Fisherman`s Guide to Astronomy

Transcription

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Fisherman’s Guide to Astronomy
Preface
Four friends went out on a night fishing expedition.
Looking at the Moon smiling down on them, inspiration comes knocking…
Motivated by the module GEK 1506 Heavenly Mathematics, Group 39 proudly presents:
“Fisherman’s Guide to Astronomy”
This handy guide is specially catered for all salt-water fishermen around the world, whom
oftentimes wonder how the environment around them has a myriad of impacts on his
fishing productivity.
More importantly, it is for the fishermen who look at the Sun and the Moon yet do not
know much those celestial bodies affect salt-water fishing.
We hope with this short guide, some questions relating salt-water fishing and astronomy
will be answered.
GROUP 39
AIDIL FADLY BIN FADIL (U036028U)
MUHAMMAD KHAIDIR BIN MOHD AMIN (U036304Y)
MUHAMMAD FARHAN BIN MOHD JAIS (U036046M)
MOHAMED TAUFIQ BIN MOHD ALI (U036043A)
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Content Page
1. Introduction
-4-
2. Astronomical Concepts and Fishes
a. Astronomy Behind the Tides
Introduction to Tides
Moon’s Impact on Tides
The Sun’s Role on the Moon and Tide Model
Impact of Declinations of Sun and Moon on Tides
Elliptical Distance Between the Sun and Moon
Types of Tides
Tides and Fishes
-5-7-9-11-13-14-15-
b. Astronomy Affecting Climate, Ocean Currents, Precipitation and Fishes
The Astronomy of Earth
Climate
Ocean Currents
Precipitation
-16-19-20-21-
c. Moon Phases
Phases of the Moon
Effects on Fishes
d. The Seasons on Earth
Seasons
Effects on Fishes
-24-24-
-25-26-
e. Distribution of Fishes in the Various Climatic Zones
The Frigid Zone
The Temperate Zone
The Tropical Zone
-27-30-33-
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3. Methods of Salt-Water Fishing
a. Inshore Fishing
In-shore Salt-Water Fishing (Angling)
In-shore Casting (Angling)
Net-Casting (Bulk)
b. Offshore Fishing
-37-37-39-40-41-
¾ Big-Game Fishing (Angling)
Trolling
Offshore Bottom Fishing
Ice Fishing
-41-42-42-
¾ Bulk Fishing
Dredging
Gillnetting
Long-Line Fishing
Purse-Seining
Trawling
-43-43-44-44-45-
4. Final Note from the Authors
-46-
5. References
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Introduction
Since the dawn of civilization, Man has been scouring the Seven Seas for treasures
hidden deep beneath the oceans. Treasures of sunken bounties, pearls and greater riches
had been found and lost through the sands of time. However there is one treasure that still
occupies the oceans, inexhaustible in nature and has been of utmost significance to the
lives of Men. Not gold, not silver… but fish!
It is a known fact that sea fishing has been an important activity that is productive both in
an economical and recreational way. Fishing is influenced by factors such as forces of
tides, temperature and climate among other things. However, a lesser known fact is that
these factors are governed by position and orientation of the Sun, the Moon and the
Earth. The movements of these heavenly bodies are a major component in the study of
astronomy.
Sea fishing can generally be divided into two main categories, namely inshore and
offshore fishing. In terms of quantity of the catch, there are also two kinds of fishing
which are angling (rod and reel) and bulk fishing (nets, trawls and loglines)
Basically, inshore fishing involves fishing near the shoreline or mainland. The types of
inshore fishing covered here are shore casting and in-shore casting (angling) and netcasting (bulk). Offshore fishing however takes place in the deep sea, far away from the
shore and mainland. The types of offshore fishing covered are trolling, offshore bottom
fishing and ice fishing (angling) and dredging, gillnetting, long-line fishing, purse-seining
and trawling (bulk).
Here, we are going to present the different types of both inshore and offshore fishing. At
the same time, we are going to show how astronomy affects external factors namely tides,
climate, moon phases and seasonal changes which in turn affect these fishing practices.
ASTRONOMICAL CONCEPTS AND FISHES
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THE ASTRONOMY BEHIND TIDES
Introduction to tides
The rise and fall of tides are common occurrences at every coastal region in the world.
However most people will undoubtedly be at a loss to the underlying forces at work in
generating tides and its effect on the fisheries.
The first Greek observers correctly concluded that the tides were related to the motion of
the moon, following a cyclic pattern. However, there is more to that. Sir Isaac Newton
and his universal law of gravity assisted in the explanation of tides.
Forces behind tides
Tides are generated through a combination of gravity and motion among the Earth, Sun
and Moon. The Sun’s gravity is the force that holds all the planets together in the Solar
System. This tugging force admittedly has to be large in order to hold massive planets in
their respective orbits. However, the Sun is not a major player in the generation of tides.
From Sir Isaac Newton’s gravitational law, it states that the attractive force is directly
proportional to the product of two masses in question and is inversely proportional to the
square of the distance between the masses.
Gravitational force = G m1m2/r2
However, tide-generating force is inversely proportional to the cube of the distance
between the two masses in question.
Tide-generating force = m1m2/r3
Hence, the distance becomes a substantial factor in calculating the tide generating force
than in gravitational force.
Moon – the dominant force behind tidal patterns
The Sun is 390 times further away from Earth than the Moon. Hence, although the Sun is
more massive than the Moon and should have a greater tidal generating force, this force
has to be reduced by a factor of 3903 owing to the tide-generating formula. This results
in the Sun’s tidal generating force to be only about 46% that of the Moon.
Therefore, for the first analysis on tides, only the effect of the moon is taken into
consideration since it has a greater affect on the Earth and thus tides.
