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Oceans as a Resource
Oceans cover two‑thirds of Earth, regulate climate via heat distribution and act as carbon sinks.
Resource potential:
Food: fish (cod, herring), molluscs (clams, oysters), crustaceans (shrimp, lobster), reptiles (turtles), mammals (whales), seaweed.
2012: ~160 million tonnes caught/produced (≈19.2 kg/person).
Building materials & chemicals:
Sea salt, limestone mined on land.
Seawater → sodium chloride, magnesium.
Seabed minerals: manganese, phosphorites, zinc, copper, gold.
Offshore sand/gravel for construction → risk of coastal erosion.
Power generation: offshore wind farms, wave/tidal generators, tidal barrages.
Tourism: 11% of global GDP, 200M jobs; coastal tourism → reef/mangrove destruction if unsustainable.
Transport: 9.93 billion tonnes freight (2013); container ships, bulk carriers, tankers → pollution risks.
Drinking water: desalination (reverse osmosis, distillation). Expensive, energy‑intensive; ~1% of global freshwater.
Coastal Salt Mining (Cape Verde)
Main Maritime Shipping Routes
World Fisheries
Ocean Currents
Driven by tides, winds, thermohaline circulation (temperature + salinity differences).
Warm currents spiral clockwise (N hemisphere), anticlockwise (S hemisphere).
Cold currents sink at poles → conveyor belt circulation (~1000 years per cycle).
Upwelling: nutrient‑rich water rises → supports dense fish populations.
Distribution of Marine Fish
70% catch from Pacific, 20% from Atlantic.
Key areas: continental shelves, coastal waters, coral reefs, upwelling zones, oceanic islands.
Photosynthesis by phytoplankton → base of food webs.
El Niño Southern Oscillation (ENSO)
Occurs every 2–7 years; weakens trade winds, reverses currents.
Warms eastern Pacific by 4–8°C → suppresses Humboldt Current upwelling.
Fish stocks collapse (e.g., Peruvian anchoveta ↓80%); Peru’s GNI ↓5% in El Niño years.
Impact of Exploitation of the Oceans
Overfishing
2012: 158 million tonnes fish, worth US$130B.
12% of world population depends on fishing/aquaculture.
WWF report: 39% decline in marine species (1970–2010).
Super trawlers & fish factories (e.g., Lafayette) → industrial scale depletion.
UN (2011):
28.8% stocks unsustainable.
61.3% fully exploited.
9.9% underfished.
Tuna species (skipjack, bluefin, big eye, albacore, yellowfin) under threat globally.
Super Trawler
Factory Ship
Greenpeace Protest
Bycatch & Discards
Non‑target species caught in nets → discarded dead.
Shrimp nets worst: 1 kg shrimp → 5.7 kg bycatch.
Sharks, dolphins, seabirds affected → biodiversity loss.
Aquaculture
Fastest growing food production system.
2011: 66.6M tonnes from aquaculture (62% in China).
Benefits: reduces pressure on wild stocks, employment, controlled growth.
Challenges: pollution, disease transfer, reliance on wild fish for feed.
Shrimp Boat Bycatch
Open Water Fish Farm
Management of the Harvesting of Marine Species
Net Types and Mesh Size
Fine mesh nets → catch juvenile fish → stock depletion.
Larger mesh nets → allow young fish to escape → sustainable populations.
Species‑specific nets (e.g., turtle‑excluder devices) reduce bycatch.
Other Species‑Specific Methods
Pole and line fishing:
Traditional, selective method.
Reduces bycatch, sustainable for tuna.
Labor‑intensive, lower yield compared to industrial trawlers.
Quotas
Governments set catch limits per species.
Prevents overfishing, ensures long‑term stock survival.
Requires monitoring and enforcement to be effective.
Closed Seasons
Fishing bans during breeding/spawning periods.
Allows populations to recover.
Example: North Sea cod closed season in spring.
Protected Areas and Reserves
Marine Protected Areas (MPAs): zones where fishing is restricted or banned.
Protect biodiversity, nursery grounds, coral reefs.
Example: Kiribati Phoenix Islands Protected Area (largest MPA).
Conservation Laws
National laws regulate fishing gear, quotas, and protected species.
Example: EU Common Fisheries Policy.
Penalties for illegal fishing (fines, vessel confiscation).
International Agreements
UNCLOS (United Nations Convention on the Law of the Sea): defines Exclusive Economic Zones (EEZs).
Regional Fisheries Management Organizations (RFMOs): set quotas, monitor compliance.
Challenges: enforcement at sea, illegal/unreported fishing.
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