FEEIRUARY 1984 

DIVING PATTERNS OF THE HAWAIIAN 

MONK SEAL, LlSlANSKl ISLAND, 1982 

Fredrick V. Schlexer 

, 

NOAA-TM-NMFS-SWFC-4 1 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Menioranduni NMFS 

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NOAA Technical Memorandum NMFS 

This TM series is used lor documentation and timely communication of preliminary results imterim reports. or special purpose inlormation, and have not received complete lormal review. editorial conlrol. or detalletl editmg 

FEBRUARY 1984 

DIVING PATTERNS OF THE HAWAIIAN 

MONK SEAL, LlSlANSKl ISLAND, 1982 

Fredrick V. Schlexer 

Southwest Fisheries Center Honolulu Laboratory 

National Marine Fisheries Service, NOAA 

Honolulu, Hawaii 968 12 

NOAA-TM-NMFS-SWFC-4 1 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige. Secretary 

National Oceanic and Atmospheric Administration 

John V. Byrne. Administrator 

National Marine Fisheries Service 

William G. Gordon, Assistant Admlnlstrator for Flsheries 
IlTRODUCT ION 

A pilot depth-of-dive study (DeLong et al. in press), conducted on 

Lisianski Island, Northwestern Hawaiian Islands during the summer of 1980, 

indicated regular use of shallow to moderate depth waters (10-40 m) by six 

adult male monk seals, Monachus schauinslandi, and occasional dives to at 

least 121 m by some individuals. 

shallows and reef slope areas around the island, which are extensive at 

Lisianski (Clapp and Wirtz 1975). In addition to obtaining six records 

with multiple depth of dive recorders (MDR's) developed by Kooyman et al. 

(19831, the 1980 pilot study demonstrated the feasibility and reliability 

of the attachment and retrieval of the small instrument package. 

These depths correspond to the reef 

Information on the hauling patterns of monk seals and the depths to 

which they dive is needed to extend the basic knowledge of this endangered 

species, so management decisions can be made relating to habitat protection 

and population recovery. 

radio transmitters and MDR's to these seals and monitoring their 

activities . Such information can be obtained by attaching 

This report will outline the progress of a continuing study of the 

diving behavior of the Hawaiian monk seal to define the foraging patterns 

of seals by sex and various age classes. 

MATERIALS AND METHODS 

During this 1982 field study, which lasted from 1 July through 14 

September, monk seals on Lisianski Island were instrumented with radio 

transmitters and MDR's. These instruments were identical to those used 

during the pilot study (DeLong et al. in press). Eight seals were 

captured, restrained, and instrumented, as described in Schlexer and 

Bowlby.' 

juvenile male, and one juvenile female. 

following Stone. 

These included five adult males, one subadult female, one 

The seals were classified by age 2 

'Schlexer, F. V., and C. E. Bowlby. Restraint and instrumentation on 

adult Hawaiian monk seal, Monachus schauinslandi. Manuscr. in prep. 

Southwest Fish. Cent. Honolulu Lab., Natl. Mar. Fish. Serv., NOM, 

Honolulu, HI 96812. 

2Stone, H. S. Hawaiian monk seal population research, Lisianski 

Island. Manuscr. in prep. Southwest Fish. Cent. Honolulu Lab., Natl. Mar. 

Fish. Serv., NOAA, Honolulu, HI 96812. 
2 

RESULTS AND DISCUSSION 

Of the eight MDR's deployed, one was inoperative. All other MDR's 

exhibited transducer calibration drift, resulting in widening of the 

targeted depth ranges as well as preventing complete recording coverage for 

the full duration of attachment. This drift occurred at a rate of about 

0.5 to 2.0 psi per day, incapacitating the recorder after 5 to 20 days, 

when the minimum threshold reached 0 psi (MDR's were initially set to only 

record dives deeper than 6.8 m or 10 psi), 

The MDR's remained on the seals for 12 to 46 days (mean, 24.9 days) 

(Table 1). All seals made dives to depths greater than 36 m (20 fathoms). 

Due to the minimum threshold drift mentioned above, the majority of 

The mean'depth of the 

The mean number of dives per day was 102.5 

recorded dives, about 67%, were in the 0-10 m range. 

dives was greater than 36 m. 

(range 22-258). Seal 514, a subadult female, made 84 dives in 21 days to 

the maximum recorded depth range of 123-180 m (70-100 fathoms). 

During this study no adult male seal made dives deeper than 70 m, All 

Overall diving behavior patterns recorded in this 

of the seals instrumented in 1980 were adult males and only one seal made 

dives deeper than 85 m. 

study agree with those observed in the pilot study, which showed the 

majority (59%) of dives in the 10-40 m depth range (DeLong et al. in 

press), 

closely related Mediterranean monk seal, E. monachus (Sergeant et al. 1979) 

wherein one was caught on a tuna hook set at a depth of 75 m. 

The only other published depth record for a.monk seal is for the 

The dive profiles for the subadult female (514) and juvenile female 

(351) show a pattern different than that of the adult males. 

made fewer dives in the shallow range (0-40 m) than most of the adult 

males. However, they did make many dives to depths greater than 40 m, down 

to the maximum recorded depth range of 150-180 m. 

These seals 

This may indicate a fundamental difference in the foraging patterns of 

adult versus immature seals but must be confirmed with more data from young 

seals. Causes of this difference are highly speculative. Rauzon and 

Kenyon (1982) have observed the inshore diving behavior of monk seals from 

the surface, in water 2-9 m deep. They saw adult seals threatening 

juveniles passing through the observation area, which contained several 

known prey species (spiny lobster, octopus, and conger eels). Such 

behavior by adults could force subadult seals to forage on deeper offshore 

areas. It is also possible that adult seals, being more experienced at 

catching prey, may deplete these species in favorable inshore reef habitat, 

causing immature seals to forage on the outer reef slope areas where prey 

would be more plentiful. 

