Biology of the Megamouth Shark,
Megachasma pelagios (Lamniformes: Megachasmidae)
Kazuhiro Nakaya

Graduate School of Fisheries Sciences, Hokkaido University
3-1-1, Minato-cho, Hakodate, Hokkaido 041-8611, Japanemail: nakaya@fish.hokudai.ac.jp

Abstract
All records to date (end of June, 2008) of the megamouth shark, Megachasma pelagios wereanalyzed and the biology of the megamouth shark was inferred from them. The megamouth shark is a
wide-ranging species, distributed from the tropical to temperate seas, with the most numerous occurrencesin the western North Pacific Ocean. Young individuals tend to be distributed in warmer waters, while
Kazuhiro Nakaya

mature individuals broaden their habitat to higher latitudes. Males become mature at about 4 m in total
length and females at about 5 m. The megamouth shark may copulate all year round, giving birth to young
in warmer waters, and may be spatially segregated by sex.

The discovery of the megamouth shark was one of the ichthyological highlights of the last century.
The first specimen of the megamouth shark was accidentally collected in Hawaii in 1976, and the species was
eventually named Megachasma pelagios by Taylor, Compagno and Struhsaker (1983). The second specimen
was captured in 1984 in California, U.S.A., eight years after the capture of the first Hawaiian specimen(Lavenberg and Seigel, 1985).

The third

specimen was found stranded in 1988 offwestern Australia in the Indian Ocean (Berraand Hutchins, 1990). Then, the fourth andfifth specimens were reported from Japan in
1989 (Nakaya, 1989; Miya et al., 1992). The
sixth specimen was captured and released in
California with a sonic transmitter (Lavenberg,
1991), and its horizontal and verticalmovements were recorded for a few days
(Nelson et al., 1997). These specimens were69

Fig. 1. Megamouth shark (#7), stranded in Fukuoka
Prefecture, Japan. (Photograph by Marine World
Umino-Nakamichi, Fukuoka, Japan)

all giant males of about five meters in total length, except for the fifth one of unknown sex, and finally the firstfemale megamouth (Fig. 1) was caught in Japan in 1994 (Takada et al., 1997).
At present, the worldwide total of megamouth shark captured, found stranded or sighted is forty
specimens. Some of the specimens were studied for their morphology and phylogenetic relationships, but
most of them were discarded, consumed or not studied. Among the few studies available, Nelson et al.
(1997) reported part of their way of life, showing that the megamouth shark makes clear daily verticalmovements within depths shallower than 200 meters. However, most of the biology of the megamouth
shark still remains to be disclosed.
The purposes of the present study are to synthesize the scattered information of the 40 specimens
recorded as of June, 2008, to study the morphological and biological evidence of each specimen, to analyze
their capture data, and to discuss the biology of the megamouth shark.

Materials and methods
This paper is based on information from the 40 specimens captured, stranded or sighted in the worldby the end of June, 2008 (Table 1). Information on each specimen was obtained from published papers,
internet reports, the homepage of the American Elasmobranch Society, and/or directly from the collectorsof the specimens. Maturity stages follow Nakaya and Stehmann (1998). Precaudal length (PCL) wasand Hutchins (1990) and Nakaya et al. (1997).

Results and discussion

Kazuhiro Nakaya

converted into total length (TL) by referring to proportional measurements in Taylor et al. (1983), Berra

Size and sex ratio
Forty records of the megamouth shark are summarized in Table 1. The smallest megamouth everfound was 176.7 cm TL collected in Indonesia, and the most reliable largest specimen was 627 cm TL (4.2m PCL) from Ecuador. Thirteen individuals were males, 21 were females and six individuals were of
unknown sex.

History of megamouth records
Figure 2 shows the records of the megamouth shark by year. The first Hawaiian specimen was caught
in 1976, and the second one was captured in 1984, eight years after the first discovery. Four specimens were
captured or photographed during 1988 and 1990. Eight more specimens were captured, observed, or landed
before 2000, totaling to 14 specimens in the 20th century. However, 26 specimens have already been
captured, landed, or sighted to date in the 21st century (2001-2007).
During the twenty years since the capture of the first megamouth in Hawaii, records of the megamouth shark were quite few, i.e., one more record in the first decade (1976-1985) and seven records in thesecond decade (1986-1995). However, the records suddenly increased to 24 in the third decade (1996-2005).
Seven megamouth sharks were recorded in 2006 and 2007.

