) 

X = estimate of mothers which would have been classed as female 

without presence of pup. 

In the above population where 20% of the non-mothers were sexed, 

X = (25) (15)/75 = 5, indicating that of the 25 mothers, only 5 would have 

been sexed using the normal sexing techniques. 

sexed using the normal methods, a total of 10 females result. When 

compared to the 10 seals sexed as male, the corrected sex ratio becomes 

1:l. 

Added to the 5 females 

In practice this correction factor will not eliminate all problems as 

other biases in both aging and sexing animals exist. It should, however, 

reduce the problem during the pupping season. 

useful when comparing counts from FFS with other populations where counts 

differ in percentage of seals sexed or include disproportionate numbers of 

mothers with pups, 

It would be particularly 

2. Missing seals. A second major problem complicating the analysis 

of sex ratio data concerns the unknown percentage of seals that are not 

ashore during a count (often over two-thirds of the population at Laysan). 

Since the island use patterns of each age/sex class vary throughout the 

year, the sex ratio of animals ashore.does not necessarily representGthe 

sex ratio of the population. For example, most previous counts of monk 

seals at FFS have been made during the spring and summer months when 

females have outnumbered males, 

are examined, such as those available for 1977 (Rauzon et ale 1978) and 

1980, females outnumbered males from April through August, but males 

outnumbered females during the fall and winter months (Fig. 8). 

When counts from other times of the year 

3. Incomplete censuses. A third bias in the sex ratio data occurs 

when some haul-out areas are not included in a census. Data from long-term 

studies at Laysan and elsewhere have all shown that certain haul-out areas 

can be used predominately by one sex. To get accurate data on the sex 

ratio of seals hauled out at an atoll, all haul-out areas should be 

included in a census. Unfortunately, age/sex data were not collected on 

seals using Disappearing Island in 1980, and were rarely collected on Shark 

Island. Limited data from these two islands in previous years (Rauzon 

1979; Rauzon et al. 1978) indicate-they may be used by a larger percentage 

of adult males than other haul-out areas. If so, adult males would be - 

underrepresented in the 1980 FFS count data. 
24 

I 1 I 1 1 

1 3 %ONTI$ 9 11 

FIGURE 8 SE% RRTIO FROM FFS COUNTS, 

CORRECTED FOR FEMALE-WITH-PUP BIBS. 

EXCLUDING SHARK & DISAPPEfiRINCr AND 

Comparative Data 

Although sex ratio data from counts cannot be used directly to 

determine the population sex ratio, they can be compared to counts made at 

the same atoll in other years, or to counts made at other atolls. These 

comparisons must be between data collected in the same month or the same 

relative point in the pupping or molt seasons. 

Table 7 presents the sex ratio data collected during the study for all 

censuses which included Gin and Little Gin Islands (N = 21). Because of 

problems to be discussed later (Age Structure section), no adult/immature 

breakdown is given. In general, however, the sex ratio of seals classed as 

immature was closer to 1:1 than the sex ratio of adults. 

The best data available for comparison between years at FFS are from 

May of 1977 and May of 1980 (May is the only month when more than one count 

was made in two separate years). The comparison, corrected for the femalewith-pup bias, indicates that 37% of the seals ashore were male in 1977, 

and 35% were male in 1980. Uncorrected for the female-with-pup bias, the 

numbers were 26% and 25%, respectively (all numbers exclude data from 

Disappearing and Shark). This indicates the sex ratio at FFS changed 

little between 1977 and 1980. Continued collection of sex ratio data could 

serve as an early indicator of problems in the FFS population by detecting 

any major increase in the proportion of adult males. 

Counts of monk seals at areas which showed declines in the past 20 

years (Kure, Lisianski, and Laysan) consistently report more males than 

females. 

from 60% to 77% of the yearly mean'counts.) 

typically report more females. 

(During 4 years of observations on Laysan, counts of males ranged 

Counts from FFS, in contrast, 
25 

Table 7.--Mean monthly number of seals sexed on all censuses 

including Gin and Little Gin Island (N = 21). 

Actual count Corrected count 

Month Male Female Ratio Male Female 1 Ra ti02 

Mar. 

Apr . May 

June 

July 

Aug . Sept . Oct . NOV 

42 

19 

22 

24 

27 

34 

44 

39 

-- 

46 

58 

61 

49 

48 

32 

22 

14 

-- 

10: 11 

10:31 

10:31 

10:20 

10:18 

10: 9 

10: 5 

10:4 

42 

19 

22 

24 

27 

34 

44 

39 

_- 

46 

35 

42 

36 

45 

31 

22, 

14 

-- 

10: 11 

10: 18 

10: 19 

10: 15 

10: 17 

10: 9 

10: 5 

10:4 

'Totals corrected for female-with-pup bias. 

