Maturation of the life history of turtles from the North Pacific
Ishihara Takashi
Maturation of the life history of turtles from the North PacificLife History in Maturation Process of Loggerhead Turtles (Caretta caretta)
in North Pacific 2011Tokyo University of Agriculture and Life Sciences
Department of Ecosystem Studies Ishihara Takashi Takashi Ishihara Supervisor
Visiting Associate Professor, University of Tokyo Tatsuki Tadashi Kamezaki
Table of Contents
Chapter 1 Introduction
1
Once Kinoe Takeshi beginning of sexual maturation and sexual maturity Kinoe Takeshi Chapter 252-1. Purpose
52-2. How06
2-3. Result and discussion
08
Growth and maturation of the tail in Chapter 3
12
3-1. Purpose
123-2. How
13
3-3. Results
14
3-4. Study
15
Readmission to the size of breeding area around Japan is in Chapter 420
4-1. Purpose
20
4-2. How
21
4-3. Result and discussion
22
Age of sexual maturity and growth rate in the North Pacific Chapter 526
5-1. Purpose
26
5-2. How
29
5-3. Results
33
5-4. Study
35
5-4-1. Growth rate36
5-4-2. Mature Kinoe Takeshi
38
Kind of sea turtle life history Chapter 6 - Growth and habitat 42
6-1. Overview of the life history of sea turtle species

42
6-2. Loggerhead turtle (Caretta caretta) Life history43
6-2-1. Spawning frequency
43
6-2-2. Distributed escape hatch
44
6-2-3. And growth of juvenile habitat45
6-2-4. Readmission to the breeding grounds
46
6-2-5. Sexual maturity
46
6-3. Comparison with other sea turtle species life history49
6-3-1. Ecology of juvenile period
49
6-3-2. Sexual maturity
51
Chapter 7 General discussion
54
7-1. Conservation importance in Japanese waters
54
7-2. Loggerhead turtle mortality in the Sea of Japan
55
7-3. Threats to the North Pacific loggerhead turtle
57
7-3-1. Threats in sand58
7-3-2. Dispersed into the ocean threat to juvenile
59
7-3-3. The threat of coastal
60
7-4. Conservation measures required by the Sea of Japan
61
Acknowledgment
62
Abstracts of the papers
65
References
69
Appendix
94
Appendix98
Appendix List
Table 2-1. Classification criteria based on the maturation state of gonads and reproductive tract morphology.
94
Table 2-2. Cloacal cavity condition and the presence of testicular sperm.
95
Table 5-1. Growth rate Kinoe Takeshi backwards from the line width by growth arrest.
96
Table 6-1. Turtle species (Dermochelidae and Chelonidae) Kinoe Takeshi mature.

97
Appendix List
Figure 1-1. Loggerhead turtle.
98
Figure 2-1. The main study area.
99
Figure 2-2. Loggerhead turtle gonads and reproductive tract.
100
Figure 2-3. Instep different distributions of male and female sexual maturity class.
101
Figure 2-4. Instep of sexual maturity for each class size composition.
102
Figure 2-5. Kinoe Osa-class moving sexual maturity.
103
Figure 3-1. Onaga measurement position.
104
Figure 3-2. Onaga-Relative maturity of class.
105
Figure 3-3. Correlation relative to the head of the instep of both sexes Onaga.
106
Figure 4-1. Size composition instep of loggerhead turtles caught in nets by the emplacement of Muroto, Kochi
Prefecture.
107
Figure 5-1. Sectioning part of the humerus and turtles.
108
Figure 5-2. Growth arrest lines and cross-sectional slices of the humerus.
109
Figure 5-3. Radius and width of the line segment growth arrest was left humerus.
110
Figure 5-4. The growth curve in the North Pacific loggerhead turtles.
111
Figure 5-5. Age structure of loggerhead turtles in the Sea of Japan.
112
Figure 5-6. Age-length relationship and instep.
113
Figure 6-1. Floats in juvenile sea turtles hatch.
114
Figure 6-2. The loggerhead turtle hatchlings - Schematic diagram of the distribution and migration across the oceansubadult.
115
Figure 6-3. Sexing using an endoscope.
116
Figure 6-4. Kind of sea turtle habitat.
117
Figure 6-5. Black sea turtles found in Muroto, Kochi Prefecture.
118
1
Chapter 1 Introduction
Organisms started to use the land as part of the biosphere in the process of evolution from fish to amphibians,
reptilesCompletely adapted to terrestrial life and to evolve into. However, while the transition to life in the water again
Or are those, in the present department reptiles turtle turtles commonly collectively known as (Cheloniidae) andOhDepartment Sagame (Dermochelidae) is one of their typical peers.
Santanachelys
gaffneyi
The Lower Cretaceous of eastern Brazil (approximately 110 million years ago) were found in the earliest window
strataMigame (Hirayama, 1998) that is, its form is close to the already extant turtles, and sea turtles
To form the broad outline had already finished at this time. The five extant species of sea turtles Cheloniidae 6
Species, seven species have only one species of a genus Dermochelyidae, distribution range is very wide, turtle
fungusDistributed worldwide, except in the ocean and Kemp. Mesozoic turtles that live in the present family
Has appeared in all the Cretaceous (Pritchard, 1979), that it still survives
It seems to suggest that the marine environment to better accommodate the turtles. While the evolution of its
own, a million years
Continued to keep his turtles are said to be little more than an invaluable presence in biology.
But the kind of sea turtle populations and to expand the human social activity dropped sharply in recent years
Began to endangered. Turtle meat and eggs were used as industrial products and regional foodAre overfished and in the development of sophisticated fishing technology has increased the number of sea turtle
bycatchAre believed to have added. Take only a sea turtle conservation policies that can better accommodate a habitat
There have been endangered.
In Japan, Okinawa during the turtles from Kanto (Caretta caretta), But the Ogasawara Islands and Yakushima
Ryukyu Islands during the green turtle (Chelonia mydas) To lay eggs, hawksbill (Eretmochelys imbricata) Has also
been observed spawning in the Ryukyu Islands slightly. In addition, do not lay eggs near the
The Leatherback sea (Dermochelys coriacea) And Ridley (Lepidochelys olivacea) And also visiting And, by fishing or
bycatch are sometimes stranded on the beach or to the body. These window In Migame, loggerhead turtles,
especially in Japan, whereas a large number of turtles laying nests most North Spawning grounds in the Pacificoutside of Japan do not exist (Kamezaki et al., 2003), all played by Japanese conservation The role is getting
big. Japan's coastline has been confirmed dead in the head every year hundreds of turtles that washed ashore And(Sea Turtle Association of Japan, 2010), in order to conserve the North Pacific loggerhead turtle the state bunch
握Shi, measures should be based on the life history and ecology of turtles.
History of the loggerhead turtles in Japan, ecology and behavior of the 1990s, spawning further Including
embryonic development and genetic research, and to have been made in studies of spawning beaches Merely(Kamezaki Matsui, 1997), when their lives are spent most of his life ocean Such studies can trace the whole history
has not been made. In recent years, after migrating from satellite transmitters
Examined the migration and movement of marine biotechnology by using a logging road and track and data logger
Studies have been done for, but they can track their time is short, their life history Ino Takeshi Showed only a small
portion of piecemeal. For Japan, North Pacific loggerhead turtle Breeding area is the only place to do activities in
the coastal breeding population gathered from the North Pacific
There. However, systematic research on the ecology of turtles living in Japanese waters has been Not. In the life
history of turtles and consequently, as the spawning grounds near Japan Maybe it is not clear ecological role inwhat other functions.
In this study, as part of the research to clarify the natural history of turtles from the North Pacific Ocean We
studied the following in order to obtain basic data necessary for ecological and conservation. Or
3
Without, to observe the gonads of the loggerhead turtle bycatch in the nets of the stationary Muroto, Kochi
Prefecture, in Chapter 2, male andTo identify and sexual maturity is complete Kinoe Takeshi Kinoe Takeshi beginning of sexual maturation in femalesof the second male in Chapter 3
Expression of symptoms during analyzed the process of growth or tail. In Chapter 4, analysis bycatch individuals
Revealed that the size and maturity for migratory Pacific Ocean near Japan again. In addition, the fifth
Chapter, we will assess the humerus for age, age at entry into Japanese waters again, age at maturity, growth rate
Were estimated. In addition, based on their results, about the life history of sea turtle species extensively in
Chapter 6 General

They are summarized. Of these, Chapter 2 and Chapter 3, Chelonian Conservation and Biology, the first
Current Herpetology in Section 4, Chapter 5 in Copeia, the journal Nature turtle Chapter 6 (東京大Science Publishing Society) is to be published as follows.
Chapter 2 and Chapter 3
Ishihara T., and N. Kamezaki. Size at Tail Elongation and Sperm Production in Male
North Pacific Loggerhead Turtles (Testudines: Cheloniidae). Chelonian Conservation
and Biology. (in press: in review)
Chapter 4
Ishihara T., Kamezaki N., Matsuzawa Y., Iwamoto F., Oshika T. Miyagata Y., Ebisui C.,
and Yamashita S. Re-entering of Juvenile and Sub-adult Loggerhead Turtles into theJapanese Natal Waters. Current Herpetology. In press.
Chapter 54Ishihara T. and Kamezaki N. Age at Maturity and the Growth Rate of Sub-Adult Maleand Female Loggerhead Turtles in North Pacific Estimated by Skeletochronological
Analysis. Copeia. In preparation Posts
Chapter 6
Ishihara Takashi. Life History - Growth and habitat. Nature magazine turtles (Chapter 4). University of Tokyo
Press. (Last School
Naka Masashi)
5
Once Kinoe Takeshi beginning of sexual maturation and sexual maturity Kinoe Takeshi Chapter 2
2-1. Purpose
When you try to reveal the life history and ecology of some species or populations, information related to breeding
Is very important. Also, for the development of reproductive physiology, sexual maturation, ie in the history of life
Occupies an important position in ecology and to examine the relationship at the time of sexual maturation
process and is important
There.
Loggerhead turtle (Caretta caretta) Life history, in the North Pacific and North Atlantic populations, relatively light
Whether they are (Bolten, 2003). According to the report, the east coast of the United States and Japan,
respectively孵
Hatching juveniles are widely distributed in the ocean by化Shita Gulf Stream and Kuroshio, respectively, many
individuals
Move to the other side of Mexico and offshore Africa, where the Iku Shigeru. Then east across oceans at some
stage
Migration towards the west and went back to Japan and the U.S. East Coast is where the breeding and spawning in
Everywhere. In this process, which begins sexual maturation time, become more complete or clear
Not. To be able to determine the maturity of the loggerhead turtle population can be measured easily Kinoe
Takeshi
It is very important to make a conservation strategy based on the ecological integrity of this study is not
Currently, to determine the maturity of loggerhead turtles is difficult to be found everywhere.
In this study, the North Pacific loggerhead turtles lay eggs on in Japan, gonadal maturation
Check the related state and instep length, was found to complete Kinoe Takeshi Kinoe Takeshi beginning of sexual
maturation and sexual maturity.
06
The reproductive characteristics of loggerhead turtles, for example, a number of eggs per nest, spawning one per
Spawning times, the world's major spawning grounds and spawning age regression, the variation among
populations or breeding
Known that there are (Dodd, 1988; Miller, 1997). These breeding populations are genetically more
Has been isolated (Bowen, 2003), spawning female Kinoe Takeshi is also known among different populations

Ru (Dodd, 1988; Tiwari and Bjorndal, 2000; Kamezaki, 2003). Ecological particular geographic variation in theseIt also found more sex, it is expected that there is also geographic variation in life history, including the process ofsexual maturation
Be. And can reveal these populations are genetically isolated breeding several respective
Geographical characteristics of the habitat, life history adaptation and how did we do understand that thedifferentiation
Biologically interesting evolution.
2-2. How
In order to clarify the completion Kinoe Takeshi beginning of sexual maturation and sexual maturity Kinoe Osa,died shortly after
Individual sample was 152 turtles. These samples, the presiding Tadashi Kinoe each individual standard (SCL:
straight
carapace length) were then measured and observed to the gonads and reproductive tract anatomy. These samples
2005
Kitamuro nets gun, Mie Prefecture, Kita Osamu town Misaki Muroto Muroto, Kochi city and during the month ofApril 8, 2010
The catch (Figure 2-1), many individuals are drowned. May determine, after the autopsy, gonadal morphology,
Performed by the testes or ovaries to determine that. Limpus and Limpus state of sexual maturity(2003) and Miller and Limpus (2003), according to three classes of sexual maturity, ie, juvenile, sub adult07
Body was divided into adults. Each of the classification criteria in Table 2-1, shown in Figure 2-2. The edge ofjuvenile sexual maturation
Individuals are not waiting, the one with the subadult gonads, but not complete sexual maturation has begun
Body of adult individuals with sexually mature gonads, may be considered. In addition, the adult classification
The male is due to the small number of samples, of the survivors were captured by stationary nets in Kochi Muroto
In addition to the sample considered as a mature male sperm from eight plants was confirmed by prominentcloacal cavity tail elongation
Eta.
The appropriateness of using that as an indicator of sexually mature sperm cloacal cavity
Was examined. Two adult male population to determine the class of gonad maturation in subadult eightindividuals,
The presence of sperm in the testes and cloacal cavity, were investigated using optical microscope. As a result, theadult decision
From two individuals were observed by the cloacal cavity of sperm in the population classified as subadult testes
Cloacal cavity sperm even if the sperm were seen in (Table 2-2). Thus, the accuracy cloacal cavity
It is determined that no harm in addition to a sample of the adult male population were children.
Juvenile samples, subadult, adult classified by, the length distribution of the instep of each maturity
It is possible to know. We rank the maturity of the juvenile to subadult from the beginning of sexual maturation
Kinoe Takeshi
Migrating SCL, is transferred to the adult class from subadult maturation to sexual maturity is complete Kinoe
Takeshi defined as SCL
The definition. SCL sexual maturity begins the range and scope of the minimum from the maximum juvenile
subadult,
SCL completes the range of sexual maturity, the adult minimum and maximum values of subadult. In addition,
sexual maturation
SCL start the beginning of sexual maturation Kinoe Takeshi half of the individuals, and to complete half of thesexually mature individuals of SCL
08
Calculated as the Kinoe Takeshi completed sexual maturation. SCL 20 mm samples of each class separately, each
Proportion of juvenile and subadult subadult total in class, or the percentage of total adult subadult and adult
Asked the proportion of subadult or adult = K / (1 + b · e
-C
-

SCL
) And logistic regression curve, its
And 50 percent of the SCL was determined. Completion of sexual maturation and sexual maturity it starts Kinoe
Takeshi
The length and carapace.
2-3. Result and discussion
Determine from the external morphology of dissected gonads with 152 loggerhead sea turtle populations. As aresult, maleThe 46 individuals were determined, it is determined that the female population was 106. Each length standard
Tadashi Kinoe(SCL: mean ± SD [min-max]), the males 745 ± 56 mm (577-877 mm), and females 758 ± 59 mm (601-919mm), respectively. As a result of class to determine the morphology of the reproductive tract and sexually mature
gonads, six juvenile males
Female population is 12 individuals, 67 subadult females in the population of 36 male individuals, 27 adult females
in four male individuals
Were classified into the body. In addition to the four individual adult male population of sperm was found in 8
males with cloacal cavity, which
After 12 individuals were analyzed as the adult males.
Sexual maturity for each class SCL (mean ± SD) are 680 juvenile males of ± 65 mm (577-750 mm, n = 6) in females
688 ± 38 mm (601-726 mm, n = 12), 745 sub-adult male ± 38 mm (686-826 mm, n = 36) in females
744 ± 44 mm (636-853 mm, n = 67), 838 adult males of ± 43 mm (range: 778-902 mm, n = 12) in females
The 821 ± 43 mm (738-919 mm, n = 27) (Fig. 2-3). SCL is obtained here with the juvenile Kochi
09
Bycatch of juveniles in the sample was large stationary nets in Mie Prefecture in the value of SCL. Young turtles
hatch
SCL body is 41.9 ± 1.51 mm (Matsuzawa Sakamoto, 2002) that, except for juvenile males hatched
680 ± 65 mm, 688 ± 38 mm for females was visiting the area were the juvenile. The results were classified as
subadult
The most common body was found near Japan that the area began to complete sexual maturation.
Second, males were classified as 838 ± 43 mm in adults, females 821 ± 43 mm, respectively. Adult females andminutes
The individual species, all eggs were maintained with a shell in the oviduct. This is in the study area
Adult females and an excursion off the coast of Mie Prefecture, Kochi said, all the individuals for the purpose oflayingIt shows. In addition, the adult female was captured in late April-August breeding season falls
Was limited in early. Tokino Shika adult females lay eggs again, away from the coast indicate thatThat. Post-spawning females left the Japanese coast, they moved into the Pacific Ocean and offshore feeding
grounds Higashishinakai
The results have been suggested to be tracked by satellite transmitters sure (Sakamoto et al., 1997; Hatase etal., 2002a; Hatase et al., 2002b; Sea Turtle Association of Japan, unpublished data).
In addition, juvenile, subadult, adult in any of the SCL there was no significant difference in male andfemale (p> 0.05,
Mann-Whitney U-test). This is the same as the male and female sexual maturity with the growth of loggerhead
turtles
Shows that progress. Kamezaki (2003) is a mature male and female turtles on Yakushima Island waters
Are not different reports that the length of carapace, mature male and female populations in the South Pacific andMediterranean
Instep length difference is not recognized (Limpus, 1985; Casale et al., 2005). Therefore, since both sexes
Analyzed together.
10
Next, we estimated to complete sexual maturation and Kinoe Takeshi Kinoe Takeshi begins the sexual
maturity. The sexual maturity Hajima

Ru Kinoe Takeshi Kinoe Takeshi is a shift from juvenile to subadult, maximum 636mm minimum subadult juveniles
fromThe beginning of sexual maturation in the range of 750mm to prove SCL (Fig. 2-3). Similarly, ofOnce maturity is Kinoe Takeshi Kinoe Takeshi transition to the adult subadult, adult minimum 738mm from
853mm maximum ranged subadult Kinoe Takeshi complete range of sexual maturity.
In addition, sexual maturation begins the Kinoe Takeshi half of individuals in these ranges to complete sexual
maturation Party
To estimate the length, SCL 20 mm per juvenile, subadult, adult asked each population (Fig.
2-4). The percentage of the population of juvenile and subadult subadult accounted for in the range of sexual
maturation begins the Kinoe Takeshi,
Rojisute percentage of the adult population of adult and subadult in the range of sexual maturation is complete
Kinoe Takeshi
The regression curves Ikku (Figure 2-5). A logistic curve was presented in the following two equations.
Subadult ratio = 0.9585 / (1 +1.298 * 10-30
·E-0.1052 SCL)
Percentage of adults = 1.028 / (1 +1.202 * 10
-13
·E
-0.02791 SCL)
From these two expressions, sexual maturation begins half SCL is 660 mm, half to complete the sexual maturation
The SCL was determined to be 821 mm.
SCL 821 mm complete sexual maturity, the adult population classified as SCL 824 mm 3 than the average
mm smaller. Exceed the average maturity of the complete Kinoe Takeshi average adult length of instep, SouthHas been observed in the Pacific loggerhead turtles (Limpus, 1985), continued to grow slightly after sexual
maturation
Considered to be caused by Keru (Limpus, 1985; Hatase et al., 2004). In addition, the adult bycatch
11
The mean SCL of land plants in Japan, spawning SCL, 848 ± 50.8 mm (Kamezaki others, 1995) from 27
mm small. These things, adults were captured in this study to complete sexual maturation, age is lessSuggests that no progress.
Based on these results, whether considered in Chapter 3 which will start at the rank of the sexual maturation ofmale tail elongation
Consideration, which ranks sexual maturation and population living in Japanese waters to join the class during
sexual maturation of Japanese waters
Chapter 4 discusses what has been composed, discussed in Chapter 5 on the age and sexual maturity. The
From the instep of this chapter and adult sexual maturity is complete Kinoe Osa, about populations to the coast
after the appearance of mature
They discussed.
12
Growth and maturation of the tail in Chapter 3
3-1. Purpose
The friend of the degree of elongation turtles tail is to represent the progress of sexual maturation in males, except
for some species
Tail is observed with progressive growth of sexual maturity they (Kuchling, 1998). Loggerhead turtle (Carettacaretta) But thick and elongated tail is a form to determine the most distinctive adult male, but thisFeatures appear in the process of sexual maturation (Pritchard and Trebbau, 1984; Wibbels, 1999; Kamezaki,2003). Follow

I strive for as a change in tail shape representing the expression of male secondary sex characteristics, measuring
the progress of sexual maturation
Ru is expected as an indicator.
About Kinoe Takeshi turtles tail elongation starts have been reported in the Mediterranean Sea and North Pacific(Hirate, 2000; Casale et al., 2005). In other words, Casale (2005) is of the Mediterranean loggerhead turtle tracks
Kinoe Takeshi
70 cm and is estimated to start at the tail elongation, Hirate (2000) North Pacific loggerhead turtle tailThe unit elongation is initiated approximately 680 mm in length and called Nao Kinoe. However, these studies
male issues
Is that the judge in determining the length of the tail. In other words, where there is not seen in male tailelongation
Exist and are treated as if it is male, begins Kinoe Takeshi tail elongation have been calculated low
Ru possible.
Moreover, the degree of tail elongation in mature plants have been investigated in the South Pacific(Limpus, 1985). According to the report, in immature males, 20 to the tip of the tail length from the back carapacecm
13
Less than, 20 cm is considered to be mature individuals or more. However, male sexual maturation
Kinoe Takeshi reach maturity and are on the same Meru Kinoe Takeshi likely differ depending on the population in
the North Pacific
The population has been compared with the degree of elongation of the tail is not the state of sexual maturity.
Therefore, in this study and instep length and with the maturation state of Onaga on the North Pacific loggerhead
turtleWere examined.
3-2. How
To investigate the relationship between growth and sexual maturity tail turtles different sex and sexual maturity
statusTadashi Kinoe長individual standard 128 (SCL: Straight Carapace Length) and Onaga (TL: tail length) was
measured. A
Us, TL is the length of the cloacal opening to the rear end of the plastron (Figure 3-1). Of each individual is not todie
Or 120 individuals were observed to determine the morphology of the gonads and reproductive tract anatomy. In
addition, Limpus and
Limpus (2003) and Miller and Limpus (2003), in accordance with the morphology of the gonads and reproductive
tract, that male and female
The subadult juveniles in each adult classification (Table 2-1, see Chapter 2). Can not observe the gonads andreproductive tract
Eight individuals did surviving individuals, there is a sperm cloacal cavity, and it was remarkable elongation of thetail
Were divided into adult males. In addition, these individuals during the month of rooms in Kochi Prefecture from
April 8, 2010, 2005
The town was captured by stationary nets and Kobe City, Mie Prefecture, Kita Osamu.
Then, starting Kinoe Takeshi asked the male tail elongation. Starting point of the male tail elongation in male andfemale differences in Onaga
Point they begin to appear, TL divided by the SCL relative Onaga (rTL: relative tail length, TL / SCL) and14
SCL and determined as the intersection of the regression line. Regression line and the beginning of sexual
maturation that subadult
Data obtained using the adult.
In addition, to represent the degree of tail elongation, TL calculated the relative growth factor. Factor is related torelative growth
Coefficient equation Y = b · X
aThat is represented by a constant, a = 1 X at the Y on the growth of the growth of
Such as growth. Here the SCL X, TL, Y as a constant, if more than one in SCL対Su
Growth and growth of the Ru Yu TL.
3-3. Results
Morphological observations of gonads and reproductive tract, the female and male were 45 individuals in 83
populations. They also
Individuals are classified into three classes of mature adult subadult juveniles in the juvenile males 8 females in thefive individuals
Individual, the individual subadult females 55 males and 29 individuals, 20 individuals were 11 females in the maleadult population. Growth of
Onaga-Relative maturity class (rTL: mean ± SD), a juvenile male 0.149 ± 0.030 (0.121-0.187, n = 5)
The females 0.146 ± 0.026 (0.108-0.174, n = 8), in the subadult males 0.249 ± 0.070 (0.157-0.446, n = 29)
The females 0.165 ± 0.228 (0.113-0.228, n = 55), in adult male 0.423 ± 0.061 (range: 0.302-0.501, n =11) in females 0.183 ± 0.036 (0.136-0.277, n = 20), respectively.
rTL in juvenile males and females, but no difference in the length of subadult and adult males who are clearly
Sure (Fig. 3-2, p <0.001, Mann-Whitney U-test), but extends to after Onaga subadult male, rTL to
The result showed that the sex begins. The SCL for the TL in males relative growth factor
15
Of (a) of sub-adult from TL has shown excellent growth and strong (a = 4.3898, n = 29, r2= 0.5542, p <0.01, noCorrelation test), and there was no significant correlation between adult (a = 2.2384, n = 11, r2= 0.4424, p> 0.05,
Uncorrelated test.) Here, the adult females in the juvenile rTL Interestingly, significantly more than the rTL
Was greater (p <0.05, Tukey test of multiple methods.) Only the degree of relative growth of adult female
Is not requested in (a = 1.3266, n = 29, r2= 0.1084, p> 0.05, test uncorrelated), sub-adult and adult
Coefficients and relative growth along the body, more pronounced in males also shows the growth in the female
Onaga no priority ofAnd has been shown that sexual maturation and growth in the tail (a = 1.7528, n = 83, r2= 0.3366, p <0.01,
Uncorrelated test.)
Next, begin to seek out different Kinoe Takeshi tail length of males and females, and adult males and females in
each
RTL in the SCL and subadult linear regression (Figure 3-3). The regression line in males SCL = 0.001433
rTL-0.8046 (r = 0.8066) in females in SCL = 0.0001501 rTL + 0.05475 (r = 0.2547), respectively. MaleThe start of secondary sex characteristics and SCL rTL intersection of the regression line when the male andfemale, SCL was 670 mm, rTL
The .155 was determined to be3-4. StudyIn this study, elongation of the tail of the male turtles in the North Pacific can be started from SCL 670 mm
Was shown (Figure 3-3). Osabe Shin male tail is represented by a male testosterone secreted by testes
Are believed to be inspired by the sex hormones in the gonad in juvenile green turtle 42 months of age
16
Stimulating hormone was administered, has been confirmed that the growth in the male tail (Owens et al.,1978). In the second chapter of the North Pacific loggerhead turtles on, to begin sexual maturation Kinoe Takeshi
half of the individuals
The SCL 660 mm has been revealed that, starting with 670mm of male tail elongation SCL
The sexually mature to start as high as 660mm 10 mm more. This began after the development of testicularShows that the elongation of the tail begin immediately. Osabe Shin tail male sexual maturity that is open
It is suggested to respond sensitively to the increase in the amount of male hormone secreted by the testes

beginningRu.
In the past the North Pacific loggerhead turtle, Hirate (2000), about 29 individuals in the catch in Okinawa
Prefecture
To the relationship between SCL and TL Onaga, SCL 680 mm is about to start and grow a tail male in this study
Results were compared with 10 mm greater. Hirate and research (2000) and the result of differences arising
Several possible reasons are discussed. The first is Hirate (2000) and the long tail of the male population that
seems
Due, in fact, might be considered male and female individuals incorrectly. In this study, almost even male female
TOSHIBA has been shown to be elongated tail, but Hirate (2000) See Figure 12, SCL
There are 700-800 mm in the female population could have been analyzed as the male range. Therefore,
Male regression line is shifted, the intersection of the regression line of both sexes may SCL grows.
The second reason, mature individuals Hirate (2000) was compared to study the possibility of downsizing
There. Minami Miyazaki City, Tokushima Prefecture and the town and smaller individuals are spawning about 20
years
Has been reported (Kamezaki Shigeta, 2006; other Takeshita, 2006), this research measured the period from 2005
to 2010
17
The research population was tested, Hirate (2000) is smaller than the mature Kinoe Osa in 1996 and 1999
measured
Teita could. One of the factors that have smaller mature Kinoe Takeshi, one by a decline in population density
There are compensatory response to the increase in premature adult food consumption per body has been foundin cetaceans and
The (Oosumi, 1974). North Pacific loggerhead turtle nest egg production of its 50 years of the late 20th century
Are also reduced 50-90 percent (Kamezaki et al., 2003), the miniaturization of mature individuals by compensatory
response
Can not deny the possibility that progress.
The third reason is the geographical differences cited in the study area. Kamezaki others (1995), Kagoshima
Prefecture
Yakushima, Miyazaki City, Miyazaki Prefecture, Minabe Town, Wakayama Prefecture (the southern town old)compared to the length of the instep of spawning individuals place in the south
Have reported that the spawning grounds as large Kinoe Takeshi position. Muroto, Kochi Prefecture, a land surveyof the study
Cho, Mie Prefecture, and Hirate Kita Osamu (2000), which lies to the north than the island of Okinawa wasinvestigated in a North Pacific
The possibility was considered large enough population that lives in the south Kinoe Takeshi limited spawning
individuals.
Then, the extraction began after the tail of a mature male, is a significant factor when the relative growth ofsubadult
High (4.3898) was evident from. Whether to continue elongation after the tail of a mature adult male
From the correlation between the SCL and TL but not sure, SCL relative growth factor of 2.2384 for the TL and
Excellent growth trend seen in the adult. The SCL and TL, there was no correlation between the SCL
The distribution range of 778-902 mm is considered limited due to this. The males reach maturity at
rTL is considered between the minimum and maximum value of sub-adult to adult, flying has become the SCL
781 mm for the subadult and exclude rTL 0.446, rTL reach maturity and the range of 0.302-0.363
18
Or. This value is the average adult male rate of only 0.423% of 71.4-85.8. Therefore, mature
Growth of the male tail is supposed to be followed by Heck et al.
Onaga also indicate that female tachyauxesis SCL for the first time revealed in this study. Onaga female
It showed excellent growth with the maturity of the activities related to breeding females alike elongated tailSuggest that the functional significance Waru. One of spawning activity the most important breeding females
There, the turtles are dug in sand holes eggs 産Mi落Tosu 34.9-85 cm depth (Dodd,1988). At this time, females lay eggs in order to stretch into the hole dug by reversing the cloacal cavity, long tailYou can reduce the impact of a fall from a position lower than the egg 産Mi落Toshi that much Once please
Ru. However, immediately after the shell turtles laying eggs soft catch to break even
There was not even talking about (this references, personal communication), and to mitigate the impact of falling
hard to believe at the time of spawning
Not.
Osabe Shin female tail is not to spawn, may have been used to refuse to mate with males
May. Before accepting the mating spawning females laying ahead of only been about 2-4 days
(Owens, 1980; Wood and Wood, 1980), in captivity ventrally pass to go to the tail when the female refused tomate
Embedded may be observed that his hind legs together. The observation of the juvenile tail, the tailBut can not move too much due to the short, the growth in female ventral tail fold tailWill be able to hide it into the cloacal opening.
Or functional significance will also consider the possibility of innocence. Encourage male tail elongation e
19
Hormone is also present in the female body, such as migration to the region and stimulate ovulation, mating of thefemale reproductive physiology as well 関Wa'll Have (Wibbels et al., 1990). So, are also affected by female androgen, the minutes
Elongated tail that just can not deny only. Onaga elongation 関Wa breeding female actually
To find out whether there is functional significance of Ru is involved in reproductive behavior, such as during
spawning time or when mating
Behavioral observation is needed on how to use the tail.
20
Readmission to the size of breeding area around Japan is in Chapter 4
4-1. Purpose
The North Pacific loggerhead turtles (Caretta caretta) are restricted to spawning grounds located in the western
Pacific Japan
Has been to focus on the Pacific coast of southern Japan in particular (Kamezaki et al., 2003). North Pacific with nospawning
Baja California waters, and turtles also falls on the Hawaiian Islands and the eastern part of your distribution
centerRi, mitochondrial DNA haplotypes of these individuals are the same as the spawning population of Japan (Bowenetal., 1995), North Pacific loggerhead turtles that live around it which was shown in Japan 産Shita. Its
As if to prove is, off the coast of Baja California is recaptured by the tagging juvenile Japan(Uchida and Teruya, 1991), Japan across the Pacific Ocean was released from the Baja California breeding
population
Have to arrive there (Resendiz et al., 1998; Nichols et al., 2000). Thus, in the eastern North Pacific
The turtles are allowed to move in the west. Juveniles hatched from the power situation in the Kuroshio Current
andI moved into the eastern Pacific, has been suggested that the waters around Japan and return to breed again
afterwards
The.
However, mature females that live to lay eggs for the purpose of breeding sites around Japan are obvious
Of such individuals instep length distribution and maturity to actually live only a few pieces of information(Nomura, 1993; Miyawaki, 1994; Maeda Kimura, 1995; other Iwamoto, 2005b; Tanaka Ishihara, 2006). Therefore,
Japan
Loggerhead turtles in state waters of sexual maturation, and size composition and sex ratio of Party A, including
information on age structure is defined21
In what was not. Therefore, this chapter from turtles captured in nets, stationary and living in Japanese waters
To clarify the life-history stages of sexual maturation in the instep of length distribution and loggerhead turtles toreturn to breeding areas near JapanI come to discuss Kinoe Takeshi.
4-2. How
The large stationary nets Muroto, Kochi Prefecture, the total catch during the period 1392 until June 2002, July 11,2009
Turtles and a sample of the body. Since the nets are fixed in place throughout the year,
The sample was considered to have been taken at random from the population inhabiting the waters Misaki
Muroto. Nets were investigatedThat the land is located in the town where Misaki Muroto Muroto, Kochi Prefecture, the three fishing groups
located in the coastal (big blanket
Partnership) for the seven networks operated by large stationary (see Figure 2-1).Misaki Muroto in flowing water
depth 500-1000 m Kita Hutoshi
To hit the middle shelf flow Taira Hiroshi, to a localized upwelling of nutrient-rich seawater (Fukasawa, 1998).
Fishing line near the continental slope depths of 35-78 m in large stationary nets placed in the position of a fishingorganization per year
During the 1500-2000 t being caught. The main species caught yellowtail (Seriola quinqueradiata), Gomasa
Server (Scomber australasicus), frigate mackerel (Auxis rochei) and so on.
The captured turtles are transported to the fishing port, the head Tadashi Kinoe Standard (SCL: straight carapace
length) in total
After measurement, the basis was discharged within a day of offshore fishing or nets.
In this study, the SCL was captured turtles were divided into four classes of maturity. In other words, SCL 42
spiderlings hatch mm ,43-660 mm below the juvenile to subadult ,661-821 m, 822 mm or more and adult.
22
Moreover, these separate classes was used to study the following SCL. Hatching juveniles and hatchlings to
separate the SCL 42 mm,
North Pacific population of juveniles hatching 41.9 ± 1.51 mm for the SCL to be (Matsuzawa Sakamoto, 2002).
The separate juvenile and subadult SCL 660 mm to separate adult and subadult SCL 821 mm and are each half
For mature individuals Kinoe Takeshi Kinoe Takeshi half and the start of sexual maturation in the number ofindividuals (Chapter 2).
4-3. Result and discussion
The large stationary nets Kochi Prefecture Muroto individual accounts during the period 1392 until June 2002, July11, 2009
Turtles were captured, the head Tadashi Kinoe Standard (SCL) were measured. The loggerhead turtle bycatch by
the SCL are
757 ± 67 (SD) mm (range: 563-1050 mm) in, SCL showed a unimodal histogram (Figure 4-1).
Most classes in the proportion of sexually mature more subadult 77.7% (1081 individuals), accounting for 17.6
percent followed by the adult (245
Individuals), and 4.7% juvenile (66 individuals) followed by juveniles hatch is also found one individual. Among thesmallest sample
The population was 563 mm in the SCL, in the long-range juvenile instep is relatively large and had reached late in
the juvenile
You said Ru. In conclusion, the breeding grounds in coastal waters of Japan, as appearing in the late stage ofjuvenile
And showed that the abundance of subadult loggerhead turtles rather than adults. The North
The Pacific loggerhead sea turtle spawning grounds and as the only sandy beach in Japan (Kamezaki et al., 2003),
young hatching
Body immediately after hatching, but should at least have the Japanese waters, in this study also found one
individual hatched juveniles
Was from. This is a juvenile loggerhead turtles hatch after hatch, quickly dispersed into the ocean, Mexico and theKuroshio
To balance the ocean waters to higher latitudes, such as using the Gulf Stream ocean current towards Koh (Carr,
1986; Carr,
23
1987; Bowen et al., 1995; Witherington, 2002), because the coast is considered to promptly disappearedWas. The mainstream of the Kuroshio current and the nets were investigated over the offshore, moving the nets
off the coast of
Ru hatched juveniles were considered to not be caught.
And SCL's distribution of turtles in the seas around Japan, SCL has appeared in Japanese waters in the 560-570 mm
The turtles began to increase to 740-750 mm in the mode of welcome, and to decline thereafter (Fig.
4-1). This factor is the increase in re-admission into Japanese waters, death bycatch reduction factor (Peckham,
2007; FAO,
2009) and collisions with ships, the main prey of sharks (Witzell, 1987), death due to illness (George, 1997) andEtc. are considered as main factor. The decline is also likely due to emigration from the study area, the study area
north of the Taira Hutoshi
Yakushima, Kagoshima Prefecture, including the largest spawning ground of Pacific, saying Minabe Town,
Wakayama and Miyazaki city beachPlainly identified by a sign that the limbs of the adult females come to spawn in visiting the main spawning groundsorHas (Sea Turtle Association of Japan, unpublished data), the impact of emigration is not considered less significant
Was. Therefore, before the SCL at the rank of the most frequent number of individuals exceeded the number ofindividuals killed rejoining, since the most frequentClass size is suggested that the population exceeds that of the population died on the reverse readmission. Caretta caretta
To grow significantly as well as mortality and other organisms are considered to be reduced (National
Research Council, 1990), reducing the size of a large number of individuals in a class lower than the mortality ofJapanese waters
Suggesting a reduction in readmission population. For these reasons, the main size class rejoin the Sea of JapanThe following are the most frequent was suggested that SCL 560-750 mm. To Kinoe Takeshi Hama Kono rejoin theedge of sexual maturity
Individuals were also included juvenile late I have not. Thus, the addition to the Sea of Japan before re-starting thesexual maturation
24
Individuals also are entering, crossing oceans and breeding areas for progression to sexual maturity would bemade regardless of
Was.
Instep length distribution of turtles in the eastern North Pacific coast of Baja California is SCL 46.9 ± 13.0
cm (n = 39, range: 32-58 cm [Ramirez-Cruz et al., 1991]), SCL 585 ± 111 mm (n = 180, range:
266-834 mm [Gardner and Nichols, 2001]), 619 ± 21 mm (n = 15, range: 435-927 mm[Seminoff et al., 2004]) has been reported, the mean and the mode values smaller than dorsal length of theJapanese population in juvenile size
The did. Baja California coastal habitats are used during the loggerhead turtle hatchlings were hatched in Japan
It is one (Bowen et al., 1995), where individuals join and come away from here and over the years
Is considered. Loggerhead turtles stranded in the California Peninsula in the mode of the SCL 500-700 mm
Have shown a unimodal length distribution with the instep (Gardner and Nichols, 2001), this is half of California
Coastal loggerhead turtle island SCL 500-700 mm suggest that they start off around the coast reach
Ru. Class sizes start waters off Baja California is almost juvenile size, and Japanese waters
Was estimated to rejoin SCL 560-750 mm 60 in lower than the range of mm, 50 mm above the 小Sakatsu
Or.
Time it takes to cross the Pacific to the waters for breeding, or SCL 856 mm SCL 834 mm fed up
Has been confirmed by the turtles, reached in about a year moved to Japan from California Peninsula
That (Resendiz et al., 1998; Nichols et al., 2000). Also captured in the north of the Hawaiian Islands SCL
548 ± 123 mm in the wild populations of juvenile nine months 2.4-6.9 1311-5199 km westward and moved
25(Polovina et al., 2000), which was the pace can cross the Pacific in 1-2 years. In addition, Nichols et al.
(2000) and Polovina et al. (2000) is used to track individual satellite transmitter, was tracked to the north plant
Were actively moving toward the west without having to use the equatorial current. Here, the chronology of thebone in the North Atlantic