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Moon’s Impact on Tide
Tidal Bulge
The tidal pattern is primarily the result of the rotation of the Earth and Moon about their
common center of mass. This center of mass is called the barycenter and is situated at
around 4700km from the Earth’s center. If one is to assume a uniformly deep ocean and
that the moon is aligned with Earth’s equator, there will be a tidal bulge at that occur on
the equator on opposite sides of the Earth. The bulge is resulted from the action of
centripetal force towards the Moon and the gravitational pull of the Moon on the Earth.
Image from http://www.oceanservice.noaa.gov/education/kits/tides/media/supp_tide03.html
Image from Harold V.Thurman, Introductory Oceanography, 8th Edition, Fig 10-5 p. 263
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Effect on points on the Earth closest to the Moon
Centripetal force is a ‘pulling’ force that pulls an orbiting body inwards to its parent. As
it orbits around another body, this force will keep the orbiting body in its circular orbit.
This force acts equally on all parts of the Earth. Gravitational attraction however has a
greater effect on points on the Earth closest to the Moon. Hence in our assumption,
gravitational attraction will act greatest at the equator. Coupled with centripetal force, the
resultant force will be larger at the equator than at any other points on the Earth. This
results in an unequal attraction towards the Moon and results in a bulge in that direction.
Effect on points on the Earth farthest away from the Moon
At opposite side of the Earth though, inertial forces dominate. Inertia is the physical
property of mass that resists any change in motion. Since the mass of the world’s water
content is large, it can produce a considerable inertial force. As the waters nearest to the
Moon is being tugged in the direction towards it, the waters at the other end resists this
motion towards the Moon and is seen as ‘moving’ in the opposite direction. Hence, there
is an equal bulge in the other end of the Earth.
Since the Earth has a 24-hourly rotation, the bulging would occur twice each day. These
are the two high tides that occurs every 12-hourly each. If one move to higher or lower
latitude, there will be a similar tidal period though the high tides will not be the highest
since it will not be at its apex.
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The Sun’s Role on the Moon and Tide Model
We now combined the effects of the Sun and the Moon. Though the gravitational
attraction of the Sun is smaller than that of the Moon, their combined effects will have a
large bearing on the tides on the Earth.
Spring Tide
Image from http://oceanlink.island.net/oinfo/tides/tides.html
When the Sun and the Moon are aligned together with the Earth, either with the Moon
between the Earth and the Sun (New Moon) or the Earth between the Moon and the Sun
(Full Moon); the tide generating forces of the two are combined. This results in a
maximum tidal range. This maximum tidal range is called spring tide.
Neap Tide
Image from http://oceanlink.island.net/oinfo/tides/tides.html
When the Moon is in its quarter phases; that is when it is at 90◦ relative to the Earth, the
tide generating force of the Sun is at add right angles with the tide generating force of the
Moon. This results in a destructive interference and cause a minimum tidal range. This
minimum tidal range is called neap tide.
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Higher and Lower Tidal Ranges
Image from Harold V.Thurman, Introductory Oceanography, 8th Edition, Fig 10-9 p 266
From the figure above when the Earth, Sun and Moon are aligned together, the positive
resultant effect of the Moon’s and Sun’s tide-generating force results in a higher tidal
range. However at the third or first quarter, the Moon’s tide-generating force cancels out
the Sun’s tide generating forces. This will result in a lower tidal range. Halfway between
a full moon and a third quarter or a new moon and a first quarter, the tidal range will be
half-way between the spring tide and neap tide. This occurs as the Moon continues on its
orbit around the Earth.
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Impact of Declinations of Sun and Moon on Tides
Declination
Earlier, the assumption is made that the Moon and the Sun remain aligned with the
Earth’s equator. However, in reality the Earth tilts on its axis at an angle of 23.5◦ to its
ecliptic plane. Its direction of tilt also remains the same as it revolves around the Sun.
This tilt of the Earth’s axis as the Earth revolves around the Sun causes the Sun and
Moon to be at a distance from the Earth’s equator. This distance, known as the angular
distance of the Sun or Moon above or below the Earth’s equator is called declination.
Sun’s Declination
Due to the Earth’s tilt, the Sun’s declination varies between 23.5◦ North to 23.5◦ South of
the Equator on a yearly cycle. This will result in a solar tide bulge at between 23.5◦
North to 23.5◦ South of the Equator.
A solar tide is caused by the gravitational attraction of the Sun on the water bodies on the
Earth. It is of a lesser magnitude than those of a lunar tide.
Image from http://www.algonet.se/~sirius/eaae/aol/market/collaboration/soleclipse/solecl-2d.html
Moon’s Declination
In addition to Earth’s tilt, the Moon’s plane of orbit is at an angle of 5◦ to the Earth’s
plane of orbit. Hence the Moon’s declination would be at angle of 28.5◦ relative to the
Earth’s equator. However, the Moon’s plan of orbit also precesses, that is, it rotates while
still maintaining the 5◦ –angle to the Earth’s plane of orbit. The precession completes its
cycle every 18.6 years.
In one month, the Moon’s declination will change from 28.5◦ South to 28.5◦ North and
back again. However as the Moon’s plane of orbit precesses, at half-way through the
precession; the Moon’s declination will be 18.5◦ relative to the equator.
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Image from Harold V.Thurman, Introductory Oceanography, 8th Edition, Fig 10-11 p. 267
Resultant Effect of Declination of the Sun and Moon
From this analysis, one can conclude that owing to the position of the Sun and the Moon
relative to the Earth’s equator, the tide-generating force will not be at its maximum at the
equator. Since the Moon exerts a greater tide-generating force, it makes sense that the
bulge will follow the cycle of the Moon. Hence, in this case the bulge will occur mostly
at the maximum of 28.5◦ North and 28.5◦ South of the equator.
