Why have fisheries declined so precipitously in the last half-century...?
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Guiding Question 14.3
Why have fisheries declined so precipitously in the last half-century and what is the current status of the world’s fisheries?
Why You Should Care
Fisheries have declined as fish catch has increased, but that increase doesn’t have just a single cause. Protein is an important part of the human diet, and as our population continues to grow, our demand for protein does, too.
Fish is the most common source of global food protein, and technology to harvest more fish (drift nets, larger ships, etc.) became more common in the last 50 years. In poor countries, fish is the cheapest source of protein, while in rich countries, the health benefits of eating fish has doubled its consumption per year.
Today, fisheries face the perfect storm of technology that is more efficient at harvesting fish, growing demand from both poor and rich countries, and fisheries under pressure from pollution, ocean acidification, and climate change (see Chapter 13).
Test Your Vocabulary
Choose the correct term for each of the following definitions:
Term
Definition
The amount that can be harvested without decreasing the yield in future years.
The fish population is well below historic levels and the population's reproductive capacity is low, meaning that recovery will be slow, if at all.
More fish are taken than is sustainable in the long run, leading to population declines.
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1.
Why are higher trophic level (TL) species less common in food pyramids?
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Each trophic level is limited by the energy in the tropic level beneath it. This is due to entropy’s effects releasing most of its energy in “wasted” forms. This creates the pyramid shape that narrows as you go up the trophic levels.
2.
When did the TL of fish from the Grand Banks dramatically shift to lower TL species? Why did it rise again after that?
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The shift happened in1991-1995 as the slope of the line went sharply downward from a TL of 3.9 to 2.8 in 1994. It rose again because the fishery was closed.
3.
When higher TL fish are scarce, fisherman switch to lower TL species. Why does this switch slow recovery of the higher TL species?
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Since each trophic level feeds the level above it, moving down the food chain to find food limits energy available to higher levels in the future. This would slow any future recovery of higher TL species.
4.
Which of the following statements about fishery status is not true?
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5.
Why did the fish catch in the Grand Banks become mostly molluscs and crustaceans after 1993?
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The Grand Banks fishery:
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7.
Salmon are another high TL species like cod, but salmon live in a different part of the ocean. Why did their catch numbers also decrease between 1990 and 2000?