244
1
Introduction
To sustainably utilize coastal areas, human
coastal activities must be harmonized with the
natural environment (Komatsu et al. 2012 ).
Integrated coastal management perceives coastal
areas as natural systems, involves stakeholders in
a proactive role, provides integrated management
plans, and promotes the coexistence of humans
and the natural environment in coastal waters in
an integrated and planned manner. Effective integrated coastal management requires an understanding of how natural organisms use coastal
areas, to protect those species.
Tokyo Bay has historically been a productive
fi shery. Commercial fi sheries peaked at approximately 140,000 tons in 1960, but the catch has
been decreasing since then (Shimizu 1997 ). A
long-term scientifi c study of fi sh biomass conducted in Tokyo Bay using bottom trawling
showed an increase in the biomass of Japanese
sea bass ( Lateolabrax japonicus ) over time (e.g.,
Kodama et al. 2010 ). However, Japanese sea bass
spend their lives not only in the sea but also in
brackish waters (Shoji 2002 ). Knowing precisely
what areas they use would be useful so that these
areas could be appropriately managed. Because
fi shing is prohibited in many brackish waters of
Tokyo Bay, such as around ports and waterways
where large vessels pass or anchor, habitat use of
fi sh in these areas cannot be monitored by fi shing.
Recently, data loggers and a micro- underwater
video camera have become small enough to be
attached to small fi sh to measure acceleration,
water temperature, depth, and conductivity (e.g.,
Alabsi et al. 2011 ; Komatsu et al. 2011 ; Tanoue
et al. 2013 ; Kudo et al. 2007 ). The acceleration
sensor measures the intensity of swimming
behavior and the number of active burst events by
fi sh such as feeding (e.g., Tanoue et al. 2012 ).
Small ultrasonic and VHF transmitters can be
attached to the fi sh along with the data loggers to
track fi sh movement and aid in the recovery of
the data loggers after a time-scheduled release
from the fi sh. In addition, salinity data obtained
with a conductivity sensor are useful to detect
habitat use near river mouths. These technological
advances make it practical to use data loggers to
observe fi sh behaviors.
In this study, we examined habitat use of
Japanese sea bass, a representative fi sh species in
Tokyo Bay, by using micro-data loggers with
sensors for three-axis acceleration, depth, water
temperature, and conductivity, in addition to
micro-underwater video cameras and ultrasonic
and VHF transmitters.
2
Materials and Methods
2.1
Study Site
The catch of Japanese sea bass in Chiba Prefecture
(Fig. 1 ) is the greatest in Japan. Between 1958 and
1997, 85 % of the fi sh that landed from Tokyo Bay
were in Chiba Prefecture (Shoji 2002 ). Banzu
Tidal Flat is an area of 1,400 ha at the mouth of the
Obitsu River, which discharges freshwater into the
east of Tokyo Bay (Fig. 1 ). This area is near fi shing
and general ports and is a habitat of young Japanese
sea bass. The river mouth of the Obitsu River and
its neighboring areas are a fi shing ground for adult
Japanese sea bass. For these reasons, we conducted our survey in the waters near the river
mouth of the Obitsu River (Fig. 1 ).
2.2
Survey of Habitat Use by
Japanese Sea Bass by Using
Data Loggers
Field surveys of habitat use by Japanese sea bass
were conducted in October 2011. Several data
collection devices were used in two combinations. The fi rst system included a salinity data
logger (DSL, Little Leonardo Co., Japan), a
three-axis micro-acceleration data logger with
depth and water temperature sensors (ORI380D3GT, Little Leonardo Co.), an underwater video
camera (SSP Co., Japan), an ultrasonic transmitter (V9, Vemco Co., Canada), and a releasing
device (Little Leonardo Co.) with a fl oat (NiGK
Co., Japan) connected to a mount. The second
system included the same salinity and three-axis
micro-acceleration data loggers, the same releasing
H. Tanoue et al.
1
Introduction
To sustainably utilize coastal areas, human
coastal activities must be harmonized with the
natural environment (Komatsu et al. 2012 ).
