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Overfishing: When We’ve Run Out of an Endless Resource

Overfishing: When We’ve Run Out of an Endless Resource


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, well have a post about some of the most important topics for the environment, exploring and explaining the basics. Its 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.


Related stories:

How Investing In Our Fisheries Pays Off

The Bottom Line: Little Fish, Big Fishery

Coral Sea Marine Life Wait for Australia’s Protection


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Photo from LOLren via flickr

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5:57AM PDT on Jun 15, 2015

I really like this website. It appears to be inline with much of the way I think and hope for our planet EARTH! The fact that we continue to disregard so many aspects of our liveable planet without regard for future generations, gives me great pause. I can only ascertain that many people just "Don't Care!" We must care. If I am silent, then I am guilty of what I condemn. Kudos for the creators and managers of this website "!"

5:57AM PDT on Jun 15, 2015

I really like this website. It appears to be inline with much of the way I think and hope for our planet EARTH! The fact that we continue to disregard so many aspects of our liveable planet without regard for future generations, gives me great pause. I can only ascertain that many people just "Don't Care!" We must care. If I am silent, then I am guilty of what I condemn. Kudos for the creators and managers of this website "!"

8:14AM PDT on Sep 21, 2012


3:39AM PDT on Sep 16, 2012

very sad

1:32PM PDT on May 5, 2012

Grazie per le notizie.

5:10PM PDT on Apr 19, 2012

Jim G., ZPG-ers, and all: Don't get me wrong: I am not optimistic, not about short- or long-term changes. I fear the only thing that will stop our species from destroying many others will be a
great, natural collapse of our numbers; and it will make all our recent famines look jolly by comparison.

5:03PM PDT on Apr 19, 2012

At the risk of repetition, how do we curtail the number of humans quickly enough to prevent fisheries collapse if nothing else is done? This formula is suitable for application to other looming environmental disasters; e.g.: how do we curtail the number of humans quickly enough to prevent irreversible global warming if nothing else is done? To ask for such specifics is not to deny that the central importance of human overpopulation. To stress overpopulation without providing such specifics and working for them may be simply a rationalization for inaction.

3:01PM PDT on Apr 19, 2012

Will it take a total collapse of fishing stocks to get us to pay attention? If we don't curtail our numbers, Nature will do it for us. Pandemic, famine - whatever it takes. Next thing you know, we'll be eating each other.

8:34AM PDT on Apr 13, 2012

Fishermen are TOTALLY incapable of policing themselves. They rape the oceans with no thought for conservation. Cod is just one example, what about salmon, blue fin tuna, sea bass, swordfish the list is long. They blame everyone and everything for the disappearing fish stocks but themselves. They lie about their quotas, they use completely unfair and barbaric fishing methods. They take everything and leave nothing to regenerate. The bodies that oversee the various fisheries are given recommendations all the time about reducing quotas. The recommendations are sound science, yet they are overruled all the time. Noone is taking overfishing seriously and noone has the balls to tell the fishermen to stop. For the few countries (the UK is one) who follow the rules, there are many more countries that completely flout the laws, the Spanish, Italians, Koreans, Japanese, Tiwanese, Chinese, to name a few.

Its like everything else on this planet, a resource that is been raped and pillaged with no thought to the future. The oceans are overfished, a dumping ground for waste, polluted run off from agriculture, has massive "dead" areas where NOTHING lives or grows, the coral reefs are dying, it is a polluted mess. Without a healty ocean, we cannot have a healthy planet AND NOONE IS LISTENING.

4:46AM PDT on Apr 13, 2012

why does every couple want their own perfectly matched set of their own kids ...I am sick of IVF and the obsession that the millions of orphans and foster kids are third class citizens ...
we are all planet dwellers and these orphans could use the tens of thousands we waste on IVF ...on schools, hospitals, doctors, clean water and agriculture ...
ZPG is a good aim - the days of infertile couples might have fostered more good works than we do now ...
I expect to hear the screams now ...IVF was developed to transport bull and sheep semen around the world , not human accessories.

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Disclaimer: The views expressed above are solely those of the author and may not reflect those of
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