Image from Harold V.Thurman, Introductory Oceanography, 8th Edition, Fig 10-12, p. 268
Owing to the declination of the Moon and its elliptical orbit around the Earth, its
revolution will take 27 solar days. The tidal period will be 24 hrs and 50 mins.
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Elliptical Distance of the Sun and Moon
Another factor that affects the generation of tides is the changing distance of the Sun and
Moon from the Earth due to their elliptical orbits. When the Earth is closest to the Sun, it
is at its perihelion (148.5 million km away) while the opposite is aphelion
(152.2 million km away). The Moon is at perigee (375,200 km away from Earth) when it
is closest to the Earth and is at apogee (405,800 km away from Earth) when it is the
furthest.
The changing distance of the two heavenly bodies results in a greater tidal ranges. At
perigee when the Moon is closest to the Earth, the tidal range increases.
Image from http://www.oceanservice.noaa.gov/education/kits/tides/media/supp_tide03.html
It is interesting to note that the highest tide range is predicted to occur on AD3300. This
is when the Sun is at its perihelion and in conjunction or opposition with the Moon at its
perigee and when both of them have zero declination. This combination will results in a
large tide-generating force as the different tide-generating force adds together. The
maximum tidal range will occur at this time.
The closest that the Earth has experienced a greater than usual tidal range is when the
proxigean tide occurs.
The proximity of the Sun to the Earth at around December and January as it nears the
perihelion will occasionally coincide when the Moon is at or near its monthly perigee.
This will result in a larger than usual tidal-generating force that is at work. It has
happened in 1990, 1992 and 2001.
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Type of Tides
The different geometric location of the Earth, Moon and the Sun results in a different
effect on the tides on the Earth’s surface.
Image from http://www.physicalgeography.net/fundamentals/8r.html
A diurnal tide has a single high tide followed by a low tide each lunar day.
A semi-diurnal tide has two high tides and two low tides each lunar day.
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Many parts of the world experience mixed tides where successive high-water and lowwater stands differ appreciably.
Tides and Fishes
Image from www.saltyflies.com/ tides-weather.htm
The most direct relation that the sea has with the rising and falling of tides is the depth of
the water level. The depth of the water level determines the variety and abundance of
fish. The varying depth of the water also determines what kind of fishes that could get
into an area to feed. For example at high tide when the water level is high, there will be
more chances of a greater number and variety of fish.
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ASTRONOMY AFFECTING CLIMATE, OCEAN
CURRENTS, PRECIPITATION and FISHING
The Astronomy of Earth
The Earth is spherical in shape and tilted on its axis at 23.5◦ to the ecliptic. It revolves
around the Sun and rotates about its own axis. In doing so, areas near to the equator will
receive a higher concentration of sunlight whereas those nearer to the two poles will
receive lesser sunlight concentration. This results in climatic regions being formed
throughout the Earth, with the general pattern being the further away a location is from
the equator, the cooler it gets.
Image from http://koning.ecsu.ctstateu.edu/Plant_Biology/climate.html
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Astronomers and geography experts have divided the Earth into regions, each separated
by a particular circle of latitude.
A circle of latitude is an imaginary east-west circle on the Earth that connects all
locations with given latitude. It is perpendicular to all meridians anywhere on Earth. The
position on the circle of latitude is given by the longitude.
Image from http://www.answers.com/topic/circle-of-latitude
In the above diagram, the lines represent the 5 circles of latitude labeled A, B, C, D and E
where:
A is the Arctic Circle (66° 33' 38" N)
It is the southernmost location with respect to the North Pole where it is possible to have
a day without sunrise.
B is the Tropic of Cancer (23° 26' 22" N)
It is the northernmost location with respect to the Equator where the sun could be seen
directly overhead. This occurs in midsummer which is the period of time around the
summer solstice.
C is the Equator (0° N)
The Equator circles around the earth's surface, equidistant from the poles and
perpendicular to the earth's axis of rotation. It divides the earth into the Northern
Hemisphere and the Southern Hemisphere.
D is the Tropic of Capricorn 23° 26' 22" S)
It is the southernmost location with respect to the Equator where the sun could be seen
directly overhead. This occurs in midwinter which is the period of time around the winter
solstice.
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E is the Antarctic Circle (66° 33' 38" S)
It is the northernmost location with respect to the South Pole where it is possible to have
a day without sunrise.
These circles of latitude form the basis of temperature and seasonal distribution on Earth.
The differences of temperature distribution of Earth by the Sun are the chief reasons of
the climatic conditions, ocean currents and precipitation throughout the Earth.
These three factors in turn, will determine the distribution of fishes around the Earth.
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Climate
Climate changes in different parts of the world. It is directly influenced by the latitude of
the location. This plays a huge role in the distribution of fishes around the world for
different species of fishes have different water temperature preferences.
Climatic regions are areas that fall between the North Pole, the 5 circles of latitude and
the South Pole.
(a) Frigid Zones
Area between The North Pole and The Arctic Circle is called the North Frigid Zone
Area between The South Pole and The Antarctic Circle is called the South Frigid Zone
(b) Temperate Zones
Area between the Arctic Circle and The Tropic of Cancer is called the North Temperate
Zone.
Area between the Antarctic Circle and The Tropic of Capricorn is called the South
Temperate Zone.
(c) Tropical Zones (also called Torrid Zones)
This is the area between The Tropic of Cancer and The Tropic of Capricorn.
