Transcript Chapter 19

Who, What, When, Where, Why, and How of
The Ocean’s Resources
• Who harvests the ocean’s resources?
• What does “harvesting the ocean’s resources”
• When does harvesting become overharvesting?
• Where does overharvesting occur?
• Why is harvesting from the ocean necessary?
• How do humans harvest from the ocean?
Chapter 19
Harvesting the Ocean’s Resources
Key Concepts
• Fish and shellfish are renewable
resources that must be properly managed
to produce a sustainable yield.
• Increased demand for food from the sea
has placed a great deal of pressure on
natural fish and shellfish populations.
Key Concepts
• The advent of mechanized fleets and better
fishing techniques, coupled with natural
phenomena, has caused a decrease in the size
of commercial fish catches.
• Overfishing has brought some fisheries to the
brink of collapse.
• Techniques such as aquaculture have helped
relieve fishing pressure on natural populations
but not without new impacts on natural
Key Concepts
• Large numbers of noncommercial animals
are killed as a result of current,
mechanized fishing techniques.
• Our limited knowledge of the basic biology
of many commercial species hampers our
ability to properly manage and conserve
these resources.
Key Concepts
• The sea is an important source of minerals,
including salt (NaCl) and manganese, and the
sulfides of valuable metals such as gold and
• Fresh water for drinking and irrigation can be
produced from seawater by removing the salt.
• The oceans contain energy reserves in the form
of fossil fuels and methane hydrate.
Commercial Fishing
• Commercial fisheries are in trouble
– article published in the journal Science in 2006 projected
that by 2048, commercial fishers will have nothing left to
• There has been a dramatic increase in
fish/shellfish taken from the sea in the past 50
– increased demand resulted from increase in the human
population (now more than 6 billion)
Commercial Fishing
• Use of the catch has become less efficient
as more is used for fish-meal products to
feed livestock
– 10% rule of ecology
• only about 10% of energy available at one trophic
level is passed on to the next
• feeding livestock with commercial fish not efficient
• commercial fish catch consists of fish in higher trophic
levels (e.g., tuna)
• greater waste of energy than harvesting fish on lower
trophic levels
Commercial Fishing
• Fisheries management
– fish and shellfish are renewable resources as
long as animals who aren’t caught continue to
reproduce and replace those that are caught
– the goal of fisheries management is to
maintain these resources by enacting policies
and setting catch limits that will prevent
– this is difficult when the basic biology of a
commercial species is not well known
Commercial Fishing
• Fisheries management (continued)
– monitoring fish populations
• determining population distribution and movement
– some commercial species can be found over a broad
geographical range
– range is divided into stocks (separate populations) for
purposes of management
– tagging: catching fishes and marking them with identification
tags, used when they are re-caught
» by mapping locations where tagged fish are initially
caught and released and released again, biologists track
movement and distribution of members of each stock
– unique molecular markers (DNA sequences) can be used to
identify members of specific stocks
Commercial Fishing
• Fisheries management (continued)
– monitoring fish populations (continued)
• determining population size and age structure in
order to develop sound management plan
– sampling experiments are designed to determine
the number of individuals of various ages and
sizes in a given stock
– landings: the catch made by fishing vessels,
monitored as a source of fisheries data
– fishing effort: the number of boats fishing, number
of fishers working, and number of hours they
spend fishing
Commercial Fishing
– monitoring fish populations (continued)
• fishery yield
– potential yield: the number of pounds of fish or
shellfish that the stock can yield per year without
being overexploited
– sustainable yield: the maximum yield that may be
sustained over several years without stressing the
• problems in managing diverse species
– proper management of one species may conflict
with proper management of other species
– some fisheries biologists prefer to take an area or
ecosystem based approach
Commercial Fishing
• Overfishing
– occurs when fish are caught faster than they
reproduce and replace themselves
– changes in genetic diversity by selecting for or
against a certain trait
• harvesting larger specimens leaves only smaller
ones to reproduce, exerting a selective pressure
for smaller animals
• trawls: large nets that are dragged along the
bottom, capturing virtually everything that enters
• overfishing reduces population size, hence
reducing genetic diversity
Commercial Fishing
• Overfishing (continued)
– changes in species diversity
• overfishing can affect biological diversity by
reducing the number of species in an ecosystem
– changes in habitat
• fishing activities, e.g., trawling, can damage or
destroy habitat ultimately disrupting entire
Commercial Fishing
• Overfishing (continued)
– controlling overfishing
• coastal zones
– In 1977, the United States and other countries increased the
area of ocean controlled by them to 200 miles off the coast =
exclusive economic zones (EEZs)
• developing new fisheries (e.g., surimi) as a
consequence of decreasing traditional fisheries (e.g.,
• consumer education
– hoping to curb demand for endangered species
