Marine Life Decline

The air we breathe, life-saving medicines and a critical supply of food for our population all come from marine life. The ocean takes care of us and now needs our help.

Did you know?

  • Tiny phytoplankton in the ocean produce more oxygen than all the forests and plants on Earth.
  • Plant-like animals, called Bugula neritina, are the source of a family of chemical compounds currently being studied to treat a variety of cancers.
  • An estimated 1 billion people worldwide depend upon fish and shellfish as their main source of protein.

Take Action Against Marine Life Decline

Marine life is being threatened by a variety of human activities that result in habitat loss, unsustainable fishing and water pollution. The good news is that there are steps we can take every day to help marine life recover and thrive.

  • Make smart seafood choices. Buy seafood that you know is being harvested sustainably and doesn’t contain heavy metals, such as mercury, that pose a risk to human health. Consult the Monterey Bay Aquarium’s seafood guide that identifies the best choices to make to help preserve these fish stocks for future generations. Apps are also available from MBAqua regarding sustainable seafood.
  • Take shorter showers and install low-flow shower fittings like EPA’s Water Sense products.
  • Don’t purchase items that exploit marine resources unnecessarily such as coral jewelry and supplements such as coral calcium and shark cartilage. The nutrients these supplements allegedly provide are easily obtained from other food sources such as green leafy vegetables.
  • Join a marine mammal rescue center and volunteer your time.
  • Take the pledge. Return the favor by taking our pledge to protect the ocean.
  • Click here for more ways you can take action against marine life decline.

Causes and Implications of Marine Life Decline


Scientists report that 90% of large fish, such as tuna and swordfish, have been removed from the ocean through fishing . Experts estimate that 25 to 30% of the world’s major fish stocks are overexploited . Despite the U.S. having strong fishery laws, of the 267 major fish stocks, roughly 17% are not being fished sustainably . Inadequate information for another 30% of the major fish stocks and virtually all of the minor fish stocks makes it difficult to manage these fisheries sustainably.

Worldwide, for every four pounds of fish caught, more than a pound of other animals are also caught unintentionally. Many animals such as sea turtles and sharks are inadvertently caught in fishing gear. Often the unintended catch, or “by catch”, is killed in the nets or simply thrown overboard to die. For some types of gear, like shrimp trawls, the ratio is even worse: For every pound of shrimp, four or more pounds of unwanted animals are caught and discarded.

You can help protect fish populations and marine habitat by choosing only sustainably caught seafood. The Monterey Bay Aquarium has developed a guide to help consumers choose sustainable seafood alternatives. Consult their Web site for an interactive guide to choosing sustainable seafood or download their wallet-size guide. In 2008, the aquarium also published a guide to choosing sustainable sushi.

Another resource to help you choose sustainable seafood is the National Marine Fisheries Service’s Fish Watch website. For detailed information on the state of the world’s fisheries, check out the United Nations Food and Agriculture Organization’s biennial State of the World Fisheries and Aquaculture report located at the bottom of its webpage:

Coastal Development Threats to Salmon and Steelhead in California

Human development has a number of different effects on the marine environment. Population pressures can negatively affect marine life by destroying habitats, increasing pollution, and contributing to global climate change. Salmon and steelhead trout are anadromous fish, meaning that they live in fresh and ocean water at various stages of life. Salmon and steelhead hatch in small freshwater streams and then migrate downstream to estuaries to mature. They then spend two to six years in the open ocean where they mature, eventually returning to the same streams where they were hatched to spawn and ultimately die.

California Department of Fish and Wildlife release a chinook salmon into Butte Creek.
Photo courtesy

Twenty-eight species of salmonids and steelhead trout have been listed as either threatened or endangered on the West Coast. Dams, water diversions, habitat loss, water pollution, and changing ocean conditions all contribute to the declining of California salmonid species. Salmon populations may improve if more water is available in our streams and rivers. Do your part by reducing the amount of water that you use.


