Nansen’s bottle, Peterson’s grab, Dredges, Fish finding devices/methods, Remote sensing are the common instruments implied in fishing in India.

1. Oceanography Instruments
1. Nansen’s bottle:
A Nansen bottle is a device for obtaining samples of seawater at a specific depth. It was designed
in 1910 by the early 20th-century the Norwegian explorer and oceanographer Fridtjof Nansen and
further developed by Shale Niskin, are cylindrical containers that sample sea temperature and
salinity. The bottle, more precisely a metal or plastic cylinder, is lowered on a cable into the ocean,
and when it has reached the required depth, a brass weight called a "messenger" is dropped down
the cable. When the weight reaches the bottle, the impact tips the bottle upside down and trips a
spring-loaded valve at the end, trapping the water sample inside. The bottle and sample are then
retrieved by hauling in the cable. A second messenger can be arranged to be released by the
inverting mechanism, and slide down the cable until it reaches another Nansen bottle. By fixing a
sequence of bottles and messengers at intervals along the cable, a series of samples at increasing
depth can be taken. The sea temperature at the water sampling depth is recorded by means of a
reversing thermometer fixed to the Nansen bottle. This is a mercury thermometer with a
constriction in its capillary tube which, when the thermometer is inverted, causes the thread to
break and trap the mercury, fixing the temperature reading. Since water pressure at depth will
compress the thermometer walls and affect the indicated temperature, the thermometer is protected
by a rigid enclosure.
2. Peterson’s grab:
A device used to collect sediment samples for the identification of bottom-dwelling animals in
lakes and streams. The device has the appearance of a closed metal cylinder sectioned in half
through the long axis. Weights can be attached to the outside of the cylinder sections to provide a
deeper bite into the sediment. The Peterson dredge is particularly useful in the sampling of
sediments that have a high content of sand and gravel. Also referred to as the Peterson Grab. This
is a sampling device used by aquatic and marine biologists. Since 1930 the Petersen grab has been
used in fresh water for collecting macroscopic fauna in sand, gravel, marl, clay or clay

2. combinations. If used in salt water, it must be painted for protection. Since it has been widely used
over 6 decades, it is ideal for comparing samples with data collected previously by a Petersen grab.
Vent holes permit water to flow through while the grab is being lowered, minimizing diagonal
movement as well as reducing the frontal shock wave generated by descent. Jaws close clamshell
fashion.
3. Dredges:
Dredges are either mechanical or hydraulic type. Mechanical dredges work by mechanically
digging or gathering sediment from the bottom surface of a body of water typically through use of
a bucket or clamshell. Hydraulic dredges work by sucking up a mixture of sediment and water
(known as slurry) from the bottom surface and then transferring the mixture through a pipeline to a
desired location. These are gears which are dragged along the bottom to catch shellfish. They
consist of a mouth frame to which a holding bag constructed of metal rings or meshes is attached.
There are two main type of dredges; heavy dredges towed by boats (boat dredges), and lighter ones
operated by hand in shallow waters. The Dredgers are medium to large vessels (maximum 4-50 m
long) and in general with powerful engines. Some larger dredgers are outrigger type with strong
outrigger boom allowing the operation of two or more dredges at the same time.

3. 4. Fish finding devices/methods:
A fish-finder or sounder is an instrument used to locate fish underwater by detecting reflected
pulses of sound energy, as in SONAR. In operation, an electrical impulse from a transmitter is
converted into a sound wave by an underwater transducer, called a hydrophone, and sent into the
water. When the wave strikes something such as a fish, it is reflected back and displays size,
composition, and shape of the object.
The exact extent of what can be discerned depends on the frequency and power of the pulse
transmitted. Fish-finders usually have a "Fish Symbol" feature, which will display a FISH symbol
for almost any echo not connected to the bottom or the surface. A modern fishfinder displays
measurements of reflected sound on a graphical display, allowing an operator to interpret
information to locate schools of fish, underwater debris, and the bottom of body of water. Fish-
finder instruments are used both by sport and commercial fishermen. Modern electronics allows a
high degree of integration between the fish-finder system, marine radar, compass and GPS
navigation systems. The vertical sounder is also known as sonar. The horizontal sounder is
required to find the distance of fish from the gear, the phenomenon known as eco-ranging and the
device is called eco-ranger.
5. Remote sensing:
Remote sensors collect data by detecting the energy that is reflected from Earth. These sensors can
be on satellites or mounted on aircraft. Remote sensors can be either passive or active. Passive
sensors respond to external stimuli. They record radiation that is reflected from Earth’s surface,
usually from the sun. Because of this, passive sensors can only be used to collect data during

4. daylight hours. In contrast, active sensors use internal stimuli to collect data about Earth. For
example, a laser-beam remote sensing system projects a laser onto the surface of Earth and
measures the time that it takes for the laser to reflect back to its sensor. Remote sensing of ocean
properties has the potential to provide essential information for the governance of ocean
ecosystems on global and regional scales. Presently various environmental properties that
influence fish distribution, abundance, and migration and the application of remote sensing in
monitoring these factors are done through remote sensing. The remotely sensed data are provided
in near-real time to help fishermen save fuel and effort during their search for fish; to modelers
who produce fisheries forecasts; and to scientists who help develop strategies for sustainable
fisheries management.