317
determining the scope of the observation
points, which are used to give weight to estimate the observation data, in order to obtain an
estimated value at an optional point in space
(Zeiler 1999 ). Kriging has been applied by
Tanoue et al. ( 2008 ) and Minami et al. ( 2012 )
to the space interpolation of fi sh schools and
seaweed beds (Tanoue et al. 2008 ; Minami
et al. 2012 ). The total area of seaweed beds at
Hachiri-ga-se has been estimated at 2.95 km
2
,
and 94.4 % of the observation results by
underwater TV cameras at the 54 locations
agreed with the outcome obtained in this study.
4
Conclusion
As the problems of marine protected areas (MPAs),
perturbations in oceans, and resilience have been
internationally discussed, the importance not only
of seamounts in the open sea but also of hills in
offshore zones as the habitats of fi sh has begun to
be pointed out. Hachiri-ga-se, situated off Mishima
Island, Hagi, Yamaguchi Prefecture, in the southwestern part of the Japan Sea (East Sea), is one of
the representative offshore sea-hills in Japan. The
most important characteristic of Hachiri-ga-se is
its great biodiversity. It has been shown that due to
the complicated seabed topography of Hachiriga-se and the direct effects of the Tsushima Warm
Current, extensive seaweed communities have
been formed there, where a wide variety of fi sh,
larvae, and juveniles are distributed, making it an
ideal place for the stay, feeding, and rearing of
marine life. However, the loss of seaweed beds has
been increasing as a result of “isoyake” (withering
of seaweeds) in recent years, and it has become
more important than ever to check the situation of
the maintenance and preservation of seaweed
beds. Here, we proposed a new monitoring method
to estimate the area on the hills in the offshore
zone where seaweed beds are distributed by adopting the frequency difference method using multiple frequencies, the technique for identifying
plankton, larvae, and juveniles, instead of the conventional acoustic survey using a single frequency
by applying a survey method with a quantitative
echo sounder. As a result, the distribution of seaweed beds could be mapped from georeferenced
data gathered by acoustic sonar and optical camera
surveys. Based on this result, it was shown that our
proposed acoustic method would be effective as a
technique for estimating the distribution of seaweed beds and juveniles living in the offshore
sea-hills.
The protection and management of offshore
sea-hill fi shing grounds have been regarded as
important both internationally and in Japan. As
“responsible fi sheries” and the management of
marine resources have been signifi cantly
required, it is considered important to continue
the monitoring surveys and to follow their
perturbations and their resilience in the coming
years in order to promote a sustainable fi shery
production in harmony with the environment and
ecosystems and maintain and develop various
types of coastal fi sheries. The future adaptations
of societies living from the marine resources will
be established under the best conditions.
Acknowledgments We express our thanks to Dr.
N. Murase, Dr. Y. Kajikawa, Mr. T. Nakamura, and Mr.
K. Sadamitsu for their kind help in the fi eldwork at
Hachiri-ga-se and Dr. S. Ruitton and Dr. M. Mohri for
their useful comments. We are grateful to Dr. H.-J.
Ceccaldi, Dr. M. H. Tusseau-Vuillemin, Dr Y. Henocque,
and Dr. G. Stora for editing our manuscript. This work
was partially supported by the city of Hagi.
References
Greenlaw CF, Johnson RK (1983) Multiple-frequency
acoustical estimation. Biol Oceanogr 2:227–252
Hamano A, Nomura K (2002) A preliminary survey of
marine living resources around Hachiri-ga-se off
Mishima, Hagi, Japan. In: Proceedings of TechnoOcean 2002, Techno-Ocean Network Kobe, Japan.
