Oil Rig off Santa Barbara. © Wolcott Henry 2001
The ocean plays a critical role in removing carbon from the atmosphere and providing oxygen. It regulates Earth’s climate. The ocean is an increasingly important source of biomedical organisms with enormous potential for fighting disease. These are just a few examples of the importance of the ocean to life on land. Explore them in greater detail to understand why we must keep the ocean healthy for future generations.
The oceans have been fished for thousands of years and are an integral part of human society. Fish have been important to the world economy for all of these years, starting with the Viking trade of cod and then continuing with fisheries like those found in Lofoten, Europe, Italy, Portugal, Spain and India. Fisheries of today provide about 16% of the total world’s protein with higher percentages occurring in developing nations. Fisheries are still enormously important to the economy and well-being of communities.
Fish Market in the Philippines. © Wolcott Henry 2001
The word fisheries refers to all of the fishing activities in the ocean, whether they are to obtain fish for the commercial fishing industry, for recreation or to obtain ornamental fish or fish oil. Fishing activities resulting in fish not used for consumption are called industrial fisheries. Fisheries are usually designated to certain ecoregions like the salmon fishery in Alaska, the Eastern Pacific tuna fishery or the Lofoten island cod fishery. Due to the relative abundance of fish on the continental shelf, fisheries are usually marine and not freshwater.
Although a world total of 86 million tons of fish were captured in 2000, China’s fisheries were the most productive, capturing a whopping one third of the total. Other countries producing the most fish were Peru, Japan, the United States, Chile, Indonesia, Russia, India, Thailand, Norway and Iceland- with Peru being the most and Iceland being the least. The number of fish caught varies with the years, but appears to have leveled off at around 88 million tons per year possibly due to overfishing, economics and management practices.
Fish are caught in a variety of ways, including one-man casting nets, huge trawlers, seining, driftnetting, handlining, longlining, gillnetting and diving. The most common species making up the global fisheries are herring, cod, anchovy, flounder, tuna, shrimp, mullet, squid, crab, salmon, lobster, scallops and oyster. Mollusks and crustaceans are also widely sought. The fish that are caught are not always used for food. In fact, about 40% of fish are used for other purposes such as fishmeal to feed fish grown in captivity. For example cod, is used for consumption, but is also frozen for later use. Atlantic herring is used for canning, fishmeal and fish oil. The Atlantic menhaden is used for fishmeal and fish oil and Alaska pollock is consumed, but also used for fish paste to simulate crab. The Pacific cod has recently been used as a substitute for Atlantic cod which has been overfished.
The amount of fish available in the oceans is an ever-changing number due to the effects of both natural causes and human developments. It will be necessary to manage ocean fisheries in the coming years to make sure the number of fish caught never makes it to zero. A lack of fish greatly impacts the economy of communities dependent on the resource, as can be seen in Japan, eastern Canada, New England, Indonesia and Alaska. The anchovy fisheries off the coast of western South America have already collapsed and with numbers dropping violently from 20 million tons to 4 million tons—they may never fully recover. Other collapses include the California sardine industry, the Alaskan king crab industry and the Canadian northern cod industry. In Massachusetts alone, the cod, haddock and yellowtail flounder industries collapsed, causing an economic disaster for the area.
Due to the importance of fishing to the worldwide economy and the need for humans to understand human impacts on the environment, the academic division of fisheries science was developed. Fisheries science includes all aspects of marine biology, in addition to economics and management skills and information. Marine conservation issues like overfishing, sustainable fisheries and management of fisheries are also examined through fisheries science.
In order for there to be plenty of fish in the years ahead, fisheries will have to develop sustainable fisheries and some will have to close. Due to the constant increase in the human population, the oceans have been overfished with a resulting decline of fish crucial to the economy and communities of the world. The control of the world’s fisheries is a controversial subject, as they cannot produce enough to satisfy the demand, especially when there aren’t enough fish left to breed in healthy ecosystems. Scientists are often in the role of fisheries managers and must regulate the amount of fishing in the oceans, a position not popular with those who have to make a living fishing ever decreasing populations.