Observations on additional immature seals are recommended. New 

techniques, such as sonic tracking of MDR-equipped seals, will help to 

further delineate habitat use and requirements. 
3 

, 

Table 1.--Dive recorda for Hawaiian monk seals, Liaianeki Ieland, Elorthvcstern Hawaiian Ialande, 1982 (asterisk indicates a recorder malfunction, i.e., 

no data). 

Seal 

number 

Depth Total Wber Man amber 

range number of of da7r of diver 

(m) dives deployed PLr day 

Adult males 

121 

At4 

1 41 

A64 

Subadult f male 

J14 

Juvenile male 

334 

,Jwenile female 

J51 

0-10 

11-20 

21-47 

0-15 

16-41 

42-70 

0-6 

S-3 2 

0-9 

10-23 

24-50 

0-8 

9-36 

37-42 

63-122 

123-152 

,122 

0-23 

24-51 

0-5 

6-29 

30-57 

58-85 

86-1 15 

116-156 

,130 

3,092 

2 

* 

2,160 

1,539 

170 

3,392 

16 

3 37 

19 

3 

2,793 

370 

42 

263 

79 

5 

* 

95 

1,529 

454 

1 20 

106 

44 

151 

34 

12 257 47 

0*2 

46 46.5 

33.5 

3 .7 

36 94.2 

0.4 

15 22.5 

1.3 

0.2 

21 

2s 

19 

133 .O 

17 46 

2 bo 

12.5 

3.8 

0.2 

I 

3.8 

80.5 

23.9 

6 -6 

5 a6 

3.4 

7 .9 

1.8 
4 

LITERATURE CITED 

Clapp, R. B., and W, 0. Wirtz, 11. 

1975. The natural history of Lisianski Island, Northwestern Hawaiian 

Islands, Atoll Res. Bull. 186:l-196. 

DeLong, R. L., G, L. Kooyman, W. G. Gilmartin, and To R. Loughlin. 

In press. Hawaiian monk seal diving behavior. Proceedings on Marine 

Mammals and Man Symposium, Third International Theriological 

Congress, Helsinki, 15-20 August 1982. Acta 2001. Fenn. IV, 

Kooyman, G. L., J. 0. Billups, and W. D, Farwell. 

1983. 5. Two recently developed recorders for monitoring diving 

activity of marine birds and mammals. In A. G. Macdonald and I. G. 

Priede (editors), Experimental biology at sea, p. 197-214. Acad. 

Press, N.Y. 

Rauzon, M. J., and K. W. Kenyon. 

1982. Hawaiian monk seal inshore diving behavior. 'Elepaio 

42( 12) : 107-108. 

Sergeant, D., K. Ronald, J. Boulva, and F. Berkes. 

1979. The recent status of Monachus monachus, the Mediterranean monk 

seal. In K. Ronald and R. Duguy (editors), Proceedings of the 

First International Conference on the Mediterranean monk Beal, 

Rhodes, Greece, May 1978, p. 31-54. UNEP Tech. 1. Pergamon Press, 

N.Y. 
RECENT TECHNICAL MEMORANDUMS 

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

Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167. Paper copies vary in 

prlce. Microfishe copies cost $3.50. Recent issues of NOAA Technical memorandums from the 

NMFS Southwest Fisheries Center are listed below: 

NOAA TM-NMFS SWFC 31 Reestimation of three parameters associated with anchovy 

egg and larval abundance: Temperature dependent incubation 

time, yolk-sac growth rate and egg and larval retention in 

mesh nets. 

N. C. H. LO 

(May 1983) 

“NMFS guidelines on economic valuation of marine 

recreational fishing” 

D. D. HUPPERT 

(June 1983) 

“Summary of environmental and fishing information on Guam 

and the Northern Mariana Islands: A review of the plankton 

communities and fishery resources of Guam and the 

Commonwealth of the Northern Mariana Islands” 

R. N. UCHIDA 

(July 1983) 

“Some data on dolphin mortality in the eastern tropical 

Pacific tuna purse seine fishery prior to 1970.” 

T. D. SMITH and N. C. H. LO 

(July 1983) 

“Precision of age determination of northern offshore spotted 

dolphins.” 

S. B. REILLY, A. A. HOHN, and A. C. MYRICK, JR. 

(August 1.983) 

“Recovery of adult green turtles observed or originally tagged 

at French Frigate Shoals, Northwestern Hawaiian Islands.” 

G. BALAZS 

(August 1983) 

“Report of the workshop on long-range planning for the 

North Pacific albacore fishery.” 

D. J. MACKETT, Editor 

(November 1983) 

Distribution of four dolphins (Stenella spp. and Delphinus 

delphis) in the eastern tropical Pacific, with an annotated 

catalog of data sources. 

W. F. PERRIN, M. D. SCOTT, G. 4. WALKER, F. M. RALSTON 

and D. W. K. AU 

(December 1983) 

Annotated references to techniques capable of assessing the 

roles of cephalopods in the eastern tropical Pacific Ocean, 

with emphasis on pelagic squids. 

J. B. HEDGEPETH 

(December 1983) 

Summary of environmental and fishing information on Guam 

and the commonwealth of the Northern Mariana Islands: 

Historical background, description of the islands, and review 

of the climate, oceanography, and submarine topography. 

L. G. ELDREDGE 

(December 1983) 

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