'Ratio per 10 males. 

Population Sex Ratio 

Data previously presented in Fig. 8 show that when counts are made 

in all months of the year, the sex ratio is approximately equal, but that 

month-to-month patterns vary. 

An estimate of the true sex ratio for the population can be derived 

from data used for the molt estimate. As shown in Table 8, nearly equal 

numbers of molting males and females were counted but many molting seals 

were not sexed. 

based on the male to female ratio of molting animals sexed on each survey. 

The estimated totals again show the sex ratios for both adults and 

immature8 to be near 1:l. 

The sex of unsexed ariimals seen on counts was estimated, 

Like the pattern seen at FFS, data from Laysan show no particular time 

of year when the sex ratio seen on counts can be expected to represent the 

true sex structure of the population (Johneon and Johnson 1984). 

possible that count data may roughly approximate the population sex ratio 

if counts are made throughout the year. 

It is 
26 

Table 8.--Age/sex classification of molting seals seen on molt surveys. 

Actual count 1 Estimated count 2 

Adult Immature Adult Immature 

Total 

Month molting Male Female Male Female Male Female Male Female 

Apr . 

June 

July 

Aug . Sept 

Oct. 

NOV 

Total 

1 

8 

10 

56 

83 

83 

110 

75 

4 26 

+3 

429 

- 

0 

0 

0 

2 

0 

8 

30 

27 

67 

0 

4 

7 

12 

25 

9 

6 

4 

67 

0 

0 

0 

3 

12 

22 

10 

3 

50 

0 

1 

0 

5 

13 

17 

4 

6 

46 

0 1 

0 7 

0 9 

0 41 

0 32 

13 14 

65 11. 

53 9 

0 0 

0 1 

0 1 

7 7 

24 27 

32 25 

22 12 

4 9 

131 124 89 82 

+2 

84 

- 

'Excludes unsexed animals. 

2 Assigns a sex to unsexed animals 

seals of that age class. (Assumes the 

July were actually immature males,) 

based on the sex ratio of the sexed 

two "adult" males molting in early 

Estimated agefsex ratios 

Adult/immature ratio = 2551174 = 59% adult 

Malelfemale ratio = 220f208 = 51% male 

Age Structure 

As mentioned in the Sex Ratio section, using data from ground counts 

to determine sex ratio or age structure has built-in biases. In addition 

to the problems of qn unknown proportion of the population being at sea 

during counts and seals hauling out on places not included in the counts, 

there is a third difficulty with determination of age structure. 

concerns the subjective nature of assigning an age to an animal. 

This 

Unless animals were recognizable individuals, pups, or mothers with 

pups, age categories were based primarily on the observers' subjective 

estimate of size. 

sometimes useful,) 

seals to help calibrate observers size classifications, inexperience of 

observers, and infrequent chances to compare ageing criteria may have 

resulted in inconsistencies in age classification between observers. On 

(Other factors, such as pelage color and behavior were 

The lack of a photographic inventory of well-identified 
27 

Laysan, where two observers worked closely together with numerous 

identified seals as reference animals, observer differences were minimal, 

Data collection at FFS was more limited in scope and was not optimally 

designed to determine agefsex structure. The two contracted observers were 

rarely able to conduct joint censuses to compare age classification because 

they were seldom in the field at the same time. 

Figure 9 presents data on counts of adults and immatures during the 

study. 

between July and August and again between September and October. While 

this could represent an actual change, it could also be the result of 

observer bias, as both of the shifts in age structure corresponded with 

shifts in observers. 

These data appear to show dramatic reversals in age ratio occurred 

The data presented in Fig. 10 support the idea that the change was 

primarily due to observer differences. 

are compared with data from 1976 through 1979 (DeLong et al. 1976; Balazs 

1977, personal communication; Rauzon et al. 1978; FWS 1977, 1978, 

unpublished reports; Fiscus et al. 1978; Rauzon 1979)- Except for the 

July 1977 count, the data show similar patterns through August, when the 

1980 data show an increase not seen in other years. Unfortunately, no 

September counts are available for the other years. These data indicate 

observer bias could be responsible for the dramatic increase in the 

percentage of immatures, but it is also possible that observer bias merely 

accentuated an actual change in age specific haul-out patterns not seen in 

the other years. 