Integrated coastal management perceives coastal
areas as natural systems, involves stakeholders in
a proactive role, provides integrated management
plans, and promotes the coexistence of humans
and the natural environment in coastal waters in
an integrated and planned manner. Effective integrated coastal management requires an understanding of how natural organisms use coastal
areas, to protect those species.
Tokyo Bay has historically been a productive
fi shery. Commercial fi sheries peaked at approximately 140,000 tons in 1960, but the catch has
been decreasing since then (Shimizu 1997 ). A
long-term scientifi c study of fi sh biomass conducted in Tokyo Bay using bottom trawling
showed an increase in the biomass of Japanese
sea bass ( Lateolabrax japonicus ) over time (e.g.,
Kodama et al. 2010 ). However, Japanese sea bass
spend their lives not only in the sea but also in
brackish waters (Shoji 2002 ). Knowing precisely
what areas they use would be useful so that these
areas could be appropriately managed. Because
fi shing is prohibited in many brackish waters of
Tokyo Bay, such as around ports and waterways
where large vessels pass or anchor, habitat use of
fi sh in these areas cannot be monitored by fi shing.
Recently, data loggers and a micro- underwater
video camera have become small enough to be
attached to small fi sh to measure acceleration,
water temperature, depth, and conductivity (e.g.,
Alabsi et al. 2011 ; Komatsu et al. 2011 ; Tanoue
et al. 2013 ; Kudo et al. 2007 ). The acceleration
sensor measures the intensity of swimming
behavior and the number of active burst events by
fi sh such as feeding (e.g., Tanoue et al. 2012 ).
Small ultrasonic and VHF transmitters can be
attached to the fi sh along with the data loggers to
track fi sh movement and aid in the recovery of
the data loggers after a time-scheduled release
from the fi sh. In addition, salinity data obtained
with a conductivity sensor are useful to detect
habitat use near river mouths. These technological
advances make it practical to use data loggers to
observe fi sh behaviors.
In this study, we examined habitat use of
Japanese sea bass, a representative fi sh species in
Tokyo Bay, by using micro-data loggers with
sensors for three-axis acceleration, depth, water
temperature, and conductivity, in addition to
micro-underwater video cameras and ultrasonic
and VHF transmitters.
2
Materials and Methods
2.1
Study Site
The catch of Japanese sea bass in Chiba Prefecture
(Fig. 1 ) is the greatest in Japan. Between 1958 and
1997, 85 % of the fi sh that landed from Tokyo Bay
were in Chiba Prefecture (Shoji 2002 ). Banzu
Tidal Flat is an area of 1,400 ha at the mouth of the
Obitsu River, which discharges freshwater into the
east of Tokyo Bay (Fig. 1 ). This area is near fi shing
and general ports and is a habitat of young Japanese
sea bass. The river mouth of the Obitsu River and
its neighboring areas are a fi shing ground for adult
Japanese sea bass. For these reasons, we conducted our survey in the waters near the river
mouth of the Obitsu River (Fig. 1 ).
2.2
Survey of Habitat Use by
Japanese Sea Bass by Using
Data Loggers
Field surveys of habitat use by Japanese sea bass
were conducted in October 2011. Several data
collection devices were used in two combinations. The fi rst system included a salinity data
logger (DSL, Little Leonardo Co., Japan), a
three-axis micro-acceleration data logger with
depth and water temperature sensors (ORI380D3GT, Little Leonardo Co.), an underwater video
camera (SSP Co., Japan), an ultrasonic transmitter (V9, Vemco Co., Canada), and a releasing
device (Little Leonardo Co.) with a fl oat (NiGK
Co., Japan) connected to a mount. The second
system included the same salinity and three-axis
micro-acceleration data loggers, the same releasing
H. Tanoue et al.