Loggerhead turtle growth rates estimated by the method of SCL 500-599 and 600-699 mm respectively
28-38 and 27-31 mm / year and (Parham and Zug, 1997), across the Pacific during the previous 50-60
mm period growth rate is applied to the Trans-Pacific loggerhead turtle breeding area for this is 1.3-2.2 years
And suggests that. Thus, the loggerhead turtle will begin to cross the Pacific to the waters for breeding late in thejuvenile,
Japan aims to start crossing once active, and suggested that approximately 1-2 years to reach.
26
Growth rate and age at maturity of loggerhead turtles in the North Pacific Chapter 5
5-1. Purpose
Information about age and growth rate of individuals not only to clarify the life history of the animal, one
It is essential to understand the dynamics of populations sizes. Growth rate among them age and sexual maturity
Will know the time required before the next generation was born, the information necessary to predict changes in
population
The information. Loggerhead turtle (Caretta caretta) in the North Pacific is a major spawning Pacific coast ofsouthern JapanAs a place to breed. However, the number of spawning nests during the late 20th century nearly 50 years 50-90%
尐 to be reduced and have been threatened with extinction (Kamezaki et al., 2003).Therefore, appropriate
conservation
The measures will need to be taken in the North Pacific loggerhead turtles age and sexual maturity is the growthrate obviously
Or not, and when considering the efficient conservation policies, to validate the effectiveness of conservation
policies were implemented, affectThat it risks.
Age of sexual maturity in this chapter reveal turtles, old individuals are investigated using breeding
Came. Uchida (1967), breeding loggerhead turtle hatchlings from hatcheries, both reported to mature in the 6-7
years
Has been reported. However, the breeding population is growing in contrast to wild populations because of thehigh nutritional value and volume of prey
Considered earlier, the age of sexual maturity can be applied as wild populations are not (Frazer, 1982).
As a way of knowing the age of sexual maturity of sea turtle species in the wild, now mostly bone and recapture
methods
Being investigated by the growth rate and age on chronological approach.
27
Recapture method is to put a label to an individual released was captured once again ended up being captured
How to determine the amount of growth between the growth rate. The length of time and the instep of thegrowth rate obtained
Fitting the growth equation, can calculate the number of years needed to reach sexual maturity Kinoe Takeshi
growth equation based on the
It is estimated that in all ages and sexual maturity. Label is attached to the turtle species are in many cases there
forelimb
Alternatively Furippatagu is attached to the hind legs, a rigid plastic material such as titanium,
Inconel, Monel, etc. have been used (Kamezaki Matsuzawa 2008). However, even signs of a sea turtle
To trace the history of long life and durability rather as a method to reveal the age of sexual maturity is notenoughBe. In addition, there is no previous information labeling, the growth rate spanless until then. The
Yearling and individuals, the information age, individuals must be clearly understood from the appearance of age is
not obtained, its
After much older than the tracks made do not know. In addition, signs attached to, can not only recapture
If you can not examine the growth rate.
Geochronological methods of bone growth arrest lines were left inside the bone (LAG: lines of arrested growth) of
Age is estimated from the number. LAG is formed when the growth rate falls, the water turtle species
In winter the temperature falls LAG is formed, this is one that is basically one year (Zug et al.,
1986; Snover and Hohn, 2004; Snover et al., 2007). Techniques applied to species of sea turtle bone age

When the humerus is mainly used (eg Zug et al., 1986; Klinger and Musick, 1995;
Zug et al., 1995; Parham and Zug, 1997; Bjorndal et al., 2000; Zug et al., 2002; Bjorndal
et al., 2003; Zug et al., 2006), leatherback turtle has been used in small bones in the eye sclera (Zug28
and Parham, 1996; Avens et al., 2009). Relationship between body size and age and growth rate under natural
conditions,
The age at which sexual maturity can be determined by these methods. The problem with the bone chronologicalapproach,
Iki is absorbed by bone tissue grows in the heart of the bone is absorbed by the lines of arrested growth there wasThat would be. In addition, LAG and LAG are densely packed if not clear if
Etc., LAG different possible reading down or reading. Furthermore, LAG is formed of growth
Because it is a slow, 尐 no changes with seasonal growth rate by moving
If there is a temporary slowdown in growth due to illness or injury, or in a plurality of 1 LAG is formed
Could.
Caretta caretta sea turtle species are in the growth rate has been investigated relatively well age and sexual
maturity
Species. Many studies have obtained by fitting the age of sexual maturity to recapture the results of the growth
curve,
Sexual maturity is age 11-47 years in the North Atlantic (Frazer and Ehrhart, 1985), or 10-15 years(Mendonca, 1981) is estimated to be 35.9 years in the South Pacific (Frazer et al., 1994), in the Mediterranean
16-28 years (Casale et al., 2009a) have been estimated. The age of maturity for the raw bone of the humerus
The techniques are also expected chronology in the North Atlantic 22 years of age 26 (Klinger and Musick,1995), and 20-63 years (Parham and Zug, 1997) ,13-year-old 15 (Zug et al., 1986) estimated that mature in
Is a constant.
On the other hand, instep length female turtles lay eggs on land in between the populations differ in size or
maturity'll Have (Tiwari and Bjorndal, 2000; Kamezaki, 2003). The geographic variation in traits like this29
Given that, there is also variation among populations and traits growth rate and age of sexual maturity
Considered. However, in the North Pacific Research on age and growth rates have been almost
Not. In the North Pacific, the age at which sexual maturity is not being investigated, SCL 46.6 cm up to the age ofjuvenile
And growth rate (Zug et al., 1995) and spawning population growth rate (Hatase et al., 2004) have been
investigatedThat as possible. Amid such a study, this chapter, turtles, taken near JapanFor the humerus, and to estimate the sexual maturity age, living in Japanese waters Akaumiga
Revealed the growth of the media until sexual maturity.
5-2. HowAge and growth of loggerhead turtles, growth arrest lines were left in the bone by bone chronological approach(LAG: lines of arrested growth) was estimated from. Samples were washed ashore dead bycatch and mortality in
Japan
Using the loggerhead sea turtle humerus of 79 individuals. These individuals were collected before the standard
straight humerus
Kinoe Takeshi (SCL: Straight Carapace Length) to measure, we determine the gonadal sex even more.
Moreover, as Chapter 2 of the gonad maturity, female body found in white and ovarian corpus luteum, andAdult males with enlarged testes, cylindrical and mature individuals ie. In addition, the spawning grounds in JapanThe six individuals who died can not escape from juvenile hatching nest egg-laying in the sand and humerus
diameter growth SCL
Value was used as a starting point.
LAG is the minimum width of the humerus (MW: minimum width) have remained among the highest crest anddeltoid30
Is known that Ru (Zug et al., 1986; Figure 5-1). LAG to observe, this part of the electricThe circular saw cut, sharpened on the grindstone 1mm thick sections were prepared below. The center of theconcentric sections
LAG spread in a circle and the center of the transmitted light from below the reading microscope (KENIS Ltd.,NRM-2XZ/KN3102250) along the major axis for radius and LAG LAG LAG and measure the width between(See figure 5-2). However, the outermost LAG excluded from analysis because less than one year in the formationof a wide
Or. The LAG number of remaining without being absorbed at both ends of the section is different, the difference in
20 moreBook now. Therefore, the analysis of the radius and width 読Mi取Reta LAG for the large number of.
The LAG was formed in the outer part of the humerus is, MW between SCL and the linear phase
Relations that were related (Equation 5-1), LAG MW radius then you can correct the form, the
LAG LAG compensation values are formed at the time was considered to be proportional to the SCL. Thus, each
LAG
To estimate the formation of SCL, LAG MW radius and width and was corrected (Equation 5-2). In addition, LAG
The width of the next LAG shows the growth rate of the humerus of the year to be formed. Growth of thehumerusThe amount is proportional to the amount of growth of SCL, LAG LAG radius and width of each of the SCL during
the formation of its equivalent
The growth rate was calculated back in time. Back Calculation protocol so that (Zug et al., 1997).
SCL = 26.3 MW + 14.1 (R2 = 0.955, n = 79, p <1.0 x 10-42, uncorrelated test) Equation 5-1
Lrev = 2 L · R / MW Equation 5-2
Lrev: LAG correction value of the radius or width, L: LAG-width or radius, R: radius of sectionLeft in the humerus inorder to estimate the age of the LAG is absorbed in the center of the humerus was
LAG or it is necessary to estimate the number. Absorbed in order to estimate the number of LAG, Regression
And Correction Factor protocol for Growth protocol (Zug et al., 1995; Parham andZug, 1997).
Regression Growth protocol in Parham and Zug (1997) according to von Bertalanffy's growth
Length variant expression expression expression and MW 5-3 estimates obtained from age. Moreover, MW is
proportional to the related SCL
Since that relationship (Equation 5-1), when sexual maturity at the time of SCL and SCL for readmission to the MW
Demand, more expressions of 5-3 MW and re-estimated the age at entry age for sexual maturity. Here, the growth
SCL is a mature, half of all individuals reach sexual maturity determined in Chapter 2 of the SCL 821 mm, using
SCL is to re-enter Japanese waters was found in Chapter 4 for 560-749 mm.
t = ln [(a-X0) / (a-MW / 2)] / k Equation 5-3
t: age estimation, X0: MW radius of the hatched juveniles, a: asymptotic value (asymptote), k: Endogenous growth
factor(Intrinsic growth coefficient)Parameters in Equation 5-3 a, k, X0 to determine the first correction value LAG line width times the radius of
Attribution (Figure 5-3), the intercept of the regression line (A: 0.7669) and slope (B: -0.0393) a a = | A / B |, k =- ln(1
32- | B |) to assign, a to 19.514, k and asked to 0.0401. Next, the juvenile was 1.77 ± 0.12 MW hatching(SD) mm (n = 6), and X0 is a radius of 0.88 mm becomes equation 5-3 'was required.
t = ln [37.26 / (39.02-MW)] / 0.040 Equation 5-3 'Then, Regression Growth protocol for SCL in the age of the von Bertalanffy growth equations
Growth equation SCL = a '{1-exp [-k' (t'-t0 ')]} was obtained as. First, by age 1 SCL expression
Determined from 5-3, based on the parameters of growth equations that a ', k', t0 'the Microsoft Excel Solver
Calculated by the least squares method using the function.
Then, Regression Growth protocol not able to estimate for each individual in each age
For った, Correction Factor protocol was estimated in each individual age. First, each individual LAG
The average width of the compensated demand, the reciprocal of the population of the CF (correction factor), andthe estimated age

Estimated from Equation 5-4. However, Correction Factor protocol requested by individuals in each age
While that SHOULD NOT BE CONSTRUED outside of the growth rate slowed from an average width of LAG has been
derived CF
Therefore, the number of LAG absorbed, that could have been overestimated or estimated age.
t = Lm + (Li-X0) CF Equation 5-4
Lm: measured by the number of LAG, Li: LAG innermost radius compensation value
33
5-3. Results
Tadashi Kinoe 長 standard of individuals in the population 75 to 79 turtles were estimated using the age of thehumerus (SCL) of
The average value of 759 ± 61 (SD) mm (range: 577-944), the four individuals because they were damaging thecarapace
SCL could not be measured. Gonad morphology was observed to autopsy, the female and male individuals in the27
And 42 individuals, 15 individuals of which mature females, mature males were three individuals. The 10
The population is going to rot amid able to determine which of the gonads did not properly
Tta. From individuals of 9.3 ± 4.3 (range: 3-20), a total of 732 was confirmed LAG, 653 points
Width was calculated.
Back Calculation protocol determined by the average growth rate of the SCL was 13.9 ± 7.8 (SD) mm / year
(Range: 0.0-64.5), and SCL is then obtained 694 ± 75 (SD) mm (range: 374-935, n= 732), respectively. Another class of SCL growth rate, 31.7 mm / year (SCL 300-400 mm, n = 1),
29.5 ± 13.7 mm / year (SCL 400-500 mm, n = 7), 20.7 ± 12.4 mm / year (SCL 500-600 mm,
n = 58), 14.1 ± 7.4 mm / year (SCL 600-700 mm, n = 298), 11.9 ± 4.9 mm / year (SCL
700-800 mm, n = 257), 11.2 ± 5.4 mm / year (SCL 800-900 mm, n = 29), 10.4 ± 0.0
mm / year (SCL 900-1000 mm, n = 3), respectively (Table 5-1). SCL's growth rate between male and female ranks
Were compared, SCL 500-600 mm ranks only, significant differences were observed in male and female growthrate,
In this class faster than the growth rate of females to males (p <0.05, Mann-Whitney U-test, Tukey
34
By the method of multiple testing, Table 5-1).
Regression Growth protocol, the age of sexual maturation is complete, obtained in Chapter 2 of sexual maturation
Completed the SCL 821 mm is determined from the results, was estimated to be 37 years (Figure 5-4). The
Rejoin the SCL turtles around Japan is, in Chapter 4, 560-749 mm and sought at this time,
Estimated age of 18-31 years. The estimated age for each from 1 SCL, at the age of 10 381mm,
At the age of 20 599mm, at the age of 40 842mm, 60 952mm at age was estimated to grow to. Against age
The growth of the SCL expression
SCL = 1159 {1-exp [-0.03067 (t-1.619)]} Equation 5-5
Was calculated (Figure 5-4).
Correction Factor protocol was obtained in CF 2.76 ± 0.86 (n = 79, range: 1.03-5.08)
Respectively. The estimated age, 38 males mature individuals 46 years of age 47 (n = 3) 43 ± 11 in females
Age (n = 15, range: 22-61), and immature individuals 34 years old male ± 11 (n = 24, range: 16-61)
Females in the age of 39 ± 12 (n = 27, range: 17-61) (Fig. 5-5). In one immature and mature individuals
In the body, there was no gender difference in age (p> 0.05, Mann-Whitney U-test). Its
In this, we compared individuals mature and immature individuals of both sexes combined population. As a result,matureHigher than the nuclear age population consists of individuals who are immature, SCL increased significantly (p<0.05,
35
Mann-Whitney U-test). However, individuals older than individuals not well developed and matured during theMing SCL瞭 correlation was not observed, SCL So that was greater with increasing age (Figure 5-6,p> 0.05, test uncorrelated.)

5-4. Study
5-4-1. Growth rate
Back Calculation protocol was determined by growth rate, the head Tadashi Kinoe Standard (SCL) 500-600 mm of
The class is faster in females than males, SCL than those at the rank of major sex differences in growth rate
Have not been observed (Table 5-1). Kinoe Osamu when the growth rate is that gender differences, males andfemales have different habitatOr, believed to have worked, or some physiological factors. mm 500-600 SCL is
Across the Pacific toward Japan from the eastern North Pacific waters for North Pacific loggerhead turtle
Amount to the size (Chapter 4). If you are bringing a sex difference in the rate of growth of geographicalconditions,
Considered a different route toward the Sea of Japan in both sexes. However, females were caught in this study
The location is the same, mature turtles are thought to have sex on the same feeding area
The gills (Limpus, 1985; Hatase et al., 2002b), SCL 500-600 mm in the beginning with the sexual maturation
Since individuals are not (Chapter 2), the migration of habitats and just before the start of male and female sexual
maturation
Different pathways is unlikely. In addition, individuals can start a sexual maturity before the effects of sex
hormones
Also appeared unlikely that the sex difference in growth rate.
36
Other factors given sex, the sea turtle species that have temperature-dependent sex determination mechanism
incubation periodNaka Hazama likely to experience temperatures. Affect the subsequent growth if the temperature during
incubation
For example, gender differences were observed even funny the growth rate of immature individuals may
not. Loggerhead turtle, and Ao
The sea turtle hatchlings are born large enough to lower the temperature of incubation during the incubation
period (Glen et al., 2003;
Stokes et al., 2006), Stokes et al. (2006) The postnatal growth of the lower incubation temperature is estimated tofastThat. The sea turtle species are due to the increased temperature the lower the proportion of males during
incubation, after hatching
Growth rate than the male and female, faster. In this case, I observed the female growth rate of males in thisstudy
The faster than the smaller Kinoe Takeshi at faster growth rate than males, complementary to it
May be the answer. Other individuals in captivity as well as growing populations of poor early growthCatch has been observed that the instep of the head (Kamezaki personal communication), this is later than theinitial growth,
Eventually the head catches Party A other individuals, suggesting a complementary effect to work.
Second, mature SCL 821 mm (Chapter 2) in the growth rate of larger Kinoe Takeshi, SCL 800-900 mm
Also at the rank of 11.2 ± 5.4 mm / year (n = 29), SCL 900-1000 mm in the ranks of 10.4 ± 0.0 mm / year
(N = 3), respectively. The growth rate in Japan, spawning a female 2.5 ± 4.0 mm / year (Hatase et al. 2004)
And the growth rate obtained in this study was greater than this. It is collected in this study
Kita Osamu turtles were obtained in the town of Kochi Prefecture and Mie Prefecture Muroto or sample, or thecomplete mature
Probably due to many individuals that while they do not. That is, growth arrest lines left in the humerus(LAG) are not considered mature after a little to the growth rate obtained in this study
37
Regardless of the size of the SCL, the growth rate is considered at an earlier juvenile and subadult maturation iscompleted
The gills.
In this study, the growth rate of the North Pacific loggerhead turtle, not the number of data 尐 SCL 300-400 mm
Peep and the rank of 400-500 mm, SCL 500 mm or more showed. Account of the North PacificMigame growth rate has so far been measured by the growth rate of females to lay eggs recapture method

(Hatase et al., 2004), 10 years after hatching the chronological approach over previous bone SCL 466 mm 42
mm / year is estimated to grow at a rate of (Zug et al., 1995). Immature non-North Pacific
The population growth rate of the South Pacific and Mediterranean, has been investigated in the North Atlantic,
North Atlantic relatively
Have been well investigated. North Atlantic growth rate differences among even geographically instep of the samelength range
Has been known that many of the examined population growth rate in the SCL 600-700 mm, a
Chesapeake Bay in the east coast of America Gassyuukoku 14.6 ± 11.6 mm / year (n = 9, Klinger and Musick,1995), North Carolina at 18.2 mm / year (95% CI: 15.9-20.5) (n = 122, Braun-McNeill etal., 2008), Florida at 59.9 ± 22.5 mm / year (n = 7, Mendonca, 1981), respectively. The Kita Hutoshi
In this Taira Hiroshi SCL 600-700 mm in the growth rate of 14.1 ± 7.4 mm / year (n = 261), andChesapeake Bay and is close to the rate of growth of North Carolina, North Carolina's growth rate
Compared with about 1 / 4 mere. The growth rate of the Mediterranean at 325-820 mm Kinoe Takeshi song
25 ± 17 mm / year (Casale et al., 2009b) in the North Pacific SCL 374-935 mm (13.9 ± 7.8mm / year) than during the slower growth rate of 750-950 mm in the South Pacific during the song Kinoe Takeshi
9.5 ± 5.838mm / year in the North Pacific Ocean SCL 700-800 mm (11.9 ± 4.9 mm / year) or similar to or at
Seemed a little slow. However, the growth in population in geographical, such as the one seen in the North
Atlantic
North Pacific and South Pacific head speed differences, there may be the Mediterranean. Therefore, the North
Pacific
Individual differences in the degree of difference and even if you leave in the population, are required to continue
the validation of the factors that appear in the differenceRu.
5-4-2. Mature age
Correction Factor protocol is determined by the age of mature individuals, mature individuals, as mentioned
earlier growth
Mature individuals within 1-2 years because it is considered to be approximately equal to mature age.
Correction Factor protocol with an average estimated age of mature individuals (± SD) was 43 (± 10) years andRegression Growth protocol was higher than 37 years of age was estimated at maturity.This is
Correction Factor protocol outside of the humerus in the growth rate slowed to the average width of the LAG
Based on the inner LAG faster growth rate to estimate the number one, Regression Growth
protocol population growth rate than in the small Kinoe Takeshi is fast, the LAG as wide as the inner
The absorption was estimated because the number of LAG. Therefore, the mature North Pacific loggerhead turtle
We believe that an average age between 37-43 years old. The eastern and central Japan near the North PacificAge back into the sea to be age 18-31 is estimated from the Regression Growth protocol
And, compared with the age of maturity, from maturity until around Japan to rejoin the need 6-25 years
39
It is suggested to be.
Now however, Correction Factor protocol and 61-year-old too immature individuals mature individuals in the 21year-old
Must be noted also that has been discovered. While this is mature individuals 21 years old,
Mature individuals are not 61 years of age, indicating that a very wide range of mature age
That. In addition, SCL between the ages and had no clear correlation, SCL 701 mm 61 but
An elderly population and immature compared to other individuals with a relatively young age of SCL 866 mmfrom any other individuals 29 years old
Mature individuals were also (Figure 5-6). In other words, the small population of mature Not necessarily young,
large
Mature individuals is not necessarily an age was not.
So to mature and age Kinoe Takeshi directly related to the lifetime number of individuals leave their offspring, a
Is an important factor in considering the Kaumigame reproductive strategies. For example, the female lays fromone spawning season

Length of the ovary and instep of the correlation was not recognized, the number of eggs per nest is often a muchlarger population(Frazer and Richardson, 1986). Laying eggs in the spawning season can total a larger Sono Tame Kinoe Takeshi
A few more. The lifetime opportunity for the younger breeding age is considered to be more mature.
However, once mature, but it takes years to increase rather than remain Kinoe Takeshi immature.
It is premature if the growth rate, but SCL is 800-900 mm 11.0 mm / year, but some (Table
5-1), growth rate and mature 2.5 mm / year (Hatase et al., 2004) is due to the slow.
Therefore, increasing the body prior to the maturity necessary to increase the number of egg production per
spawning season 1
On the other hand is required, the immature period spent in order to increase the body away to miss theopportunity to breed.
40
While a young adult can increase the chances of reproductive life, and not the number of eggs per spawning 尐 1
Ru. I leave more offspring lifetime reproductive strategies that Neither mortality and hatchability of eggs
And also affected. Come more opportunities for breeding Once in a lifetime low mortality, spawning one
Lays eggs in the expected value of total lifetime number of eggs laid per season but a lot higher the higher the
mortality rate
Higher expected number of spawning nests of spawning soon start to have better lives.However, only this book
Explain that individuals have been identified in adult and elderly population remains small, young and mature
towering study
Not. The difference is in the growth rate, and that due to the density and biomass of prey organisms
Possible. This is a rich prey in captivity as early as 6-7 years to mature and be(Caldwell, 1962; Uchida, 1967), most mature individuals of this study was 尐 year and it was 21 years old, the foodUnderstood that a significant impact on growth rate and age of sexual maturity amount.In addition, the spawning
population feeding
Depends on the individual areas, suggesting that the instep of individuals affected the length of prey species andthe amount of spawning
Are (Hatase et al., 2002c). Thus, prey density and biomass of marine food consumption growth rate
Influenced by important because it affects the reproductive strategy Kinoe Takeshi sexual maturity age and thus tocomplete
There. However, as was revealed in this study, tens of turtles before sexual maturity
Took years, 22-61 years old in the North Pacific, the average age at which sexual maturity at age 37-43. This world
Long years of life if necessary for replacement cost, Megumi Hiroshi before you begin to breed from birth to sexual
maturity
Can change the environment and breeding ground for sea Iku Shigeru could happen is that. In addition, Akaumiga
Spawning beaches and the media has become a dynamic and unstable environment.Therefore, the data begin tobreed
41
Iku Shigeru disperse the waters and the timing, and risks to be dispersed to environmental changes
Inferred. As a result, there are now a variety of reproductive strategies among the population, a variety of
traditional
殖戦 allows for substantially to respond to environmental change, species turtles (Caretta) or appeared early
Pliocene
From 4.5-5 million years (Dodd and Morgan, 1992), we also support environmental changes such as glacial
Probably a.
42
Kind of sea turtle life history Chapter 6 - Growth and habitat 6-1. Overview of the life history of sea turtle species
One kind of turtle eggs are laid per nest several hundred dozens in a sand beach, approximately 50-80
Hatch day (Mrosovsky and Yntema, 1982; Ackerman, 1997). Afflicted with the egg-laying to hatching
Ru period varies with temperature in the sand, Nakasuna faster the higher the temperature (Mrosovsky and
Yntema, 1982; Ackerman, 1997). We also determined by the degree of sand in the incubation Atsushi Naka,

females at high temperatures
And males at low temperature, the ratio of 1:1 as the critical temperature is around 29 degrees (Ackerman,
1997). C
After hatching the spiderlings hatch Migame kind in the sand, across the sea to the table coming out of the sand(Carr, 1986;
Dodd, 1988), offshore areas off the coast moves very active period, called the foreleg Frenzy
To move to (Wyneken and Solomon, 1992). This is a small body size during the period - a large
Greater risk of being attacked by other fish and seabirds (Witham, 1974; Stancyk, 1982; Witherington
and Salmon, 1992; Gyuris, 1994; Vose and Shank, 2003), and a depth of 10m or less, especially coastal
Is because they often prey on the leaf edge (Witherington and Salmon, 1992;
Pilcher et al., 2000; Whelan and Wyneken, 2007). Juveniles hatching yolk in the body after entering the sea
Absorbed, and scattered into the ocean while we moved to the juvenile stage of their life history, Hirataumi
Turtles (Natator depressus) is highly coast only, leave the spiderlings hatch in coastal (Bolten,2003). Feeding and breeding ground waters are most different, sexual maturity is reached after a breeding season
and feeding
43
Migration to breeding areas continue to feed from the sea (Limpus, 1985; Sakamoto et al., 1997; Limpus
and Limpus; 2001; Hatase et al., 2002b; Schroeder et al., 2003). Mature females spawning season 1
The spawn multiple times, you can not spawn every year usually with an average of Lepidochelys(Lepidochelys) per year in 1-2, 2-3 in the other species of sea turtles return to lay eggs every year (Miller,
1997). Males are also participating in the annual reproductive and sexual maturation is complete (Wibbels et al.,1990;
Limpus, 1993), has also been confirmed inactive sexually mature individuals during the breeding season (Blanvillain
et al.,
2008), depending on the region and individuals may breed every other year to participate in 2 (Miller, 1997).
6-2. Loggerhead turtle (Caretta caretta) Life history
6-2-1. Spawning frequency
The turtles are spawning in temperate zones and only sea turtle species (Pritchard, 1997). Akaumiga
Media as a major spawning grounds in the North Pacific in Japan, Australia and South Pacific Nyugini
Software, United States East Coast in the North Atlantic, South Atlantic, Brazil, Greece and the Mediterranean Sea
Turkey, Libya, Cyprus, has been known in the Indian Ocean Oman (Bolten andWitherington, 2003). The spawning grounds of the Pacific and Atlantic waters toward the warm sand near the highlatitude
Are concentrated on the beach, hatchlings are believed to hatch they move to the warm waters of this latituderide
Ru (Bolten, 2003).
44
6-2-2. Distributed escape hatch
Juveniles hatched in the nest and move to the same spawning ground beneath a group, to sense a drop in surface
temperature,
During the night to escape to the surface in the evening group Hisashi Tooru (Miller, 1997). Then you into frenzy
Hatched spiderlings came swimming through the ocean and other coastal areas to sea level I sargassum
Snuggle up to those floating (Witherington, 2002), the power of both forelimbs on the carapace as a staticWill increase the time we are floating (Witherington, 1995) (Figure 6-1). This is Frenzy
The force of the waves when rushing 抗I sand, it is important to swim out as soon as possible coastal, Whereas the eyes of sensitive organisms to respond to the things that move, riding the ocean currents
Or so later would become so important that you find the hidden predator.
Swimming in the ocean after leaving, juvenile body absorbed the yolk of the Kuroshio in the North Pacific, theNorth Atlantic Meki
Ride and high-latitude warm Gulf Stream waters flow toward Mexico (Carr, 1986; Carr, 1987; Bowenet al., 1995; Witherington, 2002). Then the North Pacific and North Atlantic Current manager
Ilo (North Atlantic Gyre) and oceans that riding a large migration flows, called(Bolten et al., 1998; Bowen et al., 1995; Lohmann et al., 2001) (Figure 6-2). At this time Akaumi