Age ratio data collected in 1980 

Although only single counts are available for most months in the 1976 

to 1979 period, the data from all years indicate the ratio of adults to 

immature8 was near equal in March, and that adults outnumbered immaturee by 

2:l in April, May, and June. 

The molt data provide a different approach to determining age 

structure. Summing the number of adult and immature seals that molted 

gives the age structure of the population using the molt survey islands, 

rather than a measure of seasonal change in haul-out frequency. While the 

same problem of reliably ageing seals exists, more time was spent observing 

and classifying molting seals. 

59% of the molting seals were aged as adults and 41% as immatures. 

Table 8 presented data which showed that 

Overall, the proportion of immatures in the FFS population was similar 

to that reported for Laysan, where the mean percent immature was 51% in 

1977, 387, in 1978, and 45% in both 1979 and 1980 (Johnson and Johnson 

1984). Age data for FFS are presented in Appendix H. 
28 

P 7= 

50 E 25 

0 

f9DUl.TI 1 1 1 I I I 1 I 

3 4 5 G 7 8 91011 

MONTH 

FIGURE 9 flEAN MONTHLY COUNT Ob 

ADULTS AND IFIMATURES, FFS, 1980. 

.. 

.. 

1 I I + 1 I I I I I 

2 3 4 5 G 7 8 9 1811 

MONTH 

FIGURE 10 IMMATUREsADULT RATIO FROM COUNTS AT FFS, 1976-1988. ("+I' = DATA 

FROM SINGLE COUNTS, 1976,'78, OR '79.) 
29 

SUMMARY 

1. Objectives. The major objective was to determine if regular 

counts of molting seals could be used to estimate the population size at 

FFS. 

natality, and mortality. 

Secondary objectives included the collection of data on distribution, 

2. Methods. Counts were made of all islands regularly used by monk 

seals (except Shark and Disappearing) at 8-day intervals throughout the 

molting season (May to December). Observations were made with binoculars 

and, in the case of several small islands, from offshore. Disturbance to 

seals was carefully avoided. - 

3. Maximum Count. The maximum total atoll count of 258 seals 

occurred on 30 May. The maximum count of seals on the regularly surveyed 

islands (excluding Shark and Disappearing) was 228 in late July (no count 

was made pf both Shark and Disappearing in July or October). 

fall within the range of highest counts made during the previous 5 years 

(195-274). 

These counts 

4. Distribution. The largest number of seals hauled out on WhaleSkate followed by Disappearing, East, and Trig. Most of the pupping 

occurred on three islands, with approximately 34% of the pups born on East, 

30% born on Round, and 27% born on Whale-Skate. 

molting seals used Whale-Skate, followed by Trig. 

exclude Shark and Disappearing where molt data were not collected.) 

The greatest number of 

(Data for molting seals 

5. Pupping Season. Pups were born from March through October, with 

the peak number of births occurring in May. The maximum count of motherpup pairs was in June. 

than at Laysan or Kure. 

The pupping season at FFS was 6 to 7 weeks later 

6. Pup Production. An estimated 114 pups were born on FFS in 1980. 

Data from 1977 and 1981 indicate over 100 pups were born in each of those 

years as well. 

7. Molting Season. Molting seals were seen in all months except 

February and March, but the majority molted between 1 July and 30 November. 

The molting season for adult males was clearly later than for the other 

age/sex classes. 

males, and October for adult males. 

6 weeks later at FFS than at Laysan. 

The peak of the molting season was August for non-adult 

The molting season occurred about 5 to 

8. Population Estimate. The 8-day molt surveys counted 429 seals 

(excluding pups) but this is a conservative population estimate because 

molt counts were not made on Shark or Disappearing Islands. 

estimate of molting seals on Shark and Disappearing (extrapolated from the 

percentage hauled out on those two islands) results in a total atoll 

population of around 557 seals. Adding the estimated pup production gives 

an estimated atoll population of over 660 seals. The study demonstrated 

the molt technique is feasible for’a population like FFS, but the results 

should be conaidered tentative until additional data become available on 

Adding in an 
30 

the mean molt duration and the proportion of seals which molt on Shark and 

Disappearing . 

9. Sex ratio. The collection of sex ratio data is subject to 

several biases. 

pup bias, which should always be corrected before comparing sex ratios 

within and between atolls. The best available data indicate the sex ratio 

at FFS is near 1:l. This is considerably different from atolls to the 

northwest where males clearly outnumber females. 

The most obvious, and easily corrected is the female-with10. & Structure. Because of possible differences in the age 

classification criteria used by the two contracted observers, data on age 

structure are even more difficult to interpret than data on sex ratio. A 

rough idea of the number of immatures in the population can be taken from 

the percentage of molting seals aged as immatures (about 41%), which is 

similar to the proportion of iutmatures reported for Laysan.’ 

