Care2 Earth Month: Back to Basics
This year, Care2 decided to expand Earth Day into Earth Month, since there is so much to explore when it comes to the environment. Every day in April, we’ll have a post about some of the most important topics for the environment, exploring and explaining the basics. It’s a great tool to help you get started with helping the environment — or help explain it to others. See the whole series here.
What is Overfishing?
Overfishing can be simply defined as catching more fish than the environment is able to replace. Fish populations can replenish themselves if left alone to spawn and reproduce. However, even fish species that spawn in the millions are limited in how quickly they can grow their population over time.
Unrestrained population growth is exponential, but one of the characteristics of exponential growth is that it depends on the current population. If the population is significantly depleted, the replenishment of that population is also much slower. In contrast, careful management of fishing stocks involves taking no more fish than the remaining population can replace during the following season, keeping the population constant.
Why is it a Problem?
More than 100 million tons of fish are eaten worldwide every year, according to the United Nations, of which two and a half billion people depend on it for at least 20 percent of their protein intake. Maintaining fishing stocks is a question of global food security, but it’s especially important for the world’s poor, many of whom are heavily dependent on fish for their nutritional needs.
More than 70 percent of the world’s fisheries are fished at or over capacity. Every year that fishing stocks are overfished sees their population decline. This can eventually lead to collapse, effecting a loss of jobs and a decrease in food supply. A longer term effect is increased damage to the overall health of the world’s oceans, as biodiversity drops by another notch.
How it Works
Fishing stocks are an example of a renewable resource, like lumber. Theoretically, we have an unlimited supply of fish, since more can always be spawned to replace what we’ve taken. But we don’t have an unlimited supply every year. Just as is the case with deforestation, if the number of cod born are fewer than were taken in a given season, the overall population has to decrease.
And each subsequent season of overfishing does greater damage. Consider a population of cod with a ten percent growth rate. In an ideal situation, the number of cod will fluctuate, say from 100 to 110 (million). Fishermen will take the extra 10 each year, then stop. By the following season, the remaining 100 will grow their population again by another 10. But what if we instead take 20 cod per season?
Then we have 110 – 20 = 90 cod. With ten percent growth, in one season we can get back up to 99, and an additional season (if no fishing occurs) will get us almost back to 110. But if we keep doing this we get 79 at the end of the second season, the population will recover to about 87, then dropped down to 67.
Within five years, the cod population is down to half of what it was before. But not only is the population cut in half, the population growth is also cut in half. With only 50 million cod, we can only expect a replenishment of five million that season. Five years of doubling one’s catch will then require more than five years of no fishing at all before the population recovers. In the long term, overfishing means more work for less food on average, which is also available only sporadically.
Cod: The Story of a Lost Renewable
Those numbers were made up for the purpose of illustrating how overfishing works, and the math is a little bit simplified (for example, it’s a little more complicated than a straight exponential growth situation, since the growth rate is potentially a little higher when the population is low), but this is broadly how it works. It’s also no accident I chose cod as the hypothetical victim of overfishing.
Cod was one of the great gifts of the Atlantic for centuries, for a plethora of coastal and ocean-going civilizations. In his book, “Cod: A Biography of the Fish That Changed the World”, Mark Kurlansky points out that the travels of the Vikings, from Norway to Iceland to Greenland to Canada’s Newfoundland, followed the effective range of Atlantic cod exactly. There seemed an unlimited supply of it. This nutritious, abundant fish was like manna from heaven.
But Canadian cod was declared functionally extinct in 1992. Two decades since the collapse of the Canadian cod industry, stocks still have not recovered. We managed to find the end of an endless supply.
What We Can Do
Do a little research on your seafood purchases and make sure the grocery stores and restaurants you frequent stock sustainably fished or farmed seafood products. The Monterey Bay Aquarium has a handy guide.
Tell your friends and family to do the same. If you’re a big seafood eater, you may also decrease your intake of fish to once or twice a week, to ease the pressure on the oceans.
And contact your government representatives about your concerns. This is a global issue and it doesn’t matter what country you’re in, every government needs to be on board.
Photo from LOLren via flickr
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