The two main questions facing fisheries management are:
- What is the carrying capacity of the ocean? How many fish are there and how many of which type of fish should be caught to make fisheries sustainable?
- How should fisheries resources be divided among people?
Fish populate the ocean in patches instead of being spread out throughout the enormous expanse. The photic zone is only 10-30 m deep near the coastline, a place where phytoplankton have enough solar energy to grow in abundance and fish have enough to eat. Most commercial fishing takes place in these coastal waters, as well as estuaries and the slope of the Continental Shelf. High nutrient contents from upwelling, runoff, the regeneration of nutrients and other ecological processes supply fish in these areas with the necessary requirements for life. The blue color of the water near the coastlines is the result of chlorophyll contained in aquatic plant life.
Most fish are only found in very specific habitats. Shrimp are fished in river deltas that bring large amounts of freshwater into the ocean. The areas of highest productivity known as banks are actually where the Continental Shelf extends outward towards the ocean. These include the Georges Bank near Cape Cod, the Grand Banks near Newfoundland and Browns Bank. Areas where the ocean is very shallow also contain many fish and include the middle and southern regions of the North Sea. Coastal upwelling areas can be found off of southwest Africa and off South America’s western coast. In the open ocean, tuna and other mobile species like yellowfin can be found in large amounts.
The question of how many fish there are in the ocean is a complicated one but can be simplified using populations of fish instead of individuals. The word “cohort” refers to the year the fish was born and is used to gather population statistics. Cohorts start off as eggs with an extremely high rate of mortality, which declines as the fish gets older. Juvenile fish close to the age where they can be fished are called “recruits”. Cohort mortality is tied in with the species of fish due to variances in natural mortality. The biomass of a particular cohort is greatest when fish are rapidly growing and decreases as the fish get older and start to die.
Scientists use theories and models to help determine the number and size of fish populations in the ocean. Production theory is the theory that production will be highest when the number of fish does not overwhelm the environment and there are not too few for genetic diversity of populations. The maximum sustainable yield is produced when the population is of intermediate size. Yield-per-recruit theory is the quest to determine the optimum age for harvesting fish. The theory of recruitment and stock allows scientists to make a guess about the optimum population size to encourage a larger population of recruits. All of the above theories must be flexible enough to allow natural fluctuations in the fish population to occur and still gather significant data; however, the theories are limited when taking into account the effect of humans on the environment and misinformation could result in overfishing of the ocean’s resources.
Other factors that must be taken into account are the ecological requirements of individual fish species like predation and nutrition and why fish will often migrate to different areas. Water temperatures also influence the behavior of ecosystems, causing an increase in metabolism and predation or a sort of hibernation. Even the amount of turbulence in the water can affect predator-prey relationships, with more meetings between the two when waters are stirred up. Global warming could have a huge economic impact on the fisheries when fish stocks are forced to move to waters with more tolerable temperatures.
In many countries, commercial fishing has found more temporarily economical ways of catching fish, including gill nets, purse seines, and drift nets. Although fish are trapped efficiently in one day using these fishing practices, the number of fish that are wasted this way has reached 27 million tons per year, not to mention the crucial habitats destroyed that are essential for the regeneration of fish stocks. In addition, marine mammals and birds are also caught in these nets. The wasted fish and marine life is referred to as bycatch, an unfortunate side-effect of unsustainable fishing practices that can turn the ecosystem upside-down and leave huge amounts of dead matter in the water. Other human activities like trawling and dredging of the ocean floor have bulldozed over entire underwater habitats. The oyster habitat has been completely destroyed in many areas from the use of the oyster patent tong and sediment buildup draining from farm runoff.