70

Table 1. Megamouth sharks recorded to date (by June 30, 2008).
1, Taylor et al. (1983); 2, Lavenberg and Seigel (1985); 3, Berra and Hutchins (1990); 4, Nakaya (1989);
5, Miya et al. (1992); 6, Lavenberg (1991); 7, Nakaya et al. (1997); 8, Seret (1995); 9, Amorim et al.
(2000); 10, Yano et al. (1999); 12, Yano et al. (1998); 17, Smale et al. (2002); 23, White et al. (2004); 25,
Iida (2004)

Kazuhiro Nakaya

#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

Country
Hawaii, USA
California, USA
Mandurah, W. Australia
Shizuoka, Japan
Shizuoka, Japan
California, USA
Fukuoka, Japan
Dakar, Senegal
Southern Brazil
Mie, Japan
Cagayan de Oro,
Mie, Japan
Manado, Indonesia
California, USA
California, USA
East Indian Ocean
Western Cape, South Africa
Cagayan de Oro,
California, USA
Hualien, Taiwan
Shizuoka, Japan
Guayas, Ecuador
Sumatra, Indonesia
Chiba, Japan
Shizuoka, Japan
Iloilo, Philippines
Mie, Japan
Macajalar Bay, Philippines
Hualien, Taiwan
Hualien, Taiwan
Hualien, Taiwan
Hualien, Taiwan
Hualien, Taiwan
Bayawan, Philippines
Cagayan de Oro,
Zhejiang, China
Kanagawa, Japan
Tortugas Bay, Mexico
Shizuoka, Japan
far off Ibaragi, Japan

Capture date
1976.11.15
1984.11.29
1988.8.18
1989.1.23
1989.6.12
1990.10.21
1994.11.29
1995.5.4
1995.9.18
1997.4.30
1998.2.21
1998.4.23
1998.8.30
1999.10.1
2001.10.19
2002.1.18
2002.4.20
2003.1.6
2003.5.26
2003.7.3
2003.8.7
2004.3.8
2004.3.13
2004.4.19
2004.4.23
2004.11.4
2005.1.23
2005.1.30
2005.4.25
2005.5.2
2005.5.4
2005.5.5
2005.5.5
2006.1.26
2006.3.12
2006.3.23
2006.5.2
2006.11.16
2007.6.7
2007.7.9

TL(cm)
446
449
515
400<
490
495
471
180
190
544
ca 549550(*520)
ca 500ca 17 ftca 18ft FL
235
ca460
497
20-25 ft
ca 250425.5
420 PCL
176.7
563
490
504
528
417
?
?
480
570
?
500
7 ft 5 inch
570
568.8
214.9
540
320 PCL

Sex
♂
♂
♂
♂
?
♂
♀
♂
♂
♀
♂
♀
?
♀
♂
♂
♀
♀
?
♀
♂
♂
♂
♀
♀
♀
♀
♀
?
?
♀
♀
?
♀
♀
♀
♀
♀
♀
♀

MethodEntangled
Gill net
Stranded
Stranded
Set netGill net
Stranded
Purse seine
longline
Purse seine
Stranded
Set netWatching
Gill net
Gill net
Purse seine
Stranded
Gill netspottedGill net?
Purse seine
Gill net
Stranded
Stranded
Set netStranded
Purse seine
Gill net
Gill net
Gill net
Gill net
Gill net?
Gill net
Gill net?
Set netGill net
Set netPurse seine

StatusSpecimen
Specimen
Specimen
Lost
Released
ReleasedSpecimen
Discarded
Specimen
Specimen
Consumed
Discarded
Disappeared
Released
Released
Discarded
Specimen
Consumed
Disappeared
ConsumedSpecimen
ConsumedSpecimen
Jaw preserved
Discarded
Specimen
MountedBuriedConsumed
ConsumedSpecimen
Specimen?
Buried?
MountedMountedSpecimen
Releasd
Specimen

Depth(m)
165
< 38

< 40
23

15-40
< 150
35-40
0

150
ca180

200

35

35
70

The sudden recent increase in records may simply reflect an increase in reports of catches orsightings, as the megamouth shark has been steadily gaining public attention and the interest of people
worldwide because of its very impressive morphology.