CD-ROM. Daishin Planning, Kobe, 4 p
Hamano A, Shinagawa S (2010) Meanings of the protection and management of offshore sea-hill fi shing
grounds, collection of the lectures at the symposium
on the conservation of Hachiri-ga-se fi shing grounds,
Mishima Island. Hagi city, 3 p (in Japanese)
Hamano A, Uchida K (2000) Report of the survey on fi shing grounds at Hachiri-ga-se, Mishima Island, Hagi, in
1999. Hagi city, 15 p (in Japanese)
New Monitoring Method to Assess the Marine Algae Distribution and Fish School…
determining the scope of the observation
points, which are used to give weight to estimate the observation data, in order to obtain an
estimated value at an optional point in space
(Zeiler 1999 ). Kriging has been applied by
Tanoue et al. ( 2008 ) and Minami et al. ( 2012 )
to the space interpolation of fi sh schools and
seaweed beds (Tanoue et al. 2008 ; Minami
et al. 2012 ). The total area of seaweed beds at
Hachiri-ga-se has been estimated at 2.95 km
2
,
and 94.4 % of the observation results by
underwater TV cameras at the 54 locations
agreed with the outcome obtained in this study.
4
Conclusion
As the problems of marine protected areas (MPAs),
perturbations in oceans, and resilience have been
internationally discussed, the importance not only
of seamounts in the open sea but also of hills in
offshore zones as the habitats of fi sh has begun to
be pointed out. Hachiri-ga-se, situated off Mishima
Island, Hagi, Yamaguchi Prefecture, in the southwestern part of the Japan Sea (East Sea), is one of
the representative offshore sea-hills in Japan. The
most important characteristic of Hachiri-ga-se is
its great biodiversity. It has been shown that due to
the complicated seabed topography of Hachiriga-se and the direct effects of the Tsushima Warm
Current, extensive seaweed communities have
been formed there, where a wide variety of fi sh,
larvae, and juveniles are distributed, making it an
ideal place for the stay, feeding, and rearing of
marine life. However, the loss of seaweed beds has
been increasing as a result of “isoyake” (withering
of seaweeds) in recent years, and it has become
more important than ever to check the situation of
the maintenance and preservation of seaweed
beds. Here, we proposed a new monitoring method
to estimate the area on the hills in the offshore
zone where seaweed beds are distributed by adopting the frequency difference method using multiple frequencies, the technique for identifying
plankton, larvae, and juveniles, instead of the conventional acoustic survey using a single frequency
by applying a survey method with a quantitative
echo sounder. As a result, the distribution of seaweed beds could be mapped from georeferenced
data gathered by acoustic sonar and optical camera
surveys. Based on this result, it was shown that our
proposed acoustic method would be effective as a
technique for estimating the distribution of seaweed beds and juveniles living in the offshore
sea-hills.
The protection and management of offshore
sea-hill fi shing grounds have been regarded as
important both internationally and in Japan. As
“responsible fi sheries” and the management of
marine resources have been signifi cantly
required, it is considered important to continue
the monitoring surveys and to follow their
perturbations and their resilience in the coming
years in order to promote a sustainable fi shery
production in harmony with the environment and
ecosystems and maintain and develop various
types of coastal fi sheries. The future adaptations
of societies living from the marine resources will
be established under the best conditions.
Acknowledgments We express our thanks to Dr.
N. Murase, Dr. Y. Kajikawa, Mr. T. Nakamura, and Mr.
K. Sadamitsu for their kind help in the fi eldwork at
Hachiri-ga-se and Dr. S. Ruitton and Dr. M. Mohri for
their useful comments. We are grateful to Dr. H.-J.
Ceccaldi, Dr. M. H. Tusseau-Vuillemin, Dr Y. Henocque,
and Dr. G. Stora for editing our manuscript. This work
was partially supported by the city of Hagi.
References
Greenlaw CF, Johnson RK (1983) Multiple-frequency
acoustical estimation. Biol Oceanogr 2:227–252
Hamano A, Nomura K (2002) A preliminary survey of
marine living resources around Hachiri-ga-se off
Mishima, Hagi, Japan. In: Proceedings of TechnoOcean 2002, Techno-Ocean Network Kobe, Japan.
CD-ROM. Daishin Planning, Kobe, 4 p
Hamano A, Shinagawa S (2010) Meanings of the protection and management of offshore sea-hill fi shing
grounds, collection of the lectures at the symposium
on the conservation of Hachiri-ga-se fi shing grounds,
Mishima Island. Hagi city, 3 p (in Japanese)
Hamano A, Uchida K (2000) Report of the survey on fi shing grounds at Hachiri-ga-se, Mishima Island, Hagi, in
1999. Hagi city, 15 p (in Japanese)
New Monitoring Method to Assess the Marine Algae Distribution and Fish School…