Juvenile turtles have been washed away, not only does the ocean current direction of the geomagnetic field while
taking advantage of ocean currents
That is going to know anything about the direction to go themselves (Lohmann et al., 2001;
Lohmann and Lohmann, 2006).
45
6-2-3. And growth of juvenile habitat
Hatchlings dispersed by ocean currents to the use of the North Pacific off the coast of the Hawaiian Islands, theAzores in the North Atlantic
Kinoe Takeshi songs off the coast of Madeira Island 200-600 mm known that individuals inhabit
Ru (Bolten et al., 1993; Wetherall et al., 1993; Bjorndal et al., 2000; Polovina et al., 2004;
Kobayashi et al., 2008). He returned back to the spawning grounds around the stage before sexual maturity,
breeding grounds
Rejoins the coastal areas near the (Musick and Limpus, 1997; Bolten, 2003; Chapter 4.)
However, there is also shifted to individuals from coastal habitats before returning to breeding grounds in the
North Pacific
The coast of Baja California Tadashi Kinoe length of 500-700 mm 200-300 mm is also focusing on individual plants
Observed (Gardner and Nichols, 2001). This area is rich upwelling rush of the world's leading
And sea turtles hot spots (hot spot) is one of the place called(Peckham et al., 2007). We found no mature individuals prior to the beginning of sexual maturation
From east to west across the Pacific Ocean near Japan is moving to the breeding grounds (Chapter 4).
The growth rate was fastest around the time of year juveniles hatched loggerhead turtles in the Pacific, 50.9 mm /year
(Director Tadashi Kinoe), Mediterranean 118 mm / year (Kinoe Takeshi songs) have been reported (Zug et al.,
1995; Casale et al.,2009b). Even faster in captivity, the turtles head 565 about a year and a half UPPER-mm after hatching
Sometimes growth (Swingle et al., 1993). The units to be 300-500 mm Kinoe Takeshi, the growth rate
Populations in the North Pacific off the coast of the Hawaiian Islands 34.0-38.9 mm / year (Zug et al., 1995),
Oonishi Kita
The population in the Chesapeake Bay Science 29.6 mm / year or 52.8 mm / year (Klinger and46
Musick, 1995), at Georgia 30-40 mm / year (Parham and Zug, 1997), Nosukyarora
The INA 15.8 mm / year (Braun-McNeill et al., 2008), in Florida, 73.6 mm / year (Mendonca,1981), BS 157 mm / year (Bjorndal and Bolten, 1988b), 25 populations of the Mediterranean
mm / year and 36.4 mm / year (Casale et al., 2009a; Casale et al., 2009b) becomes, among populations
Differences can be seen not only in the population.
6-2-4. Readmission to the breeding grounds
Kinoe Takeshi to rejoin the nearby coastal waters are breeding grounds vary even within the same population, the
The North Pacific Kinoe Osa, South Pacific, the head respectively in the Atlantic Tadashi Kinoe 560-750 mm, 700
songs about Kinoe Takeshi mm,
Kinoe Takeshi song is about 500-600 mm (Bjorndal et al., 2000; Limpus and Limpus, 2003; Chapter 4)
In this study, the North Pacific in the age 18-33 years was estimated to be (Chapter 5).
Individuals rejoin the coastal areas we are feeding in open water (Sakamoto et al., 1997;
Hatase et al., 2002b; Hatase et al., 2002c; Hatase et al., 2007; others Nakashima, 2007), and the pelagic zone
The process of progressing sexual maturation while migrating to shallow waters (Chapter 4).
6-2-5. Sexual maturity
In the beginning of the maturation process of individual species is not unlike the external morphology of male andfemale turtles were not observed outside
To determine the gender of the form can not. In females, morphological changes can be seen to mature and47
Error-free, the greater the strength of the male foreleg claws and tail extends significantly to the development of
testicular maturation begins the
Please curved (Hughes, 1974; Kamezaki, 2003; Chapter 3). Sexual maturity from the edge of these features will
For males, but Tta may be able to determine from the external morphology, allowed determination of allindividuals
Of a function, in the North Pacific loggerhead turtles Tadashi Kinoe 800 mm in length over time (Chapter 3).
The male turtles from the start of the tail extension of about 100-150 mm greater degree Kinoe Takeshi
Maturation was completed around (Casale et al., 2005; Chapter 3), and they mature females from morphologicalNot know whether. When the external forms of sex discrimination does not attach, if you are mature
Can not determine if the observations are valid forms of gonads and reproductive tract.Individuals have died
But it is possible to directly observe the autopsy if the gonads, the size of individuals living
How to observe the gonads into the abdominal cavity with a thin endoscope (Wood et al., 1983) it is used
U now (Figure 6-3). Development of the egg by a non-invasive ultrasound refrained from laying eggs if the female
You can also observe the degree of.
Slower growth after sexual maturation, and mature individuals are not sexually mature individual instep similar inchief
The growth rate in the North Pacific is 11.0 mm / year from 2.5 mm / year (Hatase et al., 2004; Chapter 5)
The South Pacific is 8.3 mm / year from 1.2 mm / year falls to (Limpus, 1985).
Kinoe Takeshi mature individuals in the population of spawning is measured primarily from relatively easy tocapture and measure
And the length of the Atlantic and Indian Ocean respectively, Tadashi Kinoe 877-1053 mm ,876-936 mm greatly,
underground654-794 mm and the smallest of the sea (Dodd, 1988; Tiwari and Bjorndal, 2000; Kamezaki,
482003). Error-free, the greater the strength of the male foreleg claws and tail extends significantly to thedevelopment of testicular maturation begins the
Please curved (Hughes, 1974; Kamezaki, 2003; Chapter 3). Sexual maturity from the edge of these features will
For males, but Tta may be able to determine from the external morphology, allowed determination of all
individuals
Of a function, in the North Pacific loggerhead turtles Tadashi Kinoe 800 mm in length over time (Chapter 3).
The male turtles from the start of the tail extension of about 100-150 mm greater degree Kinoe Takeshi
Maturation was completed around (Casale et al., 2005; Chapter 3), and they mature females from morphologicalNot know whether. When the external forms of sex discrimination does not attach, if you are mature
Can not determine if the observations are valid forms of gonads and reproductive tract.Individuals have died
But it is possible to directly observe the autopsy if the gonads, the size of individuals living
How to observe the gonads into the abdominal cavity with a thin endoscope (Wood et al., 1983) it is used
U now (Figure 6-3). Development of the egg by a non-invasive ultrasound refrained from laying eggs if the female
You can also observe the degree of.
Slower growth after sexual maturation, and mature individuals are not sexually mature individual instep similar inchief
The growth rate in the North Pacific is 11.0 mm / year from 2.5 mm / year (Hatase et al., 2004; Chapter 5)
The South Pacific is 8.3 mm / year from 1.2 mm / year falls to (Limpus, 1985).
Kinoe Takeshi mature individuals in the population of spawning is measured primarily from relatively easy tocapture and measure
And the length of the Atlantic and Indian Ocean respectively, Tadashi Kinoe 877-1053 mm ,876-936 mm greatly,
underground654-794 mm and the smallest of the sea (Dodd, 1988; Tiwari and Bjorndal, 2000; Kamezaki,
482003). 848 Pacific loggerhead turtle in northern and southern hemispheres, respectively Tadashi Kinoe 長 mm, 887
mm and inside
Between the size of an (Limpus, 1985; other Kamezaki, 1995). Large and small North Atlantic Kinoe Takeshi sexual
maturity
Mediterranean in the Strait of Gibraltar is connected, some individuals traveling between the Mediterranean andNorth Atlantic
Have (Carreras et al., 2006), spawning female mitochondrial DNA haplotype frequencies
Is different (Encalada et al., 1998; Bowen et al., 1993; Bowen et al., 2004). This site
Produced in the North Atlantic loggerhead turtle was caught in Nakaumi juvenile, focused on coastal areas ofnorthern Africa
For you, from the eastern Mediterranean loggerhead turtles in the Mediterranean coast of western Europe spread
Concentrated in the region, probably because that is somewhat geographically isolated (Bowen et al., 1993;
Bowen et al., 2004; Carreras et al., 2006). But has also been observed in the same haplotype(Encalada et al., 1998), some genetic exchange has happened can not be denied that sexual maturity
Approximately 200-250 mm Kinoe Takeshi is interesting that different.
Age of sexual maturity in captivity have been reported very early in the 6-year and mature in 7 (Caldwell,1962; Uchida, 1967). However, the growth of species such as sea turtles by nutritional conditions and ambient
temperature
Because significant changes in growth rate and age at maturity, years longer than the wild populations are
breeding population
Over mature (Frazer, 1982). Estimated age at sexual maturity is the wild turtles in the north37-43 years in the Pacific (Chapter 5), the South Pacific over the age of 30 (Limpus, 1979) or 35 years old(Frazer et al., 1994), 16-28 years old in the Mediterranean (Casale et al., 2009a) and is, in the North Atlantic
10-15 years (Mendonca, 1981), or 13-15 years (Zug et al, 1986) ,22-year-old 25 (Klinger and49
Musick, 1995) ,30-year-old 47 (Frazer and Ehrhart, 1985) ,20-year-old 63 (Parham and Zug, 1997)
And wide. The mature individuals of known age in the wild exactly, giving a biological marker in the South PacificAnd for 29 years after the first spawning or hatching juveniles (C. Limpus, unpublished data), early sexual
maturation
Has been suggested that individuals can take 30 years.
6-3. Comparison with other sea turtle species life history
6-3-1. Ecology of juvenile period
Spiderlings hatch and swim out into the ocean to go after entering the sea turtles from the beach, except Hirata
Is common (Bolten, 2003). But then once dispersed into the ocean, including the loggerhead turtle,
Green turtle (Chelonia mydas), hawksbill (Eretmochelys imbricata), Kenpuhimeumiga
Media (Lepidochelys kempii), Western Pacific and Australia Ridley(Lepidochelys olivacea) on the occurrence of the juvenile to the coastal ocean, and Leatherback(Dermochelys coriacea) and Eastern Pacific ridley times spawning during the breeding season to matureindividuals
Except that does not appear to play little coastal (Bolten, 2003) (Figure 6-4). In addition, the coastal habitats andAmong the species utilized, from loggerhead sea turtle green turtle, hawksbill turtle from the green turtle and Ke
Kinoe Takeshi appear more Npuhimeumigame coast has been known that small (Musick and
Limpus, 1997), Party A loggerhead sea turtle as described above length of 500-700 mm for the occurrence ofcoastalTo, in the North Atlantic green turtle is 200-250 mm, in the North Pacific and South Pacific 300-400 mm (Balazs,
50
1980; Bjorndal and Bolten, 1988a; Limpus, 1993; Limpus et al., 1994), Hawksbill Hokudai
In the western Caribbean Kinoe Takeshi 200-250 mm, 350 mm over the Indian and Pacific Kinoe Takeshi (Kamezaki
andHirate, 1992; Boulon, 1994), also little changed Hawksbill Kemp 250-350 mm
Occurring in the coastal (Ogren, 1989). Hawksbill and age appear in about 1-3 years old coast, Kenpuhi
Has been estimated at more than two years in Meumigame (Kamezaki and Hirate, 1992; Boulon, 1994; Zuget al., 1997), younger than 18-33 years of loggerhead turtle (Chapter 5).
To subscribe to the coast is thought to be associated with specific types of food that appeared after the coast,
seaweed and
The green turtle 専食 seaweed (Mortimer, 1982) and sponges 専食 the hawksbill (Mortimer,
1982; Meylan, 1988; Bjorndal, 1997), 50 m water depth in shallow Kenpuhimeumiga the crab 専食
In the media (Shaver, 1991), 200-400 mm is probably limited Kinoe Takeshi's creatures have become a predator
Would transfer to coastal habitats because. Meanwhile, the loggerhead turtle in the coastal crustaceans andsnails,But to feed on bottom invertebrates such as bivalves of (Mortimer, 1982; Dodd, 1988; Bjorndal,

1997), feeding on algae that flow as a time of planktonic animals and even subadult and adult individuals
Also (Dodd, 1988; Bjorndal, 1997), may be opportunistic 専食 low (other Iwamoto, 2005a; Iwamoto
Others, 2006). The reason appears to Kinoe Takeshi large coastal species than the coastal biological 専食 This also
One might.
As a feature of juvenile loggerhead turtles during, at least in the North Pacific and the South Pacific, North Atlantic
Orbit to be raised to the oceans and ocean currents used in (Bowen et al., 1995;
51
Bolten et al., 1998; Boyle et al., 2009). Other species of sea turtles in these eco-known you
Spite, or developed and how the ocean orbiting the ecological significance of juvenile loggerhead turtles areinterested in
Despite the deep is not clear at present.
6-3-2. Sexual maturity
Kinoe Takeshi's largest leatherback turtle populations spawning, green sea turtles, Caretta caretta, or Hiratau
Migame, hawksbill, Kemp, or follow the order of Olive Ridley (Zug and Parham,
1996; Hirth, 1997; Kamezaki, 2003; Limpus, 2007) (Table 6-1). Thus, the loggerhead turtle comparison
The kind of large sea turtles say. Adult male sex Kinoe Takeshi green turtle and loggerhead turtle
Has been examined, the turtles will make no difference to the length of male and female UPPER (Kamezaki,
2003; Casale et al., 2005; Chapter 2), the males are smaller than in female green turtles (Godley et al.,2002). In addition, no differences in male and female turtles also growth rate, age, sexual maturity is not evengender (Article
Chapter 5.) For information on other species of sea turtles instep length difference Since there are mature males
and females
Therefore, that are often sexual maturity Kinoe Takeshi instep length spawning population.
The green sea turtles as well as the length of spawning individuals instep length 990-1118 mm in the Atlantic
Tadashi Kinoe
Significantly, in the Mediterranean and the small 920-960 mm Kinoe Takeshi songs (Hirth, 1997). However, thesmallest
Ino Tadashi Kinoe is 814-829 mm in length and eastern Pacific populations (Hirth, 1997), this population clock
B Sea Turtle (Chelonia mydas agassizzi), also called, is recognized as a subspecies of green turtle
52
The (Bowen et al., 1992) (Figure 6-5). Kinoe Takeshi loggerhead turtles and green turtles are sexually mature, thickeast
Except for the green turtle population Taira Hiroshi large in the Atlantic and Indian Ocean, Mediterranean and low
pointsPass. This shows that acts of sexual maturation Kinoe Takeshi geographical factors.Sono Kaname
Once factors clearly leads to understanding the physiological mechanism is necessary for sexual maturity, toprotect the effectivenessThat may provide important information, 見Ataranai leading hypothesis at present.
The Department of turtles is a tendency of higher age at maturity Kinoe Takeshi higher maturity. Caretta caretta
The large green sea turtles from Kinoe Takeshi sexual maturity is age and maturity of over 30 (Zug et al.,2002), and the difference is not that of turtles. The hawksbill turtle is approximately subsequently
20-30 years old, Olive Ridley and Kemp are each around 13 years to mature at the age of 11-16
It is estimated that (Zug et al., 1997; Zug et al., 2006). Meanwhile, the growth of the leatherback turtle leatherback
turtle department
Despite the largest Kinoe Takeshi carefully, as early as 5-6 years, approximately 13-14 years to mature (Zug andParham, 1996). Age of sexual maturity and ridley Leatherback Ken smallest turtles in the family
Puhimeumigame is similar to the mature age of about half the green turtle and loggerhead turtle
Will be. Leatherback sea turtles which Cheloniidae than the growth rate is significantly faster
Is for length, instep of approximately 60 mm at hatching, but even in the wild 350 mm per year to grow about
about
In the year 1000 song Kinoe Takeshi reached 4 mm (Zug and Parham, 1996). Such rapid leatherback turtle
Growth is thought to be related to mechanisms specific area of cartilage. Leatherback turtle in the cartilage

To encourage the growth of cartilage and capillaries has been growing at the base of the rapid absorption andcartilage calcification
53
Go fast (Rhodin et al., 1996). Such a mechanism, including the loggerhead turtle, the turtle family
Are evident.
54
Chapter 7 General discussion
7-1. Conservation importance in Japanese waters
North Pacific loggerhead turtle (Caretta caretta) after hatching in the sandy beaches of Japan, the Kuroshio andNorth PacificWidely distributed through the eastern Pacific ocean using (Bowen et al., 1995; Uchida and Teruya,
1991; Kobayashi et al., 2008), Tadashi Kinoe 長 Standard (SCL) at 560-750 mm, with 18-33 years of age
Rejoins the coastal waters of Japan at the time of his birth (Chapter 4; Chapter 5). Then Japanese waters for at
Sexual maturity while in progress, half of them participate in SCL 821 mm ,37-breed sexually mature at age 43
completed
It begins with the life history (Chapter 2; Chapter 3; Chapter 4; Chapter 5). Life history in this account
Migame has been exposed to various threats, in order to conserve this species is one that gives each threat
Need to understand the impact on populations.
First, the change in population size or population, and is represented by several kinds of sea turtles nest egg
production
The (Meylan, 1982). The number of spawning nests is roughly represents the number of spawning populations,spawning in the year
May be a relatively accurate estimate of the adult female population. In Japan, many organizations and individuals
Which are investigating around on the beach, the result is the Japanese Sea Turtle Conference (Japan Nonprofit
Sponsored by the Sea Turtle Association) has been compiled in the year.Approximately 50 of the spawning nests inthe late 20th century
Fell by 50-90 percent annually (Kamezaki et al., 2003), since 1997, you turned on the rise
Ri (Sea Turtle Association of Japan, 2009), in the meantime seems to have survived the extinction.
However, green turtles and coastal fisheries bycatch dead turtles (Chelonia mydas)Has become a major threat (Ishihara and Kamezaki, 2010), and after the spawning beaches
Such signs are not stem the loss of retirement (Matsuzawa, 2009; Sea Turtle Association of Japan, 2010). North
Pacific
55
For the conservation of turtles, as well as Japan, Hawaii extends offshore tuna marlin
Have also been conducted in coastal fisheries and fishing rope Baja California (Peckham et al., 2009;
Simonds, 2009). The coastal population of Japan are composed of 77.7% subadult, and juvenile madeLarger than the population Kinoe Osa Peninsula is off Hawaii and California (Wetherall, 1993;
Gardner and Nichols, 2001; Chapter 4) and high reproductive value indicating the number of expected offspring ina lifetime Leave.
Therefore, the contribution to the population per plant was relatively high increase of population in the Sea ofJapan
The impact on the overall population decline is significant.
However, the loggerhead turtle conservation policies have been implemented in Japan to protect the spawning
grounds of public limited almost
Has been (Matsuzawa, 2009), conservation policies are not going to subadult. Akaumi the coast excursion
As regulations to protect the turtles, Area Fishery Adjustment Committee and fishing regulations and coordination
Species Preservation Law
While passing is prohibited in principle, directed by Riya Yuzuru Sales of sea turtles, these
The regulatory effect of reducing the death accidental bycatch of fishing is not occurring.The loggerhead turtle
near JapanThe majority, to protect the reproductive value Ino Takashi subadult individual, following spawning, the accountsof the North PacificBe very effective on some measures to conserve sea turtles is no doubt.

7-2. Loggerhead turtle mortality in the Sea of JapanTo promote effective conservation activities in Japanese waters, in order to make a correct prediction of the futurenow
It is important to understand the situation of the population of loggerhead turtles inhabiting the Japanese waters,in this study
Sexual maturity and knowledge of population structure obtained is useful. We also predict changes in population
Population is necessary for the disappearance and death to the population of newly born juveniles hatched,
Hatching juvenile population, but for which a valid indicator of the number of spawning nests each year, thenumber of dead individuals
56
There is no information about any. Then, using the results of this study, the mortality rate estimated at aroundJapan
It was fixed.
To estimate the mortality in the Sea of Japan, based on distributions of SCL 50 mm instep of your Chapter 4
Together with a number of individuals, rate of population change using annual growth rate in Chapter 5 (X)obtained (Equation 7-1,
Table 5-1).
Xi = (Ni +1 / Ni - 1) / (50 / gi) 7-1 expression
X: Annual rate of change, N: number of individuals, g: growth rate (mm / year)
Annual rate of change of X is equal to the difference in mortality rates and readmission into Japanese waters near
Japan, X> 0, then watch
Readmission rate or the second, X <0 then represents the apparent mortality. The main end of readmission SCL
750 mmMore (Chapter 2) at the rank of the X <0, the apparent mortality, SCL 750-800, 800-850, 850-900,
900-950, 950-1000 mm respectively in 11.1, 10.2, 15.6, 18.2, 20.8% were.
As the mortality rate is as large as the population increased, the mortality rate is generally the larger the
population
Reduced (National Research Council., 1990). Factors include the increased mortality of subadult stage
Two points were considered overvalued growth rate of readmission in adult and continuing. In the former SCL 750
mm are also present in the trees while reducing the rate from becoming or re-admission, readmission rate
The mortality rate was lower was considered as the apparent relatively high class sizes small. The latter
In Chapter 5, the growth rate is determined by those of subadult also significantly reduce the growth rate of adultApplied for, and a high mortality rate was estimated by the growth rate was overvalued
Considered. Thus, the apparent mortality rate is underestimated subadult size classes, and support for adult57
Was thought to have been overestimated in Izukurasu. Underestimate the size of adult mortality in sub-class
Value that had been the practice of subadult mortality is at least 11.1% of SCL 750-800 mm
Seemed to be over. The Toi has been estimated that over-size classes of adult mortality
That U is the actual death rate of adult SCL 950-1000 mm and 20.8% lower than inferred.
And mortality rates differ dramatically between the adult and subadult is hard to believe, so red around Japan
11.1-20.8% annual mortality rate of turtles was suggested that there was between them.
Then, how much percentage of the breeding turtles around Japan rejoined the annual mortality from thisCan calculate how can you survive until you join. Caretta caretta around Japan are 18-31 years old
For readmission, the age of sexual maturity is age 37-43, to participate in breeding until 6-25 years of near-JapanAnd spend in the ocean (Chapter 5), 11.1-20.8% mortality per year between them, then rejoined pieces
50.6-99.7% of the body suggests that died before maturation. Individuals die before sexual maturity is
automatically
These offspring can not be contributing to the maintenance of future population is not.Therefore,
Protection of nests and lay eggs as well as spawning population, accounts can reduce the mortality of immatureindividuals
Is important for the conservation of Migame.
7-3. Threats to the North Pacific loggerhead turtle
Threat organisms as well as events and individuals will continue to grow and change.Mortality in Japanese waters

Can affect the breeding population is indicated by 7-2 in the near future, you deploy a more effective conservation
The projector been any threats at every stage of life history, or that the physical impact on how muchConstrued, it is important that we remove a major threat from the impact. So, from here
Through life history, which examines threats to the North Pacific loggerhead turtles.
58
7-3-1. Threats in sandPredators targeting the spawning population of green sea turtles and green sea turtles in Costa Rica
Furenchigiana,
Olive Ridley (Lepidochelys olivacea), Leatherback (Dermochelys coreacea) Jaguar attack(Panthera onca) and have (Sehoe et al., 2007; Harrison et al., 2008), total egg production in Japan
Predator body aimed not known. Food after the conclusion of World War II had landed on an individual humanbeing
The charges were also used as a community, is about to be consumed in the region, and now they can see it
Not (Kamezaki Matsuzawa, personal communication). After laying eggs hanged from the early 1970s after WorldWar II
Miyazaki and Yakushima Island in Kagoshima Prefecture, but most of them had been collecting eggs, held by a local
research organization
In the late 1970s by the enactment of the Protection Act and research activities and the real protection is to use it
for loggerhead sea turtle eggs
In no (Omuta 2002; Matsuzawa, 2009).
Then, after laying eggs and hatching juvenile sand crab (Ocypode spp.), And wild dogs, pigs and wild boar (Susspp.),
Raccoon (Procyon lotor) are predators and various other animals (Stancyk, 1982), feeding it
Call. In many parts of Japan and the Ryukyu raccoon, Akamata, raccoons, etc. I
Predation has occurred Ru (Mori et al., 1999, other Matsuzawa, 2010; Sea Turtle Association of Japan, unpublisheddata).
Degree of damage by sand, unlike almost any subject can be victimized beach spawning nests all
Some fall prey to harm beaches (Matsuzawa, personal communication). Of the damage on the beach, do not get
dug up the nest egg production
The individuals and organizations to take measures to protect local Uni work has been achieved to minimize thedamage.
Japan has one of the beach erosion in the most serious threat for North Pacific loggerhead sea turtle (turtle
Kawasaki, 2003; Matsuzawa, 2009). In addition to the reduction of beach erosion in the supply of sand and riversand collected by the dam
To be caused by a change in the alluvial and coastal port facilities and detached breakwaters (Matsuzawa,2009). Its
59
Results of the turtles can lay eggs, they are under water laying eggs even during the storm or
Sand has been increasing, and for long-term threat to the North Pacific loggerhead turtles.
After entering the sea from the beach out of the water depth and reef edge, especially in the 10m or less - a large
fish and seabirds
And the prey (Witherington and Salmon, 1992; Pilcher et al., 2000; Whelan andWyneken, 2007). Hatcheries in the vicinity of such a high density of spawning nest predation rates, especially in the
coastalIncreases (Glenn, 1996; Wyneken and Salmon, 1996; Pilcher et al., 2000). Into the sea
Proportion of juveniles after hatching is through the coastal areas is not known, and the rustle of the nest
spawning aggregation
Under the influence of artificial hatching and stocking of juvenile frenzy is past the stage of survival to the ocean
until
Degradation is a concern. Advanced spawning nests on the beach erosion at risk from the far side of thesubmerged sandPorting or hatcheries that are considered to be unavoidable treatment, removal of juvenile hatch
When 近付Kerubeki think out under natural conditions as much as possible.

7-3-2. Dispersed into the ocean threat to juvenile
Predation mortality of juvenile predators and distributed to the main ocean, from the difficulty of the check, I
Please do not understand that, in the pelagic sharks, and perhaps - and imagine that a large predator fish
Be. The Killer Whale (Orcinus orca) has been reported to attack leatherback turtle (Caldwell andCaldwell, 1969; Pitman and Dutton, 2004), Fisheries Research Development Agency
Deep-sea research in Nature magazine and a 2006 photo of killer whale attack Topics Loggerhead turtle
Since being introduced truly one of Orca's main predators in the open sea turtles
Possible. Turtles from the ocean spread in the North Pacific SCL 56-75 cm, South Pacific
70 songs in Kinoe Takeshi cm, 46-64 cm Kinoe Takeshi songs in the North Atlantic ocean to grow up (Bjorndal
60
et al., 2000; Limpus and Limpus, 2003; Chapter 4), and will be limited predator grows
Possible.
Juvenile loggerhead turtle populations are identified in the open ocean is primarily bycatch in pelagic longline(Boltenet al., 1994; Bolten et al., 2004; Lewison et al., 2004; Pinedo and Polacheck, 2004), this
Bycatch has become a threat itself (Gilman et al., 2007; FAO, 2009). Currently, needle-shaped window
You can change that kind Migame swallow, swallow every bait or squid as bait 食Itsuita
Sabah and modify them, such as deep or deeper than the gear set up on the turtle species, mixed
Which help reduce mortality and the number caught (FAO, 2009). The large-scale flow has been operating on thehigh seas
Had been the juvenile loggerhead turtle bycatch and also net (Wetherall et al., 1993), by United Nations
resolutions
Operation since 1992, has been banned.
7-3-3. The threat of coastal
The main predators are sharks in the large coastal, among them tiger shark (Galeocerdo cuvier)Turtle species are especially fond of prey (Stancyk, 1982; Fergusson et al., 2000;
Simpfendorfer et al., 2001). However, a large population of sharks is said to be in decline
And (Musick et al., 1993), and a tiger shark is getting better though (Baum and Blanchard,2010), a key factor in reducing populations of loggerhead turtle predation by large sharks and if
Will not.
One of the factors kind of artificial sea turtle mortality in recent years, impact on coastal fisheries species of sea
turtlesHas been concern worldwide (Gilman et al., 2010), coastal fishing waters in Japan, Caretta caretta
Is considered a major mortality factor (Ishihara and Kamezaki, 2010). However, a coastal fisheries
61
The size of the concrete impact Kaumigame is not clear, moreover, said coastal fishing
Scale fishing and also offers a variety of operating time also, which are by-catch by fishing in any season in any
regionWhat is also clear that there is no death.
7-4. Conservation measures required by the Sea of Japan
Yakushima, Kagoshima Prefecture, Miyazaki Prefecture, and about 30 years to be gone a lot of egg collection
Since 1997-1998, the number of nests has increased egg production (Sea Turtle Association of Japan, 2010). These
two regions,
More than half of the total number of spawning nests only for this important North Pacific loggerhead turtle
The spawning grounds (Sea Turtle Association of Japan, 2010). North Pacific loggerhead turtle population in theearly age of 22
Result has been that mature (Chapter 5), the number of nests increased egg production from egg collecting is
prohibited
Coincide with the period. ,1997-Spawning nest so many times in the Kyushu district, especially noticeable since1998
The protective effect of egg recovery in the 1970s is considered to be significant, protection of eggs outstandingachievements
Say that.