71

Fig. 2. World occurrences by year.

Geographical distribution
Figure 3 shows the latitudinal occurrence of the megamouth shark. Megamouth sharks are reported
from the tropical to temperate waters of the world oceans between 36°5'N and 33°9'S. Thirty five records
come from the northern Hemisphere, and only five are from the southern Hemisphere. Sixteen records

Kazuhiro Nakayacame from the waters of 33°N and north. The second most frequent records are between 24-27°N.

Fig. 3. World occurrences by latitude.

Thirty four specimens (or 85 % of the total records) have been reported from the Pacific Ocean, andonly two (5%) and four (10%) specimens were captured or confirmed in the Atlantic Ocean and in the
Indian Ocean, respectively (Fig. 4). Twenty six specimens (76% of 34 Pacific records) were recorded in
the western North Pacific, with 12 records from Japan, six each from Taiwan and the Philippines, and one
each from Indonesia and China. Seven records came from the eastern Pacific, with five from the UnitedStates (California) and one each from Mexico and Ecuador. The Ecuador specimen is the only one fromsouthern latitudes in the Pacific. No specimens are known from the western South and central South
Pacific Ocean.

72Fig. 4. World geographical occurrences. Red star indicates the holotype. One small star indicates one
occurrence. Larger stars indicate plural occurrences shown by the number.

The Atlantic records are scattered, one each from Senegal and Brazil. No reports have been madefrom the western North Atlantic nor from the eastern North Atlantic north of Senegal. Three of the fourIndian Ocean records were reported in the eastern region, and one specimen was stranded in South Africa.
Kazuhiro Nakaya

No reports have been made from the middle and western north Indian Ocean.
The first megamouth from Hawaii, 16th from the Indian Ocean and 40th from Japan are the pelagic
records. All the other specimens were caught or sighted in waters near the continents, with eight stranding
records.
As seen above, reports of the occurrences of the megamouth sharks appear to be strongly biased,
perhaps as a result of sampling artifacts, such as differences in fishing effort, fishing gear, or interest of thelocal people, or they may indeed indicate actual differences in local population sizes of the shark.

Seasonal distribution
Figure 5 shows the monthly occurrence of the species. Seven specimens were recorded in May, andsix specimens each were in January and April, followed by five records in November. No specimen has
been captured in December.
Table 2 is a combination of the monthly and latitudinal occurrences for the world, indicated by thecatch number shown in Table 1. Megamouth sharks occurred throughout year except in September andDecember in the northern Hemisphere, but occurrences for the southern Hemisphere are scattered, oneeach in January, March, April, August and September.
Eight records were reported from the waters of lower latitudes during January through March.
More than half (23 records) of the total records were reported from the waters north of 
of the Pacific
Ocean from January to November, with six records in May and five records in April.

73

Only fourFig. 5. World occurrences by month.
Table 2. Latitude and month of each capture (by June 30, 2008). Number indicates the serial individual
number of the catch given in Table 1.
Jan

Feb Mar

4,27

Apr

May

10, 12, 24, 25

19, 3729

30, 31, 32, 33

Jun

Jul Aug Sep Oct
40 21
5,39
6,15
14

Nov

Dec

2,7
38

36

20
1

8
34
18,28 11

16

1
26

2
4
1
1
2

35
23
13

22

9
3
6

1

4

17
6

7

Total
1
15
1
2
6
1

2

2

3

1

3

5

0

Kazuhiro Nakaya

Latitude36-39N
33-36N
30-33N
27-30N
24-27N
21-24N
18-21N
15-18N
12-15N
9-12N
6-9N
3-6N
0-3N
0-3S
3-6S
6-9S
9-12S
12-15S
15-18S
18-21S
21-24S
24-27S
27-30S
30-33S
33-36S
Total

