Environmental Management (0680) | World fisheries

Welcome to World Fisheries: Study Notes (IGCSE Environmental Management 0680)

Hello future Environmental Managers! This chapter is all about where we find fish in the massive ocean, why they are found there, and, most importantly, how we can manage this vital food resource sustainably.
Understanding fisheries is crucial because fish provide protein for billions of people, but our methods of catching them can severely damage marine ecosystems. Let's dive in!

Quick Review: Why are Oceans Important? (5.1 Oceans as a resource)

Before discussing fish, remember that oceans are valuable for much more than just food (fishing). Other resources include:

• Food (fish, shellfish)
• Energy (wave and tidal power)
• Building materials and chemicals (salt, minerals)
• Tourism and transport (shipping)
• Potential source of safe drinking water (via desalination)

5.2 Distribution of Major Marine Fish Populations

If you look at a map, you will see that most major fishing areas (fisheries) are not in the deep, open ocean. They are concentrated in specific, highly productive zones. Why? Fish need food, and food (plankton) needs sunlight and nutrients.

1. The Importance of Continental Shelves

The greatest fish populations are typically found above the continental shelves.

• What is the Continental Shelf? It's the shallow, submerged edge of the continent before the ocean floor drops sharply.
• Why are they productive? Because they are shallow, sunlight can penetrate all the way down to the seabed. This allows phytoplankton (tiny plant-like organisms, the base of the marine food web) to photosynthesize effectively. This means more food for smaller fish, and therefore more food for larger, commercially valuable fish.

Think of it like a sunny, shallow garden compared to a dark, deep forest floor. The garden produces much more food!

2. The Role of Ocean Currents

Ocean currents act like massive conveyor belts, moving water (and heat) around the globe. The key fishing areas occur where specific currents meet.

• Cold Ocean Currents and Warm Ocean Currents meeting cause mixing.
• This mixing brings cold, nutrient-rich water from the deep ocean up towards the surface (a process called upwelling, though you just need to know the effect).
• These lifted nutrients fuel massive blooms of phytoplankton, creating enormous food sources that attract huge fish populations.
• Example: The meeting of currents off the coast of Japan or the Grand Banks off North America.

Key Takeaway (5.2 Distribution): High fish populations are found in shallow waters (continental shelves) and areas where cold and warm currents mix because both conditions ensure high levels of sunlight (for photosynthesis) and high levels of nutrients (for plankton growth).

The El Niño Southern Oscillation (ENSO) (5.2)

Don't worry if this sounds complicated—it's just a pattern of changing ocean temperatures and air pressures in the Pacific Ocean that has huge global impacts, especially on fishing.

What is ENSO?

ENSO is a climate pattern that fluctuates between three states:

1. Normal Conditions (or La Niña): Strong trade winds push warm surface water towards Asia/Australia. Cold water rises off the coast of South America (e.g., Peru/Ecuador), bringing deep, nutrient-rich water to the surface. This supports huge fisheries (like the Peruvian anchovy).
2. El Niño Conditions: Trade winds weaken or reverse. Warm water flows back towards the coast of the Americas.

Effects of El Niño on Fisheries (Pacific Coast of South America)

When El Niño hits, it causes dramatic changes for the fishing industry in countries like Peru:

• The warm surface water prevents the vital cold, nutrient-rich water from rising to the surface. This stops the process that feeds the plankton.
• Without nutrients, the phytoplankton population crashes.
• The fish that feed on the plankton (like anchovies) starve or migrate away to find colder, richer waters.
• This leads to a massive decline or collapse of the local fish populations, causing severe economic damage to fishing communities.

Did you know? El Niño means 'The Little Boy' in Spanish, named because it often appears around Christmas time.

5.3 Impact of Exploitation of the Oceans (Fisheries)

As the global population grows, our demand for fish increases. Modern fishing technology (large trawlers, radar, sonar) makes it easy to find and catch enormous numbers of fish. This exploitation has severe consequences.

