The World's Food and Fisheries

World's Food Supply. 1

We learn: 1

Introduction. 2

The Availability of Productive Land. 2

The Green Revolution. 3

Towards Improved Agriculture. 4

What Fraction of the World's NPP do Humans Appropriate. 5

Summary. 5

Suggested Readings and Links: 5

World Fisheries: Declines, Potential and Human Reliance. 6

We learn: 6

1.  Fish Stocks and Fish Harvests 6

2. The Importance of Fish. 8

3. Principles and Terms 8

4.  Evidence of Over-Exploitation. 9

5.  New Methods, New Targets, and Over-Capacity. 11

The Peruvian Anchovy Fishery. 12

6.  Maximum Sustained Yield of the World's Oceans 13

A Paradox: "Fishing Down" reduces yields. 18

7.  Solutions 18

What can you do? 19

Suggested Readings: 20


World's Food Supply

We learn:

  • Is the world food supply keeping pace with population growth?
  • What are the means of increasing the world's food supply?
  • How much can we increase the world's food supply?
  • What are the limits to the world's food supply?



As we have seen, world population is projected to continue increasing well into the next century. Can global food production be increased to provide for the coming population expansion? Because many people are malnourished today, it will be necessary to increase current levels of food production more than proportional to population growth, so as to provide most humans with an adequate diet.


Whether food supply can keep pace with an expanding human population is an old question. In 1798, Thomas R. Malthus predicted that population growth would outstrip food supply, causing great human suffering. In the early 1960s, most nations were self-sufficient in food, but alarm about a rapidly growing population (~2% annually) caused many to echo Malthus' prediction. Then, the Green Revolution (high-yield crops and energy intensive agriculture) brought about remarkable increases in crop production. World grain output expanded by a factor of 2.6 from the 1950s to the 1980s. Today, per capita production has now slowed and appears to be declining.


To increase food production, we can farm more land, or we can increase the yield from each unit of land. As we shall see, the future lies in increasing yields. We shall also see that humans are appropriating an ever-larger fraction of the world's productive capacity.

The Availability of Productive Land

Of the world's total land area of 150 million km2 (16 X the area of the US), much is not suitable for agriculture. Arable land comprises 10% of the total. Permanent crops are 1%; meadows and pastures, 24%; forest and woodland, 31%. The remaining 34% is land surface that supports little or no vegetation: Antarctica, deserts, mine sites, urban areas. Nearly all of the world's productive land is already exploited. Most of the unexploited land is either too steep, too wet, too dry or too cold for agriculture. In Asia, nearly 80% of potentially arable land is now under cultivation.


In Global Change I, we saw that the ecosystems of the world varied greatly in their net primary production (NPP). Isn't it surprising that some parts of the Earth's land surface are much more productive than others. Most of the "good bits" have been in agriculture for a long time. Some of the remaining land surface, such as tropical rain forests, is highly productive under native vegetation (hence not much use for feeding people), and, at least with the farming methods of today, not very productive when converted to agriculture. In fact, cropland per capita is declining world-wide, as agriculture land is degraded, or urbanized. Increasing the yields from available farmland appears to be the key to increased food production.

The Green Revolution

In the 1960s, the efforts of agriculture scientists began to be realized in increased crop production in many areas of the world, especially Asia. Selective plant breeding produced high yielding varieties of rice and other crops, particularly maize, sorghum, and wheat. These high yield varieties (HYVs) perfromed best under high applications of fertilizer, and also required more expenditures for pesticides, irrigation, farm machinery, etc. Rice is a particular success story, and as the leading cereal crop, helps to pull the world yield rates upwards. Soybean production also has climbed dramatically overall, and stayed somewhat ahead of population growth.

Fig. 1: Growth Rates of World Agriculture Production and World Cereals Production, 1961-92


The overall consequence is that per capita food production has contradicted the doom-sayers of the 1960s: during the greatest episode of population growth in human history, food supply per capita grew. Note that Asia did better than the world average, while Africa did worse. The Green Revolution's great success with rice explains the former; lack of success with breeding new arid-land crop varieties, combined with a large dose of political instability, explain Africa's worsening condition. Per capita grain production in Africa is down 12% since 1981 and down 22% since 1967. Some 20 years ago, Africa produced food equal to what it consumed; today it produces only 80% of what it consumes.