1
1
1
40

megamouth sharks appeared in the waters between and 
from April to December. One each was



 








April, August and September.
Figure 6 shows the monthly and latitudinal occurrences for Pacific megamouth sharks. Thirty threeout of 34 records were from the North Pacific (north of the Equator), and only one was collected in theSouth Pacific off Ecuador. The megamouth shark occurred throughout the year in the higher latitudes(north of 20°N). For the records of the lower latitudes (20°N and south), six specimens were recorded
during January and March, and one specimen each appeared in August, and in November. All of the74

Fig. 6. Latitudinal occurrences in the Pacific Ocean by month. Solid blue diamond, male; solid red
diamond, female; open diamond, unknown sex.

records from the lower latitudes are actually confined in the waters of 10°N and south. There are no reports
from the waters between 10°N and 20°N.
These facts suggest that the megamouth shark is distributed in the waters of higher latitudes all the
Kazuhiro Nakaya

year round, and the absence of records from the lower latitudes during April and October might mean thatthe sharks leave the lower latitudes for several months.
The records from the Atlantic and Indian Oceans are too few for speculation about their seasonal
movements.

Geographical distribution by size
The latitudinal occurrences by size are given in Figure 7. Smaller specimens less than 2.5 meters
are confined in the lower latitudes between 27°39'N and 27°08'S, and do not appear in the higher latitudes
north of 30°N and south of 30°N. Specimens between three and four meters have not been recorded. On
the other hand, specimens larger than 4 meters appeared not only in the lower latitudes south of 30°N, butalso in the higher latitudes north of 30°N in the North Pacific Ocean. In addition, 4.6 m TL and 5.15 m TL
specimens were recorded in the higher latitudes at 34°S and 32°S, respectively, in the Indian Ocean. Morethan half of the larger specimens have been captured or sighted in waters of the higher latitudes.
As mentioned above, individuals smaller than 2.5 m TL and specimens larger than 4 m TL havenumerously been reported, while those between 2.5 m TL and 4 m TL have not yet been reported.
These facts may indicate that while they are young, the megamouth sharks are rather confined in thelower latitudes, and as they grow, they broaden their distribution to the higher latitudes. The complete
absence of 2.5-4 m TL specimens might reflect some kind of sampling artifact, but this is rather strange,
because so many individuals of the smaller or the larger sizes were frequently recorded. These facts might75

also suggest some biological characteristics of the megamouth shark.

Maturity
The maturity stages of the available specimens are summarized in Fig. 8. The data on the maturity
were taken either directly from the specimens or photographs, or from the descriptions in reports ofKazuhiro Nakaya

Fig. 7. World latitudinal occurrences by total length. Solid blue diamond, Pacific male; solid red
diamond, Pacific female; open diamond, unknown sex (Pacific); blue cross, Indian/Atlantic
male; red cross, Indian female.

occurrence.
Specimens between 190 cm TL and 235 cm TL (three males and one female) were all immature,
which is shown as maturity stage 1 in Fig. 8. A male of 426 cm TL (#21) has well developed claspers, andthis is the smallest mature male (maturity stage 3) among available specimens. A 449 cm male (#2) was
oozing spermatophores from its claspers（Lavenberg and Seigel, 1985）. The larger males were fully
mature. Two females of 460 cm TL (#17; Smale et al, 2002) and 471 cm TL (#7; Castro et al., 1997) wereadolescent, with developing reproductive organs (maturity stage 2).

Females of 497cm TL (#18;

Compagno et al., 2005), and 544 cm TL and 550 cm TL (#10 and #12, respectively; Yano et al., 1999) had
mating scars on their bodies. A 563 cm TL female (#24) was fully mature without embryos (personalcommunication with M. Miya). These are shown as maturity stage 3.
These facts indicate that the megamouth shark reaches maturity at about 4 meters (less than 4.3
meters) in males, and about 5 meters in females.