Diseases interact with other pressures on marine species and contribute to marine life decline. The southern sea otter (Enhydra lutris nereis) was decimated in the 1700’s and 1800’s by hunters seeking their pelts. The California population has grown from a group of about 50 survivors off Big Sur in 1938 to just over 2,700 today. Sea otters still face serious risks, often from disease. Recent studies show Toxoplasma gondii, a water- borne pathogen that is hosted by cats and spread through their feces, is a major cause of sea otter mortality in California by causing brain damage and seizures. You can help by properly disposing of kitty litter in trash receptacles instead of flushing it down the toilet. Microcystin, a product of blue-green algae, is another fatal toxin that can be a byproduct of algae blooms. Nutrient runoff and other land-based pollution can increase the number of harmful algae blooms and toxic events.

Sea otters. Photo: Madralynn Haye

Invasive Species

Invasive species are organisms that have been brought by humans (either intentionally or not) to areas where they do not historically occur, and that cause harm to the environment, create economic costs, or create risks to public health. Some invasive species cause harm by competing with, feeding on, or parasitizing native species. As of 2005, of the species listed as threatened or endangered all over the world, 42% were listed because of negative interactions with invasive species (like competition). Once invasive species arrive in a new location, they may be difficult or impossible to eradicate.

In California, the invasive overbite clam was introduced from Asia and has been linked to the decline of endangered delta smelt. The delta smelt is recognized as an important indicator of ecosystem health, and is also threatened by water pollution. Researchers believe that the overbite clam removes key microorganisms from the water, which form the basis of marine food chains. Without these microorganisms, smelt and other fish species starve.

Delta smelt, which are threatened by the invasive overbite clam.
Photo: Department of Water Resources photo library

Another invasive species that has caused marine life decline is the North American comb jelly, introduced to the Black Sea from North American waters. This invasive species has contributed to declines in important commercial fish stocks in the Black Sea by competing with native fish for food and consuming fish eggs.

Marine Protected Areas

As of December 2012, California has established a network of 124 marine protected areas (MPAs) that cover approximately 16% of state waters. This historic achievement used strong science and input from stakeholders from across the state to protect our ocean for future generations. MPAs address some reasons for the decline in marine life populations and the health of ocean ecosystems by designating where some human activities are prohibited, such as oil drilling or fishing, in order to protect the ecosystems and marine life around that area. Marine reserves, sometimes known as “no-take” areas, are one type of MPA in which the extraction of marine resources is prohibited and comprise 9.4% of California’s state waters.

You can find information about the different types of MPAs, their location, and the history of how they were developed at the California Department of Fish and Wildlife’s website: Learn about your local MPAs and go for a visit!

Interpretive panel located at Ano Nuevo State Marine Conservation Area and Greyhound Rock State Marine Conservation Area along the Central Coast of California (

California is also home to five National Marine Sanctuaries off the West Coast, which boast 36 species of marine mammals, including whales, dolphins, seals, sea lions and sea otters. Some of these species of marine mammals and seabirds are listed as endangered under the federal Endangered Species Act (ESA), including the Short-tailed Albatross, Marbled Murrelet, California Clapper Rail, southern sea otter, Steller sea lion and several species of whale.

Photo: Humpback whales. Photo: Silke Stuckenbrock

For more information on the critters that live off California’s coast, please visit the West Coast Field Guide of the National Marine Sanctuaries.

For more information regarding MPAs, please visit our new MPA web page dedicated to this issue. MPAs will not protect against all types of human impacts affecting the ocean. They are a tool that should be used to complement other marine management policies, such as fishing limits, gear restrictions and regulations on pollutant discharges into the ocean.

Many resources are available on the web for information on marine invasive species. Here is a good place to start:

Laws and Government Actions that Combat Marine Life Decline

Clean Water Act – Administered by the EPA, the Clean Water Act is federal government’s primary tool to governing pollution. It can be found here: http://

Marine Protected Areas (MPAs) – MPAs are areas where some causes of marine life decline are limited or banned. Information on MPAs can be found on our MAP page: /threats/marine-life-decline/marine-protected-areas/

Marine Mammal Protection Act – The Marine Mammal Protection Act bans any take of marine mammals in US waters and also bars US citizens in international waters. More information can be found here: