Fish location is the phenomenon of locating fish in the sea at a given area. It also an indirect method where fishes are detected/found not directly detection the fish themselves but by some other factors like water temperature, turbidity, food availability etc.

1. Fish Location and Detection

2. Fish location
• Fish location is the phenomenon of locating
fish in the sea at a given area.
• It also an indirect method where fishes are
detected/found not directly detection the
fish themselves but by some other factors
like water temperature, turbidity, food
availability etc.

3. Factors considering for fish location:
1. Water temperature (at different season of the year,
fishery strategy).
2. Oxygen concentration.
3. Sun light.
4. Nutrient content.
5. Salinity.
6. Water depth.
7. Turbidity.
8. pH of water.
9. Osmotic pressure at different water depth.
10.Plankton monitoring.
11.Fishing chart.
12.Zones of convergence and zones of divergence.

5. Attraction of fish/fish response to
stimuli
Attraction is the process or series of processes
in which some stimulant suitable lure or
baits, light, chemicals, etc. are used to
attract the fish or fish school to a particular
area from where they may or may not get
out or escape.
Fish response or attraction to the stimulants
may be of two types:
i) Positive attraction
ii) Negative attraction

6. Types of various stimuli for
attracting fish
1. Luminous (visual) – Light, net colour
2. Sonorous (auditory)- Whistle, rattles
3. Mechanical (touch)- Baits
4. Chemical (smell)- Protein, amino acid, vitamin
5. Electrical (electric field)- Electro fishing
6. Miscellaneous

7. 1.Light (visual stimuli)Use of light
• light may attract fish toward gear or frighten
• Torches, fire baskets, lamps are used to attract the
fish and then caught mostly using wounding gears
• Fish with highly developed sense organ will be more
attracted than the less developed
• Any deviation from environmental illumination will
effect the movement of fish
e.g. Notopterus is attracted by light

8. 2. Use of sound
- Sound like whistles are used to attract fish
- Sound of particular wave length attracts fish
of particular species
- In recent years- new scientific equipment
like hydrophone, tape recorder are
developed and helps fishermen to direct the
movement of fish
- In commercial fishery, the application of
sound in attracting fish has not yet
recognized

9. 3. Mechanical (baits)
a) Natural bait
- earthworm, frog, eggs of many fish, eggs and
larvae of ants and bee
- Cow dung
- Smell and vision plays important role
b) Artificial bait
- shinny coloured artificial baits are used to attract
fish
- artificial baits are used in line fishing
- e.g. fish skin, feathers, pearls etc.
- here the sense of vision is more important then
the smell

10. 4. Chemicals
- Fishes give response to chemical stimuli
- Chemical stimuli plays an important role in
the use of bait and lures. They are attractant
(e.g. amino acids, esters, oil, vitamins, etc.)
and repellent (e.g. extracts of the skin of
mammals)
- It helps the fish to be attracted to definite
direction

11. 5. Electricity
- Using electrical stimuli also catches fish
- As soon as a fish enters that field two thing occur:
• If the conductivity of water were lower as in fresh
water; the current would use the fish as a better
conductor and flow a great extent through it.
• Thus, the fish is shocked and swim towards the
anode from which they are collected by a scoop net
• If the conductivity of water were good the current
would then flow around the fish
- The conductivity of water depends on the dissolved
solutes and temperature
- Electro fishing can be done in both fresh and marine
water

12. 6. Miscellaneous
Some fish are attracted because of their liking of the
net
- Colour
- Odour
- Mesh size
Factors need to be considered for the attraction
of fish
a) Depth of water where a net is used
b) Reaction of fish approaching a net
c) Influence of light
d) Colour of the net

13. Fish detection
• Fish detection refers to locate the actual position of
a fish school
• Fish detection is the direct communication between
fish and men or fish and some device/equipment in
a water body.
• The position of fish is first detected and then net or
other fishing gear is used to catch those fish from
different water depth.
• Thus, detection of fish is very important to reduce
the fishing cost and time in the vast sea water.