Geographical distribution by sex and maturity
Based on the above discussion, the maturity stages of the unknown individuals were determined76Fig. 8. Maturity stages. 1, immature; 2, adolescent; 3. mature. Blue, male; red, female.

Kazuhiro Nakaya

Fig. 9. Latitudinal occurrences by maturity stage and total length. Solid blue diamond, mature male
(Pacific Ocean); solid red diamond, mature female (Pacific); red triangle, adolescent female(Pacific); red cross, immature female (Pacific); green solid diamond, mature male (Indian);green open triangle, adolescent female (Indian); green cross, immature male (Indian/Atlantic).
a, Atlantic Ocean; i, Indian Ocean.

77according to the following rule. The males smaller than 2.5 m TL were treated as immature, and thoselarger than 4 m TL as mature. The females smaller than 2.5 m TL were treated as immature, those between
4 and about 5 m TL (excluding the 497 cm TL specimen, which had bite marks) were treated asadolescents, and those larger than 5 m TL (including the 497 cm TL specimen above) were mature.
Figure 9 shows latitudinal and length distribution by maturity stages for world records. Among
Pacific megamouth sharks, the immature individuals (only females) appeared in the lower latitudes south of
28°N. Atlantic/Indian immature individuals (only males) appeared in the lower latitudes between 15°N and
28°S.
Pacific adolescent females appeared between 8°N and 37°N, expanding their distribution to more
northern waters higher than 30°N, and a single adolescent Indian female was recorded at 34°S. Adolescentmales have not yet been found.
Mature Pacific females appeared between 8°N and 36°N. Mature Pacific males appeared between
35°N and 3°S, and a single mature Indian male appeared at 32°S.
These facts suggest that the megamouth sharks stay in the waters of lower latitudes while immature,and invade waters of higher latitudes as they mature, although some mature individuals still stay in thelower latitudes.
Figure 10 shows occurrences in the four local regions of the Pacific Ocean by sexual maturity

In Japanese waters, three adolescent and six mature females of larger sizes, and two mature males(including one of unknown length, but with developed claspers) were captured, but no immature individual
is known. In Taiwan/China, only four females (one immature, one adolescent and two mature individuals)
are known, with three individuals of unknown sex.

Kazuhiro Nakayastages, i.e. Japan (A), Taiwan/China (B), the Philippines/Indonesia (C) and the Central/Eastern Pacific (D).

In the Philippines/Indonesia, five females (oneimmature, one adolescent and three mature individuals) and one mature male were captured, and one
individual of unknown sex was sighted and photographed.
In the Central/Eastern Pacific, five mature males (including one individual of unknown length), one
mature female of unknown length, one immature female and one individual of unknown sex/length wererecorded.
Many adolescent and mature females, and only a few males appeared in the western Pacific Ocean(Fig. 10, A-C), while five mature males and two females were seen in the eastern Pacific Ocean (Fig. 10,D). The sexual bias seen between the western and the eastern Pacific Oceans may suggest spatial
segregation by sex in the megamouth shark.
In the western Pacific, immature, adolescent and mature females occurred in Taiwan/China and thePhilippines/Indonesia, while many adolescent and mature females occurred, and no immature female wasfound in Japan. These facts also might suggest that females tend to move into the waters of higher latitudes
as they mature.
For the Indian Ocean, one adolescent female was found in the western part, and three males (twoimmature and one mature) were reported in the eastern part.

78

Kazuhiro Nakaya

Fig. 10. Regional occurrences by maturity stages. A, Japan; B, Taiwan/China; C, The Philippines/Indonesia; D,
the Eastern Pacific/Hawaii. Blue, male; red, female.

