Chapter 19

1. Harvesting the Ocean’s Resources Chapter 19

2. 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.

3. 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.

4. 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.

5. 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.

6. Commercial Fishing • 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 • Recently, the world catch has not increased proportionately to the fishing effort • Use of the catch has become less efficient as more is used for fish-meal products to feed livestock

9. 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

10. Commercial Fishing • Fisheries management (continued) • monitoring fish populations • determining population distribution and movement • range is divided into stocks (separate populations) • tagging—catching fishes and marking them with identification tags, used when they are re-caught • unique molecular markers (DNA sequences) can be used to identify members of specific stocks

12. Commercial Fishing • Fisheries management (continued) • monitoring fish populations (continued) • determining population size and age structure • sampling experiments • landings—the catch made by fishing vessels • fishing effort—the number of boats fishing, number of workers working, and number of hours they spend fishing

13. Commercial Fishing • Fisheries management (continued) • 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

14. Commercial Fishing • Overfishing • occurs when fish are caught faster than they reproduce and replace themselves • changes in genetic diversity • 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

16. Commercial Fishing • Overfishing (continued) • changes in species diversity • overfishing can reduce the number of species in an ecosystem • changes in habitat • fishing activities can damage or destroy habitat • controlling overfishing • coastal zones • exclusive economic zones (EEZs) • developing new fisheries • consumer education

18. Commercial Fishing • Other factors affecting marine fisheries • destruction 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”) • drift nets—large nets composed of sections called tans which are set in the evening and retrieved in the morning

20. 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

21. 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 are collected and attached to ropes suspended from rafts

24. Commercial Fishing • Other factors (continued) • aquaculture (continued) • shrimp farming • eco-friendly aquaculture • problems associated with aquaculture • mangrove ecosystems are destroyed in Ecuador to make room for shrimp farms • large numbers of fish must be caught to supply food for shrimp and salmon aquaculture, making these fish unavailable to their natural predators • antibiotics and pesticides used in aquaculture become harmful runoff into coastal waters

25. Commercial Fishing • Case studies • anchovies • overfishing caused a reduction in fish size, so more fish had to be caught to meet demands • a record catch in 1972 + ENSO dramatically reduced the catch in 1973 • quotas were instituted to protect the anchovies fishery • since then, the anchovies catch has periodically been decreased by ENSO

28. Commercial Fishing • Case studies (continued) • 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

30. Commercial Fishing • Case studies (continued) • salmon • to maintain salmon fisheries, overfishing must be avoided and their spawning grounds preserved • 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

33. Commercial Fishing • Case studies (continued) • shellfish • 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

36. Salt and Water • 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 • in cold regions, ice (which is nearly pure water) is removed, leaving concentrated seawater which is heated to evaporate the remaining pure water

37. 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

38. 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 • Manganese • used as a component of several alloys • nodules are found on the ocean floor • attempts to develop mining technology were largely suspended in the 1980s

39. Sand and Gravel • Most widespread seafloor mining operations extract sand and gravel for use in cement, concrete and artificial beaches • Calcium carbonate deposits • lime, cement, calcium oxide for removing magnesium from seawater, gravel • Tin is extracted from sand in coastal regions of Southeast Asia

40. 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

41. Energy Sources: Coal, Oil, Natural Gas, and Methane Hydrate • Coal • formed from prehistoric swamp plants • 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

42. Energy Sources: Coal, Oil, Natural Gas, and Methane Hydrate • Methane hydrate • methane hydrate—ice crystals that trap methane, and can be burned • world’s largest known fuel reserve • methane gas rapidly escapes from the crystals when they are brought to the surface • experiments indicate it may be possible to exploit this resource, but geologists and biologists have concerns