14. Fish detection methods
A fish school can be detected by using the
following methods:
a. Sampling
b. Aerial scouting
c. Use of instrument

15. a. Sampling:
- Detection of fish school can be performed by
using gill nets, trawl nets, long lines etc.
- By naked eye and/or binoculars from on board
the vessel
b. Aerial Scouting:
- Use of powerful camera from aeroplane
- Fish school sighted- in evening and morning
- Pilot or skipper give direction and guidance to the
fishing vessels
- Deep sea large water bodies can be surveyed
within short time
- Can detect from a distance of up to 10 miles

16. c. Use of instruments
Most instruments used are
1. Echo ranger
2. Echo sounder
3. SONAR
1. Detection by Echo ranger:
- With the help of echo ranger fish can be detected
horizontally which extends up to 2 miles from ship
- Sound beams travel horizontally
- Specially used to detect pelagic or mid water fish

17. 2. Fish finder (echo sounder)
Vertically detects the presence of any objects
An echo sounder or fish finder is used to measure
i). The depth of water
ii). Bottom topography and
iii). Fish shoals/schools at different depth of water

18. Principle of Echo sounder:
•This instrument is designed to radiate wave of
known frequency vertically through a transducer
(set at the bottom of fishing vessel) in water down
to get the reflections or echoes from the bottom or
fish shoals or some other objects in front of the
transmitted wave.
•This wave again is received by the transducer
which it send back to a recorder and the return
time is processed electronically and recorded on
paper or displayed on CRT (Cathode Ray Tube).

21. 3. SONAR (Sound Navigation and Ranging)
SONAR includes all underwater acoustic systems used
for the detection of the underwater objects, though
recently the term Sonar has been used for an echo
sounder for horizontal detection in a narrow sense.
The sonar records or displays the reflected wave
from an object under the water on recording paper
or a cathode ray tube (CRT) by scanning the
transducer horizontally.
Recently most sonar has been designed for either
horizontal or vertical or both (by using large beam
wave) use.

23. Why should we use Echo-Sounder
• Don’t need to waste time and fuel to catch fish at
the places where there are few fish or no fish at all.
• Can catch more fish because easy detecting of fish
• Shows the depth of the water
• Can see rocks, wrecks of boats or rubbish at the
bottom and so avoid losing or tearing your nets
• Can place the net near the rocks without fearing of
losing or tearing nets
• Can find new fishing grounds
• Echo-sounder can help to find a lost ship or gear

24. Fish location Fish detection
Method of detecting fish by
observing different factors
related to water
Method of detecting
fish by using acoustic
equipments
Indirect method Direct method
No direct communication
between man and fish
Direct communication
Following factors to be
considered- water temp,
nutrient content, plankton
monitoring, oxygen
concentration, water depth
etc.
Following equipments
are used- SONAR,
Echo-sounder, Echo-
ranger, binocular, aerial
scouting etc.
Natural based system Mechanical dependent
system

25. Electro-fishing
• Electro-fishing uses electricity to stun fish before
they are caught.
• Electro fishing is a common scientific survey method
used to sample fish populations to determine
abundance, density, and species composition.
• When performed correctly, electro fishing results in
no permanent harm to fish, which return to their
natural state in as little as two minutes after being
stunned.
• It is a quick method of harvesting large number of
fish.
• During fishing an electric field is created between
two electrodes called anode and cathode.

26. Advantages of electro-fishing:
• It is an unconventional method of fish collection
trough saving time, labour, money and manpower
• This method doesn’t affect the growth, viability and
reproductive capacity of the fish
Disadvantages of electro-fishing:
• Extensive electricity current may damage the fish
population
• High conductivity bottom materials tend to short
circuit which reduce the effectiveness of electro-
fishing
• Need trained personnel to operate
• Other fish population may also be damaged by
electricity

28. Infrared photography
• In infrared photography, the film or
image sensor used is sensitive to
infrared light.
• The part of the spectrum used is
referred to as near-infrared to
distinguish it from far-infrared, which is
the domain of thermal imaging.
Wavelengths used for photography
range from about 700 nm to about
900 nm.

30. General applications of
infrared photography:
-long distance photography
-portraiture
-survey and reconnaissance
-in the dark
-document inspection
-scientific and industrial

31. Use of infrared photography to aquaculture and
fisheries
a) Water quality
i) areas affected by acid rain
ii) land used and crop yields
iii) effluent discharges and other pollutants
iv) suspended and cohesive sediment
concentrations
v)salinity
vi) phytoplankton concentrations
b) Water temperature
c) Water quantity
d) Economic production functions related to distance
factors or population distribution

32. e) Climatic factors
f) Soils
g) Relief
h) The existence of shelter for cage
culture
i) Bathymetry
j) Mapping of aquatic vegetation