Seasonal distribution by sex and maturity
Figure 11 shows monthly latitudinal distribution by maturity level for the world. Among Pacificmegamouth sharks, the females of all maturity stages appeared from November through May. Females
appeared between 8°N and 34°N in January, 8°N and 28°N in March, 33°N and 35°N in April, 24°N and
35°N in May, 35°N in June, 24°N and 36°N in July, and 10°N and 34°N in November. Pacific mature
males were found in January (34°N), February (8°N), March (2°N), August (34°N), October (33°N) andNovember (21°N and 33°N).
Atlantic immature males appeared in May (15°N) and September (27°S), and Indian immature
males appeared in January (2°S) and March (5°N). One adolescent female was found in April (33°S) andone mature male in August (32°S) in the Indian Ocean.
For Pacific megamouth sharks, it seems that the adolescent and mature individuals of both sexes
stay in the waters of the lower to higher latitudes from November through March. Because of their almost
complete absence in the lower latitudes from April through October, it may be presumed they leave thelower latitudes during this period. The immature individuals, however, may be found year-round in thelower latitudes within the distributional range of the species.

79Reproduction
Spermatophores were oozing from the claspers of a 449 cm TL male (#2, arrow 2 in Fig. 11)
captured in November, 1984 in California（Lavenberg and Seigel, 1985, and a 495 cm TL male (#6, arrow 6

Kazuhiro Nakaya

Fig. 11. World latitudinal occurrences by month. Arrow with record number indicates individual with matingscars or active claspers (see text). Solid blue diamond, mature male (Pacific); solid red diamond, mature
female (Pacific); open red triangle, adolescent female (Pacific); red cross, immature female (Pacific);solid green diamond, mature male (Indian); open green triangle, adolescent female (Indian); green cross,immature male (Indian/Atlantic); open blue circle, unknown length and/or unknown sex (Pacific).

in Fig. 11) captured and released in October, 1990 in California had evidence of recent use of the claspers(Lavenberg, 1991). Fresh mating scars were found in a 544 cm TL female (#10, arrow 10 in Fig. 11) andhealing mating scars were reported in a 550 cm TL female (#12, arrow 12 in Fig. 11), both captured in
April in Japan (Yano et al., 1998, 1999). In addition, a 497 cm TL female (#18, arrow 18 in Fig. 11), fromthe Philippines in January was reported to have mating scars (Compagno et al., 2005). These facts may
indicate that the megamouth shark mates all year round.
It may be also inferred that they give birth to young in the waters of lower latitudes, because theimmature individuals are reported only in the lower latitudes between 28°N and 28°S, and the immatureindividuals may stay in the waters of the lower latitudes for a while.

Depth distribution
The few depth data available at present show sharks being caught in depths between 23 and 200
meters. Daily movements of a megamouth shark (#6) were recorded by Nelson et al. (1997), and the shark
showed a very clear vertical movement. The shark swam at depths a little shallower than 200 meters in
depths during the daytime, moved to the surface at dusk, stayed around 20 meters during nighttime, andsank again to the original deeper layers at dawn. The present available depths of capture are almost within80the ranges shown by Nelson et al. (1997), but because no accurate time of capture was reported in mostrecords, the vertical movements cannot be conclusively speculated upon here. The only exception is theIndonesian individual (#13), which was sighted and photographed during an attack by a sperm whale. The
photograph was taken at the surface at 10:00 am, the time megamouth sharks normally stay deep, near 200
meters below the surface. This case appears to be abnormal.

Length weight relationshipThe length-weight relations of the megamouth shark are given in Fig. 12. As the body lengths andthe body weights, especially of larger individuals, are often inaccurate and were reported as estimates, only
lengths and weights that seem to be reliable are included in the figure. The specimens around 2m in total
length range from 176.7cm TL (13.8 kg, #23) to 235 cm TL (120 kg, #16) for males, and 214.9 cm TL(27kg, #38) and 226 cm TL (70kg, #35) for females. Body weights of those around the 5m TL range from
700 to 1,000 kg. A Taiwanese specimen (ca 250 cm TL, 490 kg, # 20 in Fig. 11), and a South African
specimen (ca 460 cm TL, 260 kg, #17 in Fig. 11) are somewhat different from the others.

Kazuhiro Nakaya

Fig. 12. Length/weight relationship. Number indicates record number. Blue, male; red, female.

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Kazuhiro Nakaya

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