20
The main spawning season of Ezo abalone at
this site is from late August to early October
( Nakaie and Takami 2012 ). In December 2009,
small juveniles (4.6–12.5 mm SL) which were
reproduced in the 2009 spawning season were
observed as the cohort with higher CPUE than the
2008 year class. Then, the CPUE of the 2009 year
class did not markedly decrease until June 2010.
From December 2010 to February 2011, newly
recruited juveniles, which were spawned in 2010,
were detected as a single cohort. During the same
period, juveniles of the 2009 year class grew to
more than 25 mm SL with lower CPUE. In June
2011, 3 months after the tsunami, no individual of
the 2010 year class was not observed, whereas the
CPUE of the 2009 year class did not change obviously between before (February 2011) and after
(June 2011) the tsunami (Fig. 4 ).
From the results of quadrat sampling and CPUE
survey on juveniles, it was demonstrated that the
impacts of tsunami on Ezo abalone Haliotis discus
hannai were different among stations and their
growth stages. After the tsunami, although signifi -
cant difference was not marginally detected, abalone densities by quadrat sampling tend to decrease
in station A which was dominated by CCA.
Newly recruited juveniles inhabit near station
A was more severely affected by the tsunami than
older individuals. Juveniles reproduced in 2010
were not detected after the tsunami, and such a
collapse of the youngest year class has not been
observed before the tsunami. Naylor and
McShane ( 2001 ) suggest that the wave action
caused by even usual storm disturbances is an
important contributor to the mortality of new
recruits in the New Zealand abalone H. iris
because of the relatively weaker adhesion of
juveniles to substrate than that of adults.
Similarly, the much more serious disturbance by
the tsunami event could specifi cally infl uence the
survival of smaller abalone in the present study
site. The distribution pattern of juvenile abalone
also had signifi cant consequences for their survival. Juveniles mainly inhabit crustose coralline
algae, which were more severely disturbed than
0
1
2
3
4
5
A
D
E
G
Abalone density (inds m
-2
)
Before (Oct 2009)
After (Jun 2011)
b
a
a
a
a
a
a
ab
Fig. 2 Changes in density of Ezo abalone Haliotis discus
hannai collected in stations A , D , E , and G between before
and after the earthquake and tsunami
Fig. 3 Changes in size distribution of Ezo abalone Haliotis discus hannai collected in stations A , D , E , and G between
before (October 2009, upper row ) and after (June 2011, lower row ) the earthquake and tsunami
H. Takami and H. Nakaie
The main spawning season of Ezo abalone at
this site is from late August to early October
( Nakaie and Takami 2012 ). In December 2009,
small juveniles (4.6–12.5 mm SL) which were
reproduced in the 2009 spawning season were
observed as the cohort with higher CPUE than the
2008 year class. Then, the CPUE of the 2009 year
class did not markedly decrease until June 2010.
From December 2010 to February 2011, newly
recruited juveniles, which were spawned in 2010,
were detected as a single cohort. During the same
period, juveniles of the 2009 year class grew to
more than 25 mm SL with lower CPUE. In June
2011, 3 months after the tsunami, no individual of
the 2010 year class was not observed, whereas the
CPUE of the 2009 year class did not change obviously between before (February 2011) and after
(June 2011) the tsunami (Fig. 4 ).
From the results of quadrat sampling and CPUE
survey on juveniles, it was demonstrated that the
impacts of tsunami on Ezo abalone Haliotis discus
hannai were different among stations and their
growth stages. After the tsunami, although signifi -
cant difference was not marginally detected, abalone densities by quadrat sampling tend to decrease
in station A which was dominated by CCA.
Newly recruited juveniles inhabit near station
A was more severely affected by the tsunami than
older individuals. Juveniles reproduced in 2010
were not detected after the tsunami, and such a
collapse of the youngest year class has not been
observed before the tsunami. Naylor and
McShane ( 2001 ) suggest that the wave action
caused by even usual storm disturbances is an
important contributor to the mortality of new
recruits in the New Zealand abalone H. iris
because of the relatively weaker adhesion of
juveniles to substrate than that of adults.
Similarly, the much more serious disturbance by
the tsunami event could specifi cally infl uence the
survival of smaller abalone in the present study
site. The distribution pattern of juvenile abalone
also had signifi cant consequences for their survival. Juveniles mainly inhabit crustose coralline
algae, which were more severely disturbed than
0
1
2
3
4
5
A
D
E
G
Abalone density (inds m
-2
)
Before (Oct 2009)
After (Jun 2011)
b
a
a
a
a
a
a
ab
Fig. 2 Changes in density of Ezo abalone Haliotis discus
hannai collected in stations A , D , E , and G between before
and after the earthquake and tsunami
Fig. 3 Changes in size distribution of Ezo abalone Haliotis discus hannai collected in stations A , D , E , and G between
before (October 2009, upper row ) and after (June 2011, lower row ) the earthquake and tsunami
H. Takami and H. Nakaie