However, the deterioration of spawning grounds is advanced by the erosion of sandy beaches further from thestandpoint of disaster prevention
It is important to focus on avoiding erosion.
Also, after re-joining ,50.6 -99 .7% of Japanese waters is also a reason to mature individuals died before
Death due to coastal fisheries bycatch measures are not going Ru. The future of coastal fishing sea turtles as soon
as possible
To understand the impact of more species, bycatch mortality of turtles and other turtle species
It is desirable to reduce. The cause of death not only by the turtles and fisheries
Itame, including bycatch mortality factors other than freezing to death and poaching ship collision predators suchas hunger, disease
Also necessary to assess the impact of each well. My main
University of Tokyo School of Agricultural and Life Sciences Division Kameari の Visiting Associate Professor Naoki
Kawasaki に は し carry out this study を, に Papers
ま と め る に あ ta ri guidance often 々 と ご sincerely humble い な の Royal Review article を っ ta thanks.さら に, Kobe City this year wa
Bang Hai Suma Aquarium Park の に も became principal of さ れ, for example, ま に し て Royal on how busy
most ma ru, the night guiding い ま で ご ta
だ い ta. Ku ku thick application of deep gratitude on the げ し ま す.
University of Tokyo School of Agricultural and Life Sciences Research Office of the waters の Zuoye Guang Yan
preservation science professor at Tokyo Big Wild Ming DS
Honorary Professor, Research Associate Professor Okamoto, Mr. Shigeru Aoki に は を line of remote で う に 様々 な あ ta ri cheap 図 を って い と と も く ta da ni, wo give useful guidance な ご っ ta wa. Ma ta, kind of 様 々 な 々 ご を お confused
mind hanging with ご け
し が ta, Hiroshima heart で い て め ended by け い い ta da ta. Thank yo ri ku heart deep meaning の を table
します.
This study used に い ta ga ア カ ウ メ ミ の は specimen agreement Japan will ウ メ ミ の ga Nakamura's yourstudents, thousands of Ami Yamazaki さ Greeceん, Eguchi Sakae for s, it should be s Kusakabe, Tianzhong Yu-hui's, Secretary's Qi Huang Teng, Zhu sound Abe san,Matsumoto Mina san,Sen Meng san, Sato Granville's, Mizuno's generals, see Meng's in there, Fu Jia Hong Huang's, the former U.S.
security sub-san, University of Tokyo
School of Science Research and the Japanese waters, preservation of ウ ミ の ga メ agreement will rock the Taiji's,
Island Tiangui Yu's, Okamoto's celebration, excellent
Google truth, san, large dressing mix の Takaoka Jason's foot, and Maeda's Min, Chang Division's Yamashita,
Ogasawara and び ni Lee's by theMembers are 様 の, Shiina combination of a large dressing mix long の Angang Yukio Hashimoto's health, Komatsu
Zhao Shishi, plant Tianjing Shi, Xian head and
Fortunately, s, and all び の 様 に by members, three Jin Yan Rong Jingbang Fisheries Cooperative の は じ め と sを し 様 all ta, Room Kobe Cape
Shiina-machi Machida region の 様 fresh fish shop, fish shop in the Temple 様, three-chun, a large dressing mix areの の 様 by members, chamber Kobe East Cape Fishing Association
63
Takaoka Branch are 様 の, Room Kobe Fishing Association Shiina Eastern Cape branch are 様 の, Muro-gun, Mie
Prefecture, North Island, Katsuura-cho, Chi North の training the right footS, Sachiko Yamashita san, Yamashita Koushi will ん く, Yamashita ゴ ん ン too ku, Yu Li's home, the public's
Tsumura は じ め と を し ta
Are 様, Shimane Prefecture, aquarium stand し ま ね の Murakami Chang I's, Moriya を は じ め ho s ta are 様 とし, Tottori Prefectural Museum legislation
Sawa's a museum の, Yasushi Kawakami's は じ め と を し 様 all ta, Tottori Prefectural Fisheries セ cultivation
are 様 の ー ン タ, Tottori Prefecture Li

Aquatic field testing 験 の 様 の are much support な ご る と ご に よ っ て third collection す る こ と が で kita. Smithsonian
Institute, National Museum of Natural History, Dr. George Zug の に は ウ ミ の ga メ Class age rangeに し て set off investigations dating tactics bone Professor い を ご い ta da ta. Kobe University, Faculty ofAgriculture Ying の animal subjects ratio of Lu Nan
Associate Professor Chi や ー チ Minami Chita Bldg ド ラ ン の は 黒 に ウ Liu Kenji's メ ミ の ga related toreproductive に 様 々 な わ る を ご handle things
Professor い い ta da ta. Ma ta, the main な と な っ ta investigation in Kochi Prefecture, Kobe City Room で は ホ
ニ ュ ー ル Room Te Kobe are 様 の,Nakamura woodworking are all 様 の, Yuan Elementary School are 様 の, Takaoka Shiina Mitsuya の の 方 々 にregional big words に 変 な お Worldっ ta.の の こ ち ta party support え が な け れ ば carry out research を す る こ と で は な か っ ta
ki. Association of Japan ウ メ ミ ga
Parliament will celebrate Dr. の Song Kanazawa, Tatsuya's Island, Gong Xiao's good form, Jiro Mizuno's HealthStudy に は す る に Dui を ご made the top assistantKi, rotten see Kenichiro's large deer of Mi's, if the month-tree's, fields and into Kameari's, Valley of the reasons sansand, Taniguchi san truth,
Yusuke's Round East, Eguchi Sakae for s, in the Mariko san, san Naomi Inoue, Naoko Miyahara san, Sugiyama enjoy
Shi,
Saito macro Christine's, Ouchi Yugui Shi, Hiromi Yoshida san, san three Kanako, heavy dance village san に は 様 々な surface Hibi
Help け て い で い ta da ta. Ma ta, Kobe Municipal Suma Aquarium Park Sea Bang の 様 に は Hibi all research
activities の を う field line
The opportunity と を え て い with い ta ta da. Minami Chita Bldg ン ド ラ ー チ, Japan and the Junior Museum
う み が め ッ カ レ タ, Hime
Road City Aquarium, Himeji City Zoo are の 様 に は ご anatomical guide や Mika 験 に ご い third い ta da
ta. Three major64
メ イ ga school ウ ミ ル ー ク サ カ Hikaru security survey "め っ か Bru ri" の 様 に は survey were dissected
hand 伝 を っ て
い い ta da ta. Sugihara Chennai Central sub-san desu を は じ め る と, University of Tokyo School of Agriculturaland Life Sciences, save water
Science Lab の に は's degree students in the various confusing お 々 ご を お か け lots し off wa ta ら ず に も,
い つ も い か ご warm support
Assistance を い い ta da ta.こ こ に す と と も に mind, all parties 様 に し heart thank yo ri, Li Shen し the げ
お ま す.
The は Independent Administrative Institution Japan Society for the Promotion "Heisei 21 year Funded (Special
Fellow House International Action
Charges) ", a specific non-profit activities, play groups are legal in Japan ウ メ ミ agreement will ga, black tide of
biological research contributed to fiscal Tuan, Jing Tuan with Japan
Nature Conservation Fund, the Hitachi Environmental NPO to help the environment as financial Tuan, water ハ ウ
ス ン マ ッ チ ム グ プ ラ ロ グ, ラ ッ シ ュ
ン ジ ャ パ, patagonia Japan by け て の を line support れ ま し ta wa. Li Shen し く thick on the げ お ま す.
65
To aimChapter 1 Introduction
ア カ ウ メ ミ ga (Caretta caretta) の の North Pacific spawning individual groups there に は し Japan, larvae は
too
Cross-sectional Pacific を し, カ リ フ ォ Hikaru ニ ア bait domain Peninsula coast を と し て She grew su ru.その, then び PacificJapanese coastal waters transverse し に を っ て く る 戻.し か し, Pacific, so っ く を ta Hiro の 中 で life
history, ど の period
The beginning of sexual maturity に ま が ri, い つ す る の か は finished out ら か に な っ て い な い.そ こ で,で は north of the study
ウ production ア カ Pacific ga メ ミ の に お け sexual maturation process life cycle を る ら か に す る Ming
ため, Chapter 2, a long で
Relationship between sexual maturity と の に つ い て, Chapter 3 で と sexual maturation of secondary Zheng,particularly of secondary Cheng に の の form of matter II
で あ る に つ い て tail elongation, Chapter 4 で へ 戻 ru Japanese coastal waters of a long と に つ い て matureclass, Chapter 5
Age range at sexual maturity で と に つ い て growth rate of じ ta. Ma ta, the results of this study の え な が らを delivery, Chapter 6 で
ウ wa ga メ ミ の like the whole life history class に つ い て ま と め, Chapter 7 で は ら れ ta perception was
based づ ki ni ni off security
す る っ ta put words を line.
Chapter 2 of the mature の は じ ま る と sexual maturity a long-ru su ga over a long
Japan で す る ア カ spawning ウ メ ミ に つ い て ga, a long と の of gonad maturation を と の 様 々 な
relatedA long-dead individuals の を べ tone was て, の は じ ま sexual maturity a long ru が と sexual maturity over along を す る ら か に Ming
し ta. Specimen の は と し ta death し て も な い 152 individuals between the ア カ ウ ミ の メ で ga, standard
straight carapace length (SCL:
straight carapace length) を し ta measurement, the anatomy of sexual maturity と し て sexual discrimination
class を し ta. Sexual maturity class
Beginning of sexual maturity は し て い る を を individual larvae, the process of sexual maturation に あ る のを Ami individual adult, sexually mature over のIndividual を し て い る と し ta adult. Ma ta, ta sperm の confirm the existence of individual 8 さ れ を
individual adult male と み の な
Add に し え ta test results expected, the total of 54 individual male は, 106 individual female は に な っ ta.
Larvae, Ami adult, adult の す べ て の で sexual maturity class and poor a long に は ら れ ず see, the female
dynasty の は Analysis
Male co-wa せ て を っ ta line. Sexual maturity が の は じ ま る SCL Fan Tong を Ami adult minimum value か らの の largest larvae
Value ま で と し, sexual maturity over す る が の Fan Tong SCL adult を か ら の 亜 minimum value maximum
value of adult ま で と のする と, そ ぞ れ れ 636-750mm ,738-853mm で あ っ ta. Ma ta, こ れ ら の 中 で の half of Van Tong
Sexually mature individuals が で の は じ ま る と a long, sexually mature ga over a long su ru su ru presumption
を ため, と 亜 into larvae
Body, Ami adult と を adult seeking め の cut together, Te ィ ッ ス ロ ジ で ク curve back Vesting し ta.そ のresult, half of the ga sex
は じ め る を mature SCL は 660 mm, half of the sexually mature ga su ru finished を は 821 mm SCL seeking め
られとTa.
Chapter 3 male tail elongation と の sexual maturity
カ メ class male で は の の 発 of secondary Cheng representatives are を す る と し て shape of the tail 変 のが あ る elongation.ア カ ウ
そ ga メ ミ も な く の は で exceptions, tail elongation の の は conduct a condition of sexual maturity indicators
を と し て measured ru looking さ れ
Ru.そ こ で, Chapter 3, the North Pacific の で は ウ ア カ メ ミ に つ い て ga sexual maturation と お よ び along tail66と の に つ い て related discussion し ta Jian.
Specimen と し て い ta by set net で の は さ れ ta 128 individuals captured ア カ ウ ミ の メ で ga, Chapter 2,
the same 様 とSexual maturity of the class に と を し ta classification results of individual larvae で は male female ga ga 5 8
individual, Ami adult male wa ga 29
が で 55 individual individual female, 11 male adult ga female individual で で あ っ ta 20 individuals.こ れ ら のは individual SCL と End
Length (TL: tail length) が さ れ measurement, SCL Dui す る に さ を said TL の す long tail length relative to Dui(rTL: relative taillength, TL / SCL) が め ら れ ta find. Ma ta, tail elongation の の を table su ta め extent, TL Department の growthphase Dui
を め ta find a few. Growth factor-phase Dui と は Y = b · Xa で さ れ る shows the number of a given の こ と で
あ ri, a set number of a ga 1
Excellent growth of more than な ら ば と し ta.
rTL larvae で は は が difference between male and female share め で ら れ っ か na ta ga, Ami adult や で は
explicit adult male の 方 が に long
Ku (p <0.001, Mann-Whitney U-test), Ami ta adult に な っ が after the end of the elongation ni su male の こ とが out ru
ら か に な っ ta. Male tail elongation の の を starting point of the tail length of male and female の い がviolation is れ に は じ め る と し point, male and female
れ に 亜 そ ぞ れ お よ び adult adult タ か ら の デ ー と rTL SCL line の と の back Vesting requirementsintersection を と め ta
こ ろ, the male tail elongation の は じ ま る が は SCL 670 mm, そ の の rTL when seeking め と は .155 ら れta.
Ma ta, SCL ni su ru Dui Dui TL growth factor の か ら phase male tail elongation の は の 亜 adult period was で がXian (a= 4.3898, n = 29, r2 = 0.5542, p <0.01, no correlation Jian be), adult ら か に な っ て も し 続 け る こ elongationと が さ れ ta show instigate. Ma ta, female adult と の 亜 adult を あ わ せ て growth coefficient phase Dui
seeking め る と を, males Mizuho ど
Xian was で の は な い も の と と も に sexual maturity tail elongation す る こ と が が さ れ show (a =1.7528, n = 83, r2= 0.3366, p <0.01, no correlation Jian be), female tail に も が と っ て す る こ と に elongation breeding
activities related wa ru ni
Meaning function が あ る と な え ら れ ta test.
Chapter 4 で あ る breeding Japanese coastal waters へ の イ ズ add サJapan, the only North Pacific の は ウ ア カ メ ミ の ga spawning で あ ri, mature female ta が し す る こ と はlive tomorrow
ら か で あ る.し か し, や immature male individuals の の に つ い て は ecological fragments of information がないつかあるく
ぎ su に な い.そ こ で, this chapter set net で で は さ れ ta capture ウ ア カ メ ミ か ら ga, ni live in Japan's
coastal waters
ア カ ウ ru su ga メ ミ や の length distribution of a life history に お け る の sexual maturity specified inparagraph order を ら か に し, Japan offshore へ
戻 っ て く る や a long stage of sexual maturity に つ い て paragraph discussion し ta.
Specimen と し ta ga ア カ ウ メ ミ は Kobe City, Kochi Prefecture room large set net で の July 2002 か ら 11,
2009
During the month ま で の に さ れ not captured as a ni ta 1392 individual で あ る.こ れ ら の は measurementof individual SCL の し ta
Value に よ っ て, hatched larvae, larvae, Ami adult, adult の 4 つ の に classification of sexual maturity class され ta. Categories のSCL baseline と な る に は seeking Chapter 2 で め が half ta を は じ め sexual maturity SCL 660 mm る と でhalf ofRu su ga over mature SCL 821 mm, さ ら に, 日本 の の hatching individuals with an average value 42 mm を い
ta. Capture
さ れ ta ga ア カ ウ メ ミ の は SCL 757 ± 67 (SD) mm (range: 563-1050 mm) で, SCL の distribution
Show the peak of radiolabeling は を し ta.こ れ ら の を sexual maturity of individual sub-paragraph order で け
る と の 亜 all adult ga 77.7% (1081
Individual) を め ta share.
Distribution of SCL の か ら, ア カ ウ メ ミ ga ga 560-570 mm SCL は で the beginning of the Japanese coastal
waters め に し appear,
The most frequent values 740-750 mm で を え る ま で welcome to increase in し, そ 転 の に じ ta after the
reduction.こ こ で の は due to increase in to67
Japanese coastal waters add で あ へ の ri, the main に SCL 560-750 mm larvae の の か ら 亜 late adult の が at
the individual
Then add the offshore に す る と さ れ ta push the police. Ma ta, the North Pacific ア カ ウ ミ の メ ga ga She
baits a つ の と し domainて す カ リ フ over ご ニ ル ォ ア Peninsula coast で は, SCL distribution か ら の に up し 500-700 mm ha ta ni
coast
を れ は じ め る from the show instigate と さ れ, the Japanese coastal waters ni su ru then add the individual
difference や と の の SCL, prior studies でら か に さ れ Ming North Atlantic ta growth rate や で の 発 letter satellite tracking device に よ る か ら のtrack, カ リ フ ォ Hikaru
ニ ア Peninsula か ら ま で は 1-2 years of Japan-Pacific を で す る こ と が transverse instigate さ れ ta show.
Chapter 5 of the North Pacific に お け る と growth rate of an age range of sexual maturity
This chapter で は, を over su ru sexual maturity age range on the wrist に を さ れ ta residual growth of the stop
line (LAG: lines ofarrested growth) ら か で bone chronological approach presumption し, さ ら に に live in Japan's coastal waters
ア カ ウ ru su ga メ ミ
Ga su ru sexual maturity over を ま で の を growth rate next ら か に し ta.
Specimen Japan で は お よ び bycatch mortality floating dead ta ア カ ウ ミ し メ の male ga 27 individuals, 42
female individuals,
Sexual discrimination が で の か な っ ta ki individual 79 individual 10-meter individual の の を with い ta on thewrist. LAG を 観 police su ru
ため, on the wrist か ら さ 1 mm thick slices the following の を し cut out ri, LAG の を measurement radius とし ta pieces. LAG
1 year wa ki ni an で と さ れ て お ru ri, LAG SCL の の は 1 year increase ta ri の あ に growing proportion of theamount し ta.
Growth rate は Back Calculation protocol increases か ら の で LAG inverse し, then LAG の の を SCL
Radius か ら め ta request. Age range of individual ご と の で は Correction Factor protocol requirements め ta
ga, ga too large an age rangeに さ れ る お そ presumed れ め が あ る ta, Regression Growth protocol の で は von Bertalanffy growthType を め demand, SCL ma ta の は increase on the wrist bone age range と と の か ら relationship presumed
age range を し ta.
Each individual 本 か ら 9.3 ± 4.3 (range: 3-20), total で 732 LAG の が さ れ confirmed, the で 653 ge
LAG calculated の が さ れ ta pieces. Back Calculation protocol で め ta seek an average growth rate の は 13.9 ±7.8(SD) mm / year (range: 0.0-64.5) で あ ri, ta was seeking め ら れ の は SCL 694 ± 75 (SD) mm (range:
374-935, n = 732) で あ っ ta. Regression Growth protocol で は mature age range を す る, Chapter 2 で seeking

め を over sexual maturity ta ru su SCL 821 mm か ら め ta find the results, 37 歳 と さ れ ta presumption. With様 に, Japan
Add offshore に は す age range 18-31 yrs old ru presumption と さ れ ta. Correction Factor protocol で は,
mature しTa male individual で は が 38, 46, 47 yrs old (n = 3) で が 43 ± 11 yrs old female (n = 15, range: 22-61) で あ っta. MaTa, ta individuals mature し の は immature form of individual age range yo ri も く か が high, SCL も っ か large
ki ta ga (p <0.05, Mann-Whitney U-test), SCL が け れ ば large ki ga age range between the high い う と は い set into ri na ta
っか
Ta. (P> 0.05, no correlation Jian be).こ こ と の は, individuals with じ お に い て も group growth ば に ら と つsexual maturity
Ki が あ る こ と を し て い る instigate said.
Chapter 6 Class ウ メ ミ の ga life cycle - growth と live domain Chapter 6 で は ア カ ウ ミ の ga メ を his life history ウ ミ の メ class ga comparison の と し て life history, ウ
メ ミ class ga
Full-like life cycle に つ い て の じ ta on.
68
Chapter 7 総 joint study
Japanese coastal wa ga ア カ ウ メ ミ の か ら larvae into the body of the late の ま で が し て い る use.す な
わ ち, reproductionに い are good places together の で あ る な く だ け で, ア カ ウ ga メ ミ の と し て live environment suitable
していることがInstigate さ れ ta show. Ma ta, sexual maturity で に す る ま し て side hatch 37-43 years in も の が あ る こ とnecessary が でMing ら か に な ri, in the future ni wa ta を っ て individual group to maintain su ru ta め に は, egg productionof individual や と み さ れ ta drop
Larvae hatching eggs や な く だ け で, Japan offshore に し add na ta immature larval ecology や も の 亜 watch
adult desu
る 必要 が あ る.
69
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94
Table 2-1. Classification criteria based on the maturation state of gonads and reproductive tract
morphology. Limpus and Limpus (2003) and Miller and Limpus (2003) created based on the.
Subadult juvenile adultThat the male testes enlarged cylindrical. * Close to having an oval cross section. - With a flat oval cross-section.
Hanging from the side wall of the lower body wants to clear an enlarged epididymis.Edge can be clearly
distinguished from the body wall. • No body swollen from the wall.
Female ovaries ovarian stroma has been expanded.
Megu's blood vessels yellow · 0.3-3.0 cm
What has developed from egg yolk was, there
Alternatively there is the white body corpus luteum atretic follicle
Ru.
Kaho - The ovarian stroma are being expanded
Com is expanding.
White body - corpus luteum atretic follicle 見Ata
They do not.
- Develop ovarian stroma is observed.
* CL White vitellogenic stage follicles
Atretic follicle 見Ataranai body.
Oviduct 呈Su pink.
- Complex collapsed, and the ovary
At least 1.5 cm in diameter of the joint
There.
- 呈Su pink.
- Has collapsed somewhat
Elliptical cross-section diameter 0.3-1.5cm.
- 呈Su white.
- Which almost collapsed slightly
Straight stretches, the cross-section cylinder
Or slightly oval shape.
95
Table 2-2. Cloacal cavity condition and the presence of testicular sperm. Maturity of the testes and testicularmorphology and state
Was determined based on the presence of testicular sperm and cloacal cavity. SCL: Tadashi Kinoe 長 standard, TL:
Onaga, rTL:
Relative Onaga (TL / SCL). Sperm density was measured using a blood count sheet ,++:> 105 sperm / ml, +:1-104 sperm / ml, -: no sperm / ml, blank: unconfirmed, as represented. Check in testicular sperm
Among individuals, the sperm were observed from cloacal cavity is the only adult, drawing a significant tailHave long decided that if confirmed the adult male sperm cloacal cavity.
Date ID # SCL (mm) TL (mm) rTL (TL / SCL) cloacal 腔性 testicular maturation
1 868 345 0.397 + + adult 2005/4/24
2 380 788 0.482 + + adult 2005/4/24
3 300 805 0.373 + + adult 2005/5/18
4 390 839 0.465 + adult 2005/8/19
2005/12/7 5 180 743 0.242 + - subadult
2006/1/8 6 686 108 0.157 - subadult
2006/1/18 7 435 873 0.498 + + + + adult
2006/2/1 8 694 118 0.170 - - subadult9 307 808 0.380 + + adult 2006/4/24
2006/4/30 10 718 122 0.170 - - subadult
2006/5/10 11 248 826 0.300 - - subadult
2006/5/14 12 439 877 0.501 + + + adult
13 357 878 0.407 + adult 2006/6/2
2006/6/25 14 388 902 0.430 + adult
15 237 785 0.302 + adult 2006/7/3
2007/4/1 140 16 698 0.201 - - subadult
2007/4/4 255 17 726 0.351 - - subadult
July 3, 2007 180 18 759 0.237 - subadultSperm density
96
Table 5-1. Growth rate Kinoe Takeshi backwards from the line width by growth arrest.Tadashi Kinoe 長 Standard(SCL) line growth rate and growth arrest were left humerus (LAG) and width or radius
Were counted backward from. Note that the total field that also includes determination of the individual could
not. The growth rate decreased with an increase in SCL
Was. The gender differences in the growth rate is faster SCL 500-600 mm in females than males (*: p <0.05, MannWhitney U-test), is recognized in other classes
Me not.
SCL (mm) Male Female Total
300-400 31.7 (n = 1) 31.7 (n = 1)
400-500 38.8 ± 15.3 (n = 3) 22.5 ± 8.3 (n = 4) 29.5 ± 13.7 (n = 7)
500-600 15.3 ± 7.4 (n = 23) 24.1 ± 14.9 (n = 25) 20.7 ± 12.4 (n = 58)
600-700 13.2 ± 7.7 (n = 107) 13.6 ± 6.7 (n = 154) 14.1 ± 7.4 (n = 298)
700-800 12.3 ± 4.3 (n = 62) 11.7 ± 5.2 (n = 170) 11.9 ± 4.9 (n = 257)
800-900 12.2 ± 2.7 (n = 5) 11.0 ± 5.8 (n = 24) 11.2 ± 5.4 (n = 29)
900-1000 10.4 ± 0.0 (n = 3) 10.4 ± 0.0 (n = 3)
Growth rate (mm / year)*
97
Table 6-1. Turtle species (Dermochelidae and Chelonidae) Kinoe Takeshi mature. The average spawning
populations in each region
Values obtained from the population. Song Kinoe Takeshi (CCL) was shown in those Teas (1993) using theconversion formula
Tadashi Kinoe to 長 (SCL) was converted to. But still showed marked with * Kinoe Takeshi song.
Sea SCL (cm) the maximum number of individuals individuals individuals the minimum (n) Source of total area

Zug and Parham (1996)
Western Atlantic 164 5 1031 189 135
158 * 228 3 125 185
Ocean 1 8 165 147 154
178 126 2 134 161 *Western Pacific 161 110 2 178 145 *5 662 188 120 143 eastern Pacific
Hirth (1997)
Pacific
Oceania 99 75 14 2192 116
Western and central North Pacific 92 2 393 80.8 110.5
Eastern Pacific (Chelonia mydas agassizii) 3 82 60 102 879
Atlantic Ocean
Nanbei 110 2677 8 123.5 83.8
North and Central America 102 187 83.2 10 118.9
Africa 41 3 88 87 102
Indian Ocean
Africa 107 91 658 10 125
6 551 114 95 77 Arabian Peninsula
Kamezaki (2003)
Oonishi Hiroshi 91 11 1096 110 70
107 520 2 90 76 Indian Ocean
South Pacific 106.9 73.2 89 1 2207
North Pacific 101.5 69.2 85 1 1154
74 Mediterranean - - 3 52
Limpus (2007)
Australia 89.4 67.0 12 1437 100 *Hirth (1980)
Oonishi Hiroshi 83.1-84.1 74.9 91.4 - 2
Taiheiyou 68 93 80.5 - 1
Indian 66-85.5 53.3 87.5 - 3
Hirth (1980)
Oonishi Hiroshi Caribbean 68.5-66.6 75 63 - 2
Indian 67 59 71 - 1
Eastern Pacific 62.9-65.2 52.5 72.5 - 3
Hirth (1980)
Caribbean 64.6 59.5 75 - 1
Kemp (Kemp's ridley turtle: Lepidochelys kempi)
Turtle fungus (Flatback turtle: Natator depressus)
Leatherback turtle (Leatherback turtle: Dermochelys coreacea)
Caretta caretta (Loggerhead turtle: Caretta caretta)
Green Sea Turtle (Green turtle: Chelonia mydas)
Hawksbill turtle (Hawksbill turtle: Eretmochelys imbricata)
Lepidochelys olivacea (Olive ridley turtle: Lepidochelys olivacea)
98
Figure 1-1. Loggerhead turtle. Bycatch in the area where a large stationary nets Misaki Muroto Muroto Kochi city
to identify and measure individual
Loggerhead turtle was transported to a port for the installation of signs for another (Caretta caretta).
99
Figure 2-1. The main study area. Katsuura Shima Kita Osamu place where town and county where land Kitamuro
Town, Mie Prefecture, Kochi Prefecture, Misaki Muroto Muroto
The main study area and a large stationary nets, indicated by arrows.
Kita Osamu cho, Mie-gun KitamuroMisaki Muroto Muroto city Kochi
100
Figure 2-2. Loggerhead turtle gonads and reproductive tract. The testes of adult males, but cylindrical, and thesubadult
Ellipse, the juvenile has a flat section. In the adult epididymis is enlarged to clearly juvenile
Clearly not in the boundary between body wall. In the adult female ovary and corpus luteum white or yellow yolk
to the development of
Body has closed follicles, are seen in subadult Moisture expansion ovarian follicles 見Ataranai well-developed
The development is seen in juvenile ovarian stroma. Tubal adult enough to be white to pink,
We collapsed along with the elongation complex. A: adult male (length standard Tadashi Kinoe [SCL] 873 mm),
B: subadult male (SCL 720 mm), C: male juvenile (SCL 577 mm), D: adult females (SCL 727 mm), E: Female
Subadult (SCL 727 mm), F: female juvenile (SCL 679 mm).
101
550
600
650
700
750
800
850
900
950
Subadult female adult male adult female juvenile male subadult male juvenile female
SCL (mm)
Sex male female sex
Adult subadult juveniles
Figure 2-3. Instep different distributions of male and female sexual maturity class. For each male and female
juveniles (males: n = 6,
Female: n = 12), subadult (males: n = 36, female: n = 67), adults (male: n = 12, female: n = 27) Standard Tadashi
Kinoe
Length (SCL) shows the distribution of. Bars in the figure are the maximum and minimum values, boxes and acentral third quartile
Shows the first quartile value. Between male and female sexual maturation in both classes recognize the difference
between SCL
No Therefore, gender differences in the process of sexual maturation, and no it was suggested (p> 0.05, MannWhitney
U-test).
102
0
1
2
3
4
5
800 900 700 500 600
Population
SCL (mm)
0
5
10
15
20
800 900 700 500 600

Population
SCL (mm)
0
2
4
06
08
10
800 900 700 500 600
Population
SCL (mm)
0
2
4
06
08
10
800 900 700 500 600
Population
SCL (mm)
0
2
4
06
08
10
800 900 700 500 600
Population
SCL (mm)Juvenilen = 18Subadultn = 103Adultn = 39Figure 2-4. Sexual maturity for each class size composition instep. Juvenile, subadult, the head of each standard
adult Tadashi Kinoe (SCL)
Population showed a 20 mm each.
103
0.0
0.2
0.4
0.6
0.8
1.0
800 900 700 500 600
Proportion of subadult
SCL (mm)
n=311
5
16
19
19

20
9 17
0.0
0.2
0.4
0.6
0.8
1.0
800 900 700 500 600
Percentage of adult
SCL (mm)
n=3
12
1717
1923
14
10 6
11
07
2
Figure 2-5. Kinoe Osa-class moving sexual maturity. Adult, subadult, the head of each standard Tadashi Kinoe
juvenile (SCL)
Once in 20 mm each population, the juvenile subadult, adult sexual maturity is transferred from the subadult class
Asked the SCL line. Subadult / (juvenile + subadult), the percentage of sub-adult (top), adult / (adult + subadultBody), the percentage of adults (bottom), and begin to sexually mature individuals of the half SCL 660 mm (top),
half ofIndividuals to complete the sexual maturation of SCL is 821 mm (bottom) was determined to be. In the figure, thepopulation figures
Shown.
104
Figure 3-1. Onaga measurement position.
Onaga is a straight line distance to the center of the rear end of the cloacal opening plastron indicated by red
arrows.
105
0.1
0.2
0.3
0.4
0.5
0.6
Subadult male adult female adult male subadult female juvenile male juvenile female
Data 1 2010/12/13 1:52:52
rTL (TL / SCL)
n=5
29
20
55
08
11 **
**
Sex male female sex
Adult subadult juveniles
0.6

0.5
0.4
0.3
0.2
0.1
rTL (TL / SCL)
Figure 3-2. Onaga-Relative maturity of class. Relative Onaga (rTL) Nao Kinoe standard length (SCL) for Onaga(TL) (rTL = TL / SCL) as determined. Juvenile sexual maturity classes not beginning of sexual maturation, sexual
maturation
Subadult maturation has not reached the beginning, that is divided into sexually mature adult. The figure
The number represents the number of individuals, the Mann-Whitney U-test ** at p <0.001 significant differenceswere detected kite
Indicate this.
106
Male: rTL = 0.001433 × SCL-0.8046
R = 0.8066
Female: rTL = 0.0001501 × SCL +0.05475
R = 0.2547
0.000
0.100
0.200
0.300
0.400
0.500
0.600
1000 900 800 700 500 600
rTL (TL / SCL)
SCL (mm)
Adult male
Subadult male
Male hatchlings
Adult females
Subadult female
Female juvenile
Figure 3-3. Correlation relative to the head of the instep of both sexes Onaga. ■: growth was confirmed cloacal
cavity of adult male sperm
Mature males (n = 11), ■: subadult male (n = 29), ■: juvenile males (n = 5), ●: adult female (n = 20), ●: female
Subadult (n = 55), ●: juvenile female (n = 8), SCL: Tadashi Kinoe 長 standard, rTL: Relative Onaga (rTL = TL / SCL, TL
The Onaga). Osabe Shin male tail intersection of the regression line and higher subadult male and female, ie theedge of secondary sexual characteristics
Considered an average Kinoe Takeshi whole, the SCL is 670 mm, respectively. 120
900 1100 1050 1000 950 850 800 750 700 600 650 500 550
Population
SCL (mm)n = 1392
Figure 4-1. Size composition instep of loggerhead turtles caught in nets by the emplacement of Muroto, Kochi
Prefecture. 757 ± 67 mm mean
(SD) at least 563 mm, up to 1050 mm.
108
Figure 5-1. Sectioning part of the humerus and turtles. Growth arrest lines in the humerus (LAG) is a minimum
width of
(MW) and the deltoid crest (DPC) is left between the best without being absorbed (Zug et al., 1986). Therefore,
This chapter DPC cut the end part of the humerus, from reading the sections were created LAG.

109
Figure 5-2. Growth arrest lines and cross-sectional slices of the humerus. Growth arrest lines (LAG) is formed in
one year(Snover and Horn, 2004).
110
Width = -0.0393 × LAG LAG radius + 0.7669
R = 0.3715 (p <0.001)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
20 18 16 14 12 10 8 6
LAG Width (mm)LAG radius (mm)Width = 0.767 0.0393 × LAG LAG radius ー
n = 653, R = 0.372 (p <0.001)
LAG radius (mm)
LAG Width (mm)Figure 5-3. Radius and width of the line segment growth arrest was left humerus. Growth arrest lines (LAG)
diameter of the humerus (MW)Shows the relationship between the radius and width approximates a correction.Humerus sections LAG order toobserve more
め, MW cut off close to the crest of the humerus from the deltoid, it was created.Therefore, the formula for a 5-2
LAG MW at the time they formed to be amended to fit. Intercept of the regression line obtained (A)And slope (B) from the parameters in Equation 5-3 a, k is, a = | A / B | = 19.514, k =- ln (1 - | B |) =Obtained as 0.0401.
111
0
200
400
600
800
1000
0 20 40 60 80 100
SCL (mm)
Estimated age (years)
Figure 5-4. The growth curve in the North Pacific loggerhead turtles. The growth equation SCL = 1159 {1-exp [0.03067 (t-1.619)]} and represented.
112
0
1
2
3
4
5
06
07
60 55 50 45 40 35 30 15 20 25

Population
Estimated age (years)
Immature male
0
1
2
3
4
5
06
07
60 55 50 45 40 35 30 15 20 25
Population
Estimated age (years)
Immature female
0
1
2
3
4
5
06
07
60 55 50 45 40 35 30 15 20 25
Population
Estimated age (years)
Adult male
0
1
2
3
4
5
06
07
60 55 50 45 40 35 30 15 20 25
Population
Estimated age (years)
Adult female
Figure 5-5. Age structure of loggerhead turtles in the Sea of Japan. Age Correction Factor protocol for
Was estimated by. The age structure of male black bar, gray bar shows the age structure of females. The
The above figure immature individuals, individuals below the age structure showed maturity.
113
500
600
700
800
900
10 80 70 60 50 40 30 20 0
SCL (mm)
Estimated age (years)
Male
500

600
700
800
900
10 80 70 60 50 40 30 20 0
SCL (mm)
Estimated age (years)
FemaleFigure 5-6. Age-length relationship and instep. Age was estimated by the Correction Factor protocol. Above
The male, age below the standard length of female Tadashi Kinoe (SCL) shows the relationship. In addition, ● Themature individuals, ○Shows an immature individual. SCL is greater than the age and composition population of mature individuals whoare immature,
SCL class size in Japanese waters after readmission between the ages and their correlation is clearly observed
Not (p <0.05, test uncorrelated.)
114
Figure 6-1. Floats in juvenile sea turtles hatch. Carapace sedentary ride on the forelimbs. Predator
Adaptation is considered to be less noticeable.
115
Figure 6-2. The loggerhead turtle hatchlings - Schematic diagram of the distribution and migration across the oceansubadult. Caretta caretta
The ride across the ocean from the warm waters towards high latitudes born. After growing to some extent,
Considered to make an active migration into the area toward sexual maturity before the birth.
116
Figure 6-3. Sexing using an endoscope. The juvenile and subadult males and females can determine from theexternal morphology is not easy
Because you are not inserted into the abdominal cavity of a small diameter endoscope, which may determine byexamining the gonads directly.
117
Figure 6-4. Kind of sea turtle habitat. Life history strategy is different depending on the species, except for sea
turtle fungus
All species and habitats to pelagic juvenile stage. Join Kinoe Takeshi coast varies with species and populations
Be considered to be greater individual differences. (Bolten, modified from 2003).
118
Figure 6-5. Black sea turtles found in Muroto, Kochi Prefecture. The current green turtles Chelonia mydas agassizii
Asia
The species is, some species to move. Against the cream-colored green turtle exhibit abdominal
To sea turtles from gray to black is a black body 呈Su including the abdominal cavity.This will narrow the rear endof the carapace
Major characteristic of both.