The word “shipping” refers to the activity of moving cargo with ships in between seaports. Wind-powered ships exist, but more often ships are powered by steam turbine plants or diesel engines. Naval ships are usually responsible for transporting most of trade from one country to another and are called merchant navies. The various types of ships include container ships, tankers, crude oil ships, product ships, chemical ships, bulk carriers, cable layers, general cargo ships, offshore supply vessels, dynamically-positioned ships, ferries, gas and car carriers, tugboats, barges and dredgers.
In theory, shipping can have a low impact on the environment. It is safe and profitable for economies around the world. However, serious problems occur with the shipping of oil, dumping of waste water into the ocean, chemical accidents at sea, and the inevitable air and water pollution occuring when modern day engines are used. Ships release air pollutants in the form of sulphur dioxide, nitrogen oxides, carbon dioxide, hydrocarbons and carbon monoxide. Chemicals dumped in the ocean from ships include chemicals from the ship itself, cleaning chemicals for machine parts, and cleaning supplies for living quarters. Large amounts of chemicals are often spilled into the ocean and sewage is not always treated properly or treated at all. Alien species riding in the ballast water of ships arrive in great numbers to crash native ecosystems and garbage is dumped over the side of many vessels. Dangerous industrial waste and harmful substances like halogenated hydrocarbons, water treatment chemicals, and anti-fouling paints are also dumped frequently. Ships and other watercraft with engines disturb the natural environment with loud noises, large waves, frequently striking and killing animals like manatees and dolphins.
Tourism is the fastest growing division of the world economy and is responsible for more than 200 million jobs all over the world. In the US alone, tourism resulted in an economic gain of 478 billion dollars. With 700 million people traveling to another country in the year 2000, tourism is in the top five economic contributors to 83% of all countries and the most important economy for 38% of countries. The tourism industry is based on natural resources present in each country and usually negatively affect ecosystems because it is often left unmanaged. However, sustainable tourism can actually promote conservation of the environment.
Dive boat with recreational divers, Key Largo, Florida. © Wolcott Henry 2001
The negative effects of tourism originate from the development of coastal habitats and the annihilation of entire ecosystems like mangroves, coral reefs, wetlands and estuaries. Garbage and sewage generated by visitors can add to the already existing solid waste and garbage disposal issues present in many communities. Often visitors produce more waste than locals, and much of it ends up as untreated sewage dumped in the ocean. The ecosystem must cope with eutrophication, or the loss of oxygen in the water due to excessive algal bloom, as well as disease epidemics. Sewage can be used as reclaimed water to treat lawns so that fertilizers and pesticides do not seep into the ocean.
Other problems with tourism include the overexploitation of local seafood, the destruction of local habitats through careless scuba diving or snorkeling and the dropping of anchors on underwater features. Ecotourism and cultural tourism are a new trend that favors low impact tourism and fosters a respect for local cultures and ecosystems.
Humans began to mine the ocean floor for diamonds, gold, silver, metal ores like manganese nodules and gravel mines in the 1950’s when the company Tidal Diamonds was established by Sam Collins. Diamonds are found in greater number and quality in the ocean than on land, but are much harder to mine. When diamonds are mined, the ocean floor is dredged to bring it up to the boat and sift through the sediment for valuable gems. The process is difficult as sediment is not easy to bring up to the surface, but will probably become a huge industry once technology evolves to solve the logistical problem.
Metal compounds, gravels, sands and gas hydrates are also mined in the ocean. Mining of manganese nodules containing nickel, copper and cobalt began in the 1960’s and soon after it was discovered that Papua New Guinea was one of the few places where nodules were located in shallow waters rather than deep waters. Although manganese nodules could be found in shallow waters in significant quantities, the expense of bringing the ore up to the surface proved to be expensive. Sands and gravels are often mined for in the United States and are used to protect beaches and reduce the effects of erosion.
Mining the ocean can be devastating to the natural ecosystems. Dredging of any kind pulls up the ocean floor resulting in widespread destruction of marine animal habitats, as well as wiping out vast numbers of fishes and invertebrates. When the ocean floor is mined, a cloud of sediment rises up in the water, interfering with photosynthetic processes of phytoplankton and other marine life, in addition to introducing previously benign heavy metals into the food chain. As minerals found on land are exploited and used up, mining of the ocean floor will increase.