Fig. 2: Trends in World Food Production, 1961-94


Fig. 3: Trends in per capita Food Production, 1961-94


From the perspectives of feeding a growing population, the Green Revolution was a smashing success. Lurking behind this success story, however, are some disturbing issues:

  • Planting with identical HYV's reduces genetic diversity and increases vulnerability to pests, necessitating heavy use of pesticides.
  • Agriculture makes heavy use of fresh water.
  • High dependency on technology.
  • Questionable sustainability.


Towards Improved Agriculture


Continued improvements in agricultural practices and land management, hopefully will allow us to both increase yields and minimize some of the negative effects of agriculture. Some areas that hold much promise include: better pest management, water-conserving irrigation, conservation tillage, and development of new crops through breeding or genetic modification.


The use of pesticides multiplied by a factor of 32 between 1950 and 1986, with developing countries now accounting for a quarter of the world's pesticide use. However, inappropriate and excessive use can cause contamination of both food and environment and, in some cases, damage the health of farmers. Pesticides also kill the natural enemies of pests, allowing them to multiply; meanwhile the number of pest species with resistance to pesticides has increased from a handful 50 years ago to over 700 now.


Crops and foods can produced using recombinant DNA techniques which enhance their agronomic potential, nutritional characteristics, or one or more features of pest protection (insect and viruses) and tolerance to herbicides. More than 40 such transgenic crop varieties have been cleared through the federal review process. New varieties of plants are being developed using genes from wild varieties with inbuilt disease resistance. Genes from the wild have been used to protect Brazil's coffee plantations; while a Mexican wild maize confers resistance to seven major diseases. According to the American Medical Association, these foods are "substantially equivalent to their conventional counterparts," and no long-term side effects have yet been detected.


While it is difficult to estimate the gains in food production that we may obtain from exploring new crop species, this could make a large contribution. Ninety percent of the world's food is derived from just 15 plant and 8 animal species. Wheat, rice, maize (corn), millet, and sorghum provide nearly all (70%) the food energy (calories) and up to 90% of all protein consumed by the world's people. Cereal grains are humankind's major food, contributing more than two-thirds of the world production of edible dry matter and half of the world's protein.


What Fraction of the World's NPP do Humans Appropriate

In order to determine how much food the world can produce, and what fraction of that production is captured by humans, we will re-visit a topic discussed in Global Change I: The Flow of Energy: Higher Trophic Levels


On land, one species, Homo sapiens, commands about 40% of the total terrestrial NPP. This has probably never occurred before in earth's history. Human "carrying capacity" on earth is hard to estimate, because it depends upon affluence of a population and the technology supporting that population. But at present levels of affluence and technology, a population 50 to 100% larger than we have today would push our use of terrestrial NPP to well over 50% of the available production, and the attending degradation of ecosystems on earth (e.g., air and water pollution) would be of major concern.


The Food and Agriculture Organization of the United Nations (FAO) has published a study on the food production outlook through the year 2010. The FAO forecasts that production increases can, in fact, accommodate effective demand and rising world population, although malnutrition will become an increasing problem in developing countries. It is also assumed that continuing substantial investments in agricultural research are essential.


  • The expectation that population growth will outrun its food supply has a long history. Surprisingly, from the 1950s to the 1990s, which experienced the most dramatic increase in human population ever, per capita world food production increased.
  • The Green Revolution - high-yield varieties of cereal crops - resulted in enormous increases in yield per hectare. However, environmental costs are high.
  • Most arable land already is farmed, and the land area under agriculture had slightly declined. Improved agricultural methods that increase yields while minimizing environmental impacts hold the greatest promise for increasing world food supplies.
  • At present, humans use or co-opt a substantial fraction of the world's terrestrial net primary production, raising doubts about our ability to greatly increase food supply to humans.


Suggested Readings and Links:


Click here to take a short self test on this lecture's materials.




World Fisheries: Declines, Potential and Human Reliance

We learn:

         What is the importance of fish in the diet of humans?
What are the important marine resources, and are they harvested sustainably?
         What is the sustainable yield of the oceans?
What possible solutions might allow humans to more sensibly obtain food from the seas? 

1.  Fish Stocks and Fish Harvests

We can group economically important marine organisms in to five major families:

Demersal fish. These are bottom-living fish such as cod and haddock. These species tend to concentrate on broad continental shelves, especially of the North Atlantic

Pelagic fish. Pelagic fishes are species that inhabit the water column, such as herring, mackerel, anchovy, and tuna. The most spectacular fish catches are made of surface-shoaling pelagic species. Demersal fishes and Pelagic fishes combines make up the majority of the fish catch--about 72 million tons per year.