北太平洋産アカウミガメの性成熟過程における生活史石原孝北太平洋産アカウミガメの性成熟過程における生活史

Life History in Maturation Process of Loggerhead Turtles (Caretta caretta)
in North Pacific2011東京大学大学院農学生命科学研究科
生圏システム学専攻
石原孝

Takashi Ishihara

指導教員
東京大学客員准教授
亀崎直樹

目次

第 1 章 緒言

1

第2章

5

性成熟のはじまる甲長と性成熟が完了する甲長

2-1．目的

52-2．方法62-3．結果と考察

8

第3章

尾部伸長と性成熟

123-1．目的123-2．方法13

3-3．結果14

3-4．考察15第4章

繁殖海域である日本近海への再加入サイズ

20

4-1．目的20

4-2．方法21

4-3．結果と考察

第5章

北太平洋における成長速度と性成熟年齢

2226

5-1．目的26

5-2．方法29

5-3．結果33

5-4．考察35

5-4-1．成長速度

365-4-2．成熟する甲長

38

第6章

ウミガメ類の生活史―成長と生息域―

426-1．ウミガメ類の生活史の概要

426-2．アカウミガメ(Caretta caretta)の生活史

43

6-2-1．産卵地

43

6-2-2．孵化・脱出と分散

44

6-2-3．幼体の生息地と成長

45

6-2-4．繁殖地への再加入

46

6-2-5．性成熟46

6-3．他のウミガメ類の生活史との比較

49

6-3-1．幼体期の生態

496-3-2．性成熟

51

第7章

総合考察

54

7-1．日本近海における保全の重要性

54

7-2．日本近海におけるアカウミガメの死亡率

55

7-3．北太平洋のアカウミガメに対する脅威

57

7-3-1．砂浜における脅威

58

7-3-2．外洋へ分散した幼体への脅威

59

7-3-3．沿岸域での脅威

60

7-4．日本近海で必要な保全策

61

謝辞

62

論文内容の要旨

65

引用文献

69

付表

94

付図

98

付表一覧

表 2-1．生殖腺と生殖管の形態に基づく性成熟状態の分類基準．

94

表 2-2．精巣および総排泄腔内の精子の存在状況．

95

表 5-1．成長停止線の幅から逆算された甲長の成長速度．

96

表 6-1．ウミガメ類 (Dermochelidae と Chelonidae)の成熟甲長．

97

付図一覧

図 1-1．アカウミガメ．

98

図 2-1．主な調査地．

99

図 2-2．アカウミガメの生殖腺および生殖管．

100

図 2-3．雌雄の性成熟階級別の甲長の分布．

101

図 2-4．性成熟階級ごとの甲長組成．

102

図 2-5．性成熟階級の移行する甲長．

103

図 3-1．尾長計測位置．

104

図 3-2．性成熟階級ごとの相対尾長．

105

図 3-3．雌雄の甲長に対する相対尾長の相関．

106

図 4-1．高知県室戸市の定置網で捕獲されたアカウミガメの甲長組成．

107

図 5-1．アカウミガメの上腕骨と切片作成箇所．

108

図 5-2．上腕骨切片の断面と成長停止線．

109

図 5-3．上腕骨切片に残された成長停止線の半径と幅．

110

図 5-4．北太平洋におけるアカウミガメの成長曲線．

111

図 5-5．日本近海におけるアカウミガメの年齢構成．

112

図 5-6．年齢と甲長の関係．

113

図 6-1．海面に浮くアカウミガメの孵化幼体．

114

図 6-2．アカウミガメの幼体-亜成体の分散と大洋を横断する回遊の模式図．

115

図 6-3．内視鏡による性判別．

116

図 6-4．ウミガメ類の生息域．

117

図 6-5．高知県室戸市で発見されたクロウミガメ．

118

第１章 緒言

生物は魚類から両棲類に進化する過程で陸上を生活圏の一部として利用し始め，爬虫類へと進化するとともに完全に陸上生活に適応した．しかし，中には再び水中生活へ移行したものもおり，現生爬虫類では一般にウミガメと総称されるウミガメ科 (Cheloniidae)とオ
サ ガメ科 (Dermochelidae) の仲間 がそ の代表 的な ものの 一つで ある ． Santanachelys

gaffneyi はブラジル東部の白亜紀前期 (約 1 億 1 千万年前)の地層から発見された最古のウ
ミガメ (Hirayama, 1998)であるが，その形態はすでに現生のウミガメに近く，ウミガメとしての形態の大綱はこのときすでに出来上がっていた．現生のウミガメはウミガメ科 5 属 6種，オサガメ科 1 属 1 種の計 7 種にすぎないが，分布範囲は非常に広く，ヒラタウミガメとケンプヒメウミガメを除いて世界中の大洋に分布する．現生するウミガメの科は中生代
白亜紀にはすべて出現しており (Pritchard, 1979)，それが現在でも生き残っているということはウミガメが海洋環境に良く適応していることが伺える．独自の進化をしつつ，1 億年
以上もほとんど変わらぬ姿を保つウミガメは生物学的に非常に貴重な存在であると言える．
しかし，人類が社会的活動を拡大するとともにウミガメ類の生息数は激減し，近年では絶滅が危惧されはじめた．地域の食料として利用されていたウミガメの肉や卵は産業品となり乱獲され，科学技術の発達により高度化された漁業では混獲されるウミガメの数も増加したと考えられている．生息環境に良く適応したウミガメであっても保全策を講じなけ
れば絶滅のおそれがある．
日本では関東から沖縄にかけてアカウミガメ (Caretta caretta)が，小笠原諸島と屋久島から南西諸島にかけてアオウミガメ (Chelonia mydas)が産卵し，タイマイ (Eretmochelys
1imbricata)の産卵も僅かながら南西諸島で確認されている．この他，産卵はしないものの近海にはオサガメ (Dermochelys coriacea)やヒメウミガメ (Lepidochelys olivacea)も来遊しており，時折漁業によって混獲されたり，死体が海岸に漂着したりしている．これらのウミガメの中で，特にアカウミガメは日本では最も産卵巣数の多いウミガメである一方，北太平洋には日本以外の産卵地は存在せず (Kamezaki et al., 2003)，保全上日本の果たすべ
き役割は大きい．日本の海岸線には漂着したアカウミガメの死体が毎年数百頭も確認されており (日本ウミガメ協議会, 2010)，北太平洋のアカウミガメを保全するためには現状を把握し，アカウミガメの生態や生活史に基づいた対策が必要である．
日本におけるアカウミガメの研究史は，1990 年代までは産卵に関する生態や行動，さらに胚発生や遺伝学的な研究など，産卵場所である砂浜における研究が行われてきているに過ぎず（亀崎・松井，1997），生涯のほとんどを過ごしている海洋にいるときの彼等の生活史全体を追跡できるような研究は行われていなかった．近年では衛星発信器による回遊経路の追跡やデータロガーを用いたバイオロギングによって海洋での移動や回遊を明らかにするための研究が行われてはいるものの，その追跡可能な時間は短く，彼等の長い生活史のごく一部を断片的に明らかにしたに過ぎない．日本は北太平洋のアカウミガメにとって唯一の繁殖海域であり，その近海は北太平洋から集まってきた個体が繁殖活動を行う場である．しかし，日本近海に生息するアカウミガメの生態に関して体系的な研究は行われていない．また，それに伴ってアカウミガメの生活史において，日本近海が産卵場としての機能以外にどのような生態学的役割を担っているかも明らかにされていない．
そこで本研究では北太平洋産アカウミガメの自然史を明らかにする研究の一環として，また保全のために必要な生態学的基礎データを得るために以下のような研究を行った．ま2

ず，第 2 章で高知県室戸の定置網で混獲されるアカウミガメの生殖腺を観察し，雄および雌の性成熟のはじまる甲長と性成熟が完了する甲長を明らかにし，第 3 章で雄の第二次性徴の発現過程，すなわち尾部の伸長の過程の解析を行った．第 4 章では，混獲個体を解析し太平洋から再び日本近海に回遊するサイズや成熟度に関して明らかにした．さらに，第 5章では，上腕骨を用いた齢査定を行い，日本近海への再加入年齢，成熟年齢，成長速度の推定を行った．また，それらの結果を踏まえ，第 6 章で広くウミガメ類全般の生活史についてまとめた．このうち，第 2 章と第 3 章は Chelonian Conservation and Biology に，第4 章は Current Herpetology に，第 5 章は Copeia に，第 6 章はウミガメの自然誌 (東京大学出版会)に下記の通り発表予定のものである．

第 2 章と第 3 章
Ishihara T., and N. Kamezaki. Size at Tail Elongation and Sperm Production in Male
North Pacific Loggerhead Turtles (Testudines: Cheloniidae). Chelonian Conservation
and Biology. (投稿中：査読中)第4章
Ishihara T., Kamezaki N., Matsuzawa Y., Iwamoto F., Oshika T. Miyagata Y., Ebisui C.,
and Yamashita S. Re-entering of Juvenile and Sub-adult Loggerhead Turtles into theJapanese Natal Waters. Current Herpetology. in press.

第5章
3Ishihara T. and Kamezaki N. Age at Maturity and the Growth Rate of Sub-Adult Maleand Female Loggerhead Turtles in North Pacific Estimated by Skeletochronological
Analysis. Copeia. 投稿準備中

第6章
石原孝．生活史－成長と生息域．ウミガメの自然誌 (第４章)．東京大学出版会．(最終校

正中)

4

第2章

性成熟のはじまる甲長と性成熟が完了する甲長

2-1．目的ある動物種または個体群の生活史や生態を明らかにしようとする時，繁殖に関わる情報は非常に重要である．また，繁殖に向けた生理学的な発達，すなわち性成熟は生活史の中で重要な位置を占めており，性成熟の過程とその時の生態との関連を調べることは重要である．
アカウミガメ (Caretta caretta)の生活史は，北太平洋や北大西洋の個体群で，比較的明らかにされている (Bolten, 2003)．それによると，それぞれ日本やアメリカ合衆国東岸で孵化した孵化幼体はそれぞれ黒潮とメキシコ湾流によって大洋に広く分散し，多くの個体は対岸のメキシコやアフリカ沖まで移動し，そこで成育する．その後，ある段階で大洋を東から西に向かって回遊し，繁殖場所である日本やアメリカ東海岸にもどり，そして産卵に至る．この過程の中で，どの時期に性成熟が始まり，さらに完了するかは明らかになっていない．容易に計測できる甲長からアカウミガメの個体の成熟度を判断できるようにする
ことは保全生態学に基づいて保全戦略をたてるために非常に重要であり，この研究がない
現在，いたるところで発見されるアカウミガメの成熟度を判断するのはむずかしい．
そこで本研究では，日本で産卵する北太平洋のアカウミガメについて，生殖腺の性成熟状態と甲長の関連を調べ，性成熟のはじまる甲長と性成熟が完了する甲長を明らかにした．
5

また，アカウミガメの繁殖に関する特性，例えば，１巣あたりの卵数，1 産卵期あたりの産卵回数，産卵の回帰年数などが世界の主要な産卵地，すなわち繁殖個体群間でばらつきがあることが知られている (Dodd, 1988; Miller, 1997)．さらにこれらの繁殖個体群は遺伝的に隔離されており (Bowen, 2003)，産卵する雌の甲長は個体群間で異なることも知られている (Dodd, 1988; Tiwari and Bjorndal, 2000; Kamezaki, 2003)．このような地理的変異が生態特性にも見られることより，性成熟の過程を含む生活史にも地理的変異があることが予想される．これらを明らかにできると，いくつかの遺伝的に隔離された繁殖個体群が，それぞれの生息環境の地理的特性に，どのように生活史を適応，分化させていったかがわかり，
進化生物学的にも興味深い．

2-2．方法
性成熟のはじまる甲長と性成熟が完了する甲長を明らかにするため，死亡して間もない
152 個体のアカウミガメを試料とした．これらの試料は，個体毎に標準直甲長 (SCL: straightcarapace length)を計測したのち，解剖して生殖腺と生殖管を観察した．これらの試料は 2005
年 4 月から 2010 年 8 月の間に高知県室戸市室戸岬町および三重県北牟婁郡紀北町の定置網で混獲され (図 2-1)，多くは溺死した個体である．性の判別は，解剖した後，生殖腺の形態，
すなわち卵巣か精巣かを判別することにより行った．性成熟の状態は Limpus and Limpus(2003)および Miller and Limpus (2003)に従い，３段階の性成熟階級，すなわち，幼体，亜成
6体，成体に分類した．それぞれの分類基準は表 2-1, 図 2-2 に示した．幼体は性成熟のはじ
まっていない個体，亜成体は性成熟が始まっているものの完了していない生殖腺をもつ個
体，成体は性的に成熟した生殖腺をもつ個体，と考えることができる．また，成体と分類される雄は試料数が少なかったため，高知県室戸市の定置網で捕獲された生存個体のうち尾部伸長が顕著で総排泄腔内から精子が確認された 8 個体を成熟した雄とみなし試料に加えた．
また，総排泄腔内の精子を性的に成熟していることを示す指標として用いることの妥当性を検討した．生殖腺から性成熟階級を判別した雄の成体 2 個体，亜成体 8 個体において，総排泄腔内と精巣内の精子の存在を，光学顕微鏡を用いて調べた．その結果，成体と判断された 2 個体からは総排泄腔内に精子が観察されたが，亜成体と分類された個体では精巣内に精子があっても総排泄腔内に精子は見られなかった (表 2-2)．従って，総排泄腔内に精子のみられた個体を成体の雄の試料に加えても差し支えないと判断された．
試料を幼体，亜成体，成体に分類することによって，それぞれの成熟段階の甲長分布を知ることが可能である．そこで，性成熟がはじまる甲長を幼体から亜成体に性成熟階級が移行する SCL，性成熟が完了する甲長を亜成体から成体に性成熟階級が移行する SCL と定義した．性成熟がはじまる SCL の範囲は幼体の最大値から亜成体の最小値までの範囲とし，性成熟が完了する SCL の範囲は，亜成体の最大値から成体の最小値とした．また，性成熟の始まる SCL を半数の個体が性成熟をはじめる甲長，性成熟を完了する SCL を半数の個体7

が性成熟を完了した甲長として求めた．試料を SCL 20 mm ごとの階級に分け，それぞれの階級で幼体と亜成体に占める亜成体の割合，あるいは，亜成体と成体に占める成体の割合を求め，亜成体あるいは成体の割合 = K / (1+b・e-c・SCL)のロジスティック曲線で回帰し，その割合が 50％となる SCL を求めた．それを性成熟のはじまる甲長および性成熟が完了する甲長とした．

2-3．結果と考察
アカウミガメ 152 個体を解剖して生殖腺の外部形態より性を判別した．その結果，雄と判別されたのは 46 個体，雌と判別されたのは 106 個体であった．それぞれの，標準直甲長(SCL: mean ± SD [min–max])は，雄が 745 ± 56 mm (577–877 mm)で，雌が 758 ± 59 mm (601–919mm)であった．また，生殖腺と生殖管の形態より性成熟階級を判別した結果，幼体は雄が 6個体で雌が 12 個体，亜成体は雄が 36 個体で雌が 67 個体，成体は雄が 4 個体で雌が 27 個体に分類された．これに総排泄腔内に精子が見られた雄 8 個体を雄の成体 4 個体に加え，雄の成体を 12 個体として以後の解析を行った．
性成熟階級ごとの SCL (mean ± SD)は，幼体の雄が 680 ± 65 mm (577–750 mm, n = 6)で雌が688 ± 38 mm (601–726 mm, n = 12)，亜成体の雄が 745 ± 38 mm (686–826 mm, n = 36)で雌が744 ± 44 mm (636–853 mm, n = 67)，成体の雄が 838 ± 43 mm (range: 778–902 mm, n = 12)で雌が 821 ± 43 mm (738–919 mm, n = 27)であった (図 2-3)．ここで求めた幼体の SCL は高知県と8三重県の大型定置網で混獲された試料中の幼体の SCL の値である．アカウミガメの孵化幼
体の SCL は 41.9 ± 1.51 mm (松沢・坂本, 2002)であることから，孵化幼体を除くと雄では680 ± 65 mm ，雌が 688 ± 38 mm の幼体が調査地に来遊した．また，亜成体に分類された個体が最も多く，日本近海は性成熟が始まり完了する海域であることが明らかになった．
次に，成体と分類された雄が 838 ± 43 mm で，雌が 821 ± 43 mm であった．雌で成体と分類された個体は，すべて，卵管内に殻のついた卵を保持していた．このことは，調査地である高知県や三重県の沿岸に回遊する成体の雌は，すべて，産卵を目的とした個体であることを示している．また，成体の雌が捕獲されたのは産卵期にあたる 4 月の下旬から 8 月の上旬に限られていた．これも雌の成体が産卵のときしか，沿岸に近づかないことを示している．産卵後の雌は日本の沿岸を離れ，東シナ海や太平洋の沖合の餌場へと移動していくことが衛星発信器による追跡結果から示唆されており(Sakamoto et al., 1997; Hatase etal., 2002a; Hatase et al., 2002b; 日本ウミガメ協議会, 未発表データ)．
また，幼体，亜成体，成体のいずれでも SCL に雌雄の有意差が認められなかった (p > 0.05,

Mann-Whitney U-test)．これは，アカウミガメが成長に伴って雌雄とも同じように性成熟が進行することを示している．Kamezaki (2003)は屋久島近海の成熟したアカウミガメで雌雄の甲長に差が見られないことを報告しており，南太平洋や地中海の個体群でも成熟した雌雄の甲長に違いは認められていない (Limpus, 1985; Casale et al., 2005)．そのため，以後，雌雄を合わせて解析を行った．
9

次に，性成熟がはじまる甲長および性成熟が完了する甲長を推定した．性成熟がはじまる甲長は幼体から亜成体へと移行する甲長であり，亜成体の最小値 636mm から幼体の最大値 750mm までの範囲が性成熟の始まる SCL であることが分かる (図 2-3)．同様にして，性成熟が完了する甲長は亜成体から成体へと移行する甲長であり，成体の最小値 738mm から亜成体の最大値 853mm までの範囲が性成熟を完了する甲長の範囲であった．
また，これらの範囲の中で半数の個体で性成熟がはじまる甲長と，性成熟が完了する甲長を推定するため，SCL 20 mm 単位で幼体，亜成体，成体それぞれの個体数を求めた (図2-4)．性成熟がはじまる甲長の範囲内での幼体と亜成体に占める亜成体の個体数の割合も，性成熟が完了する甲長の範囲内での亜成体と成体に対する成体の個体数の割合もロジステ
ィック曲線で回帰された (図 2-5)．ロジスティック曲線は以下の 2 式で示された．
亜成体の割合 = 0.9585 / (1+1.298・10-30・e-0.1052 SCL)
成体の割合 = 1.028 / (1+1.202・10-13・e-0.02791 SCL)
これらの２式より，半数が性成熟をはじめる SCL は 660 mm，半数が性成熟を完了する
SCL は 821 mm と求められた．
性成熟を完了する SCL 821 mm は，成体に分類された個体の SCL の平均 824 mm より 3mm 小さかった．成体の甲長の平均値が性成熟を完了する甲長の平均値を上回ることは，南太平洋のアカウミガメでも観察されており (Limpus, 1985)，性成熟後も僅かながら成長を続けることに起因すると考えられる (Limpus, 1985; Hatase et al., 2004)．また，混獲された成体
10の SCL の平均値は日本で産卵上陸する個体の SCL，848 ± 50.8 mm (亀崎他, 1995)より 27mm 小さい．これらのことは，本研究で捕獲された成体は性成熟を完了して，さほど年数が経過しないことを示唆している．
これらの結果を基に，雄の尾部伸長が性成熟のどの階級で開始されるのかを第 3 章で考察し，日本の近海に加入する際の性成熟階級や日本近海に生息する集団がどの性成熟階級で構成されているかを第 4 章で考察し，性成熟と年齢について第 5 章で考察する．また，
この章では性成熟が完了する甲長と成体の甲長から，成熟後に沿岸への出現する個体について考察した．

11

第3章

尾部伸長と性成熟

3-1．目的
カメ類の仲間では尾部伸長の程度は雄の性成熟の進行状況を表すとされ，一部の種を除いて性成熟の進行に伴う尾部の伸長が認められる (Kuchling, 1998)．アカウミガメ (Caretta

caretta)でも太く長く伸びた尾は成熟した雄を判別するのに最も特徴的な形態であり，この特徴は性成熟の過程で現れる (Pritchard and Trebbau, 1984; Wibbels, 1999; Kamezaki, 2003)．従って，尾部伸長は雄の二次性徴の発現を代表する形態変化として，性成熟の進行状況を測る指標として期待される．
アカウミガメの尾部伸長の始まる甲長については地中海と北太平洋における報告がある(平手, 2000; Casale et al., 2005)．すなわち，Casale (2005)は地中海のアカウミガメは曲甲長
70 cm で尾部伸長を開始すると推定しており，平手 (2000)は北太平洋のアカウミガメの尾部伸長が開始されるのは直甲長で約 680 mm と求めた．しかし，これらの研究の問題は雄の判別を尾部の長さで判断していることである．つまり，尾部の伸長の見られない雄が存在し，それが雄として扱われていない場合，尾部の伸長が始まる甲長は低く算出されている可能性がある．
また，成熟した個体での尾部の伸長程度については南太平洋において調べられている(Limpus, 1985)．それによると，未成熟な雄では，背甲後端から尾部先端までの長さが 20 cm
12未満であり，20 cm 以上あれば成熟した個体とみなすとしている．しかし，雄が性成熟をはじめる甲長や成熟に達する甲長は個体群によって異なっている可能性が高い上，北太平洋の個体群では性的な成熟の状態と尾部の伸長の程度が比較されたことはない．
そこで，本研究では北太平洋のアカウミガメについて性成熟状態と甲長および尾長との関連について検討した．

3-2．方法
尾部の伸長と性成熟との関係を調べるため，性別や性成熟の状態が異なるアカウミガメ
128 個体の標準直甲長 (SCL: Straight Carapace Length)と尾長 (TL: tail length)を計測した．なお，TL は腹甲後端から総排泄口までの長さとした (図 3-1)．個体ごとの性は，死亡していた 120 個体では解剖により生殖腺と生殖管の形態を観察して判別した．また，Limpus and

Limpus (2003)および Miller and Limpus (2003)に従い，生殖腺と生殖管の形態より，雌雄それぞれで幼体・亜成体・成体に分類した (表 2-1，第 2 章参照)．生殖腺と生殖管を観察できなかった生存個体 8 個体は，総排泄腔内に精子があり，尾部の伸長が顕著であったことから雄の成体に分類した．また，これらの個体は 2005 年 4 月から 2010 年 8 月の間に高知県室戸市と三重県紀北町の定置網で捕獲された．
次に，雄の尾部伸長がはじまる甲長を求めた．雄の尾部伸長の開始点は雌雄の尾長に違いが現れはじめる点とし，TL を SCL で除した相対尾長 (rTL: relative tail length, TL/SCL)と13

SCL との回帰直線の交点として求めた．回帰直線は性成熟のはじまっている亜成体および成体のデータを用いて求めた．
また，尾部の伸長の程度を表すため，TL の相対成長係数を求めた．相対成長係数とは関係式 Y = b・Xa で示される定数 a のことであり，a = 1 の時に X の成長に対する Y の成長は等成長となる．ここでは SCL を X，TL を Y として，定数 a が 1 以上であれば SCL に対す
る TL の成長は優成長とした．

3-3．結果生殖腺と生殖管の形態観察の結果，雄は 45 個体で雌は 83 個体であった．また，これらの個体は幼体・亜成体・成体の 3 つの性成熟階級に分類され，幼体では雄が 5 個体で雌が 8個体，亜成体は雄が 29 個体で雌が 55 個体，成体が雄 11 個体で雌が 20 個体であった．性成
熟階級ごとの相対尾長 (rTL: mean ± SD) は，幼体では雄が 0.149 ± 0.030 (0.121–0.187, n = 5)で雌が 0.146 ± 0.026 (0.108–0.174, n = 8)，亜成体では雄が 0.249 ± 0.070 (0.157–0.446, n = 29)
で雌が 0.165 ± 0.228 (0.113–0.228, n = 55)，成体では雄が 0.423 ± 0.061 (range: 0.302–0.501, n =11)で雌が 0.183 ± 0.036 (0.136–0.277, n = 20)であった．
rTL は幼体では雌雄で差が認められなかったものの，亜成体や成体では明確に雄の方が長く (図 3-2, p < 0.001, Mann-Whitney U-test)，亜成体になった後に雄の尾長が伸長し，rTL に性差が生じはじめることが明らかになった．また，雄では SCL に対する TL の相対成長係
14

数 (a)から亜成体の TL は強い優成長を示したが (a = 4.3898, n = 29, r2 = 0.5542, p < 0.01, 無相関検定)，成体では有意な相関が認められなかった (a = 2.2384, n = 11, r2 = 0.4424, p > 0.05,
無相関検定)．ここで，興味深いことに雌においても成体の rTL が幼体の rTL よりも顕著に大きくなっていた (p < 0.05, Tukey の方法による多重検定)．雌の相対成長の程度は成体だけ
では求められなかったが (a = 1.3266, n = 29, r2 = 0.1084, p > 0.05, 無相関検定)，成体と亜成体をあわせて相対成長係数を求めると，雌の尾長も雄ほど顕著ではないものの優成長を示し，性成熟とともに尾部が伸長することが示された (a = 1.7528, n = 83, r2 = 0.3366, p < 0.01,
無相関検定)．
次に，雌雄の尾部の長さに違いが出はじめる甲長を求めるため，雌雄それぞれで成体と亜成体における SCL と rTL を直線で回帰した (図 3-3)．回帰直線は，雄では SCL = 0.001433
rTL‐0.8046 (r = 0.8066)で，雌では SCL = 0.0001501 rTL + 0.05475 (r = 0.2547)であった．雄の二次性徴が開始される SCL と rTL を雌雄の回帰直線の交点とした時，SCL は 670 mm，rTL
は 0.155 と求められた．

3-4．考察本研究では北太平洋での雄のアカウミガメの尾部伸長は SCL 670 mm から開始されることが示された (図 3-3)．雄の尾部伸長は精巣から分泌されるテストステロンに代表される雄性ホルモンによって促されると考えられており，アオウミガメでは 42 ヶ月齢の幼体に性腺
15

刺激ホルモンを投与したところ，雄の尾部が伸長したことが確かめられている (Owens et al.,1978)．第 2 章では北太平洋のアカウミガメについて，半数の個体が性成熟を開始する甲長は SCL 660 mm であることが明らかにされており，雄の尾部伸長がはじまる 670mm の SCL
は性成熟を開始する 660mm より 10 mm だけ大きい．
このことは精巣の発達がはじまった後，直ちに尾部の伸長がはじまることを示している．このことから雄の尾部伸長は性成熟の開始によって精巣から分泌される雄性ホルモンの量の増加に敏感に応答することが示唆される．
これまで北太平洋のアカウミガメでは，平手 (2000)が沖縄県で混獲された 29 個体について SCL と尾長 TL の関係から，SCL が約 680 mm で雄の尾が伸び始めるとしており，本研究の結果にくらべて 10 mm 大きな値であった．本研究と平手 (2000)との結果に生じた違いを説明する理由はいくつか考えられる．一つめは平手 (2000)が尾部の長くみえる個体を雄としたため，実際には雌の個体を誤って雄とした可能性が考えられる．本研究では雌も雄ほどではないが尾部が伸長することが示されており，平手 (2000)の図 12 をみると，SCL
700–800 mm の範囲に雄として解析されているが雌の可能性もある個体がいる．そのため，
雄の回帰直線がずれ，雌雄の回帰直線の交点の SCL が大きくなった可能性がある．
二つめの理由としては，成熟した個体が平手(2000)の研究当時に比べ，小型化した可能性がある．徳島県美波町や宮崎県宮崎市ではおよそ 20 年の間に産卵個体が小型化しているとの報告があり (重田・亀崎, 2006; 竹下他, 2006)，2005 年から 2010 年の期間に計測した本研
16究の供試個体は，平手 (2000)が計測した 1996 年から 1999 年に比べて成熟甲長が小型化していた可能性がある．成熟甲長が小型化する要因のひとつに，個体群密度の減少により個体あたりの餌量が増加することで成熟が早まる補償的応答があり，鯨類などで確認されている (大隅, 1974)．北太平洋のアカウミガメは 20 世紀後半の約 50 年の間にその産卵巣の数が 50–90％も減少しており (Kamezaki et al., 2003)，補償的応答によって成熟個体の小型化が進んでいる可能性は否定できない．
三つめの理由としては，調査地の地理的な違いがあげられる．亀崎他 (1995)は鹿児島県
屋久島，宮崎県宮崎市，和歌山県みなべ町 (旧南部町)の産卵個体の甲長を比較し，南に位置する産卵地ほど甲長が大きいことを報告している．本研究の調査地である高知県室戸市と三重県紀北町は平手 (2000)の調査した沖縄島よりも北に位置しており，北太平洋の中では産卵個体に限らず南に生息する個体ほど甲長が大きい可能性も考えられた．
次に，成熟がはじまった後の雄の尾部伸長は，亜成体の時に著しいことが相対成長係数の高さ (4.3898)から明らかであった．成熟した後も雄の尾部伸長が継続するかどうかは成体の SCL と TL の相関からは確かではないが，SCL に対する TL の相対成長係数は 2.2384 と成体でも優成長する傾向は見られた．SCL と TL の間に相関が認められなかったのは SCLの分布範囲が 778–902 mm と限られているためと考えられる．また，雄が成熟に達する時の
rTL は成体の最小値から亜成体の最大値の間にあると考えられ，飛び値となっている SCL
781 mm の亜成体の rTL 0.446 を除外すると，成熟に達する rTL は 0.302–0.363 の範囲となっ
17

た．この値は雄の成体の平均値 0.423 の 71.4–85.8 %の割合に過ぎない．そのため，成熟してからも雄の尾部の伸長は続くと推測される．
雌も尾長が SCL に対して優成長を示すことは本研究で初めて明らかとなった．雌の尾長が成熟に伴って優成長を示したことは，雌にとっても尾部が伸長することに繁殖活動に関わる機能的な意義があることを示唆する．雌にとって最も重要な繁殖活動のひとつに産卵があり，アカウミガメでは砂浜に掘った 34.9-85 cm の深さの穴に卵を産み落とす (Dodd,1988)．この時，雌は総排泄腔を反転させ掘った穴の中へ伸ばして産卵するため，尾部が長くなればその分だけ卵をより低い位置から産み落として落下の衝撃を和らげることができる．しかし，産卵直後のアカウミガメの卵の殻は柔らかく，キャッチボールをしても割れなかったとの話もあり(照本, 私信)，産卵時の落下による衝撃を緩和するためとは考えにくい．
雌の尾部伸長は産卵のためではなく，雄との交尾を拒否するために使われているのかもしれない．産卵前の雌が交尾を受け入れるのは産卵に先駆けた 2-4 日間程度だけとされ(Owens, 1980; Wood and Wood, 1980)，飼育下では雌が交尾を拒否する際に尾部を腹側にたたみ込み，後肢を合わせている姿が観察されることがある．幼体の尾部を観察すると，尾部は短いためにあまり動かすことができないが，尾部が伸長した雌では尾部を腹側にたたみ込むことで総排泄口を隠すことができるようになる．
あるいは機能的意義はないという可能性も考えるべきであろう．尾部伸長を促す雄性ホ18

ルモンは雌の体内にも存在し，交尾域への回遊や排卵を促すなど，雌の繁殖生理にも関わっている (Wibbels et al., 1990)．そのため，雌も雄性ホルモンの影響を受けており，その分だけ尾部が伸長したにすぎないことは否定しきれない．実際に雌の尾長伸長に繁殖に関わる機能的意義があるかどうかを知るには，交尾時や産卵時など繁殖に関わる行動の際の，尾部の使い方に関する行動学的な観察が必要である．

19

第4章

繁殖海域である日本近海への再加入サイズ

4-1．目的北太平洋ではアカウミガメ (Caretta caretta)の産卵地は太平洋西部に位置する日本に限定されており，特に南日本の太平洋岸に集中する (Kamezaki et al., 2003)．産卵地のない北太平洋の中央部や東部海域にあたるハワイ諸島やカリフォルニア半島近海にもアカウミガメは分布しており，それらの個体のミトコンドリア DNA のハプロタイプは日本の産卵個体と同一で (Bowen etal., 1995)，北太平洋各地に生息するアカウミガメは日本で産したものであることが示された．それを裏付けるかのように，日本から標識放流された幼体がカリフォルニア半島沖で再捕獲され(Uchida and Teruya, 1991)，カリフォルニア半島から放流した飼育個体が太平洋を横断して日本まで辿り着いている (Resendiz et al., 1998; Nichols et al., 2000)．このように，北太平洋では東西でのアカウミガメの移動が認められている．こうした状況から孵化幼体は黒潮および海流に乗って東部太平洋へと移動し，その後再び繁殖海域である日本近海に戻ってくることが示唆されている．