11. Breeding. Only one breeding encounter was observed, involving a 

A 

single male/female pair. Multi-male breeding encounters, like those seen 

at Laysan resulting in serious injury to the female, were not observed. 

comparison of the frequency of adult female dorsal scars, possibly breeding 

related, showed dorsal midline scars were significantly more common on 

Laysan than FFS. 

ACKNOWLEDGMENTS 

We would like to thank Susan Schulmeister and Ruth Ittner for their 

interest and assistance in this study. The study would not have been 

possible without the logistic aid and support of the Hawaiian Islands 

National Wildlife Refuge and NMFS Honolulu Laboratory for which we 

are very grateful. We also thank Robert Schulmeister, Jon Gravning, and 

John Andre for their time and help in conducting the surveys, and 

William G. Gilmartin and others at NMFS Honolulu Laboratory for their 

review and suggestions on the manuscript. 

Marine Mammal Commission and administered through the NMFS Honolulu 

Laboratory (Contract No. 80-ABC-00124). 

Funding was provided by the 
31 

REFE RENC E S 

Amerson, A.B., Jr. 1971. The natural history of French Frigate Shoals, 

Northwestern Hawaiian Islands. Atoll Research Bulletin 150. 

Balazs, G.H. 1980. Synopsis of biological data on the green turtle in the 

Hawaiian Islands. U. S. Department of Commerce, NOAA Technical 

Memorandum, NMFS , NOAA-TM-NMFS- SWFC-7. 

DeLong, R.L., C.H. Fiecue, and K.W. Kenyon. 1976. Survey of monk eeal 

(Monachue schau i n s l a n d i ) populations of the Northwestern (Leeward) 

Hawaiian Islands. Preliminary report. Northwest Fieheriee Center, 

Marine Mammals Division, NMFS Processed Report, 36 p. 

Fiscus, C.H., A.M. Johnson, and K.W. Kenyon. 1978. Hawaiian monk eeal 

(Monac hue sc hau inslandi) survey of the Northwes t ern Hawaiian Ielande , July, 1978. NMFS Processed Report, 26 p. 

Johnson, A.M., R.L. DeLong, C.H. Fiscus, and K.W. Kenyon. 1982. 

Population status of the Hawaiian monk eeal (Monachue echauinslandi), 

1978. Journal of Mammalogy 63:415-421. 

JohnSon, B.W., and P.A. Johnson. 1981a. Estimating the Hawaiian monk eeal 

population on Laysan Island. National Technical Information Service 

NO. PB82-106113, 29 p. 

Johnson, B.W., and P.A. Johnson. 1981b. The Hawaiian monk seal on Lapsaa 

Island: 1978. National Technical Information Service No. 

PB-82-109661, 17 p. 

Johnson, B.W., and P.A. Johnson. 1984. Obeervatione of the Hawaiian monk 

seal on Laysan Island from 1977 through 1980. Unpublished NMFS 

Report, Contract 80-ABC-00124, 79 p. 

Kenyon, K.W., and D.W. Rice. 1959. Life history of the Hawaiian monk 

seal. Pacific Science 13:215-252. 

Rauzon, M.J. 1979. Survey of Hawaiian monk seal (Monachus echauinslandi), 

Northwestern Hawaiian Islands, 9-25 May, 1979. Unpublished Report. 

U.S. Fish and Wildlife Service, Anchorage, Alaeka. 

Rauzon, M.J., K.W. Kenyon, and A.M. Johnson. 1978. Observations of monk 

seals, French Frigate Shoals, 17 February to 27 May 1977. Unpublished 

Report. U.S. Fish and Wildlife Service, Anchorage, Alaeka, 34 p. 

Rice, D.W. 1960. Population dynamics of the Hawaiian monk seal. Journal 

of Mammalogy 41:376-385. 

Schulmeister, S. 1981. Hawaiian monk seal numbers increase on Tern 

Island. 'Elepaio 41(7):62-63.. 
32 

Schulmeister, S. 1984. Summary of Hawaiian monk seal (Monachus 

schauinslandi) data collected at French Frigate Shoals from July 1979 

through December 1981. Unpublished Report. National Marine Fisheries 

Service, Honolulu, Hawaii. 

Stone, H.S. 1984. Hawaiian monk seal population research, Lisianski 

Island, 1982. Report to NMFS (draft), Honolulu, Hawaii. 