Crustaceans. This group consists of bottom-dwelling species (crabs and lobsters) as well as swimming invertebrates (krill, shrimp)Crustacean fisheries are important to many countries and regions, such as the Chesapeake Bay of the U.S. About 4 million tons of this group are harvested each year.

Molluscs and Cephalopods. These include various species of squid, cuttlefish, and octopus. More cephalopod stocks are harvested by the Japanese than by any other nation. They also serve as an important source of protein for many Mediterranean and developing countries. About 2.5 million tons of cephalopods are harvested each year.

Marine mammals. This group has been heavily exploited for oil and meat, although they make a relatively small portion of the global fish catch. Following the commercial extinction of the large baleen whales such as the blue, humpback, and fin, smaller species such as the minke and sei are being taken. Dolphins and porpoises are hunted locally, particularly in some tropical archipelagos. 

Figure 1: Families of economically important fish


2. The Importance of Fish

Why are we concerned about the status of our global fisheries? In addition to more lofty environmental reasons, such as the preservation of biodiversity, humans have stock in the status of our world's fisheries. Here are some statistics to give you an idea of the scope of human dependence on marine life:

         Over 90% of the world's living biomass is contained in the oceans, which cover 71% of the Earth's surface. At present, we harvest about 0.2% of marine production. (You might think that there is room for growth).

         Marine sources provide about 20% of the animal protein eaten by humans. Another 5% is provided indirectly via livestock fed with fish.
60% of fish consumption is by the developing world.

         In Asia, about 1 billion people rely on fish as their primary source of protein.

         Estimates suggest that seafood production from wild fish stocks will be insufficient to meet growing U.S. and Global demand for seafood products in the next century.

         The fishing enterprise employs some 200 million people worldwide.

3. Principles and Terms

First, we need to become familiar with some terms used when discussing fish populations and the fishing industry.

         Stock. A stock is the portion of a species or population that is harvestable.

         Stock Assessment is the estimation of abundance of a resource, rate at which it is being removed, and reference rates for sustainable yields.

         Fishing Mortality Rate is a function of the fishing effort (amount, types of gear, etc.)

         Harvest Rate The harvest rate is the fraction or amount of stock harvested per year.

         Production Rate. The production rate is the sum of growth in weight of individual fish, plus the addition of biomass from new recruits, minus loss in biomass to natural mortality.

         Production Function shows the relationship between production rate and fishing effort. As effort increases, the biomass drops and the production function typically goes through a fairly stable maximum. 

To aid in fish management, we can assess stocks by using a combination of three methods: 

         biological sampling

         annual catch statistics

         catch per unit effort statistics 

Stock assessment and management is becoming increasingly important, as is illustrated by these statistics on the global harvest history:

         Total catch has climbed fairly steadily since the 1950's. 

         Now, about 100 million metric tons/year are taken from the sea. This figure seems to be stabilizing.

         However, the harvest per capita has grown little (see Figure 2). This implies that if the current limit can not be increased, seafood availability per person will shrink as population expands. This will lead to rising prices. 

Figure 2: Global absolute and per capita fish catch, 1950-2000

4.  Evidence of Over-Exploitation

We can assemble a large amount of evidence that points to the fact that our marine resources have been over-exploited. First, there is a long list of over-utilized resources. These are some species which have been overfished:

         New England groundfish and flounder

         Southeast Spiny Lobster

         Atlantic Bluefin Tuna and Swordfish

         Main Hawaiian Island Bottomfish and Pelagic Armorhead

         Large Coastal Sharks

         Gulf of Mexico King Mackerel and Pink Shrimp

         Atlantic/Gulf of Mexico/Caribbean Reef Fish Complex

         Pacific Ocean Perch

         North Pacific Albacore

         Oysters, Hard Clams, and Abalones in many location

Secondly, the dates at which over-fishing began for various North Atlantic fisheries are alarming. From the table below, we can see that as we overfished one species, we simply moved to another and overfished that as well.

