A remote-controlled
instrument platform for fish behaviour studies and sound monitoring
Ingvald Svellingen, Bjørn Totland and Jan Tore Øvredal
Institute of Marine Research Fish Capture Division
P.O. Box 1870 5817 Bergen Norway
Email: ingvald.svellingen@imr.no, bjørn.totland@imr.no, jan.tore.ovredal@imr.no
Introduction
A new remote-controlled instrument platform for in situ recording of behaviour-specific
fish sound and synchronous video observations has been developed. Such
studies have normally been carried out using a cable connection between
the hydrophone and the observing vessel, which must be positioned relatively
close to the hydrophone itself and generate noise. Vessel generated noise
will not only affect the recorded sound pattern, but may also have an
impact on the behaviour of the fish studied.
The new remote-controlled platform allows operation at distances up to
10 nautical miles and has therefore been developed to omit such problems
during behaviour studies of wild fish in their natural environments.
Description of the system
The instrument platform consists of two main units (fig 1); a surface
buoy and an underwater electronic bottle capable of operating at depths
down to 500m. The surface buoy contains a high-speed, full duplex, 115
kbps, data telemetry radio and a video link transmitter. It is connected
to an underwater bottle via a 12 lead Kevlar cable. The underwater bottle
is made of an anodized aluminum cylinder mounted on a stainless steel
frame and houses a full feature single-board computer in order to control
various instruments, and to log data from different sensors. Two rechargeable
batteries provide power, 24 VDC, to the electronics. All electronic parts
have been chosen to minimize power consumption, making it possible to
run the system continuously for approximately 20 hours before recharging.
For sound recording a hydrophone is used and connected to the amplifier in the electronic bottle via a sub-sea connector on the end lid. All amplifier settings are fully remote controlled from the observing vessel via the radio telemetry link, and its output is connected to the PC sound card. The digitized signal is temporarily stored on a flash memory in order to avoid mechanical noise from a hard disk drive which might disturb the received signal. The recording program allows automatic frequency, level- and pre trigging facilities, which makes it suitable for a selective sound recording.
A low light video
camera placed on the top of the bottle is used for simultaneous video
observations. Both sound- and video signals are transmitted to the observing
vessel and monitored in real time.
A number of sub-sea connectors on the electronic bottle allow connection
of different sensors and equipment like pan/tilt unit, artificial light,
echo sounder etc., making the system suitable for a variety of tasks.
Modification of the underwater unit can easily be done to support different
instrumentation needed for a wide range of studies.
The video transmitter and the data link enable the instrument platform
to be operated from an observing vessel at a distance of up to 1 nautical
miles for video transfer, and up to 10 nautical miles with data link only.
The remote controlled instrument platform has so far been successfully used to record fish sounds with synchronous video observations from cod, haddock, saithe, and tusk. The advantages of a remote-controlled instrument platform over a system with long cables have been clearly demonstrated in these studies.
s
Fig. 1. Fish behavior and sound production can be monitored from a distance with the remote-controlled instrument platform, using radio link.
This paper vas originally presented as a poster at symposium titled Fish Bioacoustics. The symposium was held in Chicago, USA May 30- June 2 2001. The paper will also be published in the journal Bioacoustics.