The ocean is an integral component of the world’s climate due to its capacity to collect, drive and mix water, heat, and carbon dioxide. The ocean can hold and circulate more water, heat and carbon dioxide than the atmosphere although the components of the Earth’s climate are constantly exchanged. Because the ocean can store so much heat, seasons occur later than they would and air above the ocean is warmed. Heat energy stored in the ocean in one season will affect the climate almost an entire season later. The ocean and the atmosphere work together to form complex weather phenomena like the North Atlantic Oscillation and El Niño. The many chemical cycles occurring between the ocean and the atmosphere also influence the climate by controlling the amount of radiation released into ecosystems and our environment.
The atmosphere directly above the ocean does not absorb much heat by itself, so in order for it to warm up, the temperature of the ocean has to rise first. The two other ways for the atmosphere to warm near the ocean are by reflection of light off of the surface of the ocean or by the evaporation of water from the ocean surface. The temperature of the ocean controls the climate in the lower part of the atmosphere, so for most areas of the Earth the ocean temperature is responsible for the air temperature.
The main forms of climate buffering by the ocean are by the transport of heat through ocean currents traveling across huge basins. Areas like the tropics end up being cooled and higher latitudes are warmed by this effect. Air temperatures worldwide are regulated by the circulation of heat by the oceans. The ocean stores heat in the upper two meters of the photic zone. This is possible because seawater has a very high density and specific heat and can store vast quantities of energy in the form of heat. The ocean can then buffer changes in temperature by storing heat and releasing heat. Evaporation cools ocean water which cools the atmosphere. It is most noticeable near the equator and the effect decreases closer to the poles.
Gases in the atmosphere like carbon, nitrogen, sulfur and oxygen are dissolved through the water cycle. The gases that are now crucial to all ecosystems and biological processes originally came from the inside layers of the earth during the period when the earth was first formed. The rate of flow for oxygen as well as other gases is controlled by biological processes, especially metabolism of organisms like prokaryotes and bacteria. Prokaryotes have been around since the beginning of the Earth, have evolved to be able to use chemical energy to create organic matter and are capable of both reducing and oxidizing inorganic compounds. Bacteria that can reduce inorganic compounds are anaerobic and those that oxidize inorganic compounds are aerobic. Aerobic bacteria release oxygen as a by-product of photosynthesis.
Approximately two billion years ago, aerobic bacteria began producing oxygen which gradually filled up all of the oxygen reservoirs in the environment. Once these “sinks” were filled, molecular oxygen began to build in the atmosphere, creating an environment favorable for other life to inhabit the Earth. Sinks included reduced iron ions and hydrogen sulfide gas. Evidence of this process can be found in the banded iron formations created when iron minerals were precipitated. The oxygen started to fill the atmosphere up and new bacteria evolved that could use oxygen to oxidize both inorganic and organic compounds. Bacteria that were accustomed to an oxygen-poor atmosphere only survived in anaerobic environments like sewage, swamps, and in the sediments of both marine and freshwater areas.
Phytoplankton account for possibly 90% of the world’s oxygen production because water covers about 70% of the Earth and phytoplankton are abundant in the photic zone of the surface layers. Some of the oxygen produced by phytoplankton is absorbed by the ocean, but most flows into the atmosphere where it becomes available for oxygen dependent life forms.
U.S. Global Change Research Information Office – How Bountiful are Ocean Fisheries? by Brian J. Rothschild
United Nations Atlas of the Oceans
GESAMP on environmental aspects of tourism ‘The world’s biggest industry ever — but poorly managed for the environment’
Underwater Mining Companies – Wealth Daily
WHOI : Oceanus : Ocean Resources
Department of Earth and Environmental Sciences at Columbia University
Global Marine Oil Pollution Information Gateway • Facts • SHIPPING – NOT JUST OIL POLLUTION