Table 2: Peak catch year of some fish species


Peak Year

Peak Catch

1992 Catch

(in millions of tons)

Percent Change

Pacific herring






Atlantic herring






Atlantic cod






South African Pilchard












Peruvian anchovy






Polar cod






Cape hake






Silver hake






Greater yellow croaker






Atlantic redfish






Cape horse mackerel






Chub mackerel






Blue whiting






South American Pilchard






Alaska pollock






North Pacific hake






Japanese pilchard












Source: FAO

Finally, specific examples of fishery declines highlight the over-consumption problem. 

5.  New Methods, New Targets, and Over-Capacity

Numerous statistics point to over-capacity:

Despite warnings of a slowdown in the marine catch in the 1970's and 80's, the fishing industry increased fishing efforts. Over the past 40 years, the technology used in fishing has improved. Now, boats are more powerful, fish are located electronically through sonar, larger nets are used, and there are just more fishing operations.

Today, the industry is twice as large as necessary. It could go back to the smaller, fewer boats of 1970 and still produce the same yield. This overcapacity is global: Norway is 60% over, while the European Union is 40% over. In the U.S., there are ten times the number of boats needed for the surf clam industry.




Figure 3: Drift-net in use.





How did this overcapacity develop? Competition led to an all-comers welcome approach. More competition for declining resources leads to overcapitalization in ever larger boats and nets.

Drift nets (see Figure 3) are a spectacular example of the new more efficient fishing methods. These monster nets (50 feet by up to 65 km) kill all that they encounter. They are banned by every fishing country within its own territorial waters. The combination of Japanese, Korean, and Taiwanese drift nets cast every night in international waters reaches about 48,000 km--enough to encircle the globe.

Another piece of evidence suggesting that we are overharvesting our seas is that we have been relegated to fishing for previously unfished stocks. We are now eating species heretofore thought of as "bait". 

The Peruvian Anchovy Fishery

To illustrate how overcapacity works, we will study the example of the Peruvian anchovy, which in boom years was the largest new fishery in the world. 

Figure 4: Annual catch of the Peruvian
Anchovy Fishery from 1960-1990

Before 1950, fish in Peru were harvested mainly for human consumption. The total annual catch was 86,000 tons. In 1953, the first fish meal plants were developed. Within 9 years, Peru became the number one fishing nation in the world by volume. This lead to a period of boom years in Peru. 1,700 purse seiners exploited a 7-month fishing season.

Fearing a crash, in 1970, a group of scientists in the Peruvian government issued a warning. They estimated that the sustainable yield was around 9.5 million tons, a number that was currently being surpassed (see Figure 4). The government turned a deaf ear toward its own scientists. Due to the collapse of the Norwegian and Icelandic herring fisheries the previous year, Peru was more poised than ever to earn yet more hard currency. Therefore, in 1970, the government allowed a harvest of 12.4 million tons. The following year, 10.5 million tons were harvested. In 1972, the combination of an El Nino year and the prolonged overfishing led to a complete collapse of the fishery. It has not recovered.




6.  Maximum Sustained Yield of the World's Oceans

Figure 5: Relative productivity of ocean zones















To fish our waters more sustainably, we need to know what the sustained maximum yield is. One theoretical estimate puts the estimated annual production at 240 million metric tons. The estimated annual harvest is half of this: 100-120 mmt. The current annual harvest is about 100 mmt.

Not all areas of the ocean are equally productive (Figure 5). As you can see from this figure, the coastal margins such as mangroves and saltmarshes are much more productive relative to their volume than the open ocean. Therefore, to accurately estimate the maximum yield of the ocean, we must look at the zones separately. The estimate used above was obtained by dividing the ocean into three zones: open ocean, coastal areas, and upwelling areas. 

The estimate for the productivity of each of the three zones was estimated based on three values: primary plant production, food chain length, and food chain efficiency. To further understand the relationship these values and productivity, you may want to review some lectures from last semester:

         The Flow of Energy: Primary Production explains how primary production is estimated in marine waters, and

         The Flow of Energy: Higher Trophic Levels discusses ecological efficiency of the food chain and the loss of energy with each trophic transfer (the "10% Rule"). 

Figure 6: High phytoplankton production zones










Figure 6 shows the areas of highest phytoplankton production. It is these areas upon which we most rely for our fish. Blooming across large regions, phytoplankton form large fields that sustain the marine food web. A high proportion of these productive zones are found where the ocean is rich in minerals. 99% of the worldwide annual commercial ocean catch comes from coastal waters, within 200 nautical miles of the coastline. These narrow coastal fringes of the world's oceans are at once its most productive and most vulnerable zones. The following figure (Figure 7) displays why these areas are most productive.

