Fishie Friends


A Study of the effects of global warming on fish

Who we are:

Hello! You have reached the webpage of Barbi Evans and Sarah Graham, we can't come to the server right now, so if you could please leave a message at the beep… Just kidding! This is our webpage all about fish and what global warming is doing to them. We are students in a chemistry class at Hilliard Davidson High School in Ohio working in collaboration with a statistics class at Bellarmine Prep School in Washington as a part of a project called Earth On Fire. Earth On Fire is a research project of aspects of global warming and their effects on earth.


 The basic facts

 The effects of rising sea levels and increasing water temperature

 The effects of wetland loss, changes in ocean currents, and changes in water composition on fish

 Previous research and statistics on fish



 The basic facts

Fish are a vital part of the ecosystem.

Earth's waters are affected by global warming through temperature changes, melting of polar ice caps, etc.

It has been predicted that global warming may be one of the most important factors affecting fisheries.

Fish populations have declined about 5% per year since 1986.

Since there is still a debate among some scientists as to whether or not global warming exists, researchers cannot say with absolute certainty, that global warming is the cause of biological changes in the earth's water but they contend that current impacts and effects are consistent with global warming, and that if indeed global warming is occurring, what would be expected to happen would look very similar.

Currently, 20 to 40% of the carbon dioxide added by humans to the atmosphere is believed to be absorbed in the oceans, most of it by plankton.

El Nino was first noticed because of fish. Back in the 1500's, fishermen along the Pacific coast of northern Peru started noticing changes in fish abundance and species. Millions of sea birds washed up on the beaches as their prey, anchovies, disappeared. Gathers of the bird feces for fertilizer purposes also fell on hard times, as the nutrient rich droppings were no longer on the beaches. Sailors also played a role as they observed changes in coastal currents ad rainfall, as did farmers who noticed torrential rains in the typically arid region.

An anchovy and sea birds


Most species of fish tolerate, and many require, winter cooling and summer warming by tens of degrees.

One-fifth of global animal protein intake comes from fish.

Rising sea levels

If sea levels continue to rise, wetlands are lost, a predicted up to 2.5 million acres by 2100 in the U.S. alone. In the near future, fish production could rise, due to the decomposing of marshes and the nutrients from the soil being added to the water.

Another impact of sea level rise would be the inland penetration of saltwater into rivers, bays, wetlands, and aquifers, which would be harmful to some aquatic plants and animals.

Rising sea level would increase water pollution by lifting the water table in low lying coastal areas, releasing contaminants from dump sites and viruses and bacteria from septic systems into coastal waters and waterways. Such contaminants would entire estuarine and inshore food chains and pose a hazard for human consumers.

Graph of sea levels

 Increases in water temperature

Arctic Temperature Trends (above picture)

Arctic temperature trends from 1961-1990. Red areas represent hot spots where temperatures have warmed over the past 30 years. Alaska is one of those hot spots. Data collection and analysis by John Walsh. Image model by Amanda Lynch.

Species unable to move or adapt to temperature changes may suffer population declines or extinction. However, warmer water results in faster growth and maturation among fish, lower winter mortality rates, and expanded habitats. Negative factors include increased summer anoxia, increased demand for food due to higher metabolic rates, and reduced habitat for cold water species. Also, as ocean temperatures increase, coral polyps lose the symbiotic algae inside them, causing them to die, which threatens coral reefs, an important aspect of the ocean environment.

This development cycle of fish maybe sped up if water temperatures increase.

As ocean waters warm, the growth of algal blooms increases. These are already responsible for an estimated 25% of the atmospheric sulfur that causes acid rain. Acid rain causes the acidification of spawning ponds and streams. Algal blooms sometimes develop into "toxic tides" or "red tides" which poison marine life. At the end of the bloom's cycle, decaying algae exhaust the water's oxygen. Plants starve, fish suffocate. Also associated with marine algal blooms is an increased risk of the disease cholera for humans.

An increase in temperatures would change the timing of ecological events, such as the spring plankton outburst, influencing the match or mismatch of larvae with their food supply and their predators.

  Temperatures are progressively increasing.

Warmer water may also enable fish in cold ocean waters to grow more rapidly, but some bodies of water may become too warm for the fish that currently inhabit that area.

Most species of fish tolerate, and many require, winter cooling and summer warming by tens of degrees. As the waters warm, the fish will have to retreat to cooler waters. In larger rivers, this can be solved by swimming upstream, or in waters such as the Great Lakes, by swimming to greater depths. Unfortunately for smaller lakes and rivers flowing east or west, they do not cover as wide of a range of temperatures, and warmer temperatures could make these waters completely uninhabitable for the fish that live in them. Salmon and a few other fish that migrate between inland rivers and the ocean could move to more northern waters, but most freshwater fish cannot tolerate salt water and will never make this journey on their own. People would be necessary to transport these fish to colder waters.


