Preview
IB DP ESS — Topic 4: Water (HL Extension) | Higher Level | Paper 1 & Paper 2A/2B
🎯 Learning Intentions By the end of this note, you will be able to:
- Define maximum sustainable yield (MSY), overfishing, and bycatch using IB-aligned ESS terminology.
- Explain how fish populations function as renewable resources within marine ecosystems and the conditions under which they become unsustainable.
- Describe the biological and ecological risks associated with harvesting fish stocks at or beyond MSY, including trophic cascades and ecosystem collapse.
- Analyse the causes and consequences of overfishing using ESS analysis parameters: scale, sustainability, trade-offs, multiple perspectives, and uncertainty.
- Evaluate the effectiveness of marine policy instruments — including marine protected areas (MPAs), catch quotas, and international fisheries agreements — in managing fish stocks sustainably.
- Discuss contrasting worldviews (ecocentric, technocentric, anthropocentric) in relation to marine resource management and the governance of global fisheries.
- Construct a systems diagram showing the feedback loops linking fishing pressure, fish stock biomass, and ecosystem stability.
Real-World Context & Relevance
In 1992, the Canadian government made one of the most consequential fisheries decisions in history: it imposed a complete moratorium on Atlantic cod fishing off the coast of Newfoundland. The Grand Banks, once described by early European explorers as so teeming with cod that fish could be scooped from the sea in baskets, had been fished commercially for over four centuries. By the early 1990s, the cod population had collapsed to roughly 1% of its historical biomass — a decline so severe that the ecosystem itself had restructured, with invertebrate prey species such as shrimp and snow crab exploding in abundance in the absence of their predator (Hutchings and Myers 1994). Over 35,000 people lost their livelihoods overnight, and three decades later, the cod stock has still not recovered to commercially viable levels.
The Grand Banks collapse is not an isolated tragedy. According to the Food and Agriculture Organization of the United Nations, approximately 35.4% of the world's assessed marine fish stocks were being fished at biologically unsustainable levels as of 2019 — a figure that has risen steadily from 10% in 1974 (FAO 2022). In the Mediterranean and Black Sea, that proportion exceeds 60%. Meanwhile, global demand for fish protein continues to rise, driven by population growth and dietary shifts in rapidly developing economies. The tension between short-term economic gain and long-term ecological sustainability sits at the heart of this topic — and understanding it requires a systems-level analysis of how fish populations respond to harvesting pressure.
🌊 Why This Matters Marine fisheries provide protein for over 3 billion people and livelihoods for an estimated 600 million individuals globally (FAO 2022). When fish stocks collapse, the consequences cascade through food security, coastal economies, and marine ecosystem stability simultaneously — making fisheries management one of the most urgent and complex sustainability challenges of the 21st century.
Core Concepts & Definitions
To understand why fish stocks collapse, we first need to understand how fish populations grow when left undisturbed. Like all populations in a finite environment, fish populations follow logistic growth: they grow rapidly when