Image from http://astrotulsa.com/Learn/lesson4.asp
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Ocean currents
A direct result of the climate caused by the distribution of solar rays throughout the Earth
is air pressure. Generally the air in areas receiving more solar rays (tropical areas) is
lighter since it rises in the warm atmosphere while the air in temperate and frigid areas is
heavier since it sinks in the cold atmosphere. This results in an air pressure gradient being
formed and as a result continental winds are formed as air moves from areas of high
pressure to areas of low pressure.
Oceanic currents are formed due to these continental winds. Winds in warm regions will
drag the warm waters beneath it as it moves towards the cold regions. This results in the
warm oceanic currents being formed. And while local currents affect the movement of
fishes in general, these oceanic currents are very essential in the distribution of fishes
throughout the globe. This will be highlighted later.
Image from http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/ocean_circulation.html
Blue arrows indicate cold ocean currents
Red arrows indicate warm ocean currents
Warm ocean currents are pathways of warm water moving from the tropics towards the
poles.
Cold ocean currents are pathways of cold water moving from higher latitudes towards
the equator.
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Precipitation
Besides water temperature and ocean currents another factor that has an impact on fishing
is the precipitation in that region.
Image from http://koning.ecsu.ctstateu.edu/Plant_Biology/climate.html
From the diagram, it can be seen that there is a pattern of precipitation globally. There are
several observations of the precipitation patterns here:
The concentrated heat of the sun on areas near to the Equator (The Tropical Zone) makes
the atmosphere warm, thus moist air rises, cools and falls as precipitation. These areas
experience abundant rainfall generally.
The frigid cold at the North and South Pole makes the atmosphere cold; hence dry air
descends and warms, thus explaining the scarce amount of rainfall there.
The Temperate Zones have a pattern of low precipitation at 30 degrees north and south
latitude but has significant amount of precipitation at 60 degrees north and south latitude.
These air movement patterns are driven by solar heat and earth's rotational momentum.
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Rain also affects fishing in several ways especially in shore and inshore fishing. Firstly,
rain affects the behavior of fishes. A change in weather (just before or after a storm)
would cause a ‘feeding-frenzy’ amongst the fishes. This is due to the fact that rain creates
a thin cool layer on the water surface when the water is warm. This cool layer lures the
fishes up to the surface, thus increasing the chances of our catch.
Rain also affects the amount of freshwater input into water. The interdiction of freshwater
into salt-water rivers can also increase the abundance of fish. Areas such as a culvert and
other freshwater outflow are excellent fishing spots right after a down pour as fishes such
as snook and tarpon are drawn towards these areas.
MOON PHASES
Image from www.astro.virginia.edu
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Phases of the Moon
The Moon revolves around the Earth which results in its many phases. It takes around
29.53 days for the Moon to complete its phase cycle; which runs from the new moon to
first quarter (half moon) to second quarter (full moon) to third quarter (opposite to first
quarter) and finally back to the new moon. The Moon moves through its phases in about
four weeks hence, the four phases the Moon passes lasts for approximately a week each.
As the diagram in the previous page, the relative position of the Earth, Moon and the Sun,
and the illumination of the Sun on the Moon results in the Moon’s different phases.
Effects on fishes
The position and the phase of the Moon in the sky greatly determine the feeding behavior
of fishes. The Moon acts as a source of lighting which illuminates the water surface. This
enables predator fishes which lurk down below in the dark to have a good view of
baitfish which schools near the surface. Thus, on a full moon, feeding will take place at
night. On a night of a new moon, predators would not have a good view of the baitfish.
Thus they would feed in the day. In summary, the phase of the Moon affects the best time
for anglers to fish; fish at night on a full moon and fish in the day on a night of a new
moon.
Image from http://www.pauahtun.org/Watch/watch7.html
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THE SEASONS ON EARTH
The Seasons
The tilt of the Earth at 23.5◦ to the ecliptic produce the four seasons as it revolves around
the Earth. This tilt points in the same direction throughout the Earth orbit around the
Earth. Hence, it is possible for the Northern hemisphere to have a higher amount of
sunlight as compared to the Southern hemisphere at a particular duration of time. This is
as more sunlight is received as the Sun will shine directly at the Northern Hemisphere
and is also overhead.
The Sun will shine directly on the Tropic of Cancer on the summer solstice at around
June 21st. This is the beginning of summer in the northern hemisphere. As the Earth
revolves, the Sun will shine directly on the Equator and the autumnal equinox is reached
at around September 23rd. During the winter solstice, it is the turn of the southern
hemisphere to get maximum sunlight. The Sun’s rays will fall directly on the Tropics of
Capricorn at around December 22nd. Spring in the northern hemisphere occurs at the
vernal equinox at around March 21st. Though the diagram illustrates the seasons in the
northern hemisphere, the seasons in the southern hemisphere will be the direct opposite.
Eg. The north will experience summer on June 21st but the south will experience winter.
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Effect on Fishes
Seasonal changes have a profound effect on the lives of fish living in the many temperate
and tropical waters that experience seasonal change. This change of seasons provides the
impulse and biological reaction in fishes as they await the time to spawn or migrate.
However, different reactions in fishes are observed in different parts of the world when
the season changes.
The coral trout can be found off the coast of Queensland.
Image from http://www.nps.gov/npsa/NPSAfish/fish_pops/serranid/bass40.htm
In the northern Great Barrier Reef, the coral trout spawns with an increase in the water
temperature during late spring in the south, between September to December. This is the
period of the autumnal equinox. In the southern regions, where water is cooler, spawning
occurs between October and February. This corresponds to late autumnal equinox to the
winter solstice. The time of spawning is directly related to the temperature of the water.
The warming of the sea water in spring and summer triggers the spawning behaviour.
Hence, the seasonal changes affect the spawning of the fishes by indirectly raising the sea
water temperature.
An example of a fish found in the Northern hemisphere is the striped bass or rockfish.
