Transcript Fisheries and Aquaculture Management_Lecture

Fisheries and Aquaculture Management
Lecture 4:
Aquatic Resources
Aquatic Resources
 When considering aquatic habitats, many variables come
to mind.
 Obviously, there is a continuum of salinity ranging from
essentially distilled water at glacier faces and high
mountain streams, to other freshwaters, to estuaries
where fresh and salt waters mix, to oceans, to
hypersaline environments such as the Great Salt Lake.
 Current is another factor; water may be still and
stagnant, or flow in currents of various velocities.
 Currents may be unidirectional, such as in streams, or
multidirectional, such as when waves wash across a
beach.
Aquatic Resources
 Aquatic habitats may occur in open water, or they may
be associated with the bottom of the body of water, and
both will be affected by the mechanical and chemical
makeup of the local geology.
 All sorts of daily and seasonal temperature regimes can
be expected.
 Aquatic habitats vary in the amount of light they receive
and range in size from tiny pools at the base of a plant to
the Pacific Ocean in size.
Characteristics of Aquatic environments:
Freshwater vs. Marine Habitats
 The obvious difference when comparing these two
extremes is the salinity of the water, and the differences
associated with that salinity.
 One obvious consequence of the difference in salinity is
the change in osmoregulatory strategy that must take
place.
 Many organisms in salt water are osmoconformers,
essentially isotonic in relation to the seawater, although
they may regulate certain ions at levels different from
those of the surrounding ocean.
Characteristics of Aquatic environments:
Freshwater vs. Marine Habitats
 A fair number of marine organisms are hypotonic in relation to
the seawater and must therefore actively take up water to
replace that they lose to the seawater.
 Of course, in taking on that water, they usually take in too many
ions, and they must have some mechanisms for expelling those
ions.
 Organisms in freshwater have the reverse problem. They tend to
take on water from the environment, and, in expelling the excess
water, may lose important ions.
 Since freshwater is too dilute to make a good cytoplasm, it is no
surprise that all freshwater organisms are hypertonic to the
environment and that in consequence they must be active
osmoregulators. Most have some mechanism to pump ions into
the body.
Characteristics of Aquatic environments:
Freshwater vs. Marine Habitats
 Another difference between freshwater and saltwater,
besides the ion concentration, is the depth/ light.
 The depth of freshwater systems is usually much shallower
than that of marine systems.
 Depth is not a critical factor as long as the bottom of the
body of water is above the LCP (light compensation point).
 Though, that freshwater is highly susceptible to turbidity
caused by soil erosion, thus the LCP might be artificially
raised above the bottom.
 Marine systems, at least those away from the coast, are not
usually affected by turbidity.
Characteristics of Aquatic environments:
Freshwater vs. Marine Habitats
 Temperature relations in marine systems as opposed to freshwater
systems are again largely dependent on the relative size of the
systems.
 Generally, the larger marine systems show virtually no diurnal
temperature shifts, and very small seasonal ones.
 On the other hand, small freshwater habitats may experience daily
shifts in temperature of over 300C, and pronounced seasonal
temperature changes exist even in bodies of water as large as the
Lauretian Great Lakes.
 Oceanic systems are a large part of the global weather system,
which in general moves heat from the warm equator to the cooler
poles.
 Oceanic areas exposed to currents involved in this heat transfer may
be much warmer or cooler than would be expected due to their
latitude alone, for instance, consider the relative warmth of the
ocean near Britain due to the Gulf Stream, or the cold water off the
southern California coast.
Aquatic Plants
 Thousands of plant species live in freshwater habitats around
the world
 Many species of aquatic plants are essentially cosmopolitan,
meaning that they are widely distributed around the world.
 Some of the widest distributions are attributable to human
activities.
 Humans have accidentally (sometimes intentionally)
transported seeds, fruits, or vegetative clones from one pond
or watershed to another, but many of the cosmopolitan
distributions are attributable instead to birds, particularly
waterfowl, which inadvertently transport the plant
propagules when lodged in their features or trapped in mud
on the feet.
