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| | | Pelagic Ecosystems |
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| | Pelagic, or Open Ocean, Ecosystems | | |  Pelagic means the open ocean, rather than the shores and estuaries. These ecosystems lie beyond the outer border of the littoral zone and above the abyssal zone, in a zone to which light penetrates. Pelagic organisms usually lead a free-floating existence at or near the surface of the ocean, away from the coast. Examples range from microscopic phytoplankton to dolphins of the open ocean. One-third of the fish catch of the world is small pelagics. Two large pelagic ecosystems have been chosen below: the Eastern Tropical Pacific and the California Current.
Pelagic fish schooling. Photo: Scripps Institution of Oceanography | | | | The Tuna-Dolphin Problem in the Eastern Tropical Pacific | | |  The Eastern Tropical Pacific (ETP) provides a case study of the effects of pelagic ecosystem disturbance and attempted solutions. In the ETP, yellowfin tuna, Thunnus albacares, are associated with dolphins, Stenella spp . Since the late 1950s, tuna purse-seiners have set on dolphins to catch tuna, with an incidental mortality of dolphins that attracted world wide attention by the 1960s. Since 1986, when annual mortalities were estimated at 133 000, there has been a steady reduction in by-catch of dolphins so that fewer than 1 500 individuals were killed in 2002 from a population of over 10 million (see graphs). The reduction in by-catch has been achieved by several methods including international agreements, national legislation, innovative management, improvements in fishing technology, and fishers education programs. The Inter-American Tropical Tuna Commission (IATTC), jointly with some participating nations, runs an observer program to produce mortality estimates, to identify causes of bycatch, to monitor compliance with the programs, and to collect other scientific data.
Based on Hall, M.A., Alverson, D.L. and Metuzals, K.I, 2000, By-catch: Problems and Solutions in Sheppard, C. (ed) Seas at the Millennium: An Environmental Evaluation. Elsevier Science Ltd. With permission.
Eastern spinner dolphins, Stenella longirostris orientalis, in the Eastern Tropical Pacific. Photo: NOAA Fisheries | | | | California Current | | |  The California Current is an example of a large pelagic ecosystem which has been studied by CalCOFI participants since 1949 .The North Pacific Current feeds into the Alaska Current and the California Current which moves south along the coastline of North America . It then flows far offshore in the Southern California Bight before touching the mainland again in Baja California, Mexico. The main features of the California Current are: - Decadal variation as well as variation during El Niño and La Niña events. See more
- High biological productivity (>250 mg C/sq m/day)
- Characterized inshore by an extensive kelp ecosystem. Watch the video
- Important Californian sardine fishery which collapsed in the 1940s and 50s and has now recovered
- Ongoing fishery research for squid, groundfish, tuna and salmonids
- Historic overharvesting of great whales may be partly responsible for changes to the ecosystem
- Large populations of sea birds
- Rapid urbanization in places has led to loss of habitat and discharge of pollutants
- Marine protected areas have been established.
Fifty years of research on the California Current ecosystem. Photo: CalCOFI. | | | | |
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