Image from http://www.dnr.state.md.us/fisheries/education/rockfish/rockfish.html
This fish is widely found in the Atlantic Coast and follows a migratory pattern following
the seasons. These fishes move into tidal freshwater in the late winter and spring to
spawn. After spawning, the rockfish returns to the coast. Most spend the summer and
early fall months in middle New England near-shore waters. During the late fall and early
winter, coastal striped bass migrate south to winter off the North Carolina/Virginia
Capes.
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DISTRIBUTION OF FISHES IN THE VARIOUS CLIMATIC
ZONES
The Frigid Zone (Northern Atlantic)
The target fishes here are mostly called Atlantic Ground fishes mainly because the fishes
feed and dwell at the bottom of the sea. Due to this behavior of the fishes in general,
shore fishing and in-shore fishing are quite ineffective in these areas. In contrast to that,
offshore fishing as well as bulk trawling produces much result. Atlantic ground fishes are
known to swim along the cold currents of the Atlantic. They thrive in waters of
temperatures of 2° to 10°C
The most common species of fish available in the Greenland and Northwest Atlantic is
the cod:
Image by Flescher, Don, 1997, [email protected]
Latitude found: 80°N - 35°N
Preferred Water temperature: 0 - 20°C
Ocean Depth: Anywhere from the ocean surface to depths of over 500 m
Diet: invertebrates and fish, including young cod
Fishing methods used: Long lines, trawls seines, hand lines, jiggers, traps and gillnets.
Distribution of Cod
(shaded region)
Image from http://www.oceansatlas.com/unatlas/uses/FisheriesAndAquaculture/FisheriesHistoryJTE/bioresources.html
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Cods are mainly caught in bulk in offshore fishing such as trawling. However, they make
excellent angling trophies too given the right bait.
There are also various types of cod such as the silver and white hake.
Some other common species of fishes in frigid zones includes:
Haddock:
Preferred Water temperature: 4° - 10°C
Ocean Depth: Common in ocean depths of 45m to 240 m.
Diet: Feeds mainly on small bottom-living organisms including crustaceans, mollusks,
echinoderms, worms and fishes
Fishing methods used: Trawls, longlines and gillnets
Pollock:
Preferred Water temperature: 0° - 10°C
Ocean Depth: coastal waters and on the offshore banks.
Diet: Smaller fish in inshore waters feed on small crustaceans (copepods, amphipods,
euphausiids) and small fish, while larger fish prey predominantly upon fishes.
Fishing methods: Trawls, longlines, handlines and gillnets
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Redfish:
Image by Dolgov, Andrey, 1999, [email protected]
Ocean Depth: 300 - 1000 m
Diet: Feed on euphausiids, hyperiids, cephalopods, chaetognaths and small fishes.
Fishing methods: midwater trawls but may also be fished with bottom otter trawls.
Flatfishes:
Flatfishes make up the most important of Atlantic ground fishes after cod. They are
mostly found in the deep oceans of depth ranging from 50m to 250m. Flatfishes are
known not to take bait but instead they are being harvested by trawls
Like the cod, there are also a various species of flatfishes such as the American Plaice,
Turbot, Atlantic Halibut and flounders.
Greenland Halibut (Flatfish):
Image by Dolgov, Andrey, 1999, [email protected]
Preferred Water temperature: 0 – 4°C
Ocean Depth: 1 – 2000 m
Diet: Feeds on crustaceans, fishes (Ref. 4705, 6885), eelpouts, capelin, redfishes, deep
sea prawns and other bottom invertebrates
Fishing methods: midwater trawls but may also be fished with bottom otter trawls.
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The Temperate Zone
As it can be from above, the fishes in the Frigid Zone can also be found in temperate
waters too. However the species quoted above are more dominantly found in the Frigid
Zone.
In offshore temperate waters, the low surface water temperature is a feature most fishes
that swim in schools avoid. These schools of fishes are found in deeper waters where the
temperature stability is better than that at the surface. Hence, commercial trawlers and
purse seiners will aim for deeper waters to catch these fishes in bulk. This is the same for
offshore angling. However, inshore anglers do not let these facts bother them too much
for there are certain types of fish which tend to rise to the surface and coastal areas at
certain seasons such as spawning. This is a perfect window of opportunity to start reeling
in the big ones!
The most common species of fish swimming in temperate waters is the herring. The
herring spawns in oceanic waters where the cold ocean currents meet with the warm
ocean currents. In these areas, the supply of planktons (prey for smaller bait fishes) and
crustacean are abundant since these are the most common diets of the herring, it certainly
explains why there are so commonly found in these areas.
Herring (Pacific):
Image from http://web.tcpalm.com/sports/areafish/blhering.htm
Preferred Water temperature: 0-10°C, 7-15°C when spawning
Ocean Depth: 0 - 250 m
Diet: Young feed mainly on crustaceans, but also take decapod and mollusk larvae;
adults prey mainly on large crustaceans and small fishes
Fishing methods used: herring and capelin seine, pelagic trawl, offshore angling
Besides being an important commercial fish, the herring is often used as a bait fish for
other predatory species of fishes.