Taylor, L.R., and G. Naftel. 1978. Preliminary investigations of shark 

predation on the Hawaiian monk seal at Pearl and Hermes Reef and 

French Frigate Shoals. National Technical Information Service No. 

PB-285626, 34 p. 

Wirtz, W.O., 11. 1968. Reproduction, growth and development, and juvenile 

mortality in the Hawaiian monk seal. 

238. 

Journal of Mammalogy 49:229- 
33 

APPENDIXES A - H 
34 

0000 111 

d II,I 

mo401 I I 

111 

mu%nrtm 

0000 
35 

Appendix Bo--Counts of Shark and Disappearing Islands. 

Table B-1.--Aerial and ground counts of seals on Shark and 

Disappearing Islands (Schulmeieter 1984). 

~~ ~ ~ 

Disappearing Island Shark Island 

Date Count Method Date Count Method 

3/05 27 

4/02 33 

41 29 43 

4/17 23 

5/07 31 

5/21 23 

6/02 44 

8/29 25 

9/08 40 

11/18 54 

Aerial 

Aerial 

Aerial 

Aerial 

Aerial 

Ground 

Ground 

Ground 

Ground 

Aerial 

3/05 

3 108 

4/17 

5/15 

6/18 

6/27 

7 109 

7/19 

7/25 

8/10 

9/10 

11/18 

10 

34 

24 

9 

6 

16 

5 

7 

14 

6 

13 

31 

Aerial 

Ground 

Aerial 

Off shore 

Off ehore 

Ground 

Ground 

Ground 

Of fehore 

Ground 

Ground 

Aerial 
36 

Appendix C.--Counts of small pups. 

Table C-1.--Estimated births at French Frigate Shoals during 1980 based on 

size of pups. Sm = pups classed as small (probably less than 8 day8 old); 

Add - the minimum number of births necessary to account for increase in 

number of pups over last census for each haul-out area (used when observers 

did not record the size of pups). 

Source 

P 1 anned Actual Incr e a s e d 

date date pup count Sm Add 

3/03 

3/11 

3/19 

3/27 

3/06 

-- 

-- 

3/28 

1 

2 

4/04 

4/12 

4/ 20 

4/28 

4/02 

4/09 

4/17 

4/ 28 

1 

2 

3 

19 

1 

1 

3 

1 

19 

5/06 

5/14 

5/22 

5/30 

-- 

51 14 

5/ 25 

5/30 

_- 

12 

3 

14 

7 

1 

8 

5 

2 

6 

6/07 

6/15 

6/23 

6/07 

6/18 

6/23 

15 

2 

4 

15 

2 

2 2 

7/01 

7/09 

7/17 

7/25 

7/02 

7 109 

7/19 

7/25 

2 

1 

8/02 

8/10 

8/18 

8/ 26 

8/04 

8/10 

8/19 

8/27 

4 

2 

1 

0 

4 

2 

1 

9/03 

9/11 

9/19 

9/27 

9/04 

9/10 

9/18 

9/ 27 

1 1 

10105 

101 13 

101 21 

10129 

10104 

10/10 

10121 

10130 

1 
37 

Appendix D.--Variation between atolls in the pupping and molt season. 

Pupping Season 

Table D-1 includes data on the pupping season, based on knwn birth 

dates, for Laysan and Kure Atoll. These data are compared to data from 

FFS, which include an estimate of the median birth date calculated from 

counts of small pups (Appendix C). 

The pupping seasons for Laysan (1977-1980, from Johnson and Johnson 

1984) and Kure (1964-1965, from Wirtz 1968) show similar patterns, with the 

mean and median pupping dates falling in mid-April. Data from Kure 

collected in 1981 and 1982 (N = 15) show a mean pupping date of 23 April 

and a median pupping date of 10 April (W. G. Gilmartin, personal 

communication). 

February to 13 August. Limited data from 1958 at Midway Atoll (Rice 1960) 

indicate a similar pattern, with the mean pupping date on 7 April, and the 

median date on 8 April (N = 10, including only full-term births). 

The range of births in 1981 and 1982 on Kure was 18 

The data in Table D-1 show a different pattern for FFS, with mid-range 

and median pupping dates occurring 6 to 7 weeks later than at Laysan or 

Kure. Figure D-1 presents semi-monthly birth frequency data for Laysan 

(known) and FFS (estimated). These data also indicate that the pupping 

season is later at FFS, with the modal peak occurring about 1-112 months 

later. 

Table D-1.--Pupping season dates for Kure (1964 and 19651, Laysan (1977 to 

1980), and French Frigate Shoals (1980). 