しかし，繁殖地である日本近海に産卵を目的とする成熟した雌が生息することは明らかなものの，実際に生息している個体の甲長分布や成熟度などは断片的な情報がいくつかあるにすぎない(野村, 1993; 宮脇, 1994; 前田・木村, 1995; 岩本他, 2005b; 田中・石原, 2006)．そのため，日本近海におけるアカウミガメの性成熟の状態，さらには甲長組成や性比，年齢構成などの情報は定20

かではなかった．そこで，本章では定置網で捕獲されたアカウミガメから，日本近海に生息する

アカウミガメの甲長分布や生活史における性成熟の段階を明らかにし，日本近海の繁殖海域へ戻ってくる甲長について議論した．

4-2．方法高知県室戸市の大型定置網で，2002 年 7 月から 2009 年 11 月までの期間に混獲された 1392 個

体のアカウミガメを試料とした．定置網は年間を通して一定の場所に固定されていることから，

試料は室戸岬近海に生息する集団から無作為に採取されているとみなした．調査を行った定置網が設置されているのは高知県室戸市室戸岬町の地先で，沿岸に設置された 3 つの漁業団体 (大敷組合)が操業する７つの大型定置網を用いた (図 2-1)．室戸岬には水深 500–1000 m を流れる北太平洋中層流が大陸棚にぶつかるため，栄養塩の豊富な海水が局地的に湧昇している (深澤, 1998)．

基幹漁業は陸棚斜面近くの水深 35–78 m の位置に設置された大型定置網で，1 漁業団体あたり年間 1500–2000 t が水揚げされている．主な漁獲対象種はブリ (Seriola quinqueradiata)，ゴマサ
バ (Scomber australasicus)，マルソウダ (Auxis rochei)などである．
捕獲されたアカウミガメは漁港まで運ばれ，標準直甲長 (SCL: straight carapace length)を計測した後，漁港または定置網の沖合で 1 日以内を基本として放流された．

本研究では捕獲されたアカウミガメを SCL で 4 つの性成熟階級に分類した．すなわち，SCL 42mm 以下を孵化幼体，43–660 mm を幼体，661–821 m を亜成体，822 mm 以上を成体とした．
21

また，これらの階級を分ける SCL は次の研究によった．孵化幼体と幼体を分ける SCL 42 mm は，

北太平洋個体群の孵化幼体の SCL が 41.9 ± 1.51 mm であることを用いた (松沢・坂本, 2002)．
また，幼体と亜成体を分ける SCL 660 mm と亜成体と成体を分ける SCL 821 mm は，それぞれ半数の個体で性成熟が開始される甲長と半数の個体が成熟する甲長を用いた (第 2 章)．

4-3．結果と考察

高知県室戸市の大型定置網では 2002 年 7 月から 2009 年 11 月までの期間に 1392 個体のアカウミガメが捕獲され，標準直甲長 (SCL)が計測された．これら混獲されたアカウミガメの SCL は

757 ± 67 (SD) mm (range: 563–1050 mm) で，SCL のヒストグラムは単峰性を示した (図 4-1)．

最も割合の多かった性成熟階級は亜成体で 77.7 % (1081 個体)を占め，次いで成体が 17.6 % (245個体)，幼体が 4.7 % (66 個体)で続き，孵化幼体は 1 個体も見つからなかった．試料のなかで最小の個体の SCL は 563 mm で，幼体の甲長範囲の中では比較的大きく，幼体でも後期に達していると言えた．以上のことから，繁殖地である日本の近海には，幼体後期の段階で出現するようになり，成体よりもむしろ亜成体のアカウミガメが多く生息することが明らかになった．また，北太平洋のアカウミガメは日本の砂浜を唯一の産卵地としており (Kamezaki et al., 2003)，孵化幼体は少なくとも孵化した直後には日本近海にいるはずだが，本研究では孵化幼体は 1 個体も見つからなかった．これはアカウミガメの孵化幼体は，孵化後，急速に海洋に分散し，黒潮やメキシ

コ湾流といった高緯度海域へ向かう海流を利用して外洋に分散するため (Carr, 1986; Carr,
22

1987; Bowen et al., 1995; Witherington, 2002)，沿岸からは速やかにいなくなったためと考えられた．また，黒潮の本流は調査を行った定置網よりも沖合を流れており，定置網の沖合を移動する孵化幼体は捕獲されなかったと考えられた．

SCL の分布から日本近海のアカウミガメを見ると，SCL が 560–570 mm で日本近海に出現し始めたアカウミガメは 740–750 mm で最頻値を迎えるまで増加し，その後減少に転じている (図4-1)．ここでの増加要因は日本近海への再加入であり，減少要因は混獲死 (Peckham, 2007; FAO,

2009)や船舶との衝突，主にサメによる被食 (Witzell, 1987)，疾病による死亡 (George, 1997) などが主因として考えられる．調査地からの移出による減少も考えられるが，本調査地には北太平洋最大の産卵地である鹿児島県屋久島をはじめ，宮崎県宮崎市の砂浜や和歌山県みなべ町といった主要な産卵地で産卵する成体の雌が来遊してくることが四肢にとりつけた標識によって確認されており (日本ウミガメ協議会, 未発表データ)，移出による影響はそれほど大きくはないと考えられた．従って，最頻値以前の SCL の階級では再加入個体数が死亡個体数を上回り，最頻値以後のサイズクラスでは逆に死亡個体数が再加入個体数を上回っていると推察された．アカウミガメ

も 他 の 生 物 と 同 様 に 大 き く 成 長 す る ほ ど 死 亡 率 は 低 下 す る と 考 え ら れ て お り (National

Research Council, 1990)，死亡率のより低い大型のサイズクラスでの個体数減少は日本近海への再加入個体数の減少を示唆している．以上の理由から，日本近海に再加入する主なサイズクラス

は最頻値以下の SCL 560–750 mm であると推察された．この再加入する甲長には性成熟のはじまっていない幼体の後期の個体も含まれていた．従って，性成熟のはじまる前から日本近海へ再加23入する個体もおり，繁殖海域へ向けての大洋横断は性成熟の進行とは関わりなく行われると考えられた．

北太平洋東部のカリフォルニア半島沿岸に分布するアカウミガメの甲長には SCL 46.9 ± 13.0

cm (n = 39, range: 32–58 cm [Ramirez-Cruz et al., 1991]), SCL 585 ± 111 mm (n = 180, range:
266–834 mm [Gardner and Nichols, 2001]), 619 ± 21 mm (n = 15, range: 435–927 mm[Seminoff et al., 2004])との報告があり，甲長の平均と最頻値は幼体サイズで日本の集団よりも小さかった．カリフォルニア半島沿岸は日本で孵化したアカウミガメが幼体期に利用する生息域の一つであり (Bowen et al., 1995)，ここに加入した個体は年月が経過するとここから離れていくと考えられている．カリフォルニア半島に漂着したアカウミガメでは SCL 500–700 mm に最頻値を持つ単峰性の甲長分布を示しており (Gardner and Nichols, 2001)，このことはカリフォルニア半

島沿岸のアカウミガメは SCL 500–700 mm に達した頃に沿岸を離れはじめることを示唆している．このカリフォルニア半島近海を離れはじめるサイズクラスはほぼ幼体サイズで，日本近海に再加入すると推定された SCL 560–750 mm より範囲の下方で 60 mm，上方で 50 mm 小さかった．

繁殖海域へ向けた太平洋横断にかかる期間は SCL 856 mm あるいは SCL 834 mm まで飼育されたアカウミガメで確かめられており，カリフォルニア半島から日本に移動しおよそ 1 年で到達している (Resendiz et al., 1998; Nichols et al., 2000)．また，ハワイ諸島の北側で捕獲された SCL

548 ± 123 mm の野生の幼体 9 個体は 2.4–6.9 ヶ月の間に西向きに 1311–5199 km 移動しており
24

(Polovina et al., 2000)，これは 1–2 年で太平洋を横断できるペースであった．また，Nichols et al.

(2000)と Polovina et al. (2000)は衛星発信器を用いて個体を追跡しており，追跡された個体は北赤道海流を利用することなく能動的に西へ向かって移動していた．ここで，北大西洋で骨年代学的手法によって推定されたアカウミガメの成長速度は SCL 500–599 と 600–699 mm でそれぞれ

28–38 と 27–31 mm/year であり (Parham and Zug, 1997)，前述された太平洋横断時の 50–60

mm の成長量はアカウミガメが繁殖海域に向けた太平洋横断にかける期間が 1.3–2.2 年であることを示唆している．従って，アカウミガメは幼体の後期に繁殖海域へ向けた太平洋横断を開始し，いったん横断を開始すると能動的に日本を目指し，およそ 1–2 年で到達するものと示唆された．

25

第5章

北太平洋におけるアカウミガメの成長速度と性成熟年齢

5-1．目的個体の年齢や成長速度に関する情報はその動物の生活史を明らかにするだけでなく，個体群サイズの動態を把握する上でも必要不可欠である．その中でも性成熟年齢や成長速度
は次の世代が産まれるまでに必要な期間を知り，個体数の増減を予測するために必要な情報である．アカウミガメ (Caretta caretta)は北太平洋では南日本の太平洋岸を主要な産卵地として繁殖している．
しかし，その産卵巣数は 20 世紀後半のおよそ 50 年間の間に 50-90%も減尐しており，絶滅が危惧されている (Kamezaki et al., 2003)．そのため，適切な保全策を取ることが必要となるが，北太平洋のアカウミガメでは性成熟年齢や成長速度は明らかでなく，効率的な保全策を検討する際や，実施した保全策の効果を検証する際に，支障があるのが現状である．
本章で明らかにするアカウミガメの性成熟年齢は，古くは飼育個体を用いて調べられてきた．内田 (1967)は，孵化幼体からアカウミガメを飼育し，ともに 6–7 年で成熟すると報告している．しかし，飼育個体では餌料の量や栄養価が高いために野生個体に比べて成長が早いと考えられ，野生個体の性成熟年齢として適用することはできない (Frazer, 1982)．
野生下でのウミガメ類の性成熟年齢を知る方法としては，現在では主に標識再捕獲法と骨年代学的手法によって成長速度や年齢が調べられている．
26

標識再捕獲法は，一度捕獲された個体に標識をつけて放流し，再び捕獲されるまでの期間の成長量から成長速度を割り出す方法である．また，求めた成長速度とその時の甲長を成長式に当てはめ，その成長式を基に性成熟甲長まで達するのに必要な年数を算出することで性成熟年齢も見積もられている．ウミガメ類に装着される標識は，多くの場合前肢あるいは後肢に装着するフリッパータグであり，その材質には硬質プラスチック，チタン，
インコネル，モネルなどが用いられている (松沢・亀崎 2008)．ただし，標識もウミガメの長い生活史を追跡するには耐久性がなく，性成熟年齢を明らかにする手法としては不十分である．また，標識する以前の情報がないため，それまでの成長速度は測れない．また，当歳の個体など，外見から明らかに年齢の分かる個体でなければ年齢情報は得られず，その後どれだけ追跡出来ても年齢は分からない．また，標識を装着しても，再捕獲できなけ
れば成長速度を調べることができない．
骨年代学的手法では骨の内部に残された成長停止線 (LAG: lines of arrested growth)の本数から年齢が推定される．LAG は成長速度が落ちる時期に形成され，ウミガメ類では水温の低下する冬期に LAG は形成され，
基本的に１年に１本であるとされている (Zug et al.,
1986; Snover and Hohn, 2004; Snover et al., 2007)．骨年代学的手法をウミガメ類に適用する際には上腕骨が主に用いられるが (e.g. Zug et al., 1986; Klinger and Musick, 1995;
Zug et al., 1995; Parham and Zug, 1997; Bjorndal et al., 2000; Zug et al., 2002; Bjorndal
et al., 2003; Zug et al., 2006)，オサガメでは眼球にある強膜小骨が利用されている (Zug27and Parham, 1996; Avens et al., 2009)．自然条件下での成長速度や年齢と体サイズの関係，性成熟する年齢はこれらの方法によって求めることができる．骨年代学的手法の問題点は，骨の中心部の骨組織が成長とともに吸収されていき，そこにあった成長停止線も吸収されてしまうことにある．また，LAG が密に詰まっている場合や LAG がはっきりしない場合などは，LAG の読み落としや読み違いが起こり得る．さらに，LAG が形成されるのは成長速度が低下した時であるので，季節とともに移動することで成長速度の変化が尐ない場合
や疾病や怪我による一時的な成長の停滞があった場合，1 年に複数本の LAG が形成される可能性もある．
アカウミガメはウミガメ類の中では比較的よく性成熟年齢や成長速度が調べられている種である．標識再捕獲の結果を成長曲線に性成熟年齢を当てはめて求められた研究が多く，性成熟する年齢は北大西洋で 12–47 歳 (Frazer and Ehrhart, 1985)，あるいは 10–15 歳(Mendonca, 1981)と推定され，南太平洋では 35.9 歳 (Frazer et al., 1994)，地中海では
16–28 歳 (Casale et al., 2009a)と推定されている．また，生成熟年齢は上腕骨を用いた骨
年代学的手法によっても求められており，北大西洋では 22, 26 歳 (Klinger and Musick,1995)，や 20–63 歳 (Parham and Zug, 1997)，13–15 歳 (Zug et al., 1986)で成熟すると推定されている．
一方，アカウミガメは個体群間で産卵に上陸する雌の甲長，すなわち成熟サイズが異なっている (Tiwari and Bjorndal, 2000; Kamezaki, 2003)．このように形質に地理的変異が28

あることを考えると，成長速度や性成熟年齢といった形質にも個体群間で変異が存在すると考えられる．しかし，北太平洋では年齢や成長速度に関する研究はほとんど行われていない．北太平洋では性成熟する年齢は調べられておらず，SCL 46.6 cm までの幼体の年齢や成長速度 (Zug et al., 1995)と産卵個体の成長速度 (Hatase et al., 2004)が調べられているだけである．このような研究の状況の中，本章では，日本近海で得られたアカウミガメの上腕骨を用いて，性成熟する年齢を推定するとともに，日本近海に生息するアカウミガ
メが性成熟するまでの成長を明らかにした．

5-2．方法アカウミガメの年齢および成長を，骨年代学的手法によって骨中に残された成長停止線(LAG: lines of arrested growth)から推定した．試料として，日本で混獲死および死亡漂着したアカウミガメ 79 個体の上腕骨を用いた．これらの個体は上腕骨を採取する前に標準直甲長 (SCL: Straight Carapace Length)を計測し，さらに生殖腺より雌雄の判別を行った．
また，生殖腺の成熟度から第 2 章と同じように，卵巣に黄体や白体が見られる雌，および円筒形に肥大した精巣を持つ雄を成体，すなわち成熟個体とした．また，日本の産卵地で砂中の産卵巣から脱出できずに死亡したふ化幼体 6 個体の SCL および上腕骨直径を成長の起点となる値として用いた．
上腕骨の LAG は最小幅部 (MW: minimum width)と三角筋稜の間に最も多く残存してい29

ることが知られている (Zug et al., 1986; 図 5-1)．LAG を観察するため，この部分を電動丸ノコで切り出し，砥石で削って 1mm 以下の厚さの切片を作成した．切片の中心を同心
円 状 に 広 が る LAG の 中 心と し ， 下 から の 透 過光 に よ り 読 取顕 微 鏡 (KENIS Ltd.,NRM-2XZ/KN3102250)を用いて長径に沿って LAG の半径と LAG と LAG の間の幅を計測した (図 5-2)．ただし最外の LAG では幅の形成期間が１年に満たないため解析から除外した．また，吸収されずに残った LAG の数は切片の両端で異なり，多いものではその差は 20本になった．そのため，解析には読み取れた LAG の数が多い側の半径と幅を用いた．
LAG は形成された当時は上腕骨の外縁部分であり，MW と SCL との間には直線的な相関関係が認められたことから (式 5-1)，LAG 半径を形成当時の MW に補正すれば，そのLAG の補正値は LAG が形成された当時の SCL に比例すると考えられた．そこで，各 LAG
形成時の SCL を推定するため，LAG の半径と幅を MW で補正した (式 5-2)． また，LAGの幅は次の LAG が形成されるまでの 1 年間の上腕骨の成長量を示している．上腕骨の成長
量は SCL の成長量と比例するため，LAG の半径と幅から各 LAG 形成時の SCL とその当時の成長速度を逆算した．これを Back Calculation protocol とする (Zug et al., 1997)．

SCL = 26.3 MW + 14.1 (R2 = 0.955, n = 79, p < 1.0 x 10－42, 無相関検定)

式 5-1

Lrev = 2 L・R / MW

式 5-2

Lrev: LAG 半径または幅の補正値，L: LAG 半径または幅，R: 切片半径30

上腕骨に残された LAG から年齢を推定するためには，上腕骨の中心部にあった吸収された LAG の数を推定する必要がある．吸収された LAG 数を推定するため，Regression
Growth protocol と Correction Factor protocol を用いた (Zug et al., 1995; Parham andZug, 1997)．
Regression Growth protocol では Parham and Zug (1997)に従い von Bertalanffy の成長式を変形した式 5-3 を MW から求める年齢推定式とした．また，MW は SCL と比例関係にあることから(式 5-1)，性成熟するときの SCL および再加入時の SCL に対する MW を求め，その MW より式 5-3 を用いて性成熟年齢および再加入年齢を推定した．ここで，成熟する SCL は，第 2 章で求めた半数の個体が性成熟に達する SCL の 821 mm を用い ，日本近海へ再加入する SCL は，第 4 章で明らかにした 560–749 mm を用いた．

t = ln [(a‐X0) / (a‐MW / 2)] / k

式 5-3

t: 推定年齢，X0: 孵化幼体の MW 半径，a: 漸近値 (asymptote)，k: 内因性成長係数(intrinsic growth coefficient)

式 5-3 中のパラメータ a，k，X0 を求めるため，まず LAG の半径と幅の補正値を直線回帰し (図 5-3)，回帰直線の切片 (A: 0.7669) と傾き (B:‐0.0393)を a = |A /B|，k =‐ln(131

‐|B|)に代入し，a を 19.514，k を 0.0401 と求めた．次に，孵化幼体の MW は 1.77 ± 0.12(SD) mm (n = 6)であり，その半径である X0 は 0.88 mm となり式 5-3’が求められた．

t = ln [37.26 / (39.02‐MW)] / 0.040

式 5-3’

次に，Regression Growth protocol では年齢に対する SCL の成長式を von Bertalanffyの成長式より SCL = a’ {1‐exp[‐k’(t’‐t0’)]}として求めた．まず， 1 歳ごとの SCL を式
5-3 より求め，それを基に成長式の各パラメータ a’， k’，t0’を Microsoft Excel のソルバー機能を用いて最小二乗法により算出した．
次に，Regression Growth protocol では各個体についてそれぞれの年齢を推定できなかったため，Correction Factor protocol で個体ごと年齢を推定した．まず，個体ごとに LAG
幅の補正値の平均を求め，その逆数をその個体の CF (correction factor)とし，推定年齢を
式 5-4 より推定した．ただし，Correction Factor protocol では各個体で年齢を個別に求めることができる一方，成長速度の遅くなった外側の LAG 幅の平均から CF が導かれている
ため，吸収された LAG の数，すなわち推定年齢が過大評価されている可能性があった．

t = Lm + (Li‐X0) CF

式 5-4

Lm: 計測された LAG の本数，Li: 最も内側の LAG 半径の補正値
325-3．結果
上腕骨を用いて年齢を推定したアカウミガメ 79 個体の内 75 個体の標準直甲長 (SCL)の平均値は 759 ± 61 (SD) mm (range: 577–944)で，4 個体では背甲が損壊していたために
SCL を計測できなかった．解剖して生殖腺の形態を観察したところ，雄は 27 個体で雌は42 個体であり，そのうち成熟した雌は 15 個体，成熟した雄は 3 個体であった．また，10個体では腐敗が進行しており，生殖腺が正常に認められなかったために性を判別出来なかった．各個体から 9.3 ± 4.3 本 (range: 3–20)，合計で 732 本の LAG が確認され，653 箇所
で幅が算出された．
Back Calculation protocol で求めた SCL の成長速度の平均は 13.9 ± 7.8 (SD) mm/year(range: 0.0–64.5)であり，求められた当時の SCL は 694 ± 75 (SD) mm (range: 374–935, n= 732)であった．SCL の階級別の成長速度は，31.7 mm/year (SCL 300–400 mm, n = 1),
29.5 ± 13.7 mm/year (SCL 400–500 mm, n = 7), 20.7 ± 12.4 mm/year (SCL 500–600 mm,
n = 58), 14.1 ± 7.4 mm/year (SCL 600–700 mm, n = 298), 11.9 ± 4.9 mm/year (SCL
700–800 mm, n = 257), 11.2 ± 5.4 mm/year (SCL 800–900 mm, n = 29), 10.4 ± 0.0
mm/year (SCL 900–1000 mm, n = 3)であった (表 5-1)．SCL の階級間で雌雄の成長速度を比較したところ，SCL 500–600 mm の階級のみ，雌雄の成長速度に有意な違いが認められ，この階級では雌の成長速度が雄に比べて速かった (p < 0.05, Mann-Whitney U-test, Tukey
33

の方法による多重検定, 表 5-1)．
Regression Growth protocol では，性成熟が完了する年齢を，第 2 章で求めた性成熟の完了する SCL が 821 mm であることから求めた結果，37 歳と推定された (図 5-4)．また，
アカウミガメが日本近海に再加入する SCL は，第 4 章で 560–749 mm と求めたが，この時の推定年齢は 18–31 歳であった．また，1 歳ごとに推定した SCL から，10 歳で 381mm，
20 歳で 599mm，40 歳で 842mm，60 歳で 952mm まで成長すると推定された．年齢に対する SCL の成長式は

SCL = 1159{1‐exp[‐0.03067 (t‐1.619)]}式 5-5と算出された (図 5-4)．
Correction Factor protocol において求めた CF は 2.76 ± 0.86 (n = 79, range: 1.03–5.08)であった．推定された年齢は，成熟した個体では雄が 38, 46, 47 歳 (n = 3)で雌が 43 ± 11
歳 (n = 15, range: 22–61)であり，未成熟な個体では雄が 34 ± 11 歳 (n = 24, range: 16–61)
で雌が 39 ± 12 歳 (n = 27, range: 17–61)であった (図 5-5)．成熟した個体でも未成熟な個体でも，性別による年齢の違いは認められなかった (p > 0.05, Mann-Whitney U-test)．そこで，雌雄の個体数を合わせて成熟した個体と未成熟な個体を比較した．その結果，成熟した個体の方が未成熟の個体よりも構成年齢が高かく，SCL も大きかった (p < 0.05,
34

Mann-Whitney U-test)．しかし，成熟した個体も未成熟な個体も年齢と SCL との間に明瞭な相関関係は認められず，
SCL が大きければ年齢が高いというわけではなかった (図 5-6,

p > 0.05, 無相関検定)．

5-4．考察5-4-1．成長速度
Back Calculation protocol により求めた成長速度は，標準直甲長 (SCL) 500–600 mm の階級では雌が雄よりも速かったが，それよりも SCL の大きな階級では雌雄の成長速度に差は認められていない (表 5-1)．成長速度に性差のある甲長の時には，雌雄で生息地が異なる
か，あるいは何らかの生理的な要因が働いているものと考えられる．SCL 500–600 mm は
北太平洋のアカウミガメにとって北太平洋東部から日本近海へ向かって太平洋を横断する
サイズにあたる (第 4 章)．地理的な条件が雌雄の成長速度に差をもたらしているならば，日本近海へ向かうルートが雌雄で異なると考えられる．しかし，本研究では雌雄が捕獲された場所は同一であり，成熟したアカウミガメは雌雄が同じ摂餌海域を利用していると考えられ (Limpus, 1985; Hatase et al., 2002b)，SCL 500–600 mm では性成熟のはじまっている個体はいないことから (第 2 章)，性成熟が開始される前にだけ雌雄の生息地や回遊の経路が異なるとは考えにくい．また，性成熟がはじまる前の個体では性ホルモンの影響で雌雄の成長速度に違いが出たとも考えにくい．
35

性差を与えるその他の要因としては，温度依存性決定機構を持つウミガメ類では孵卵期間中に経験する温度が考えられる．孵卵期間中の温度がその後の成長に影響を与えるなら
ば，性成熟前の個体の成長速度に性差がみられてもおかしくはない．アカウミガメやアオウミガメでは孵卵期間中の温度が低いほど大きな孵化幼体が生まれ (Glen et al., 2003;
Stokes et al., 2006)，Stokes et al. (2006)は孵卵温度が低い方が孵化後の成長は速いと推測している．ウミガメ類では孵卵期間中の温度が低ければ雄の割合が増えるため，孵化後は雄が雌より成長速度は速いこととなる．この場合，本研究で見られた雌の成長速度が雄よりも速かったのは，より甲長が小さい時には雄の成長速度が速く，それに対する補完的な応答なのかもしれない．飼育下では初期に成長の悪かった個体も成長するとともに他個体の甲長に追いつくことが観察されており (亀崎私信)，このことは初期の成長が遅くとも，
やがて他個体に甲長が追いつく，補完的な作用が働くことを示唆している．
次に，成熟する SCL 821 mm (第 2 章)より大きな甲長での成長速度は，SCL 800–900 mmの階級でも 11.2 ± 5.4 mm/year (n =29)，SCL 900-1000 mm の階級でも 10.4 ± 0.0 mm/year(n = 3)であった．日本で産卵する雌の成長速度は 2.5 ± 4.0 mm/year (Hatase et al. 2004)
であり，本研究で求めた成長速度はこれと比較して大きかった．これは，本研究で収集した試料である高知県室戸市と三重県紀北町で得られたアカウミガメは，成熟が完了してから間もない個体が多いことが原因と考えられる．つまり，上腕骨に残された成長停止線(LAG)は，成熟した後のものがほとんどないと考えられ，本研究で求められた成長速度は
36

SCL の大きさに関わらず，成熟が完了する以前の亜成体や幼体の時の成長速度であると考えられた．
本研究では北太平洋のアカウミガメの成長速度が，データ数の尐ない SCL 300–400 mmと 400–500 mm の階級をのぞき，SCL 500 mm 以上で明らかになった．北太平洋のアカウ
ミガメの成長速度はこれまで，標識再捕獲法によって産卵する雌の成長速度が計測され(Hatase et al., 2004)，骨年代学的手法によってふ化後 10 年で SCL 466 mm まで平均 42
mm/year の速度で成長すると推定されている (Zug et al., 1995)．北太平洋以外での未成熟な個体の成長速度は，南太平洋と地中海，北大西洋で調べられており，北大西洋で比較的よく調べられている．北大西洋の中でも成長速度は同一の甲長範囲でさえ地理的に違いがあることが知られており，調べられた個体数の多い SCL 600–700 mm での成長速度は，ア
メリカ合衆国東海岸の Chesapeake 湾で 14.6 ± 11.6 mm/year (n = 9, Klinger and Musick,1995)，North Carolina で 18.2 mm/year (95% CI: 15.9–20.5) (n = 122, Braun-McNeill etal., 2008)，Florida で 59.9 ± 22.5 mm/year (n = 7, Mendonca, 1981)であった．また，北太平洋ではこの SCL 600–700 mm での成長速度は 14.1 ± 7.4 mm/year (n = 261)であり，Chesapeake 湾や North Carolina の成長速度に近かったが，North Carolina の成長速度に比べるとおよそ 1/4 に過ぎなかった．また，地中海の成長速度は曲甲長 325–820 mm の時に 25 ± 17 mm/year (Casale et al., 2009b)で，北太平洋の SCL 374–935 mm (13.9 ± 7.8mm/year)の時より遅く，南太平洋の成長速度は曲甲長 750–950 mm の時の 9.5 ± 5.837mm/year で，北太平洋の SCL 700–800 mm (11.9 ± 4.9 mm/year)の時と同程度かあるいは
やや遅いようであった．しかし，北大西洋に見られたような同一個体群内でも地理的な成長速度の違いが北太平洋や南太平洋，地中海にもあるかもしれない．従って，北太平洋においても個体群内での差や個体差の程度，差の現れる要因の検証を続けることが求められ
る．

5-4-2．成熟する年齢
Correction Factor protocol で求めた成熟個体の年齢は，先に述べたように成熟個体は成
熟して 1-2 年以内の個体であることから，成熟した年齢にほぼ等しいと考えられる．
Correction Factor protocol による成熟個体の推定年齢の平均 (± SD)は 43 (± 10)歳であり，Regression Growth protocol で推定された成熟する年齢の 37 歳よりも高かった．これは，Correction Factor protocol では成長速度の遅くなった上腕骨外側の LAG の幅の平均値をもとに，成長速度の速かった内側の LAG の数を推定している一方，Regression Growth
protocol では甲長の小さな個体ほど成長速度は速く，内側の LAG ほど幅が広いものとして吸収された LAG の数を推定したためである．従って，北太平洋のアカウミガメが成熟する
平均年齢は 37–43 歳の間にあると考えられた．また，北太平洋の東部や中央部から日本近海に戻ってくる年齢が 18–31 歳であることが Regression Growth protocol より推定されており，性成熟年齢と比較すると，日本近海に再加入してから成熟するまでに 6-25 年が必要
38であると示唆される．
ただしここで，Correction Factor protocol では 21 歳の成熟個体や 61 歳の未成熟個体も確認されたことにも注目する必要がある．このことは 21 歳で成熟する個体がいる一方で，61 歳になっても成熟していない個体がおり，成熟する年齢の範囲が非常に広いことを示している．加えて，SCL と年齢の間には明瞭な相関関係が認められず，SCL 701 mm でも 61
歳と他個体に比べて老齢な未成熟個体や SCL 866 mm でも 29 歳と他個体より比較的若齢な成熟個体もいた(図 5-6)．すなわち，小型の成熟個体は必ずしも若いわけではなく，大型の成熟個体は必ずしも老齢なわけではなかった．
成熟する甲長や年齢はそれぞれの個体が生涯に残せる子孫の数に直接関係するため，ア
カウミガメの繁殖戦略を考える上で重要な要素である．例えば，雌では 1 産卵期に産む産卵巣の数と甲長には相関は認められないが，大型の個体ほど 1 巣あたりの卵数は多い(Frazer and Richardson, 1986)．そのため甲長が大きいほど 1 産卵期に産卵できる卵の総数は多くなる．また，成熟する年齢が若いほど生涯の繁殖機会は多くなると考えられる．
しかし，一旦成熟すると，未成熟のままでいるよりも甲長を大きくするのに年月がかかる．
これは，未成熟であれば SCL が 800–900 mm でも成長速度は 11.0 mm/year あるものの (表5-1)，成熟すると成長速度は 2.5 mm/year (Hatase et al., 2004)にまで遅くなるためである．
従って，成熟する前に体を大きくすることは 1 産卵期あたりの産卵数を多くするために必要である一方，体を大きくするために過ごした未成熟の期間は繁殖の機会を逃してしまい，
39若くして成熟することは生涯の繁殖機会を増やす一方，1 産卵期あたりの産卵数が尐なくなる．どちらの繁殖戦略がより多くの子孫を生涯で残せるかは，死亡率や産んだ卵の孵化率などにも影響を受ける．死亡率が低くなれば生涯に訪れる繁殖の機会が増えるため，1 産卵期あたりの産卵数が多い方が生涯に産む卵の総数の期待値は高くなり，死亡率が高くなれば早く産卵をはじめる方が生涯の産卵巣数の期待値が高くなる．ただし，これだけでは本研究で若く体の大きな成熟個体と高齢で小型のまま成熟する個体が確認されたことを説明できない．両者の違いは成長速度にあり，餌となる生物の密度や生物量が影響していると考えられる．これは，餌の豊富な飼育下では早ければ 6-7 年で成熟するとされ るが(Caldwell, 1962; 内田, 1967)，本研究で最年尐の成熟個体は 21 歳であったことから，餌の量が成長速度と性成熟年齢に大きな影響を与えることが分かる．また，産卵個体では摂餌
海域が個体によって異なり，餌の種や量が産卵個体の甲長に影響を与えていることが示唆されている (Hatase et al., 2002c)．このように，摂餌海域の餌の密度や生物量は成長速度に影響し，ひいては性成熟を完了する年齢や甲長に影響するため繁殖戦略にとって重要である．しかし，本研究でも明らかにされたように，アカウミガメは性成熟するまでに数十年を要し，北太平洋では 22-61 歳，平均的な年齢でも 37-43 歳で性成熟する．こうした世代交代に必要な年月が長い生物の場合，生まれてから性成熟して繁殖を開始する前の愛大に成育海域や繁殖地の環境が変化することは起こりえることである．さらに，アカウミガ
メが産卵地とする砂浜は動的で不安定な環境となっている．そのため，繁殖を開始するタ
40

イミングや成育する海域を分散させ，環境の変化に対するリスクも分散させているものと推察される．その結果，個体群の中でも多様な繁殖戦略が存在するようになり，多様な繁殖戦略は環境の変化への対応を可能にし，アカウミガメ属 (Caretta)が現れた鮮新世初期から 4.5–5 百万年もの間 (Dodd and Morgan, 1992)，氷河期などの環境変化にも対応できたのであろう．