31
Distribution of herring
(red shaded region)
Some of the other common species of fishes in temperate zones includes:
Sea Trout:
Image by McDowall, Robert M., 1997, [email protected]
Ocean Depth: Common in ocean depths of 10m
Diet: Juveniles feed mainly on aquatic and terrestrial insects; adults on mollusks,
crustaceans and small fish
Fishing methods used: Inshore fishing and angling
Common Sea Bream:
Latitude found: 57°N - 38°S
Preferred Water temperature: 17-24℃
Ocean Depth: Up to 250m deep
Diet: Feeds on crustaceans, fishes, and mollusks
Fishing methods used: Offshore fishing, trawling
Atlantic salmon (King of Fish):
Image by Helgesson, Daniel, 2001, [email protected]
Ocean Depth: Common in ocean depths of 10m
Diet: Juveniles feed mainly on aquatic insects, mollusks, crustaceans and fish; adults at
sea feed on squids, shrimps, and fish
Fishing methods used: Big-game fishing, offshore and inshore
32
33
The Tropical Zone
Tropical coastal waters support a huge variety of species of fish, from the depth of the
seabed to the surface of the water. The unique feature of tropical waters compared to
temperate waters is that the upper layers of water are rich in fishes irregardless of
seasons. This makes tropical waters much more productive for anglers than their
temperate counterparts.
However, offshore fishing takes the same stand with that of the temperate offshore
fishing. Trawlers aim deep and big-game fishing also aims the deeper recess of the sea in
search of the big ones. The rich sunlight in tropical areas mean that the sun can penetrate
into deeper waters in the tropics and hence these offshore fishermen would have to go
that extra mile to locate schools of fishes who like to dwell deep.
The tuna and the mackerel make up the bulk of fishes in the tropical zone. These fishes
are usually found in deeper tropical waters and are caught in bulk for commercial
purposes.
Tuna (Longtail):
Image by Hermosa, Jr., Gregorio V, 1995, [email protected]
Preferred Water temperature: 7−26°C
Ocean Depth: Up to 10m
Diet: Feeds on a variety of fishes, cephalopods, and crustaceans, particularly stomatopod
larvae and prawns
Fishing methods used: Purse seining, long lining, pole and line (offshore fishing), biggame fishing
34
Distribution of Tuna
(purple shaded region)
Mackerel:
Image by Randall, John E, 1995, [email protected]
Preferred Water temperature: 8−26°C
Diet: Feed primarily on small fishes like anchovies, clupeids, carangids, also squids and
penaeoid shrimps
Fishing methods used: Purse seining, longlining, pole and line (offshore fishing), biggame fishing
Distribution of Mackerel
(red shaded region)
35
Some of the other common species of fishes in the tropical zones includes:
Asian seabass:
Image by Randall, John E, 1995, [email protected]
Preferred Water temperature: 15 – 28°C
Diet: Feed on fishes and crustaceans
Fishing methods used: Offshore fishing (big-game), Shore fishing
Silver Pomfret:
Image by Gloerfelt-Tarp, Thomas, 1995
Preferred Water temperature: 19.8 – 28°C
Ocean Depth: Up to 10 m
Diet: Feeds on ctenophores, salps, medusae, and other zooplankton groups but will also
prey on small benthic animals
Fishing methods used: Purse seining and trawling
METHODS OF SALT-WATER FISHING
36
37
Inshore Salt-water Fishing
Inshore salt-water fishing involves the types of fishing which are done near the shoreline,
coast or mainland. In this project, we are going to present three different types of inshore
fishing.
They are:1) Shore casting
2) In-shore casting
3) Net casting
Shore Casting
As the name suggests, shore casting involves fishing from the coast of the beach near the
shoreline. This could be done either directly from the sandy shores of the beach or from a
suitable location near the shoreline such as on breakwaters, jetties, piers and even off the
rocks.
Shore casters usually equip themselves with a rod and reel (angling). Shore casting
involves casting the fishing line out to sea from the shore or near the shore.
Image from
http://www.bbsr.edu/pubs/CS99_Cover/CS99
_Contents/body_cs99_contents.html
Image from http://www.tep.com.au/region_fishing.htm
Image from http://www.tep.com.au/region_fishing.htm
The pictures above show the different types of shore casting; casting from the beach (left), from a
jetty (middle) and off the rocks (right).
38
¾ Shore casting and tides
The study and knowledge of tides is very useful for shore casting anglers. Firstly, a shore
casting angler could make use of the low tide to make notes about landmarks and other
features of the shore. This is to target which area to cast the line and which areas not to
cast in order to avoid the line from being stuck.
It is also an advantage for anglers to know the tide behavior in the course of the day
because fishes behave differently at different types of tide. Fishes tend to feed near the
shore on the rising tide. This is due to the fact that on the rising tide, fishes move up
towards the shore in search of food which they were unable to reach before. Thus with
this knowledge anglers would have a better chance of catching fish during this time.
Knowing the tidal behavior also affects the efficiency of fishing. For example when the
tide is stagnant, the fishing line could be positioned accurately without it getting drifted
away. However at a falling tide for example, the line would be drifted back towards shore
and not towards the sea, thus not maximizing the chances of getting fish.
Image from http://www.floridaoceanographic.org/environ/worm_reef.htm
Knowledge of the tide is very helpful for shore-casting
anglers. On example is at low tide, anglers could study the
shore-bed for what type of fish which could be available
and also take note of any obstacles to avoid the tangling of
lines (above). Another example is for the use of
equipments such as the rod holder (left). Knowledge of the
highest tide would allow anglers to position the holder at
the most suitable position without having it being washed
away.
Image from http://www.surfcasters.iinet.net.au/TipsMain.html
39
In-shore casting
In shore casting involves casting the line from the sea towards the shoreline. This is
usually done from a boat. The idea of inshore casting is to allow anglers to reach the
areas near the shore which are beyond the reach of a shore angler. In shore casting is
usually done near mangrove swamps, quiet bays, estuaries and salt water creeks.
Image from http://www.smallhope.com/Fishing.html
Image
from
http://www.definitivecaribbean.com/accommodati
on/FortRecoveryBeachVillas.aspx
¾ Inshore casting and tides
The knowledge of tides is crucial for determining which course the boat could take and
how the boat should be maneuvered. For example, at low tide, anglers could not steer
their boats into shallow waters with rocks and sandbanks as it might cause the boat to go
aground and get stuck. At high tide however, the boat could be steered into more area,
thus giving anglers more ground for fishing.