Kure (N = 57) Laysan (N = 136) FFS (N = 104) 

Range 3 11 4-7 / 27 

Mid-range 5/07 

Median 4/ 11 

Mean 4/11 

1/15-8/22 3/06-10/09 

5/05 6/24 

4/ 13 5/ 22 

4/17 -- 

The above comparisons are based on estimates of birth dates for FFS. 

Actual counts of attended pups at Laysan and FFS are more directly 

comparable. Figure D-2 presents data on the mean semi-monthly counts of 

attended pups at both areas, and again shows the modal peak occurs about 

6 weeks later at FFS. 
38 

30 tJ 20 LAYSAN 

8 

12345678918 P 

28 FRENCH FRIGATE B le 

H 

s 8 

12343678916 

MONTH 

FIGURE 0-1 SEHIHONTHLY BIRTHS# LAYSAN 

1977-1988 AND FRENCH FRIGATE 1988. 

FRENCH FRIGATE 

9 11 

NONT J 1 3 3 

FIGURE 0-2 MERN SEPll-tlONTHLY HOTHER/ 

PUP COUNT, LAVSAN '77-88 AND FFS '88. 
39 

F 

t! 

FIGURE 0-3 MEAN SEHIHONTHLY MOLT’ING 

SEALS, EXCLUDING CIOULT MALES, 1988. 

re “1 5 8 7 

254. 

20- ’ 

re.. 

-FRENCH FRIGATE 

HONTH 

FIGURE 0-4 MEhN SEMIMONTHLY MOLTING 

ADULT MCILES, LfiYSAN’78 AND FFS’80. 
40 

Molting Season 

Figure D-3 compares the mean number of molting seals (excluding 

adult males) seen on counts at Laysan and FFS in 1980 (FFS data are based 

on estimates from Table 8). 

not as clearly defined, the molting season at FFS seems to occur 1 to 2 

months later than at Laysan. 

Although the peak molting period on Laysan is 

Figure D-4 compares the average 1980 monthly count of molting adult 

males at FFS (from estimates in Table 8) with the 1978 data from Laysan 

(the only year for which data were collected throughout the peak of the 

adult male molting season). 

least 1 month later than at Laysan. 

These data also show the FFS peak occurs at 

Conclusion 

Based on the above data, it appears the timing of the pupping and 

molting seasons occur about 1-1/2 months later at FFS than at the other 

monk seal haul-out areas to the northwest. Data from haul-out areas 

southeast of FFS (Necker and Nihoa) need to be examined. 

Appendix E.--Pup production estimates based on 36-day interval counts. 

Kenyon and Rice (1959) proposed that an estimate of Hawaiian monk 

seal pup production could be obtained by summing counts of attended pups at 

intervals approximating the mean weaning age. 

the reliability of this technique on pup production data from Laysan, and 

to identify sources of variability when applying the technique to other 

populations. 

mean weaning age and early mortality of pups. 

It is possible to examine 

The effects of two sources of variability will be discussed: 

Counts were made every fourth day throughout four pupping seasons on 

During these 4 years, the mean age at weaning ranged from 

Estimates from nine series of counts, with 36 days between 

Laysan Island. 

35.7 to 36.6 days (for pups surviving until weaning), with an overall mean 

of 36.2 days. 

counts, can be calculated from the data for each year except 1978 (an 

absence from Laysan of 10 days during the pupping season resulted in the 

loss of two series for that year). 

34 estimates. 

(SD = 8.32). 

overestimating the known births. 

Table E-1 presents the results of the 

The mean estimate was 91.2% of the actual pup production 

The estimates were consistently low, with only two of the 34 
41 

Table E-1.--Estimated pup production on Laysan Island from 1977 to 

1980 based on counts of attended pups at 36-day intervals. 

Series 1977 1978 1979 1980 

Me an 

Known pup 

production 

Early deaths 

45 

39 

42 

39 

38 

41 

39 

38 

40 

40 

42 

2 

27 

28 

27 

29 

29 

30 

26 

28 

29 

1 

28 

30 

27 

21 

32 

31 

29 

30 

29 

29 

32 

3 

32 

26 

26 

27 

26 

28 

30 

28 

28 

28 

33 

5 

In using the 36-day interval to estimate pup production at other + 

areas, it must be assumed that monk seal females normally nurse pups for 36 

days. This is difficult to determine without observing a large sample of 

identifiable mothers throughout the pupping season. Examination of the 

data currently available suggests that using a 36-day interval at other 

populations may be reasonable. 

day estimate after observations at Kure and Midway during the 1950's. 

