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”

mean?• When does harvesting become overharvesting?• Where does overharvesting occur?• Why is harvesting from the ocean necessary?• How do humans harvest from the ocean?

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Chapter 19Chapter 19Harvesting the Ocean’s ResourcesHarvesting 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 environments.

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 uranium.

• 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 catch

• There has been a dramatic increase in fish/shellfish taken from the sea in the past 50 years– 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 overfishing

– 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 population

• 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 ecosystems

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., tuna)

• 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 resources

• 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

weight

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

regulated– 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 California

Mineral Resources• Sulfides

– formed when mineral-rich solutions from fractures in rift valleys come into contact with colder seawater, and precipitate

– 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 environment

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 land-

based operations