1. Overfishing of Marine Species

Overfishing occurs when fish are harvested at a rate faster than they can reproduce and replenish their population.

• Impact on Target Species: Populations fall dramatically. If fishing continues unchecked, the population can collapse entirely (meaning too few fish are left to breed successfully), potentially leading to commercial extinction (no longer profitable to catch) or biological extinction.
• Analogy: Imagine repeatedly taking money from your savings account without depositing any. Eventually, the money runs out! Overfishing depletes the 'capital' (the adult breeding stock).

2. Effect on Bycatch Species

Bycatch refers to any non-target marine animals or plants caught unintentionally by fishing gear.

• Impacts: Most bycatch is discarded, usually dead or injured. This results in the pointless death of millions of animals every year.
• Common Bycatch Examples: Dolphins, sea turtles, seabirds (caught in longlines), small, juvenile (young) fish of the target species.
• Catching juvenile fish is particularly harmful because they are removed before they have a chance to breed, contributing directly to overfishing.

Reducing Exploitation through Marine Farming (Aquaculture) (5.3)

One key way to reduce pressure on wild fish stocks is through farming marine species, often called mariculture or aquaculture.

• How it works: Fish, shellfish (like prawns), and sea vegetables are grown in controlled environments (e.g., net pens in the ocean or large tanks on land).
• Benefit: By producing food in a farm setting, it reduces the need to hunt and harvest the wild population. This gives wild stocks time to recover from overfishing.

Note: While farming helps wild stocks, it can cause other environmental problems, such as pollution from waste or farmed fish escaping and competing with wild populations (this is often discussed in case studies).

5.4 Management of the Harvesting of Marine Species

Managing fisheries is complex because fish move across national borders, and many fishing fleets operate in international waters. Successful management requires a combination of technical, regulatory, and legal strategies.

1. Technical Strategies: Controlling Fishing Methods

• Net types and Mesh Size:

  The size of the holes in the fishing net (the mesh size) is strictly controlled by law.
  A larger mesh size ensures that smaller, juvenile fish can escape and grow large enough to reproduce, helping to replenish the stock.

• Species-specific Methods (e.g., Pole and Line):

  Fishing methods designed to catch only the intended species significantly reduce bycatch.
  The pole and line method, often used for tuna, catches fish one by one, resulting in very low levels of bycatch compared to massive trawl nets. This is a much more sustainable method.

2. Regulatory Strategies: Controlling What, When, and Where

• Quotas:

  A quota is a limit set on the total amount of fish (by weight or number) that can be caught during a season.
  Evaluation: Quotas directly prevent overfishing, but they can be hard to enforce, especially in international waters, and sometimes fishermen discard illegal catches at sea ("high grading") to meet the quota weight limit with only the highest-value fish.

• Closed Seasons:

  Fishing is completely banned during certain times of the year, usually corresponding to the main breeding season of the target species.
  Benefit: This guarantees that the fish have a chance to reproduce, increasing the population for the next year.

• Protected Areas and Reserves:

  These are specific geographical areas (like coral reefs or critical nursery grounds) where fishing is severely restricted or banned completely.
  Benefit: These areas act as "safe havens" where fish stocks can recover and then spill over into surrounding, non-protected fishing zones.

3. Legal and International Strategies

• Conservation Laws (National):

  Individual countries pass laws enforcing quotas, net sizes, and closed seasons within their own territorial waters (usually up to 200 nautical miles from shore).

• International Agreements (Implementation and Monitoring):

  Since fish migrate across borders, global cooperation is essential. International agreements (treaties between countries) set shared quotas and management rules for shared fish stocks.
  These agreements require complex monitoring (tracking fishing vessels) and implementation (making sure countries actually follow the rules).

Case Study Prompt (Reminder)

Remember that for your exam, you should study a named case study that illustrates the resource potential, exploitation, impact, and management of a marine fishery (e.g., the collapse of the Newfoundland Cod Fishery and its subsequent management). You should also study an example of marine farming (aquaculture).