During the 4 years of the Laysan study presented here, the mean weaning 

age for pups remained at or very near 36 days despite a major population 

decline during 1978 when up to one quarter of the population died (Johnson 

and Johnson 1981b). Lastly, newly weaned pups seen at FFS and Lisianski 

appear similar in size and appearance to recently weaned pups at Laysan. 

Kenyon and Rice (1959) proposed using a 35- 

A secbnd source of variability wae identified in comparing actual 

birth8 on Laysan with the results of the 36-day counts. 

the estimate was less than the known pup production. 

to weaning each year. 

deaths to the estimated production equals the actual number of births in 

each of the 4 years. 

In all 4 years, 

Some pups died prior 

As Table E-1 BhOWSD adding the number of early 

On Laysan, the 36-day interval gave an accurate estimate of pup 

recruitment rather than the number of births. 

to other populations will likely also underestimate the actual number of 

births, with the degree of underestimation dependent on the rate of early 

mortality. 

Applying the 36-day interval 
42 

On Laysan it was found that a 33-day interval (the average time 

between birth and death, disappearance, or weaning of pups) would have 

more accurately estimated the number of births- However, early mortality 

of pups is known to vary considerably between atolls (Johnson and Johnson 

1984). 

under study, it seems reasonable to use the 36-day interval and risk 

underestimation of births. 

probably be discovered in the process of collecting the 36-day interval 

counts . 

Without accurate determination of mortality for the population 

Any unnaturally high degree of mortality would 

We, therefore, suggest that 36-day intervals be used to estimate pup 

recruitment (or as a conservative estimate of pup production) at atolls 

where more frequent censusing is either impossible or undesirable. 

estimate can be improved by the collection of additional data on the 

degree of early pup mortality and on the average weaning age of pups. 

This 
43 

Appendix F.--Pup Production in 1977 and 1981. 

Pup recruitment (births minus pre-weaning mortality) was estimated at 

104 pups for FFS in 1980. Using the same technique, an estimate of the 

number of pups born in 1977 and 1981 can be calculated from count 

data. 

Counts were made by varioue observers in 1977. These counts are 

listed in Table F-1. The counts marked with "*I' had three weaned pups 

that had been seen before the series began added, resulting in a total 

count of 80 pups. This series was selected because of all possible series 

with counts at least 36 days apart, it had the lowest mean interval 

between counts (45.5 days). If the mean weaning age was 36 days, ae at 

Layean, and pup mortality negligible, then pup production would be 

underestimated by 21%. 

production estimate of 101 for 1977. 

appreciable pre-weaning mortality occurred. 

Correcting the count of 80 pups gives a pup 

(The estimate would be low if 

Table F-1.--Counts of attended pups (MP) and weaned pups (WP) with the 

source of the counts for French Frigate Shoals, 1977. 

Date MP WP Source 

3/09 4 3 Rauzon et a1 

3/28* 6 2 Rauzon et a1 

4/09 26 2 Rauzon et a1 

4/24 28 4 Rauzon et a1 

5/11* 35 6 Rauzon et a1 

5/25 22 24 Rauzon et al 

.. 1978 

.. 1978 

.. 1978 

.. 1978 

.. 1978 

.. 1978 

6/24* 25 -- G. H. Balazs, persona, communication 

7/09 22 0 Geizantanner, unpublished FWS report 

8/12* 10 0 Coleman, unpublished FWS report 

9/26* 1 -- G. H. Balazs, personal communication 

* Counts used to estimate minimum pup production. 
44 

Counts of mothers attending pups were made every 36 days in 1981 

(Schulmeister 1984). Summing the counts shown in Table F-2 for WhaleSkate, Round and East, and adding the 7 pups that were known to be born on 

Disappearing and Little Gin gives an estimated pup production of 112 pups 

in 1981. 

mortality of pups occurred.) 

(Again, this estimate would be low if appreciable prereaning 

From these estimates, it appears that over 100 pups are normally born 

at FFS each year. 

Table F-2.--Counts of attended pups at French Frigate Shoals 

in 1981. 

Date count Date Count 

11 January 1 

6 March 3 

7 April 16 

21 May 32 

26 June 37 

1 August 9 

6 September 6 

24 October 0 

15 November 1 
45 

Appendix G.--Age/sex breakdown of molting seals seen on all molt surveys. 

Table G-1.--Counts of male (M), female (PI, and unsexed (U) 

seals seen at French Frigate Shoals in 1980. 