41

第6章

ウミガメ類の生活史－成長と生息域－

6-1．ウミガメ類の生活史の概要
ウミガメ類の卵は砂浜の砂中に 1 巣あたり数十から百数十個産み落とされ，およそ 50–80日で孵化する (Mrosovsky and Yntema, 1982; Ackerman, 1997)．産卵から孵化までにかかる日数は砂中の温度によって変化し，砂中温度が高いほど早くなる (Mrosovsky and
Yntema, 1982; Ackerman, 1997)．また，孵卵中の砂中温度によって性が決定し，高温で雌，
低温で雄となり，性比が 1:1 となる臨界温度はおよそ 29 度である (Ackerman, 1997)．ウ
ミガメ類の孵化幼体は砂の中で孵化した後，砂表まで出てきて海に向かい (Carr, 1986;
Dodd, 1988)，フレンジーと呼ばれる前肢を非常に活発に動かす時期に沿岸域を離れて沖合へと移動する (Wyneken and Solomon, 1992)．これは，体サイズの小さな時期には中-大型の魚や海鳥などに襲われる危険性が大きく (Witham, 1974; Stancyk, 1982; Witherington
and Salmon, 1992; Gyuris, 1994; Vose and Shank, 2003)，特に沿岸域の水深 10m 以下や
リーフエッジで捕食されることが多いためである (Witherington and Salmon, 1992;
Pilcher et al., 2000; Whelan and Wyneken, 2007)．海へ入った後の孵化幼体は体内の卵黄を吸収し，幼体へとその生活史の段階を移しながら外洋へと分散していくが，ヒラタウミ
ガメ (Natator depressus)だけは沿岸性が強く，孵化幼体でも沿岸域を離れない (Bolten,2003)．摂餌する海域は繁殖地とは異なることがほとんどで，性成熟後は繁殖期になると摂42餌海域から繁殖海域へと回遊していく (Limpus, 1985; Sakamoto et al., 1997; Limpus
and Limpus; 2001; Hatase et al., 2002b; Schroeder et al., 2003)．成熟した雌は 1 産卵期に複数回産卵するが，毎年産卵することは普通なく，平均するとヒメウミガメ属(Lepidochelys)では 1–2 年ごと，その他のウミガメ類では 2–3 年ごとに産卵回帰する (Miller,
1997)．雄は性成熟が完了すると毎年繁殖に参加するともされるが (Wibbels et al., 1990;
Limpus, 1993)，繁殖期に性的に不活発な成熟個体も確認されており (Blanvillain et al.,2008)，地域や個体によっては 2 年ごとに繁殖に参加する場合もある (Miller, 1997)．

6-2．アカウミガメ(Caretta caretta)の生活史
6-2-1．産卵地
アカウミガメの産卵地はウミガメ類で唯一温帯域にある (Pritchard, 1997)．アカウミガ
メの主要な産卵地として，北太平洋では日本，南太平洋ではオーストラリアとニューギニ
ア，北大西洋ではアメリカ合衆国東海岸，南大西洋ではブラジル，地中海ではギリシャやト ル コ ， リ ビ ヤ ， キ プ ロ ス ， イ ン ド 洋 で は オ マ ー ン が 知 ら れ て い る (Bolten andWitherington, 2003)．また，太平洋や大西洋の産卵地は高緯度海域に向かう暖流に近い砂浜に集中しており，孵化幼体はこの暖流に乗って高緯度海域へと移動すると考えられている (Bolten, 2003)．

43

6-2-2．孵化・脱出と分散
同じ産卵巣内の孵化幼体は集団で地表直下へと移動し，地表の温度の低下を感知して，
通常夕方から夜間にかけて集団で地表へ脱出する (Miller, 1997)．その後，フレンジーによって沿岸域を抜け外洋に泳ぎ出てきた孵化幼体はホンダワラ属の海藻をはじめとした海面に浮いているものに寄り添い(Witherington, 2002)，静止した状態で両前肢を背甲の上に乗せて浮かんでいる時間が増えていく (Witherington, 1995) (図 6-1)．これは，フレンジーの時期は砂浜に押し寄せる波の力に抗い，沿岸域を出来るだけ早く泳いで抜けることが重要であるのに対して，生物の目は動くものに対して敏感に反応するので，外洋の海流に乗った後は捕食者に見つからないように隠れていることが重要となるためであろう．
外洋へ泳ぎ出た後，体内の卵黄を吸収した幼体は北太平洋では黒潮，北大西洋ではメキ
シコ湾流といった高緯度海域へ向けて流れる暖流に乗る (Carr, 1986; Carr, 1987; Bowenet al., 1995; Witherington, 2002)．その後北太平洋海流やノース・アトランティック・ジャ
イロ (North Atlantic Gyre)と呼ばれる流れに乗って大洋を大きく回遊することとなる(Bolten et al., 1998; Bowen et al., 1995; Lohmann et al., 2001) (図 6-2)．この時アカウミ
ガメの幼体は海流にただ流されているわけではなく，海流を利用しながらも地磁気の向きを 関 知 し て 自 ら が 進 む べ き 方 角 へ と 進 ん で い る と さ れ る (Lohmann et al., 2001;
Lohmann and Lohmann, 2006)．

44

6-2-3．幼体の生息地と成長海流を利用して分散した幼体は北太平洋ではハワイ諸島の沖合，北大西洋ではアゾレス
諸島・マデイラ諸島の沖合に曲甲長 200–600 mm の個体が生息していることが知られている (Bolten et al., 1993; Wetherall et al., 1993; Bjorndal et al., 2000; Polovina et al., 2004;
Kobayashi et al., 2008)．その後，性成熟する前の段階で産卵地の周辺に再び戻り，繁殖地
近くの沿岸域に再加入する (Musick and Limpus, 1997; Bolten, 2003;第 4 章)．
ただし，繁殖地へ戻る前から生息域を沿岸域へとシフトする個体もあり，北太平洋ではカリフォルニア半島の沿岸には直甲長 500–700 mm の個体を中心に 200–300 mm の個体もみられる (Gardner and Nichols, 2001)．この海域は湧昇流が沸き上がる世界有数の豊かな海であり，アカウミガメのホット・スポット(hot spot)と呼ばれる場所の一つである(Peckham et al., 2007)．ここでは成熟した個体は一切見つからず，性成熟がはじまる前に
太平洋を東から西へと横断し，繁殖地である日本近海へと移動する (第 4 章)．
幼体の頃の成長速度は孵化した年が最も早く，アカウミガメでは太平洋で 50.9 mm/year(直甲長)，地中海で 118 mm/year (曲甲長)という報告がある (Zug et al., 1995; Casale et al.,2009b)．飼育下ではさらに早く，アカウミガメは孵化後約 1 年半の間で甲長が 565 mm まで成長することもある (Swingle et al., 1993)．甲長が 300–500 mm 台になると，成長速度は北太平洋の個体群ではハワイ諸島沖合で 34.0–38.9 mm/year (Zug et al., 1995)，北大西洋の個体群ではチェサピーク湾で 29.6 mm/year あるいは 52.8 mm/year (Klinger and45

Musick, 1995)，ジョージアで 30–40 mm/year (Parham and Zug, 1997)，ノースキャロラ
イナで 15.8 mm/year (Braun-McNeill et al., 2008)，フロリダで 73.6 mm/year (Mendonca,1981)，バハマで 157 mm/year (Bjorndal and Bolten, 1988b)，地中海の個体群では 25
mm/year や 36.4 mm/year (Casale et al., 2009a; Casale et al., 2009b)となり，個体群間のみならず個体群内でも差異がみられる．

6-2-4．繁殖地への再加入
繁殖地近くの沿岸域へ再加入する甲長は同種内でも個体群によって異なっており，その甲長は北太平洋，南太平洋，大西洋でそれぞれ直甲長 560–750 mm，曲甲長約 700 mm，
曲甲長約 500–600 mm であり (Bjorndal et al., 2000; Limpus and Limpus, 2003; 第 4 章)，
本研究において，北太平洋ではその年齢は 18-33 歳であると推定された (第 5 章)．
沿岸域に再加入した個体は外洋域でも摂餌を行っており (Sakamoto et al., 1997;
Hatase et al., 2002b; Hatase et al., 2002c; Hatase et al., 2007; 中島他, 2007)，外洋域と浅海域を回遊しながら性成熟の過程が進行していく(第 4 章)．

6-2-5．性成熟
ウミガメ類の性成熟のはじまっていない個体では雌雄の外部形態に違いは見られず，外部形態から性別を判断することはできない．雌では成熟しても外部形態に変化は見られな
46

いが，雄は精巣が発達し性成熟がはじまると尾部が著しく伸長し前肢の爪も大きくなり強く湾曲する (Hughes, 1974; Kamezaki, 2003; 第 3 章)．こうした特徴から性成熟のはじまった雄に関しては外部形態から性を判断できるようになるが，すべての個体で性判別が可能になるのは，
北太平洋のアカウミガメでは直甲長で 800 mm を越える頃である (第 3 章)．
雄のアカウミガメでは尾部の伸長が始まってから，およそ 100–150 mm 程度甲長が大きくなった頃に性成熟が完了し (Casale et al., 2005; 第 3 章)，雌では外部形態から成熟しているかどうかは分からない．外部形態から雌雄の判別がつかないとき，成熟しているかどうか判断出来ないときには生殖腺や生殖管の形態の観察が有効である．死亡している個体であれば解剖によって生殖腺を直接観察することが可能であるが，生きている個体では径の細い内視鏡を腹腔内に挿入して生殖腺を観察する方法 (Wood et al., 1983)が用いられるようになった (図 6-3)．産卵を控えた雌であればより非侵襲的な超音波検査によって卵の発達の程度を観察することもできる．
性成熟後の成長は遅くなり，同程度の甲長でも性成熟していない個体と成熟した個体の成長速度は，
北太平洋では 11.0 mm/year から 2.5 mm/year (Hatase et al., 2004; 第 5 章)，
南太平洋では 8.3 mm/year から 1.2 mm/year まで低下する (Limpus, 1985)．
性成熟した個体の甲長は比較的捕獲や計測がしやすいことから主に産卵個体で計測されており，大西洋やインド洋がそれぞれ直甲長 877–1053 mm，876–936 mm と大きく，地中
海が 654–794 mm と最も小さい (Dodd, 1988; Tiwari and Bjorndal, 2000; Kamezaki,
47

2003)．太平洋のアカウミガメは北半球と南半球でそれぞれ直甲長 848 mm，887 mm と中間的な大きさである (Limpus, 1985; 亀崎他, 1995)．性成熟甲長の大きな北大西洋と小さな地中海はジブラルタル海峡で繋がっており，一部の個体は地中海と北大西洋を行き来しているが (Carreras et al., 2006)，産卵雌のミトコンドリア DNA のハプロタイプ出現頻度は異なっている (Encalada et al., 1998; Bowen et al., 1993; Bowen et al., 2004)．これは地中海に入り込んだ北大西洋産のアカウミガメは幼体であり，アフリカ北部の沿岸域に集中するのに対して，地中海東部産のアカウミガメは分散しても地中海西部のヨーロッパ沿岸域に集中し，ある程度地理的に隔離されているためと考えられる (Bowen et al., 1993;
Bowen et al., 2004; Carreras et al., 2006)．しかし，同一のハプロタイプも確認されており(Encalada et al., 1998)，幾らかの遺伝的な交流は起こっていることは否定できず，性成熟
甲長がおよそ 200-250 mm も異なることは興味深い．
性成熟年齢は飼育下では非常に早く，6–7 年で成熟するとした報告もある (Caldwell,1962; 内田, 1967)．しかし，ウミガメ類は周囲の水温や栄養状態などの成育条件によって成長速度や成熟年齢が大きく変わるため，野生の個体は飼育されている個体より長い年月をかけて成熟する (Frazer, 1982)．野生下のアカウミガメで推定されている性成熟年齢は北太平洋では 37–43 歳 (第 5 章)，南太平洋では 30 歳以上 (Limpus, 1979)または 35 歳
(Frazer et al., 1994)，地中海では 16–28 歳 (Casale et al., 2009a)とされ，北大西洋では10–15 歳 (Mendonca, 1981)，あるいは 13–15 歳 (Zug et al, 1986)，22–25 歳 (Klinger and48

Musick, 1995)，30–47 歳 (Frazer and Ehrhart, 1985)，20–63 歳 (Parham and Zug, 1997)と幅広い．正確に年齢が判明している野生の性成熟個体では，南太平洋で生体標識を施した孵化幼体が 29 年後に初めて産卵をしており (C. Limpus, 未発表データ)，性成熟の早い個体でも 30 年近くかかることが示唆されている．

6-3．他のウミガメ類の生活史との比較
6-3-1．幼体期の生態
孵化幼体は砂浜から海へ入った後に外洋へと泳ぎ出て行くことはヒラタウミガメを除いて共通である (Bolten, 2003)．しかし，一度外洋へと分散した後，アカウミガメをはじめ，
アオウミガメ (Chelonia mydas)，タイマイ (Eretmochelys imbricata)，ケンプヒメウミガ
メ (Lepidochelys kempii) ， 西 部 太 平 洋 お よ び オ ー ス ト ラ リ ア の ヒ メ ウ ミ ガ メ(Lepidochelys olivacea) が 幼 体 の う ち に 沿 岸 域 へ 出 現 す る の に 対 し て ， オ サ ガ メ(Dermochelys coriacea)と東太平洋のヒメウミガメは成熟した個体が繁殖期に産卵地へ回遊する以外はほとんど沿岸域へ現れない (Bolten, 2003) (図 6-4)．また，沿岸を生息域として利用する種の中でも，アカウミガメよりアオウミガメ，アオウミガメよりタイマイやケ
ンプヒメウミガメの方が沿岸に出現する甲長は小さいことも知られており (Musick and
Limpus, 1997)，アカウミガメは前述のように甲長 500–700 mm で沿岸に出現するのに対して，アオウミガメは北大西洋で 200–250 mm，北太平洋と南太平洋で 300–400 mm (Balazs,49

1980; Bjorndal and Bolten, 1988a; Limpus, 1993; Limpus et al., 1994)，タイマイは北大
西洋のカリブ海で甲長 200–250 mm，インド洋や太平洋で甲長 350 mm 以上(Kamezaki and
Hirate, 1992; Boulon, 1994)，ケンプヒメウミガメもタイマイとほぼ変わらず 250–350 mm
で沿岸に出現する (Ogren, 1989)．沿岸に出現する年齢もタイマイで 1–3 歳程度，ケンプヒ
メウミガメで 2 歳以上と推定されており (Kamezaki and Hirate, 1992; Boulon, 1994; Zuget al., 1997)，アカウミガメの 18–33 歳よりも若い (第 5 章)．
沿岸への加入には沿岸に出現した後の種固有の食性が関連していると考えられ，海藻や海草を専食するアオウミガメ (Mortimer, 1982)や海綿を専食するタイマイ (Mortimer,
1982; Meylan, 1988; Bjorndal, 1997)，水深 50 m 以浅でカニを専食するケンプヒメウミガ
メでは (Shaver, 1991)，おそらく甲長が 200–400 mm になれば捕食者となる生物が限定されるため沿岸へ生息域を移すのであろう．一方，アカウミガメは沿岸域では甲殻類や巻貝，
二枚貝などの底性無脊椎動物を餌としているが (Mortimer, 1982; Dodd, 1988; Bjorndal,
1997)，亜成体や成体の個体であっても浮遊性の動物や時として流れ藻を摂食していることもあり (Dodd, 1988; Bjorndal, 1997)，専食性は低く日和見的である (岩本他, 2005a; 岩本他, 2006)．このことも沿岸の生物を専食する種に比べると沿岸へ現れる甲長が大きい理由のひとつかもしれない．
また，幼体期のアカウミガメの特徴として，少なくとも北太平洋と南太平洋，北大西洋
では海流を利用するなどして大洋を周回することがあげられる (Bowen et al., 1995;
50

Bolten et al., 1998; Boyle et al., 2009)．他のウミガメ類ではこのような生態は知られておらず，アカウミガメの幼体が大洋を周回する生態の意義やどのように発達したのかは興味深いものの，現在のところ明らかではない．

6-3-2．性成熟
産卵個体の甲長はオサガメが最も大きく，アオウミガメ，アカウミガメまたはヒラタウ
ミガメ，タイマイ，ヒメウミガメまたはケンプヒメウミガメの順に続く (Zug and Parham,
1996; Hirth, 1997; Kamezaki, 2003; Limpus, 2007) (表 6-1)．従って，アカウミガメは比較的大型のウミガメ類であると言える．性成熟した雄の甲長はアカウミガメとアオウミガメ
で調べられており，アカウミガメでは雌雄で甲長に違いがないのに対して (Kamezaki,
2003; Casale et al., 2005;第 2 章)，アオウミガメでは雄は雌よりも小さい (Godley et al.,2002)．また，アカウミガメでは成長速度も雌雄で差がなく，性成熟年齢にも性差はない (第5 章)．その他のウミガメ類については成熟した雌雄の甲長の違いについての情報はないた
め，産卵個体の甲長が性成熟甲長とされることが多い．
アオウミガメはアカウミガメと同様に，産卵個体の甲長は大西洋で直甲長 990–1118 mmと大きく，地中海では曲甲長 920–960 mm と小さかった (Hirth, 1997)．ただし，最も小さいのは直甲長で 814–829 mm の東部太平洋の個体群であり (Hirth, 1997)，この個体群はクロウミガメ(Chelonia mydas agassizzi)とも呼ばれ，アオウミガメの亜種として認識されて51

いる (Bowen et al., 1992) (図 6-5)．アカウミガメとアオウミガメの性成熟甲長は，東部太平洋のアオウミガメ個体群を除けば，大西洋とインド洋で大きく，地中海で小さい点で共通した．このことは地理的な要因が性成熟甲長に作用していることを示している．その要因が明らかになれば，性成熟に必要な生理的な機構も解明につながり，保全のために有効な情報となるが，現在のところ有力な仮説は見あたらない．
ウミガメ科では成熟甲長が大きいほど性成熟年齢も高い傾向が見られる．アカウミガメ
より性成熟甲長の大きなアオウミガメでは性成熟年齢は 30 歳以上とされ (Zug et al.,2002)，アカウミガメのそれと大きな違いはない．また，タイマイがそれに続いておよそ
20–30 歳，ヒメウミガメとケンプヒメウミガメはそれぞれ 13 歳前後，11–16 歳で成熟すると推定されている (Zug et al., 1997; Zug et al., 2006)．一方，オサガメ科のオサガメは性成
熟甲長が最も大きいにも関わらず，早ければ 5–6 歳，おおむね 13–14 歳で成熟する (Zug andParham, 1996)．オサガメの性成熟年齢はウミガメ科の中で最も小さなヒメウミガメやケン
プヒメウミガメと同程度であり，アカウミガメやアオウミガメのおよそ半分の年齢で成熟することになる．これはウミガメ科のウミガメに比べてオサガメは成長速度が著しく早いためであり，孵化時の甲長は約 60 mm だが，野生下でも１年間に 350 mm 程も成長し，約4 年で曲甲長 1000 mm に達する (Zug and Parham, 1996)．このようなオサガメの急激な成長には軟骨部分の特異な仕組みが関係していると考えられている．オサガメの軟骨の中には毛細血管が伸びており軟骨の伸長を促すとともに，基部では軟骨の吸収と石灰化が急52

速に進む (Rhodin et al., 1996)．このような仕組みはアカウミガメをはじめ，ウミガメ科にはみられない．

53

第7章

総合考察

7-1．日本近海における保全の重要性
北太平洋のアカウミガメ (Caretta caretta)は日本の砂浜で孵化した後，黒潮と北太平洋海流を利用して広く東部太平洋にまで分散し (Bowen et al., 1995; Uchida and Teruya,
1991; Kobayashi et al., 2008)，標準直甲長 (SCL)で 560–750 mm，年齢にして 18–33 歳の時に自身の生まれた日本の近海に再加入する(第 4 章; 第 5 章)．その後は日本近海で過ごしながら性成熟が進行し，半数は SCL 821 mm，37-43 歳で性成熟を完了し繁殖に参加し始めるという生活史を持つ (第 2 章; 第 3 章; 第 4 章; 第 5 章)．この生活史の中で，アカウ
ミガメは様々な脅威に晒されており，本種を保全するためにはそれぞれの脅威が与える個体群への影響を理解する必要がある．
まず，ウミガメ類の生息数や個体群の規模あるいはその変化は産卵巣数によって代表される (Meylan, 1982)．産卵巣数はおおまかに産卵個体の数を表しており，その年に産卵をした成熟雌の個体数を比較的正確に見積もることができる．日本では数多くの団体・個人
が各地の砂浜で調査を行っており，その結果は日本ウミガメ会議 (特定非営利活動法人日本
ウミガメ協議会主催)にて毎年とりまとめられている．産卵巣数は 20 世紀後半のおよそ 50
年間に 50–90%も減少したが (Kamezaki et al., 2003)，1997 年以降は増加傾向に転じており (日本ウミガメ協議会, 2009)，ひとまずは絶滅の危機を乗り越えたかに見える．
しかしながら，沿岸漁業による混獲死はアカウミガメやアオウミガメ (Chelonia mydas)
にとって大きな脅威となっており (Ishihara and Kamezaki, 2010)，産卵地となる砂浜の後退・消失に歯止めがかかる気配はない (松沢, 2009; 日本ウミガメ協議会, 2010)．北太平洋
54

のアカウミガメに対する保全活動は日本だけでなく，ハワイ諸島沖合のマグロ・カジキ延縄漁やカリフォルニア半島の沿岸漁業についても実施されている (Peckham et al., 2009;
Simonds, 2009)．また，日本近海の集団は 77.7 %が亜成体で構成されており，幼体で構成されるハワイ沖やカリフォルニア半島沖の集団よりも甲長が大きく (Wetherall, 1993;
Gardner and Nichols, 2001;第 4 章)，期待される生涯で残す子孫の数を示す繁殖価が高い．
そのため，1 個体あたりの個体群への貢献度は相対的に高く，日本近海における個体数の増
減が個体群全体に及ぼす影響は大きい．
しかし，日本で実施されているアカウミガメの保全策は市民による産卵地保護にほぼ限られており (松沢, 2009)，亜成体に対する保全策は進んでいない．沿岸を回遊するアカウミ
ガメを保護するための規制として，種の保存法や漁業調整規則並びに海区漁業調整委員会
指示によってウミガメ類の販売や譲り渡しが原則として禁止されているものの，これらの規制は偶発的に起こる漁業による混獲死を減らす効果はない．日本近海のアカウミガメの大多数を占め，産卵個体に次いで繁殖価の高い亜成体を保護することは，北太平洋のアカウミガメを保全する上で非常に効果のある対策であることは間違いない．

7-2．日本近海におけるアカウミガメの死亡率
日本近海において効果的な保全活動を推進し，適切な将来予測をたてるためには現在の日本近海に生息するアカウミガメの個体群の状況を把握することが重要であり，本研究で得られた性成熟や個体群構造に関する知見は有用である．また，個体数の増減を予測する
ためには新たに生まれてくる孵化幼体の個体数と死亡していなくなる個体数が必要であり，孵化幼体の個体数に関しては毎年の産卵巣数が有効な指標となるものの，死亡する個体数
55

に関しては何ら知見がない．そこで，本研究結果を用いて，日本近海における死亡率を推定することとした．
日本近海における死亡率を推定するため，第 4 章の甲長の分布をもとに SCL 50 mm ごとに個体数をまとめ，第 5 章の成長速度を用いて個体数の年間変化率 (X)を求めた (式 7-1,
表 5-1)．

Xi = (Ni+1 / Ni - 1) / (50 / gi)

式 7-1

X: 年間変化率，N: 個体数，g: 成長速度 (mm / year)

年間変化率 X は日本近海への再加入率と日本近海での死亡率の差に等しく，X > 0 ならば見た目の再加入率，X < 0 ならば見た目の死亡率を表す．主な再加入の終わった SCL 750 mm
以上 (第 2 章)の階級では X < 0 となり，見た目の死亡率は，SCL 750–800, 800–850, 850–900,
900–950, 950–1000 mm ではそれぞれ 11.1, 10.2, 15.6, 18.2, 20.8 %となった．
個体が大型になるにつれて死亡率は増大したが，一般に個体が大きくなるほど死亡率は低下する (National Research Council., 1990)．死亡率が増大した要因として，亜成体期の再加入の継続および成体での成長速度の過大評価の 2 点が考えられた．前者では SCL 750
mm 以上になってから再加入する個体が割合を減らしながらも存在しており，再加入率の比較的高くなる小さなサイズクラスほど見た目の死亡率が低くなったと考えられた．後者
では第 5 章で求めた成長速度は亜成体のものであり，成長速度が大幅に低下する成体にも適用されたため，成長速度が過大に評価されたことによって死亡率が高く見積もられたと考えられた．従って，見た目の死亡率は亜成体のサイズクラスで過小評価され，成体のサ56

イズクラスで過大評価されていると考えられた．亜成体のサイズクラスで死亡率が過小評
価されていたということは，亜成体の実際の死亡率は少なくとも SCL 750–800 mm の 11.1 %を超えると推察される．また，成体のサイズクラスで死亡率が過大に推定されていたということは，成体の実際の死亡率は SCL 950–1000 mm の 20.8 %よりは低いと推察される．
亜成体と成体の間で劇的に死亡率が異なるとは考えにくく，従って日本近海におけるアカウミガメの年間死亡率は 11.1–20.8 %の間にあると示唆された．
次に，この年間死亡率から日本近海に再加入したアカウミガメがどれ程の割合で繁殖に参加するまで生き残ることができるか計算できる．アカウミガメは日本近海に 18–31 歳で再加入し，性成熟年齢が 37–43 歳であることから，繁殖に参加するまでに 6–25 年を日本近海で過ごすこととなり(第 5 章)，その間の年間死亡率が 11.1–20.8 %ならば，再加入した個
体の 50.6–99.7 %が成熟する前に死亡していると示唆される．性成熟前に死亡する個体は自らの子孫を残すことができず，将来的な個体群の維持に貢献することはない．そのため，産卵個体や産卵巣の保護だけではなく，未成熟な個体の死亡率を減少させることもアカウ
ミガメの保全のために重要である．

7-3．北太平洋のアカウミガメに対する脅威
個体が成長するとともに脅威となる生物や事象は変化していく．日本近海での死亡率は近い将来の繁殖個体数に影響することは 7-2 で示されたが，より効果的な保全活動を展開するためには生活史のどの段階でどのような脅威が，どれほどの影響を与えているのかを理解し，より影響の大きな脅威から取り除いていくことが大切である．そこで，ここからは生活史を通して，北太平洋のアカウミガメに対する脅威について検証する．
57

7-3-1．砂浜における脅威
産卵個体を狙う捕食者にはコスタリカのアオウミガメやフレンチギアナのアオウミガメ，
ヒメウミガメ (Lepidochelys olivacea)，オサガメ (Dermochelys coreacea)を襲うジャガー(Panthera onca)などがいるが (Sehoe et al., 2007; Harrison et al., 2008)，日本では産卵個体を狙う捕食者は知られていない．太平洋戦争の終結後には人間が上陸してきた個体を食料として利用する地域も見られたが，地域で消費される程度であり，それも現在では見られない(亀崎・松沢, 私信)．産卵された後の卵は，太平洋戦争後から 1970 年代初頭にかけて鹿児島県屋久島や宮崎ではそのほとんどが採卵されていたが，地元の調査団体による保護調査活動や保護条例の制定などによって 1970 年代後半にはアカウミガメ卵の利用も実質的になくなった(大牟田, 2002; 松沢, 2009)．
次に，産卵後の卵や孵化幼体はスナガニ(Ocypode spp.)や野犬，イノシシやブタ(Sus spp.)，
アライグマ(Procyon lotor)など様々な動物に捕食されており(Stancyk, 1982)，これを食害と呼ぶ．日本の各地でもタヌキやリュウキュウイノシシ，アカマタ，アライグマなどによる食害が起きている(Mori et al., 1999, 松沢他, 2010; 日本ウミガメ協議会, 未発表データ)．
砂浜によって被害の程度は異なり，すべての産卵巣が被害に遭う砂浜もあればほとんど被害に遭わない砂浜もある(松沢, 私信)．食害のある砂浜では，産卵巣が掘り起こされないよ
うに地域で保護活動をする個人や団体が対策を取ることで，被害の最小化が図られている．
北太平洋のアカウミガメにとって最も重大な脅威のひとつに日本の砂浜の侵食がある(亀崎, 2003; 松沢, 2009)．砂浜の侵食はダムの建設や川砂採取による砂の供給量の減少に加えて，港湾施設や離岸堤などによって沿岸の漂砂が変化したことに起因する (松沢, 2009)．そ58

の結果，アカウミガメが産卵できない，あるいは産卵しても高波時に卵が水没してしまう
砂浜が増加しており，北太平洋のアカウミガメにとって中長期的な脅威となっている．
砂浜から出て海に入った後には，特に水深 10m 以下やリーフエッジで中-大型の魚や海鳥などに捕食される(Witherington and Salmon, 1992; Pilcher et al., 2000; Whelan andWyneken, 2007)．特に産卵巣の密度が高くなるような孵化場の周辺では沿岸域での捕食率が増加する (Glenn, 1996; Wyneken and Salmon, 1996; Pilcher et al., 2000)．海に入った
後に沿岸域を抜けられる孵化幼体の割合は分かっていないが，産卵巣の集約や活発に動く
フレンジー期を過ぎた孵化幼体の放流など人為的な影響下では外洋へ出るまでの生存率の低下が懸念される．侵食の進んだ砂浜では水没する危険のある産卵巣は砂浜のより奥側，あるいは孵化場へ移植することはやむを得ない処置であると考えられるが，孵化幼体の脱出に際しては自然条件下に出来る限り近付けるべきと考える．

7-3-2．外洋へ分散した幼体への脅威
外洋へと分散した幼体の主な捕食者や捕食による死亡率は，その確認のし難さから，よくわかっていないが，おそらく外洋性のサメ類や中-大型の魚が捕食者となっていると想像される．また，シャチ(Orcinus orca)はオサガメを襲うことが報告されており(Caldwell andCaldwell, 1969; Pitman and Dutton, 2004)，独立行政法人水産総合研究センター研究開発
情報誌の遠洋リサーチ＆トピックス 2006 年 1 号の表紙にはアカウミガメを襲うシャチの写真が紹介されていることから，シャチは外洋でのアカウミガメの主要な捕食者のひとつと考えられる．アカウミガメは外洋に分散してから，北太平洋では SCL 56-75 cm，南太平洋
では曲甲長 70 cm，北大西洋でも曲甲長 46-64 cm まで外洋で成長することから(Bjorndal
59

et al., 2000; Limpus and Limpus, 2003; 第 4 章)，成長とともに捕食者も限定されていくと考えられる．
外洋で確認されるアカウミガメの幼体は主に遠洋延縄で混獲された個体であり(Bolten
et al., 1994; Bolten et al., 2004; Lewison et al., 2004; Pinedo and Polacheck, 2004)，この混獲そのものが脅威となっている(Gilman et al., 2007; FAO, 2009)．現在では，針の形をウ
ミガメ類が飲み込まないよう変更したり，食いついた餌ごと飲み込まないよう餌をイカからサバなどに変更したり，ウミガメ類の利用水深より深く漁具を設置したりするなど，混獲数や死亡率の低減が図られている(FAO, 2009)．また，公海上で操業されていた大規模流し網にもアカウミガメの幼体が混獲されていたが(Wetherall et al., 1993)，国連決議によって 1992 年以降の操業は禁止されている．

7-3-3．沿岸域での脅威
沿岸域での主な捕食者は大型のサメ類であり，その中でもイタチザメ(Galeocerdo cuvier)は 特 に ウ ミ ガ メ 類 を 好 ん で 捕 食 す る (Stancyk, 1982; Fergusson et al., 2000;
Simpfendorfer et al., 2001)．ただし，大型のサメ類の個体数は減少傾向にあると言われており(Musick et al., 1993)，イタチザメは回復しつつあるとはいえ(Baum and Blanchard,2010)，大型のサメ類による捕食がアカウミガメの個体数が減少する主要な要因とはならないであろう．
ウミガメ類の人為的な死亡要因の一つとして，近年では沿岸漁業のウミガメ類への影響が世界的に危惧されており (Gilman et al., 2010)，日本近海でも沿岸漁業はアカウミガメの主要な死亡要因と考えられている (Ishihara and Kamezaki, 2010)．しかし沿岸漁業がア
60

カウミガメに与える影響の大きさは具体的には明らかではなく，また，沿岸漁業と言っても漁法や規模，操業時期も様々であり，どの時期にどの地域でどの漁法によって混獲され死亡しているのかも明らかではない．

7-4．日本近海で必要な保全策
鹿児島県屋久島と宮崎県では大量に採卵されることがなくなってから約 30 年後の
1997-1998 年以降，産卵巣数が増加している(日本ウミガメ協議会, 2010)．この 2 地域は，
ここだけで産卵巣数が全体の半数を超えるほど，北太平洋のアカウミガメにとって重要な産卵地である(日本ウミガメ協議会, 2010)．北太平洋のアカウミガメでは早い個体は 22 歳で成熟するという結果が得られており(第 5 章)，採卵が禁じられてから産卵巣数が増加するまでの期間と符合した．従って，1997-1998 年以降の特に九州地方で顕著な産卵巣数の回
復は 1970 年代の卵の保護の効果は多大であると考えられ，卵の保護は顕著な成果をあげていると言える．
ただし，砂浜の侵食による産卵地の荒廃が進んでおり，防災の面からもこれ以上の海岸侵食を避けることに注力することが重要である．
また，日本近海に再加入した後，50.6–99.7 %の個体が成熟する前に死亡する要因ともな
る沿岸漁業による混獲死への対策は進んでいない．今後，早急に沿岸漁業によるウミガメ
類への影響の詳細を把握し，アカウミガメをはじめとするウミガメ類の混獲による死亡率を軽減することが望まれる．また，アカウミガメの死亡要因は漁業によるものだけではな
いため，例えば捕食・疾病・飢餓・船舶との衝突・密漁・凍死などの混獲以外の死亡要因についてもそれぞれの影響を評価していく必要もある．
61