Function, Physical Characteristics and Adaptation
of Aquatic Plants
Q.
What roles does aquatic plants play in the
aquatic environment?
1. Microscopic plants (algae) form the base of the
aquatic food chain.
 These
are
Primary
producers
e.g.
“phytoplankton” (or, plant plankton), these plants
are eaten by zooplankton (or, microscopic animal
plankton).
 In turn, zooplankton are eaten by small fish,
which are eaten by larger fish, and so on up the
food chain to humans and other top predators.
Q.
What roles does aquatic plants play in the
aquatic environment?
2. Larger algae and flowering plants (macrophytes)
provide habitat and shelter for fish, fish food
organisms, waterfowl, and other wildlife.
3. Macrophytes provide food for insects, waterfowl, and
mammals such as muskrats and beavers. However,
bass, bluegill, and catfish do not, as a rule, eat
macrophytic vegetation.
4. Since all plants, including those that grow
underwater,
produce
oxygen
as
they
photosynthesize, they are the major source of oxygen
for aquatic animal life.
Q.
What roles does aquatic plants play in the
aquatic environment?
5. Rooted plants stabilize shorelines and bottom
sediments. They absorb nutrients and filter
pollutants from runoff, which improves water
quality.
6. A diverse aquatic plant population adds beauty to
a water body. Many people recognize and
appreciate the aesthetic value of aquatic
vegetation, whether in a backyard fishpond,
around a retention pond, or along the shoreline
of a large lake.
Q.
What roles does aquatic plants play in the
aquatic environment?
7. Control of algae. Plants are basically highly evolved algae,
and have the same essential nutritional requirements.
However, healthy aquarium plants can do a better job of
obtaining nutrients from the water by stripping phosphate
8. To encourage the breeding of fish. Many fish, such as tetras
(minnow‐like fish), practice "egg‐scattering." This breeding
strategy is exactly what it sounds like: fish lay non-adhesive
eggs all over the tank and provide minimal care. In this case,
bushy plants can keep the eggs safe from their hungry
parents. Similar strategies work with livebearers. Even
sophisticated spawners like Bettas use plants; males use
them in their bubble nests and females use them for refuge.
 Because of these benefits, some aquatic plant
growth is desirable.
 Eliminating native aquatic vegetation from a site
should never be the goal of a management plan.
 However, excessive aquatic plant growth can lead
to several common problems:
1. Too much vegetation can impair recreational
activities such as swimming, fishing, and boating.
2. Excessive plant growth can provide too much
shelter for small fish and reduce predation. This
leads to an overpopulation of prey fish.
3. An overabundance of aquatic plants and algae can reduce
oxygen levels in the water, which can contribute to fish
kills. Fish kills that are vegetation-related can occur in the
summer or winter.
4. Certain algae impart foul tastes and odors to water. This is
an extremely important concern for the managers of
municipal and private drinking water sources.
5. Excessive plant growth can impede water flow in drainage
ditches, irrigation canals, and culverts and cause water to
back up.
6. Excessive plant growth lessens aesthetic appeal and
lowers property values.
7. Excessive plant growth can trap sediment and debris,
gradually filling in bodies of water. When the plants
die and fall to the bottom, they accelerate this
process.
8. Aquatic weed growth can provide the quiet water
environment that is ideal for mosquito larvae
development.
9. Invasive plant species such as Eurasian water milfoil
and purple loosestrife can completely destroy stands
of native vegetation. This can have adverse effects on
the animals that depend on the native vegetation for
habitat and food.
Function, Physical Characteristics and Adaptation of Aquatic Plants
Characteristics common to aquatic plants:
1. Most aquatic plants do not need cuticles or have
thin cuticles as cuticles prevent loss of water.
2. Aquatic plants keep their stomata always open
for they do not need to retain water.