~~___ ~- 

Adult Immature 

Date MFU NFU To tal 

3/10 

3 /28* 

4/09 

4/28* 

5/14 

5/30 

6/07 

6/18 

6/23 

7/02 

7/09 

7/19 

7/25 

8/04 

8/10 

8/19* 

81 27 

9/04 

9/ 10 

9/18 

9/27 

10/05* 

lo/ 14 

10121 

10/30 

11/06 

11/18* 

11/22* 

12/01* 

000 

000 

001 

000 

01 1 

032 

011 

031 

030 

203 

046 

0 4 10 

0 4 10 

061 

042 

0 10 3 

051 

121 

331 

023 

424 

5 1 10 

946 

5 1 11 

11 0 13 

12 1 18 

426 

713 

404 

Total 67 67 122 

000 

000 

000 

000 

000 

010 

001 

000 

000 

001 

041 

303 

010 

123 

339 

736 

158 

555 

537 

833 

463 

214 

823 

009 

014 

110 

11 2 

1 11 

031 

50 46 74 

0 

0 

1 

0 

2 

6 

3 

4 

3 

6 

15 

20 

15 

13 

21 

29 

20 

19 

22 

19 

23 

23 

32 

26 

33 

16 

14 

12 

2P 

426 

*Gin and Little Gin Islands not visited. 
46 

Appendix H.--Age/sex breakdown of count data for all molt surveys conducted 

during 1980. The following describes the headings used on Table H-1. 

DATE : 

ADM : 

ADF : 

AD? 

SAM : 

SAF : 

SA? : 

JM : 

JF : 

J? : 

WP: 

MP : 

TOT : 

STOT: 

4;m: 

AM/C: 

AF/C : 

IM/C: 

IF/C : 

%AD : 

%FEM : 

Date of count 

Number of adult males counted 

Number of adult females counted 

Number of unsexed adults 

Number of subadult males 

Number of subadult females 

Number of unsexed subadults 

Number of juvenile males 

Number of juvenile females 

Number of unsexed juveniles 

Number of weaned pups 

Number of pups still attended by a female 

Total of all seals counted 

Total excluding WP and MP counts 

Percentage of STOT count that were not sexed 

Corrected adult male count corrected for mother with pup bias with 

a sex assigned to the unsexed adults based on the resulting sex 

ratio 

Corrected adult female count (same as AM/C) 

Corrected immature male count (includes subadult and juvenile males, 

with sexes assigned to unsexed animal8 on the basis of sex ratio 

of sexed immature8 

Corrected immature female count (same as IM/C) 

Percentage of STOT that were classified as adults 

Percentage of STOT that were sexed as female (based on the AF/C and 

IF/C totals) 
47 

z 

m (3 

W 
RECENT TECHNICAL MEMORANDUMS 

Copies of thls and other NOAA Technical Memorandums are avallabie from the National 

Technical information Service, 5285 Port Royal Road, Springfield, VA 22167. Paper coples vary In 

price. Mlcrofishe copies cost $3.50. Recent issues of NOAA Technical memorandums from the 

NMFS Southwest Fisheries Center are listed below: 

NOAA TM-NMFS SWFC 40 Summary of environmental and fishipg lnformatlon on Guam 

and the commonwealth of the Northern Mariana islands: 

Historical background, descrlptlon of the islands, and review 

of the cilmate, oceanography, and submarine topography. 

L. G. ELDREDGE 

(December 1983) 

Divlng patterns of the Hawaiian Monk Seal, Lislanski Island, 

1982. 

F. V. SCHLEXER 

(February 1984) 

“The Hawaiian Monk Seal on Laysan Island: 1982” 

D. J. ALCORN 

(April 1984) 

Atlas of airborne sea surface temperature observations in 

nearshore Cailfornia waters, 1980.1983. 

P.N. SUND 

(July 1984) 

Potential impact of deep seabed mining on the larvae of 

tunas and bl I If Ishes. 

W.M. MATSUMOTO 

(July 1984) 

Sampling commercial rockfish landings In California. 

A.R. SEN 

(July 1984) 

Histopathological manual for monitoring health of striped 

bass In relation to pollutant burdens. 

J.A. WHIPPLE, M. JUNG, R.B. MacFARLANE and R. FiSCHER 

(August 1984) 

Hawaiian monk seal population research, Llslanskl Island, 

1982. 

H.S. STONE 

(August 1984) 

“interpreting spotted dolphln age distributions” 

J. BARLOW and A.A. HOHN 

(August 1984) 

Observatlons of the Hawaiian Monk Seal on Laysan island 

from 1977 through 1980. 

B.W. ‘JOHNSON and P.A. JOHNSON 

(October 1984) 

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