Low tide however does have its uses. Anglers could take advantage of the low tide to
survey the surrounding to take note of any possible fishing-spots and also look out for
any potential obstacles which might not be seen at high tide such as protruding tree roots,
huge rocks and sandbanks.
The current of the water as a result of the falling and rising of the tide is also beneficial
for in-shore anglers. It helps to drift the fishing line and bait away from the boat. Fishes
would be scared away by the noise of the boat and people on board, thus they would stay
away from the boat. Thus the current provided by the changing tide would help drift the
line with the bait and hook away from the boat, increasing the chances of catching fish.
40
Having discussed earlier about the fishes going towards shore to feed during the rising
tide, in-shore anglers could use this fact to their advantage as they could position their
lines nearer to the shore during the period when the tide is rising.
Net-casting
Net casting involves casting a huge net on the waters near the shore to trap fishes or other
sea dwellers such as crabs and prawns within the diameter of the net. This method of
fishing catches fish in bulk and is usually done by an experienced angler as it is
extremely difficult to cast open the net with perfection. This type of fishing is the old
traditional way of catching fish but is still in practice until today.
Image from http://www.sizenken.biodic.go.jp/pc/wet_en/350/350.html
Image from http://www.my-spot.com/India2003/fishing2.htm
Net casting can be done either from the shore (top-left) or from a boat near the shore (top-right).
¾ Net-casting and tides
The rule of thumb for net-casting is that it is best done during the falling tide. This is
because as the tide is falling, the fishes would gather into groups and the smaller fishes
would gather nearer to the shoreline. Thus it is an ideal time for net-casting as there
would be many schools of fish grouped together near the shore.
Another basic use of the tide is that at low tide, net casters could study the shore-bed for
possible types of fish available. Different fishes prefer different surrounding conditions.
Thus, with the knowledge of the structure of the shore-bed and the type of soil it has, net
casters would be able to predict what kind of fishes would be available in that particular
area.
In addition, at low tide, net casters are also able to look out for possible obstacles that
might entangle or tear open their net such as huge rocks and huge rotten logs.
41
Offshore Fishing
Offshore fishing refers to fishing that is done away from the mainland and usually takes
place in the middle of the ocean. There are several types of offshore fishing but they can
all be categorized into two main groups, angling and bulk fishing.
• Big Game Fishing (Angling)
Trolling
Big game fishing is a recreational type of fishing and is also known as an offshore sport
fishing or offshore game fishing. The fishes caught are those that thrive in deep sea such
as tuna and marlin. A boat of substantial size is needed to transport the equipments
needed and this activity is often held in the open sea. Famous locations for big game
fishing are along the coastlines off Florida and Hawaii, the eastern coastline of Australia,
throughout the Caribbean and in South America.
Fishing lures that resemble these fishes’ natural
prey are used as bait and the most common ones
are lures that take the form of squids. Trolling is
used to pull these baits while the boat is on the
move. Multiple fishing lines are also used here.
The image on the left depicts an artist’s
impression of trolling.
Image from http://en.wikipedia.org/wiki/Trolling_for_fish
Some boats are equipped with modern equipments such as sonar and temperature
sensitive equipments to measure the temperature of the water. The most important part
about big game fishing is that once there is a bite, the boat has to be maneuvered in such
a way to keep the fish at the back of the boat. There are two common methods used to
fight the fish, the game chair and the body harness. The former involves the fisherman
sitting on the game chair while reeling in the fish, the chair gives additional support for
the fisherman. The latter involves the fisherman being secured to a harness while
fighting.
42
Offshore Bottom Fishing
Offshore bottom fishing is different from trolling since the latter targets ocean swimmers
while offshore bottom fishing targets bottom dwellers such as cods. Offshore bottom
fishing uses a rod, line, bait and weights. It is no different from angling except it is done
far out in the ocean. The weights are usually allowed to sink to the bottom of the sea.
The fishes caught depend on the location and time of the year. Thus, it might be hard for
beginners to get a bite as the ocean out there is vast and it takes time, knowledge, and
experience to find the right fishing spot. Some boats are equipped with the GPS system
where it’ll be easy to keep track of fishes moving in schools. However, some just have to
reply on basic navigational skills such using the latitude and longitude of the fishing spot
to keep track of the location for future fishing expeditions. This is aided by using maps
and taking note of prominent objects in the area.
It is also important to know the behavior of the fishes. Snappers can be found at the
edges of reefs but mulloway, kingfish and teranglin like high profile hard reefs.
Ice Fishing
Image from http:// www.tyeelakeresort.com/ fishice.htm
Ice fishing is a type of fishing where an opening is cut from a sheet of ice that lay above
the surface of the sea. Methods of fishing include the use of lines, hooks and spears. It is
common for fishermen to sit on a stool on the frozen water but some prefers sitting in a
heated shelter or cabin. This activity is common in frigid zones places such as Canada,
Greenland and Russia. It is also common in places that experience cold long winters
such as the United States.
Specialized equipments are needed for ice fishing. An ice spade or saw is needed to cut
an opening in the ice. It has been a practice to cut circular and rectangular openings. A
strainer is also needed to remove the new layer of ice as the surface of the water freezes.
There are basically three types of ice fishing. Rods and lures are used for the first type.
The second type makes use of tip-ups. Tip-ups are flags that will tip up when there is a
bite. These flags are attached to the fishing lines. The third type makes use of spears.
The fisherman stands over the opening while positioning himself with a spear attached to
a line. The line is not attached to any reel thus when a fish is caught, the fisherman has to
drag the line manually.