Scientists are not yet certain whether the overall level of fishing will increase or decrease in these waters. warmer temperatures often promote biological activity, biologists at these fisheries generally believe that the increase in warm water species will offset the decline of cold water species. However the total amount of fish that can be caught is not the only important consideration.


Warming would affect marine species in shallow water areas before deep oceanic species. Soft shelled clams could disappear from Chesapeake Bay if there is substantial warming. Warm water exotic species may invade large lakes , such as the Great Lakes, where invasion routes are available. Alterations in seasonal climate patterns could produce potentially greater yields of certain Great Lakes fisheries, whereas others could collapse.

Warm water fishes and other animals have migrated northward and are now common in places that they once shunned.

Warmer temperatures are likely to enhance ocean fishing. Biological activity is greater at higher temperatures and reproduction begins at an earlier age. More food is available and the fish grow faster. However, this increase will be offset by a decline in upwelling, which is the upward flow of deep ocean water to the surface layer. This water is rich in nutrients which feed aquatic plants and plankton, which are the basis of the fish food cycle. Also, global warming may increase events such as El Nino, which would increase fluctuation in ocean water temperature, increasing the effects on ocean fisheries.

Warming of water in bays near the Gulf of Mexico could cause fish to swim out to the Gulf of Mexico, making them more vulnerable to predators. Many fish will migrate north as waters warm, but some species may not be able to adjust to moving to cooler estuaries.

 Commercial fishing boats

 Wetland loss

Louisiana has the greatest potential loss of wetlands in the United States, and it is already losing 50 square miles of wetlands per year to the Gulf of Mexico. This loss is caused by the rising sea levels there. Even a 50 cm. rise in sea level could drown about one third of the coastal wetlands in the US.

Many fish use wetlands as "nurseries" for the care and habitat of their offspring. The reduction of wetland areas would directly impact the fish's ecosystem by forcing the fish elsewhere and into less adequate areas. If fish cannot reproduce properly, this would have a huge effect not only on them, but on the fishing industries.

Most of the reproduction occurs within 50-100 feet of the open water, because the fish find it more difficult to do so farther away from shore.

With a one and a half foot sea level rise by 2100, more than 2.5 million acres of wetlands could be lost in the United States. As the marshes decompose, there could be a rise in fish production, due to increased availability of nutrients, but the overall impact on fisheries will be negative, as the fish lose their habitats. The brown shrimp catch in US Gulf Coast could fall 25% with a 10 inch rise in sea level and a 14 inch rise could cause the loss of 40% of the extensive mud flats in Puget Sound, an important habitat.

Loss of wetlands could diminish habitat and alter the availability of food for some fish species.

Species that either reproduce in coastal wetlands or spend their entire lifetimes in estuaries, will be the most vulnerable to the impacts on wetlands


 Changes in Ocean Currents

If the temperature of the ocean water changes significantly enough to alter the water patterns, through atmospheric changes or water cycles, it could have a devastating effect on the underwater ecosystem. Local species could be displaced and an entirely different ecosystem may be the result. Circulation changes would likely effect species such as scallops and cod, which rely on certain currents in their life cycle.

Cod fish

Changes in ocean current could lead to changes in fish population location and abundance and the loss of certain fish populations. Changes in local currents and upwellings would affect total fish production and species dominance.


 Water Composition

The chemical composition of the water could change, as oxygen levels decrease, and pollution and salinity levels increase. The rising sea level will lead to the intrusion of salt water into estuaries, these higher salt conditions will cause species who cannot survive in the increased salinity to perish.

In rivers, low oxygen levels at low flows can severely limit fish production. One study estimated that the majority of southeastern rivers will have oxygen concentration below the level necessary to support most fish, if there is the 7 degrees of warming that could eventually occur.


 Previous research and statistics on fish

Extensive research has been done on sea surface temperatures off the coast of California, some sites have recorded temperature readings from as early as 1916, resulting in some of the most thorough ocean thermal readings in the world. After analysis of the data taken from 17 sites along the west coast in California and extending up to Oregon, a warming trend has been spotted. In 1977, sea surface temperature suddenly jumped up 2 degrees, and the average has remained about 2 degrees warmer than the previous averages. The study also reports that the rise in temperature is not just in California, but in the whole eastern half of the northern Pacific and the Gulf of Alaska. The warmer waters are linked to declines in some temperate species and to the wholesale migration into northern waters of fish and animals that normally live in the tropics. Warm surface waters are blocking the upwelling of nutrient-rich cold waters and as a result the warmer waters are lacking some of the chemicals that support plankton, which is at the base of the aquatic food chain.