Figure 7: Biological Productivity of the Oceans

Food chains tend to be short in highly productive areas, such as upwelling zones, and longer in the open ocean (see Figure 8 below).  As a consequence, not only is there less primary production in the open ocean, but it must be transferred through many more levels of the food chain before reaching the trophic level that we harvest.  Because each transfer of energy from trophic level to trophic level has an average efficiency of about 10%, much less energy is available to humans if we are consumers at the end of a long food chain.


Figure 8:  Food chains of the open ocean, continental shelves, and upwelling zones

We can now combine all of this information (Table 2).  Nutrient availability, primary production, food chain length and food chain efficiency all differ across these three zones.  We suspect that food chain efficiency is highest in the upwelling zone because organisms are concentrated within a small area.  Note that coastal and upwelling zones contribute about equally to harvestable fish production, while the open ocean's contribution is relatively small.

Table 2: Estimated Production of Harvestable Fish


Open Ocean

Coastal Waters

Upwelling Areas

Nutrient concentration




Primary Production




Food Chain Length




Ecological Efficiency




Fish Production


about half of total

about half of total

A Paradox: "Fishing Down" reduces yields.

         Pauly, Dalsgaard and colleagues analyzed diet of 220 key species to assign each species of catch to a trophic level (Science 279:860, 6 Feb 1998)

         From 1950 to 1994, catch has gradually shifted from long-lived, high-trophic level fish (e.g. cod and haddock) to low-trophic-level fish and invertebrates such as anchovy and krill.

         Paradoxically, catches stagnated or declines, as competitors (such as inedible jellyfish) fill the void. "If things go unchecked, we might end up with a marine junkyard dominated by plankton." 

7.  Solutions

The increasing trend toward aquaculture may take some of the pressure off our overfished seas. Between 1984 and 1994, aquaculture was the fastest growing supplier of fish worldwide. Fish farms now account for more than 1/8th of the worlds catch. In China, India, and Japan, aquaculture accounts for half of the total fish eaten. Aquaculture has already eased some of the pressure on shrimp. Also, aquaculture allows for more optimal use of feedgrains than the poultry or beef industury (this means less grain per pound is needed for fish than those sources). However, there is some question about the long-term sustainability of aquaculture. Negative impacts of aquaculture include disease, genetic weakening of stocks, and coastal habitat destruction.

Downsize the existing fishing fleet. It is likely that a reduction of 30-50% will be required.

Reduce subsidies to the fishing industry. As seen in the following figure, currently the cost of fishing outweighs the revenues 80 billion to 75 billion.


International agreements of fish catch limits. International agreements are crucial to prevent commercial extinction, as fish do not respect international borders. This creates a "Tragedy of the Commons" situation, where any fish that you do not take go into your neighbors mouths. Although they rarely make the evening news, there have been more fishery conflicts in the 1990's than in the whole 19th century. Some examples are:

         The Cod Wars between Norway and Iceland

         Turbot Wars between Canada/Spain, Argentina/Taiwan, and China/Marshall Islands

         The Tuna Wars of the Northeast Atlantic

         Crab Wars of the Southwest Atlantic

         Squid Wars

         Pollock Wars in the Sea of Okhotsk

         The Salmon Wars of the Northern Pacific 

What can you do?
The above solutions need to be carried out by consensus among and within governments. But you, by yourself, can make a difference by being an informed consumer. Don't buy species of fish that are over-exploited, such as Atlantic Cod, Atlantic Sea Scallops, Black Sea Bass, Farm Raised Shrimp, Gulf Shrimp, Monkfish, Redfish, Swordfish, Shark, Red Snapper, Sturgeon, and Winter Flounder. Instead, order species like Alaska Salmon, Pacific Coast Dungeness Crab, and trapped shrimp that are not currently overfished.

Suggested Readings:

         World Resources Institute. 1994. World Resources 1994-95: A guide to the global environment. Oxford.
         Norman Myers, ed. 1993. Gaia: An Atlas of Planet Management, Anchor Books.
         U.S. Department of Commerce, 1995. Fisheries of the United States , 1994, NOAA Current Fisheries Statistics No. 9400.
         Gurney, R.J, J.L. Foster, and C. L. Parkinson. 1993. Atlas of Satellite Observations related to Global Change, Cambridge Press.