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examBoard: Cambridge
examType: IGCSE
lessonTitle: Food Resources from Oceans
Oceans cover more than 70% of our planet's surface and provide an essential source of food for billions of people worldwide. Fish and seafood supply about 17% of the global population's animal protein intake and are especially important in coastal nations and island states. Understanding how we harvest food from our oceans and how to do so sustainably, is crucial for our future food security.
Key Definitions:
Trawling: Dragging large nets through the water or along the seabed. Bottom trawling can damage marine habitats.
Purse seining: Using a large wall of netting to encircle schools of fish, then drawing the bottom closed like a purse.
Longlining: Setting out long lines with baited hooks, which can extend for many kilometres.
Gillnetting: Using mesh nets that trap fish by their gills when they try to swim through.
Habitat destruction: Some fishing methods damage coral reefs, seagrass beds and the seabed.
Bycatch problems: Many fishing methods accidentally catch non-target species including dolphins, turtles and seabirds.
Ghost fishing: Lost or abandoned fishing gear continues to trap and kill marine life.
Carbon footprint: Fishing vessels burn fuel and contribute to greenhouse gas emissions.
The Food and Agriculture Organization (FAO) estimates that about 34% of global fish stocks are being fished at biologically unsustainable levels. Many of the world's most important fisheries have collapsed or are in decline due to overfishing, pollution and climate change impacts.
When fish are caught faster than they can reproduce, populations decline. Modern technology like sonar, GPS and huge factory ships have made fishing extremely efficient, putting immense pressure on fish stocks.
Rising ocean temperatures and acidification are affecting marine ecosystems. Fish populations are shifting their ranges and coral reefs that support fisheries are being damaged by bleaching events.
Plastic waste, agricultural runoff and industrial pollution all threaten marine ecosystems. Microplastics are now found in many commercial fish species, raising health concerns.
Sustainable fishing aims to maintain fish populations at healthy levels while minimising environmental impacts. Several approaches have been developed to achieve this balance:
Catch quotas: Limits on how much fish can be caught.
Size limits: Rules about minimum fish sizes to allow juveniles to reproduce.
Seasonal closures: Banning fishing during breeding seasons.
Marine Protected Areas (MPAs): Zones where fishing is restricted or prohibited to allow recovery.
Gear restrictions: Regulations on what types of fishing equipment can be used.
Certification schemes: Like the Marine Stewardship Council (MSC) blue label that identifies sustainably caught seafood.
Seafood guides: Help consumers choose sustainable options.
Traceability systems: Track fish from "boat to plate" to combat illegal fishing.
Reducing waste: About 35% of caught fish is wasted - improving processing and storage can help.
North Sea cod stocks collapsed in the 1980s due to overfishing, falling to just 36,000 tonnes in 2006 (compared to 270,000 tonnes in the 1970s). The European Union implemented strict catch limits, closed spawning areas and introduced new net designs to reduce bycatch. By 2017, North Sea cod had recovered enough to be certified as sustainable by the MSC, though recent climate impacts have caused new challenges. This case demonstrates how management measures can help fish stocks recover, but also shows the ongoing challenges from climate change.
With wild fisheries under pressure, aquaculture has grown rapidly to become a major source of seafood. Today, about half of all seafood consumed globally comes from farms rather than wild capture. Aquaculture is the fastest-growing food production sector in the world.
Marine: Farming in seawater (e.g., salmon in sea pens)
Freshwater: Farming in lakes, ponds, rivers (e.g., tilapia, carp)
Shellfish: Oysters, mussels, clams grown on ropes or racks
Seaweed: Growing algae for food, fertiliser and other products
Reduces pressure on wild stocks
Provides reliable food supply
Creates jobs in coastal communities
Can be more efficient than land-based farming
Some types (like shellfish) can improve water quality
Pollution from waste and chemicals
Disease spread to wild populations
Escaped farmed fish competing with wild fish
Feed sustainability (many farmed fish eat wild-caught fish)
Habitat conversion (e.g., mangrove destruction for shrimp farms)
In the Bay of Fundy, Canada, researchers have developed systems where multiple species are farmed together to reduce environmental impacts. Salmon are raised in pens, while mussels and seaweed grow nearby. The mussels filter waste particles from the salmon, while the seaweed absorbs dissolved nutrients. This creates a mini-ecosystem where one species' waste becomes another's food. This approach reduces pollution and creates multiple products from the same farm area. Similar systems are being tested in China, Chile and Norway.
As the global population grows and climate change intensifies, the challenge of sustainably harvesting food from our oceans becomes more critical. Several innovations and approaches are emerging to address these challenges:
Offshore aquaculture: Moving fish farms further out to sea where currents can disperse waste.
Cell-based seafood: Growing fish meat from cells without raising whole animals.
Alternative feeds: Using insects, algae or microbes instead of wild-caught fish in aquaculture feed.
Ecosystem-based management: Looking at whole ecosystems rather than single species when making fishing decisions.
International agreements: Like the UN's Sustainable Development Goal 14 (Life Below Water).
Combating illegal fishing: Which accounts for up to 26 million tonnes of fish annually.
Fishery subsidies reform: Reducing harmful subsidies that encourage overfishing.
Small-scale fisheries support: Helping traditional fishing communities adopt sustainable practices.
Oceans provide vital food resources for humanity, but we must harvest them sustainably to ensure their continued availability. The challenges of overfishing, climate change and pollution require coordinated responses from governments, industry and consumers. By combining traditional knowledge with scientific innovation, we can develop approaches that provide food security while protecting marine ecosystems for future generations.
Remember that our food choices have direct impacts on ocean health. When you choose seafood, look for sustainable options certified by organisations like the Marine Stewardship Council (MSC) or the Aquaculture Stewardship Council (ASC). These small actions, multiplied across millions of consumers, can help drive positive change in how we harvest food from our oceans.
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