Mild winters in the Wadden Sea led to changes such as higher species richness and abundance. However, greater weight loss in bivalves during the winter and low reproductive success in the summer were also observed. These effects represent what happens when the water environment is warmer and for longer periods of time.

Increased salinity, which is the presence of salt in fresh water, due to rising sea levels, has already been cited as a contributing factor to reduced oyster harvests in Delaware and Chesapeake Bays, and for converting cypress swamps in Louisiana to open lakes.

Another report's analysis, using data obtained by satellites, determined that the surface temperature of the Earth's oceans has risen sharply in the past six years. An observed temperature rise of about 1 degree from 1982 to 1988 is twice as high as scientists had previously believed the surface of the seas to be warming. The report did state that it is still to early to determine whether the warming was due to an unusual variation in ocean conditions of if it resulted from a forced rise in the earth's overall temperature due to the greenhouse effect and global warming.

The results of a 1995 EPA study suggest that the overall diversity of fishing in US rivers and streams is likely to decline. In a state where there were 14 cold and cool water species and the water temperature warmed two degrees, all but one would be forced to leave. Also, 7 out of 10 warm water species would find the water too hot. With the 7 degree warming that could eventually occur, one study estimated that the majority of southeastern rivers will have oxygen concentrations below the level necessary to support most fish.

If global warming leads to an increase in water pollution, fish populations could also decline.

New Zealand researchers from the Ministry of Agriculture and Fisheries have correlated 27 years of sea temperature data against the age structures of fish populations. They found a clear relationship between increased temperatures and increased numbers of snapper and southern blue whiting, which are important commercial fish. However, hoki, another important commercial species, there was a decline in numbers as the temperatures increased. Tuna stocks appeared to be pushed south into cooler water. This study shows that global warming's effect on the temperature of the water will have a different impact on the different kinds of fish. It will increase numbers of some, decrease others, and cause others to migrate to cooler waters.


Since 1951, the biomass of zoo plankton in the waters off the coast of southern California has decreased by 70%. During that same period the surface layer of the ocean warmed by more than 1.5 degrees Celsius in some places, and the temperature differences between the ocean layers increased. This caused less of the deep waters, which are full of important nutrients, to upwell into the surface waters, resulting in less inorganic nutrients for new biological production and therefore, supported a smaller zoo plankton population. The authors of this study say that a global temperature rise of 1 to 2 degrees Celsius in the next 40 years and an increase of stratification globally, could cause devastating biological impacts.

Research analyses has shown a greet decline in the landings of commercial fish in California since the 1970's. The anchovy has ceased to exist as a commercial species. Populations of a bird that feeds on zoo plankton, called the sooty shearwater, has shown a 90% decline in population.

The greenhouse effect can cause increased ultraviolet radiation, and a Texas A&M oceanographer has demonstrated that a 10% rise in ultraviolet radiation virtually annihilates the photo plankton, which forms the basis of the food chain feeding fish in the southern latitudes, among other marine animals.


1. Pete Johatgen at the Aquarium at Columbus Zoo. 645-3550

Has global warming effected saltwater fish any different than freshwater


No , it has had a overall bad effect on all fish.

Is temperature is important to fish?

Yes because fish are cold blooded and depend on the water temperature.

Is sunlight a necessity to fish?

No and yes, it really depends on the fish.

General Comments:

Global warming has effected the food web beginning at the base with plankton. Which all fish eat and so on.


2. Jim Reynolds at Jones Fish and Lake Management. 1-800-733-0180

Has global warming effected saltwater fish any different than freshwater fish?

Warm water has increased the amount of vegetation in fresh water ponds and other bodies of

fresh water. It has also produced smaller fish compared to normal.

Is temperature is important to fish?

Yes because they are cold blooded. When warmer water comes around the metabolic activity

is increased.

Is flooding effecting fish?

Yes it moves them to foreign places faster.

General Comments:



3. Gary at Seafood International. 527-7280

Have you seen at decline in the fish you normally receive in?


What have you seen?

The migration patterns of the fish have changed. Partly due to El Nino.

Warmer waters are spreading to northern water therefore changing the patterns. In the past salmon season, they were found off the coast of Alaska far from the normal California.


4. Doug at Bob the Fish Guy. 228-4903

Have you seen at decline in the fish you normal receive in?


What have you seen?

Migration patterns. [The] Sea's warming up so the fish swim deeper, making it

harder to catch them.


5. Bandy’s Pay Lake 235-5191

Has global warming effected saltwater fish any different than freshwater fish?

No. I really do not have any information on that subject.

Is temperature is important to fish?

I do not know.

General Comments:



6. Gary at OutBack Breeders. 279-5166

Has global warming effected saltwater fish any different than freshwater


No comment.

General Comments:

I have no comments on the subject.



Thank you for visiting our page! Feel free to email us with any comments!

Barbi Evans

Sarah Graham