謝辞

東京大学大学院農学生命科学研究科の亀崎直樹客員准教授には本研究を遂行し，論文にまとめるにあたり常々懇切なご指導と拙い文の御校閲を賜った．さらに，本年は神戸市立
須磨海浜水族園の園長にも就任され，例年にまして御多忙極まる中，深夜までご指導いた
だいた．深く厚く感謝申し上げます．
東京大学大学院農学生命科学研究科水域保全学研究室の佐野光彦教授，日野明徳東京大学名誉教授，岡本研准教授，青木茂先生には遠方で研究を行うにあたり様々な便宜を図っていただくとともに，有益なご指導を賜わった．また，種々様々なご心配ご迷惑をお掛けしたが，広い心で受け止めていただいた．心より深く感謝の意を表します．
本研究に用いたアカウミガメの標本は日本ウミガメ協議会の仲村貴生氏，山崎千亜希さん，江口栄作氏，故日下部要氏，田中宇輝氏，斉藤晃司氏，阿部朱音さん，松本美奈さん，
森萌さん，佐藤嘉威氏，水野大将氏，中里見猛氏，福家弘晃氏，原美保子さん，東京大学大学院水域保全学研究室兼日本ウミガメ協議会の岩本太志氏，島田貴裕氏，岡本慶氏，優谷真理さん，高岡大敷組合の山下傑氏，前田敏和氏，山下昌司氏，小笠原利之氏並びに乗組員の皆様，椎名大敷組合の安岡幸男組合長，橋本健氏，小松昭士氏，植田晶氏，仙頭和幸氏，並びに乗組員の皆様，三津漁業協同組合の戎井邦彦氏をはじめとした皆様，室戸岬町椎名地区の町田鮮魚店様，寺本鮮魚店様，三津大敷組合の乗組員の皆様，室戸岬東漁協
62

高岡支所の皆様，室戸岬東漁協椎名支所の皆様，三重県北牟婁郡紀北町島勝浦の山下訓右氏，山下幸子さん，山下晄将くん，山下ゴン太くん，玉置立氏，津村公氏をはじめとした
皆様，島根県立しまね海洋館の村上昌吾氏，守谷浩氏をはじめとした皆様，鳥取県立博物館の一澤圭氏，川上靖氏をはじめとした皆様，鳥取県栽培漁業センターの皆様，鳥取県立水産試験場の皆様の多大なるご支援とご協力によって収集することができた．Smithsonian
Institute, National Museum of Natural History の George Zug 博士にはウミガメ類の年齢査定に関して骨年代学的手法をご教授いただいた．神戸大学農学部応用動物学科の楠比呂志准教授や南知多ビーチランドの黒柳賢治氏にはウミガメの生殖に関わる様々な事柄をご教授いただいた．また，主な調査地となった高知県室戸市ではホテルニュー室戸の皆様，
仲村木工所の皆様，元小学校の皆様，高岡・椎名・三津の各地区の方々に大変お世話になった．この方たちの支えがなければ研究を遂行することはできなかった．日本ウミガメ協
議会の松沢慶将博士，島達也氏，宮形佳孝氏，水野康次郎氏には研究に対するご助言を頂
き，朽見健一郎氏，大鹿達弥氏，若月元樹氏，亀田和成氏，谷本理沙さん，谷口真理さん，
圓東祐介氏，江口栄作氏，中本真理子さん，井上直美さん，宮原尚子さん，杉山享史氏，
齋藤宏恭氏，大内裕貴氏，吉田博美さん，三根加奈子さん，重村舞さんには日々様々な面で助けていただいた．また，神戸市立須磨海浜水族園の皆様には日々の研究活動を行う場
所と機会を与えていただいた．南知多ビーチランド，日和佐うみがめ博物館カレッタ，姫路市立水族館，姫路市立動物園の皆様には解剖や実験にご指導ご協力いただいた．三重大
63

学ウミガメ・イルカ調査・保全サークル「かめっぷり」の皆様には調査，解剖を手伝っていただいた．杉原奈央子さんをはじめとする東京大学大学院農学生命科学研究科水域保全
学研究室の学生諸氏には度々ご迷惑お手数をおかけしたにも関わらず，いつも暖かいご支援をいただいた．ここに記すとともに，皆様方に心より感謝し，お礼申し上げます．
本研究は独立行政法人日本学術振興会「平成 21 年度科学研究費補助金（特別研究員奨励費）」，特定非営利活動法人日本ウミガメ協議会，黒潮生物研究財団研究助成，日本経団連
自然保護基金，日立環境財団環境 NPO 助成，積水ハウスマッチングプログラム，ラッシュ
ジャパン，patagonia Japan の支援を受けて行われました．厚くお礼申し上げます．

64

要 旨

第1章 緒言アカウミガメ (Caretta caretta)の北太平洋個体群の産卵地は日本に存在し，幼体は太平洋を横断し，カリフォルニア半島沿岸を摂餌域として成長する．その後，再び太平洋を横断し日本近海に戻ってくる．しかし，太平洋を広く使った生活史の中で，どの時期に性成熟が始まり，いつ完了するのかは明らかになっていない．そこで，本研究では北太平洋産アカウミガメの性成熟過程における生活史を明らかにするため，第 2 章で甲長と性成熟の関係について，第 3 章で性成熟と二次性徴，特に二次性徴の性的二型の形質である尾部伸長について，第 4 章で日本近海へ戻る甲長と性成熟階級について，第 5 章
で性成熟年齢と成長速度について論じた．また，本研究の成果を交えながら，第 6 章ではウミガメ類全般の生活史についてまとめ，第 7 章では得られた知見に基づき保全に関する提言を行った．
第2章 性成熟のはじまる甲長と性成熟が完了する甲長
日本で産卵するアカウミガメについて，甲長と生殖腺の性成熟状態との関連を様々な甲長の死亡個体を得て調べ，性成熟のはじまる甲長と性成熟が完了する甲長を明らかにした．試料としたのは死亡して間もない 152 個体のアカウミガメで，標準直甲長 (SCL:
straight carapace length)を計測した後，解剖して性と性成熟階級を判別した．性成熟階級
は性成熟を開始している個体を幼体，性成熟の過程にある個体を亜成体，性成熟の完了
している個体を成体とした．また，精子の確認された生存個体 8 個体を成体の雄とみなし試料に加えた結果，雄は合計 54 個体，雌は 106 個体になった．
幼体，亜成体，成体のすべての性成熟階級で甲長に性差は見られず，以降の解析は雌雄を合わせて行った．性成熟がはじまる SCL の範囲を亜成体の最小値から幼体の最大値までとし，性成熟が完了する SCL の範囲を成体の最小値から亜成体の最大値までとすると，それぞれ 636–750mm，738–853mm であった．また，これらの範囲の中で半数の個体で性成熟がはじまる甲長と，性成熟が完了する甲長を推定するため，幼体と亜成
体，亜成体と成体の割合を求め，ロジスティック曲線で回帰した．その結果，半数が性成熟をはじめる SCL は 660 mm，半数が性成熟を完了する SCL は 821 mm と求められた．
第3章 雄の尾部伸長と性成熟
カメ類の雄では二次性徴の発現を代表する形態変化として尾部の伸長がある．アカウ
ミガメもその例外ではなく，尾部の伸長は性成熟の進行状況を測る指標として期待される．そこで，第 3 章では北太平洋のアカウミガメについて性成熟状態と甲長および尾長65

との関連について検討した．
試料として用いたのは定置網で捕獲された 128 個体のアカウミガメで，第 2 章と同様に性と性成熟階級を分類した結果，幼体は雄が 5 個体で雌が 8 個体，亜成体は雄が 29個体で雌が 55 個体，成体が雄 11 個体で雌 20 個体であった．これらの個体は SCL と尾長 (TL: tail length)が計測され，SCL に対する TL の長さを示す相対尾長 (rTL: relative taillength, TL/SCL)が求められた．また，尾部の伸長の程度を表すため，TL の相対成長係数を求めた．相対成長係数とは Y = b・Xa で示される定数 a のことであり，定数 a が 1以上ならば優成長とした．
rTL は幼体では雌雄で差が認められなかったが，亜成体や成体では明確に雄の方が長く (p < 0.001, Mann-Whitney U-test)，亜成体になった後に雄の尾部が伸長することが明らかになった．雄の尾部伸長の開始点を雌雄の尾長に違いが現れはじめる点とし，雌雄それぞれに亜成体および成体のデータから SCL と rTL との回帰直線の交点を求めたと
ころ，雄の尾部伸長がはじまる SCL は 670 mm，その時の rTL は 0.155 と求められた．
また，SCL に対する TL の相対成長係数から雄の尾部伸長は亜成体の時期が顕著で (a= 4.3898, n = 29, r 2 = 0.5542, p < 0.01, 無相関検定)，成体になってからも伸長し続けることが示唆された．また，雌の亜成体と成体をあわせて相対成長係数を求めると，雄ほど顕著ではないものの性成熟とともに尾部が伸長することが示され (a = 1.7528, n = 83, r 2= 0.3366, p < 0.01, 無相関検定)，雌にとっても尾部が伸長することに繁殖活動に関わる
機能的な意義があると考えられた．
第4章 繁殖海域である日本近海への再加入サイズ
日本は北太平洋唯一のアカウミガメの産卵地であり，成熟した雌が生息することは明らかである．しかし，未成熟の個体や雄の生態については断片的な情報がいくつかあるにすぎない．そこで，本章では定置網で捕獲されたアカウミガメから，日本近海に生息するアカウミガメの甲長分布や生活史における性成熟の段階を明らかにし，日本近海へ戻ってくる甲長や性成熟段階について議論した．
試料としたアカウミガメは高知県室戸市の大型定置網で 2002 年 7 月から 2009 年 11月までの期間に無作為に捕獲された 1392 個体である．これらの個体は計測した SCL の値によって，孵化幼体，幼体，亜成体，成体の 4 つの性成熟階級に分類された．分類の基準となる SCL には第 2 章で求めた半数が性成熟をはじめる SCL 660 mm と半数で性成熟が完了する SCL 821 mm，さらに，日本の孵化個体の平均値 42 mm を用いた．捕獲されたアカウミガメの SCL は 757 ± 67 (SD) mm (range: 563–1050 mm) で，SCL の分布
は単峰性を示した．これらの個体を性成熟段階で分けると亜成体が全体の 77.7 % (1081
個体)を占めた．
SCL の分布から，アカウミガメは SCL が 560–570 mm で日本近海に出現し始め，
740–750 mm で最頻値を迎えるまで増加し，その後減少に転じた．ここでの増加要因は
66日本近海への再加入であり，主に SCL 560–750 mm の幼体の後期から亜成体の個体が日本近海に再加入すると推察された．また，北太平洋のアカウミガメが摂餌域の一つとして過ごすカリフォルニア半島沿岸では，SCL の分布から 500-700 mm に達した頃に沿岸を離れはじめると示唆され，日本近海に再加入する個体との SCL の差や，先行研究で明らかにされた北大西洋での成長速度や衛星発信器による追跡の軌跡から，カリフォル
ニア半島から日本までは 1-2 年で太平洋を横断することが示唆された．
第5章 北太平洋における成長速度と性成熟年齢
本章では ，性成 熟を完了 する年 齢を上 腕骨に 残 された成 長停止 線 (LAG: lines ofarrested growth)から骨年代学的手法で推定し，さらに日本近海に生息するアカウミガメ
が性成熟を完了するまでの成長速度を明らかにした．
試料は日本国内で混獲死および死亡漂着したアカウミガメの雄 27 個体，雌 42 個体，性の判別ができなかった個体 10 個体の計 79 個体の上腕骨を用いた．LAG を観察するため，上腕骨から厚さ 1 mm 以下の切片を切り出し，LAG の半径と幅を計測した．LAG
は 1 年に 1 本できるとされており，LAG の幅は SCL の 1 年あたりの成長量に比例した．
成長速度は Back Calculation protocol で LAG の幅から逆算し，当時の SCL を LAG の半径から求めた．個体ごとの年齢は Correction Factor protocol で求めたが，年齢が過大に推定されるおそれがあるため，Regression Growth protocol では von Bertalanffy の成長式を求め，SCL または上腕骨の幅と年齢との関係式から年齢を推定した．
各個体から 9.3 ± 4.3 本 (range: 3–20)，合計で 732 本の LAG が確認され，653 箇所でLAG の幅が算出された．Back Calculation protocol で求めた成長速度の平均は 13.9 ± 7.8(SD) mm/year (range: 0.0–64.5)であり，求められた当時の SCL は 694 ± 75 (SD) mm (range:
374–935, n = 732)であった．Regression Growth protocol では成熟する年齢を，第 2 章で求めた性成熟を完了する SCL 821 mm から求めた結果，37 歳と推定された．同様に，日本
近海に再加入する年齢は 18–31 歳と推定された．Correction Factor protocol では，成熟した個体では雄が 38, 46, 47 歳 (n = 3)で雌が 43 ± 11 歳 (n = 15, range: 22–61)であった．また，成熟した個体は未成熟の個体よりも構成年齢が高かく，SCL も大きかったが (p <0.05, Mann-Whitney U-test)，SCL が大きければ年齢が高いという関係は成り立たなかった．(p > 0.05, 無相関検定)．このことは，同じ個体群においても成長と性成熟にばらつ
きがあることを示唆している．
第6章 ウミガメ類の生活史－成長と生息域－
第 6 章ではアカウミガメの生活史を他のウミガメ類の生活史と比較して，ウミガメ類全般の生活史について論じた．

67

第7章 総合考察
日本近海はアカウミガメの幼体の後期から成体までが利用している．すなわち，繁殖に都合の良い場所であるだけでなく，アカウミガメの生息環境として適していることが示唆された．また，性成熟するまでに孵化して方 37-43 年もの年月が必要であることが明らかになり，将来にわたって個体群を維持するためには，産卵個体や産み落とされた卵や孵化幼体だけでなく，日本近海に再加入した未成熟な幼体や亜成体の生態も注視す
る必要がある．

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Witherington, B. E. 1995. Observations of hatchling loggerhead turtles during the first few
days of the lost years. NOAA Technical Memorandum NMFS-SEFC-361: 154-157.
Witherington, B. E. 2002. Ecology of neonate loggerhead turtles inhabiting lines of
downwelling near a Gulf Stream front Marine Biology 140: 843-853.
Witherington, B. E., and Salmon, M. 1992. Predation on loggerhead turtle hatchlings after
entering the sea. Journal of Herpetology 26: 226-228.
Witzell, W. N. 1987. Selective predation on large cheloniid sea turtles by tiger sharks(Galeocerdo cuvier). Japanese Journal of Herpetology 12: 22-29.
Wood, J. R., and Wood, F. E. 1980. Reproductive biology of captive green turtles Chelonia

mydas. American Zoologist 20: 499-505.
91

Wood, J. R., Wood, F. E., Critchley, K. H., Wildt, D. E., and Bush, M. 1983. Laparoscopy of
the green turtle, Chelonia mydas.British journal of herpetology. 6: 323-327.
Wyneken, J., and Salmon, M. 1992. Frenzy and postfrenzy swimming activity in loggerhead,green, and leatherback hatchling sea turtles Copeia 1992: 478-484.
Zug, G. R., Balazs, G. H., and Wetherall, J. A. 1995. Growth in juvenile loggerhead sea
turtles (Caretta caretta) in the North Pacific pelagic habitat. Copeia 1995: 484-487.
Zug, G. R., Balazs, G. H., Wetherall, J. A., Parker, D. M., and Murakawa, S. K. K. 2002. Ageand growth of Hawaiian green seaturtles (Chelonia mydas): an analysis based onskeletochronology. Fishery Bulletin 100: 117-127.
Zug, G. R., Chaloupka, M., and Balazs, G. H. 2006. Age and growth in olive ridley seaturtles(Lepidchelys olivacea) from the north-central pacific: a skeletochronological analysis.

Marine Ecology 27: 263-270.
Zug, G. R., Kalb, H., and Luzar, S. J. 1997. Age and growth in wild kemp's ridley seaturtles

Lepidochelys kempii from skeletochronological data. Biological Conservation 80:
261-268.
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92

Zug, G. R., Wynn, A. H., and Ruckdeschell, C. 1986. Age determination of loggerhead sea
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contributions to zoology 427: 1-34

93

94

亜成体
・楕円形に近い断面を持つ。

幼体・平坦で長円形の断面を持つ。

卵管・ピンク色を呈す。
・複雑に折りたたまれ、卵巣との接合部の直径は少なくとも1.5 cmはある。

・ピンク色を呈す。
・いくらか折りたたまれており、断面は楕円形で直径は0.3-1.5cm。

・白色を呈す。
・わずかに折りたたまれるもほぼ真っ直ぐに伸び、その断面は円筒形かやや楕円形。

精巣上体 ・はっきりと肥大し体壁から吊り下がる。
・辺縁部は体壁と明確に区別できる。
・体壁から膨らんでいない。
雌 卵巣・卵巣間質は膨張している。
・卵巣間質は膨張しつつあるかほ ・卵巣間質に発達は見られない。
・0.3-3.0 cmの黄色く血管をめぐ ぼ膨張している。
・卵黄形成期の卵胞・黄体・白らせた卵黄が発達しているか、あ ・黄体・白体・閉鎖卵胞は見あた 体・閉鎖卵胞は見あたらない。
るいは黄体・白体・閉鎖卵胞があ らない。
る。

雄 精巣

成体
・円筒形に肥大している。

表 2-1．生殖腺と生殖管の形態に基づく性成熟状態の分類基準．Limpus and Limpus (2003)および Miller and Limpus (2003)をもとに作成．

表 2-2．精巣および総排泄腔内の精子の存在状況．性成熟度は精巣と精巣状態の形態および精巣と総排泄腔内の精子の存在に基づいて判断された．SCL：標準直甲長，TL：尾長，rTL：
相対尾長 (TL/SCL)．精子密度は血球算定板を用いて計測され，++：>105 sperm/ml，+：
1–104 sperm/ml，－：no sperm/ml, blank: 未確認，として表された．精巣内の精子を確認した個体のうち，総排泄腔内からも精子が観察されたのは成体のみであり，顕著な尾部伸長があり，総排泄腔内に精子が確認されれば成体の雄と判断した．

精子密度
SCL (mm)TL (mm)rTL (TL/SCL) 精巣 総排泄腔 性成熟段階

ID #

年月日

1

2005/4/24

868

345

0.397

++

成体

2

2005/4/24

788

380

0.482

++

成体

3

2005/5/18

805

300

0.373

++

成体

4

2005/8/19

839

390

0.465

+

成体

5

2005/12/7

743

180

0.242

+

-

亜成体

6

2006/1/8

686

108

0.157

-

7

2006/1/18

873

435

0.498

++

++

成体

8

2006/2/1

694

118

0.170

-

-

亜成体

9

2006/4/24

808

307

0.380

++

成体

10

2006/4/30

718

122

0.170

-

-

亜成体

11

2006/5/10

826

248

0.300

-

-

亜成体

12

2006/5/14

877

439

0.501

++

+

成体

13

2006/6/2

878

357

0.407

+

成体

14

2006/6/25

902

388

0.430

+

成体

15

2006/7/3

785

237

0.302

+

成体

16

2007/4/1

698

140

0.201

-

-

亜成体

17

2007/4/4

726

255

0.351

-

-

亜成体

18

2007/7/3

759

180

0.237

-

95

亜成体

亜成体

96

められなかった．

± 2.7
± 0.0

15.3

13.2

12.3

12.2

500-600

600-700

700-800

800-900

900-1000 10.4

± 4.3

22.5

(n = 3)(n = 5)(n = 62)
11.0

11.7

13.6

(n = 25)(n = 4)± 5.8(n = 24)± 5.2 (n = 170)

± 6.7 (n = 154)

± 14.9± 8.3

成長速度 (mm / year)
雌(n = 23) * 24.1

(n = 3)(n = 1)± 7.7 (n = 107)

± 7.4

38.8

400-500± 15.331.7

雄300-400

SCL (mm)

10.4

11.2

11.9

14.1

20.7

29.5

31.7

合計

(n = 58)(n = 7)

± 0.0

± 5.4

(n = 3)(n = 29)± 4.9 (n = 257)

± 7.4 (n = 298)

± 12.4± 13.7(n = 1)

した．また，成長速度の性差は SCL 500–600 mm で雌が雄よりも速かったが (＊: p < 0.05, Mann-Whitney U-test)，その他の階級では認ら逆算された．合計の欄には性の判別ができなかった個体も含まれていることに注意されたい．成長速度は SCL が増大するに従って減少

表 5-1．成長停止線の幅から逆算された甲長の成長速度．標準直甲長 (SCL)と成長速度は上腕骨に残された成長停止線 (LAG)の半径と幅か表 6-1．ウミガメ類 (Dermochelidae と Chelonidae)の成熟甲長．各地域の産卵個体の平均値と個体数から求めた．曲甲長 (CCL)で示されていたものは Teas (1993)の変換式を用いて直甲長 (SCL)に変換した．ただし＊印は曲甲長のまま示した．
SCL (cm)
最小個体
最大個体個体数（ｎ）
オサガメ（Leatherback turtle: Dermochelys coreacea ）

海域

延べ地域数

出典
Zug and Parham (1996)

西部大西洋

164
158*

135
125

189
185

1031
228

5
3

インド洋
西部太平洋

154
161*
161*

147
134
145

165
178
178

8
126
110

1
2
2

東部太平洋

143

120

188

662

5

アオウミガメ（Green turtle: Chelonia mydas ）Hirth (1997)

太平洋
オセアニア
北太平洋西部および中央部
東部太平洋（クロウミガメ）
大西洋
南米
北中米
アフリカ
インド洋
アフリカ
アラビア半島

99
92
82

75
80.8
60

116
110.5
102

2192
393
879

14
2
3

110

83.8

123.5

2677

8

102
88

83.2
87

118.9
102

187
41

10
3

107

91

125

658

10

95

77

114

551

6

アカウミガメ（Loggerhead turtle: Caretta caretta )Kamezaki (2003)

大西洋
インド洋

91
90

70
76

110
107

1096
520

11
2

南太平洋
北太平洋
地中海

89
85
74

73.2
69.2
-

106.9
101.5
-

2207
1154
52

1
1
3

ヒラタウミガメ（Flatback turtle: Natator depressus ）オーストラリア

89.4*

67.0

100

Limpus (2007)

1437

12

タイマイ（Hawksbill turtle: Eretmochelys imbricata ）Hirth (1980)

大西洋

83.1-84.1

74.9

91.4

-

2

太平洋
インド洋

80.5
66-85.5

68
53.3

93
87.5

-

1
3

-

2
1
3

ヒメウミガメ（Olive ridley turtle: Lepidochelys olivacea ）大西洋・カリブ海
インド洋
東部太平洋

68.5-66.6
67
62.9-65.2

63
59
52.5

75
71
72.5

Hirth (1980)

ケンプヒメウミガメ（Kemp's ridley turtle: Lepidochelys kempi ）
カリブ海

64.6

59.5

75

97

-

Hirth (1980)
1

図 1-1．アカウミガメ．高知県室戸市室戸岬町地先の大型定置網で混獲され，計測と個体識
別用標識の装着のために港へ運ばれたアカウミガメ(Caretta caretta)．

98三重県北牟婁郡紀北町

高知県室戸市室戸岬町

図 2-1．主な調査地．高知県室戸市室戸岬町地先および三重県北牟婁郡紀北町島勝浦地先の大型定置網を主な調査地とし，矢印で示した．

99

図 2-2．アカウミガメの生殖腺および生殖管．雄の精巣の成体では円筒形だが，亜成体では楕円，幼体では平坦な断面を持つ．精巣上体は成体でははっきりと肥大しているが，幼体では体壁との境も明確でない．雌の卵巣は成体では黄色い卵黄が発達しているか黄体や白体，閉鎖卵胞があり，亜成体では発達した卵胞も見あたらないが卵巣乾湿に膨張が見られ，幼体では卵巣間質に発達が見られない．卵管は成体になるほど白色からはピンク色になり，伸長するのに伴って複雑に折りたたまれていく．A: 雄成体 (標準直甲長 [SCL] 873 mm)，
B: 雄亜成体 (SCL 720 mm)，C: 雄幼体 (SCL 577 mm)，D: 雌成体 (SCL 727 mm)，E: 雌
亜成体 (SCL 727 mm)，F: 雌幼体 (SCL 679 mm)．
100

950
900

SCL (mm)

850
800
750
700
650
600
550

雄

雌

雄

雌

雄

雌

雄 幼体 雌 幼体 雄 亜成体雌 亜成体 雄 成体 雌 成体

幼体

亜成体

成体

図 2-3．雌雄の性成熟階級別の甲長の分布．雌雄のそれぞれについて幼体 (雄: n = 6,
雌: n = 12)，亜成体 (雄: n = 36, 雌: n = 67)，成体 (雄: n = 12, 雌: n = 27)の標準直甲長(SCL)の分布を示した．図中の棒は最大値と最小値を，箱は第 3 四分位数と中央値と第 1 四分位数を示している．いずれの性成熟階級でも雌雄間に SCL の違いは認められず，性成熟する過程で性差はないものと示唆された (p > 0.05, Mann-Whitney
U-test)．

101

5

個体数

4

幼体
n = 18

3
2

1

個体数
個体数
個体数

個体数

0
20

15

亜成体600500
n = 103

700

800

900

800

900

800
800
800

900
900
900

SCL (mm)

10
5
0
10
10
600
700
10
8 500
成体
8
8 n = 39 SCL (mm)
6
6
6
4
4
4
2
2
2
0
0
0 500
600
700
500
600
700
500
600
700
SCL (mm)SCL
SCL (mm)(mm)

図 2-4．性成熟階級ごとの甲長組成．幼体，亜成体，成体のそれぞれで標準直甲長 (SCL)
20 mm ごとの個体数を示した．

102

17 9

亜成体の割合

1.0

19
16

0.8

19

20

5

0.6

0.4
0.2
n=1

0.0
500

1

600

700

800

900
2

SCL (mm)

1.0

成体の割合

3

7

0.8

11

0.6

10
14

0.4
0.2

6

1923
12
n=3 1717

0.0
500

600

700

800

900

SCL (mm)
図 2-5．性成熟階級の移行する甲長．成体，亜成体，幼体のそれぞれで標準直甲長 (SCL)
で 20 mm ごとに個体数をまとめ，幼体から亜成体，亜成体から成体に性成熟階級が移行する SCL を求めた．亜成体/(幼体＋亜成体)を亜成体の割合 (上)，成体/(亜成体＋成体)を成体の割合 (下)とし，半数の個体が性成熟をはじめる SCL は 660 mm (上)，半数の個体が性成熟を完了する SCL は 821 mm (下)と求められた．図中の数値は個体数を
示す．

103

図 3-1．尾長計測位置．
尾長は赤矢印で示した腹甲の後端から総排泄口の中心部までの直線距離とした．

104データ 1 1:52:52 2010/12/13

0.6
0.6
＊＊

0.5
0.5

11

＊＊

rTL (TL / SCL)rTL (TL/SCL)

29

0.4
0.4
0.3
0.3

20
55

0.2
0.2

n=5

8

0.1
0.1
雄

幼体雄

雌

幼体雌

幼体

雄

亜成体雄

雌

亜成体雌

亜成体

雄

成体雄

雌

成体雌

成体

図 3-2．性成熟階級ごとの相対尾長．相対尾長 (rTL)は標準直甲長 (SCL) に対する尾長(TL) (rTL = TL/SCL)として求めた．性成熟階級は性成熟のはじまっていない幼体，性成熟がはじまっているが成熟に達していない亜成体，性的に成熟している成体に分けた．図中の数字は個体数を表し，＊＊は Mann-Whitney U-test にて p < 0.001 で差が検出されたこ
とを示す．

105

0.600

雄

成体

雄

亜成体

雄

幼体

雌

成体

0.300

雌

亜成体

0.200

雌

幼体

rTL (TL / SCL)

0.500
0.400

雄: rTL = 0.001433×SCL－0.8046
R = 0.8066

0.100

雌: rTL = 0.0001501×SCL+0.05475
R = 0.2547

0.000
500

600

700

800

900

1000

SCL (mm)

図 3-3．雌雄の甲長に対する相対尾長の相関．■：雄の成体総排泄腔内に精子の確認された成熟雄 (n = 11)，■：雄の亜成体(n = 29)，■：雄の幼体(n = 5)，●：雌の成体(n = 20)，●：雌の亜成体(n = 55)，●：雌の幼体(n = 8)，SCL：標準直甲長，rTL：相対尾長(rTL = TL/SCL, TL

は尾長)．亜成体以降での雌雄の回帰直線の交点が雄の尾部伸長，すなわち第二次性徴のはじまる平均的な甲長と考えられ，その SCL は 670 mm であった．

106

120

n=1392

100

個体数

80
60
40
20
0

500 550 600 650 700 750 800 850 900 950 1000 1050 1100
SCL (mm)

図 4-1．高知県室戸市の定置網で捕獲されたアカウミガメの甲長組成．平均は 757 ± 67 mm(SD)で最小は 563 mm，最大は 1050 mm．

107図 5-1．アカウミガメの上腕骨と切片作成箇所．上腕骨内の成長停止線 (LAG)は最小幅部(MW)と三角筋稜 (DPC)の間に最も吸収されずに残っている (Zug et al., 1986)．そのため，本章では DPC の末端部分で上腕骨を切断し，作成した切片から LAG を読み取った．

108

図 5-2．上腕骨切片の断面と成長停止線．成長停止線 (LAG)は 1 年で 1 本形成される(Snover and Horn, 2004)．

109

LAG幅 = -0.0393×LAG半径 + 0.7669
R = 0.3715 (p < 0.001)
1.4
LAG幅 (mm)
LAG幅 (mm)

1.2
1
0.8

LAG幅 = 0.767 ｰ0.0393×LAG半径n = 653, R = 0.372 (p < 0.001)

0.6
0.4
0.2

0
6

8

10

12
14
LAG半径
(mm)
LAG半径 (mm)

16

18

20

図 5-3．上腕骨切片に残された成長停止線の半径と幅．成長停止線(LAG)の上腕骨直径(MW)に近似して補正した半径と幅の関係を示した．上腕骨切片はより多くの LAG を観察するため，MW より三角筋稜に近い場所で上腕骨を切断し，作成された．そのため，式 5-2 を用
いて LAG 形成当時の MW に近似されるように補正された．求められた回帰直線の切片(A)と傾き(B)より，式 5-3 中のパラメータ a, k が，a = |A /B| = 19.514，k =‐ln(1‐|B|) =0.0401 として求められた．

110

SCL (mm)

1000
800
600
400

200
0
0

20

40

60

80

100

推定年齢 (歳)図 5-4．北太平洋におけるアカウミガメの成長曲線．成長式は SCL = 1159{1‐exp[‐
0.03067 (t‐1.619)]}と表された．

111

個体数

個体数

7
6
5
4
3
2
1
0

未成熟 雄

7
6
5
4
3
2
1
0

未成熟

雌

15 20 25 30 35 40 45 50 55 60
7
成熟 雄 推定年齢 (歳)
6
5
4
3
2
1
0

15 20 25 30 35 40 45 50 55 60

15 20 25 30 35 40 45 50 55 60

15 20 25 30 35 40 45 50 55 60

推定年齢 (歳)推定年齢 (歳)成熟 雌 推定年齢 (歳)

個体数

個体数

7
6
5
4
3
2
1
0

図 5-5．日本近海におけるアカウミガメの年齢構成．年齢は Correction Factor protocol によって推定された．黒棒は雄の年齢構成を，灰色棒は雌の年齢構成を示している．また，上図は未成熟個体を，下図は成熟個体の年齢構成を示した．

112

雄

SCL (mm)

900
800
700
600
500
0

10

20

30

40

50

60

70

80

60

70

80

推定年齢 (歳)雌SCL (mm)

900
800
700
600
500
0

10

20

30

40

50

推定年齢 (歳)図 5-6．年齢と甲長の関係．年齢は Correction Factor protocol によって推定された．上図は雄の，下図は雌の年齢と標準直甲長(SCL)の関係を示している．また，●は成熟個体，○
は未成熟個体を示している．SCL や構成年齢は成熟個体の方が未成熟個体よりも大きいが，SCL と年齢の間に日本近海に再加入したあとのサイズクラスでは明瞭な相関関係は認められない (p < 0.05, 無相関検定)．

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図 6-1．海面に浮くアカウミガメの孵化幼体．前肢を背甲に乗せてあまり動かない．捕食者に対して目立たなくする適応と考えられる．

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図 6-2．アカウミガメの幼体-亜成体の分散と大洋を横断する回遊の模式図．アカウミガメは生まれた海域から高緯度域へ向かう暖流に乗って大洋を横断する．ある程度成長した後，性成熟が始まる前に出生海域へとむけた能動的な回遊を行うと考えられる．

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図 6-3．内視鏡による性判別．幼体や亜成体では外部形態から雌雄を判別することは容易でないため，小径の内視鏡を腹腔内に挿入し，直接生殖腺を確認することで性を判別する．

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図 6-4．ウミガメ類の生息域．種によって生活史戦略は異なるが，ヒラタウミガメを除いてすべての種は幼体期に外洋を生息域とする．沿岸に加入する甲長は種や個体群によって異なり，個体差も大きいと考えられる．(Bolten, 2003 より改変)．

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図 6-5．高知県室戸市で発見されたクロウミガメ．クロウミガメは現在アオウミガメの亜種とされているが，別種とする動きもある．腹腔がクリーム色を呈するアオウミガメに対して，クロウミガメは腹腔を含めて全身が灰色から黒色を呈す．背甲の後端が細くなるこ
とも大きな特徴である．

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