Fisheries: Declines, Potential and Human Reliance
we can drain the Ocean into mill-ponds,and bottle up the
of Gravity, to be sold by retail, in gas jars; then may we hope to comprehend
the infinitudes of man's soul under formulas of Profit and Loss; and
rule over this too, as over a patent engine, by checks, and valves, and
- Thomas Carlyle
(1795-1881), Scottish essayist, historian
In this lecture period, we wish to
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
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
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
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.
First, we need to become familiar with
some terms used when discussing fish populations and the fishing industry.
A stock is the portion of a species or population that is harvestable.
Assessment is the estimation of abundance of a resource, rate at which
it is being removed, and reference rates for sustainable yields.
Mortality Rate is a function of the fishing effort (amount, types of
Rate The harvest rate is the fraction or amount of stock harvested per
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.
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:
Stock assessment and management is becoming
increasingly important, as is illustrated by these statistics on the global
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
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
Large Coastal Sharks
Gulf of Mexico King Mackerel and Pink
Atlantic/Gulf of Mexico/Caribbean Reef
Pacific Ocean Perch
North Pacific Albacore
Oysters, Hard Clams, and Abalones in
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
(in millions of tons)
|South African Pilchard
|Greater yellow croaker
|Cape horse mackerel
|South American Pilchard
|North Pacific hake
Finally, specific examples of fishery
declines highlight the over-consumption problem.
5. New Methods,
New Targets, and Over-Capacity
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
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
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
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
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
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:
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.
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
|Food Chain Length
||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
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
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
Pollock Wars in the Sea of Okhotsk
The Salmon Wars of the Northern Pacific
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. See the
Monterey Bay Aquarium
website for more information.
Fisheries Self Test
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,
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
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