3. On each side of their leaves are a number of
stomata.
4. Aquatic plants have less rigid structure since
water pressure supports them.
Characteristics common to aquatic plants:
5. Since they need to float, leaves on the surface of
plants are flat.
6. The presence of air sacs enables them to float.
7. Their roots are smaller so water can spread freely
and directly into the leaves.
8. Their roots are light and feathery since they do
not need to prop up the plants.
9. Roots are specialized to take in oxygen.
Function, Physical Characteristics and Adaptation of Aquatic Plants
 Adaptation of aquatic plants is evident by their structure: deeply
dissected and waxy leaves, specialized pollination mechanism
and variation in growth pattern.
 These are the types of plants based on adaptation:
1. Totally submerged plants – Are considered true water plants or
hydrophytes. Example: Water starwort submerged in a marsh
pond, eel grass, sago pondweed, water milfoils etc
2. Floating plants – Are rooted in floating water (example: water
lily) or not rooted in the sediment just on the surface (example:
duckweed, water lilies, American lotus, spatterdock and water
shield).
3. Swamp plants – Are emergent plants with their lower part
submerged. Example: reed mace, .
Function, Physical Characteristics and Adaptation of Aquatic Animals
The characteristics of aquatic animals are as follows:
1. Most of their Species live in water and some of them live
on the land
2. They have paired and unpaired fins which help them to
swim.
3. They have either webbed limbs or limbs are modified to
paddles for swimming.
4. Their body shape is streamlined and their bones are light
and spongy.
5. The skull undergoes modification to form a slender snout.
6. The neck is reduced and external ears are disappeared.
Function, Physical Characteristics and Adaptation of Aquatic Animals
Adaptation of Aquatic Animals
 Marine organisms have adapted to the great diversity of
habitats and distinctive environmental conditions in the
marine environment.
 Adaptations are many and varied but they are generally
grouped into 3 main categories:
1. structural,
2. physiological and
3. behavioural.
Function, Physical Characteristics and Adaptation of Aquatic Animals
Adaptation of Aquatic Animals
Structural adaptations
 Seawater is much denser than air – as a result, there are vast
numbers of microscopic organisms suspended in it. Cockles, as
well as many other bivalves, are filter feeders.
 They have adapted specialised siphon structures to filter
these organisms and any other particles of food from the
surrounding water.
 Estuaries have quite variable conditions – tides, waves and
salinity fluctuations affect the animals and plants that live there
on a daily basis.
 Many animals, such as cockles, are adapted to live in these
conditions. They have strong shells that protect them from
wave action, drying out and the prying beaks of predators.
Function, Physical Characteristics and Adaptation of Aquatic Animals
Adaptation of Aquatic Animals
Physiological adaptations
 Physiological adaptations enable the organism to regulate their bodily
functions, such as breathing and temperature, and perform special
functions like excreting chemicals as a defence mechanism.
 Some marine mammals, such as whales, migrate over large distances
and may spend time in a combination of arctic, tropical and temperate
waters. To cope with these temperature changes, they are
endothermic or ‘warm blooded’. This means that they are able to
maintain a constant body temperature that is not dependent on the
surrounding water.
 Slow-moving species have adaptations that help protect them from
predators. For example, many marine organisms can only move slowly
or not all. This means they cannot easily get away from mobile
predators, and they have other adaptations to protect them from
being eaten. These can include chemical defences in their skin, for
example, sea stars.
Function, Physical Characteristics and Adaptation of Aquatic Animals
Adaptation of Aquatic Animals
Behavioural adaptations
 Behavioural adaptations are learned or inherited behaviours that help
organisms to survive, for example, the sounds made by whales allow
them to communicate, navigate and hunt prey.
 Bryozoan colonies are found in high numbers on the continental shelf
in New Zealand. They look like plants but are actually made up of
hundreds of tiny individual animals that have banded together in order
to more successfully find food and survive predation.