Commercial Fishing
• Other factors affecting marine fisheries
– destruction and development of coastal habitats
• resulted in a loss of feeding, breeding and nursery
grounds for commercial fishes
– wasteful and destructive fishing practices
• incidental catch: non-commercial species killed each
year during commercial fishing (a.k.a. bycatch or
“trash fish”), representing significant waste of marine
• drift nets: large nets made of sections called tans
which are set at night and retrieved in the morning
– Produce large amounts of bycatch
Commercial Fishing
• Other factors (continued)
– wasteful and destructive fishing practices
• trawling produces a large bycatch and damages
benthic ecosystems
– shrimp trawlers catch and kill many sea turtles
– use of turtle exclusion devices reduces turtle deaths
• inefficient use of the catch
– e.g., filleting process uses only 20 to 50% of fish’s body
Commercial Fishing
• Other factors (continued)
– aquaculture: the use of agricultural techniques
to breed and raise marine organisms
monoculture: only 1 species is raised
polyculture: several species are raised together
fish aquaculture
raft culture: juveniles of commercially valuable
molluscs (clams, mussels, oysters) are collected
and attached to ropes suspended from rafts
Commercial Fishing
• Other factors (continued)
– aquaculture (continued)
• shrimp farming
• eco-friendly aquaculture
• problems associated with aquaculture
– mangrove ecosystems are destroyed in Ecuador and Asia to
make room for shrimp farms which quickly become polluted
from accumulated wastes and abandoned
– large numbers of fish must be caught to supply food for
shrimp and salmon aquaculture, making these fish
unavailable to support many fish species in the wild
– antibiotics and pesticides along with nutrients used in
aquaculture become harmful runoff into coastal waters
Commercial Fishing
• Case studies
– tuna
• purse seines: huge nets up to 1,100 m long and
180 m deep with bottoms that can be closed by
pulling on a line
• purse seines exploit schooling behavior of tuna
• dolphins follow tuna in and get caught and killed
• Marine Protection Act passed in 1972
• backing down: procedure in which the skiff draws
the purse seine halfway toward the purse seiner;
when the dolphins are at the edge, the boat backs
up to let them escape
Commercial Fishing
• Case studies (continued)
– salmon
• to maintain salmon fisheries, overfishing must be
avoided and their spawning grounds protected
• disruption of spawning grounds has made the
spawning population quite small
• ocean ranching (sea ranching): raising young fish
and returning them to sea, where they develop into
adults and increase the size of the population
Commercial Fishing
• Case studies (continued)
– Shellfish
• invertebrates (crustaceans and molluscs) are the
most valuable commercial fisheries in New England
and along the West Coast of the United States.
• hard-hit by pollution that contaminates estuaries and
near-shore waters
– toxic algal blooms render some shellfish poisonous
• the king crab fishery declined in the 1980s and is now
– overfishing + lack of knowledge about king crab biology
have been blamed for this decline
Salt and Water
• Obvious non-fisheries products of the sea
• 30% of the salt supply comes from the sea; 70%
from deposits left when ancient seas evaporated
• Extraction of salt from seawater
– seawater is directed into shallow ponds where it is
concentrated, then evaporated
Salt and Water
• Desalination—process of removing salts
from seawater (so it is potable)
– process is energetically/financially expensive
– usually more expensive than obtaining water
from groundwater or surface sources
– used in Israel, Saudi Arabia, Morocco, Malta,
Kuwait, Caribbean islands, parts of Texas and
Mineral Resources
• Sulfides
– formed when mineral-rich solutions from fractures in rift
valleys come into contact with colder seawater, and
– no technology exists for sampling/mining at this time
• Manganese
– used as a component of several alloys
– nodules are found on the deep ocean floor
– attempts to develop mining technology were largely
suspended in the 1980s due to the depressed market for
metals and issues of ownership
Sand and Gravel
• Most widespread seafloor mining operations
extract sand and gravel for use in cement,
concrete and artificial beaches
– major costs associated with transportation distances
• Calcium carbonate deposits along Texas Louisiana
and Florida
– used for lime, cement, calcium oxide for removing
magnesium from seawater, gravel
• Tin is extracted from sand in coastal regions of
Southeast Asia
Sand and Gravel
• Uranium extracted from bottom sediments
of the Black Sea
• Platinum extracted from coastal sands in
the U.S., Australia, South Africa
• Mining sands/gravel can cause pollution
and habitat destruction in the marine
Energy Sources: Coal, Oil, Natural Gas,
and Methane Hydrate
• Fossil fuel is fuel (coal, oil and natural gas) formed from
remains of plants and microorganisms that lived millions of
years ago
• Coal
– formed from prehistoric swamp plants, e.g., ferns
– coal is mined from under the sea in Japan
• Oil and natural gas
– represent 90% of the mineral value taken from the sea
– formed from remains of diatoms and other microorganisms
– oil is mined in the Persian Gulf, North Sea, Gulf of Mexico, northern
coast of Australia, southern coast of California, and around the
Arctic ocean
– offshore reserves represent about one third of world’s total reserves
– cost of offshore drilling and extracting is 3 to 4 times that of landbased operations