43
• Bulk Fishing
Dredging
Dredging is a type of fishing where a huge metal scoop is attached to a fishing boat and
this scoop is dragged along the seabed to collect marine creatures such as scallops and
oysters that resides there. This metal scoop is called the dredge. An example of a dredge
is illustrated in the image below.
Here, the dredge is in a form of a heave metal frame that
sinks to the bottom of the sea bed. A bag of wire mesh
is attached to it. The dredge is attached to a fishing boat
where it is dragged along the sea bed trapping fishes or
marine creatures such as scallops and oysters that
resides on the seabed. Some dredges are also equipped
with a comb-like object that acts as a rake.
Image from http://www.mbayaq.org/cr/cr_seafoodwatch/sfw_gear.asp
Gillnetting
Gillnetting is a type of fishing where a gillnet is attached
to a fishing vessel and is allowed to stay suspended in
the water for some time trapping fishes. A gillnet is a
curtain of netting that is suspended in the water at
different heights depending on the types of floats and
weights. The height at which the gillnet is suspended
and the size of the net traps a different variety of fishes.
Smaller mesh is used to trap fishes such as sardines and
larger meshes are used to trap salmon and cod.
44
Long-line Fishing
Long-line fishing is also another method used for commercial fishing. In long-line
fishing, several hundreds or even thousands of baited hooks are attached to just one
central fishing line and this line can stretch up to 80km long. These hooks are attached to
smaller lines spaced at regular intervals. Swordfish and tuna are most common caught
using this method.
Purse Seining
Purse seining is a type of fishing where a long rectangular net is used to surround the
fishes at a particular area. The top of the net is attached to a floating object while the
bottom of the net is attached to a heavy object that sinks. This will encompass the area
between the water surface and the sea bed, thus preventing the fishes to escape. Two
boats are needed in purse seining, each attached to the two ends of the net. The smaller
boat is normally attached to the free and of the net. The two boats will then encircle an
area and the line that runs through the bottom part of the net is then hauled in forming a
“purse”. This closes the bottom part of the net. The enclosed area at the bottom of the
net and the water surface at the top of the net prevent the fish from escaping.
Purse seining is mainly used to catch schools of fish such as tuna. It is also used to catch
marine creatures that gather to spawn like squids. The most common fish caught by
purse seining is tuna.
45
Trawling
Trawling is a commercial fishing method where fishing nets are being pulled through the
fishing ground by one or more fishing boats. Single-boat trawling is more common
compared to those that make use of several boats. The nets are spread horizontally to
achieve a larger surface area to net in the fish and this distance is achieved through the
use of trawl doors.
There is a variety of
trawl doors and each
has a different function.
Some are used so that
the nets stay elevated in
the water. These types
of trawl doors are
mainly used to catch
fishes that thrive away
from the sea bed.
Certain trawl doors are
made to sink to the
bottom of the sea.
They are in constant
contact with the sea
floor and are used to
catch marine creatures
that live at the sea bed.
However, these trawl
doors and nets need to
be pulled through the
water for them to be
functional, thus, for
trawling, the boat has
to travel at a certain
speed for these doors to
remain standing and
functional. The speed
generally ranges from
2.5 to 4.0 nautical miles
per hour.
Image from http://en.wikipedia.org/wiki/Trawling
The image above shows both nets trawling in surface waters and nets trawling at the sea
floor.
46
Final Note from the Authors
The interdependence of the success of a leisurely fishing outing or a commercial fishing expedition is
unbeknownstly tied closely to the heavenly bodies and their interaction with Mother Earth. The concepts of
tides and currents, climate, the changing seasons and the phases of the Moon are all largely depedent on the
timeless graceful ballet of the Earth, Moon and Sun. Most animals including the fishes has revolved their
life cycles and feeding patterns based upon these natural phenomena. As such, most experience fishermen
would deemed it necessary to study these fishes in order to better their chances in getting a large catch.
We had a lot of fun in completing this project and it is our hope that with this book, readers gain a brief
insight to the world of fishing from astronomy’s viewpoint. Fishing is and forever will be an art that values
experience and practice above all. However, in everything we do, there is always a first step towards
appreciating the finer side in things. Hopefully, this guide provides that first step towards appreciating
fishing.
With that, we would like to end this with a local saying:
“ Kau nak ikan, kau kenal itu ikan”
(If you want to fish, know the fish)
Happy fishing to all!
47
REFERENCES:
Online reference:
http://koning.ecsu.ctstateu.edu/Plant_Biology/climate.html
http://www.answers.com/topic/circle-of-latitude
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/ocean_circulation.html
http://www.geography.learnontheinternet.co.uk/topics/weather.html
http://www.oceansatlas.com/unatlas/uses/FisheriesAndAquaculture/FisheriesHistoryJTE/bioresou
rces.html
http://astrotulsa.com/Learn/lesson4.asp
http://web.tcpalm.com/sports/areafish/blhering.htm
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/ocean_circulation.html
http://www.fisheries.is/stocks/herring.htm
http://www.fishbase.org
http://www.fishingnj.org/techps.htm
http://en.wikipedia.org/wiki/Fishing
http://www.mbayaq.org/cr/cr_seafoodwatch/sfw_gear.asp
http://espn.go.com/outdoors/tips/s/f_fea_04_moon_phases_FHN.html
http://www.indianriver.cc/doug's/factors.htm
Book reference:
The New Encyclopedia of Fishing, John Bailey, 2001 Revised, Penguin Company
Inshore Boat Angling (a practical guide), Russell Symons, 1991, Ward Lock
Introductory Oceanography, Harold V. Thurman, 8th Edition, 1997, Prentice Hall
.

Fisherman`s Guide to Astronomy

Transcription

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