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Regional Overview & Fact Sheet
The Gulf of California (also known as the Sea of Cortez or Mar de Cortés) is a semi-enclosed sea known for its exceptionally high levels of biodiversity and rates of primary productivity due to a combination of its topography, warm climate, and upwelling systems. It is also home to the endemic (and critically endangered) vaquita porpoise—one of the most rare marine mammals in the world—and the large, corvina-like totoaba. Upstream damming and diversion leading to decrease of fresh water input from the Colorado River has drastically changed the ecological conditions of the Upper Gulf—now a hypersaline estuarine system important for fish reproduction. Fishing, especially with gillnets, is a key activity for coastal communities of the region. However, decreases in abundance of several species of fish and changes in gear types have caused much concern. Waters off the Mexican states of Nayarit, Sinaloa, Sonora, Baja California and Baja California Sur are included in this region. The southern border of this region is generally considered, oceanographically and faunally, to stretch from Cabo Corrientes (at the northwestern tip of the state of Jalisco) on the mainland to Cabo San Lucas at the tip of the Baja California peninsula (Brusca et al. 2005).
The region includes five B2B Marine Priority Conservation Areas (PCAs): PCA 24-Corredor Los Cabos/Loreto; PCA 25-Alto Golfo de California; PCA 26-Grandes Islas del Golfo de Califonia/Bahía de Los Ángeles; PCA 27-Humedales de Sonora, Sinaloa y Nayarit/Bahía de Banderas; and PCA 28-Islas Marías (Morgan et al. 2005).
Fact Sheet
A semi-enclosed sea.
13–21°C (winter), 28–31°C (summer)
Upwelling on the east coast during winter and spring and on the west coast during the summer. Large and complex temporal eddies can occur year round, however.
Spreading rift system; very wide continental shelf in the northern Gulf, medium width shelf with abundant coastal lagoons in its eastern portion and island studded narrow shelf in the western Gulf.
shelf (roughly 0–200 m): 32%
slope (roughly 200–2,500/3,000 m): 54%
abyssal plain (roughly 3,000+ m): 14%
Mixed sands, silt, mud, rocky reefs and rhodolith beds.
Coastal lagoons, deltaic systems, mangroves, seagrass beds, rocky shores, sandy beaches, coral reefs, hydrothermal vents and rhodolith beds.
High productivity ecosystem (>300 gCm-2yr-1). Is one of the most productive marine ecosystems in the world. The northern Gulf has two main natural fertilization mechanisms: tidal mixing around the large islands and the wind-induced upwelling along the eastern central gulf.
About 10 percent of the Gulf of California fish fauna is endemic—80 of the 821 bony fish and 4 out of the 90 cartilaginous fish species are endemic (L. T. Findley, pers. comm.) These include totoaba, Gulf weakfish, bigeye croaker, Cortez clingfish, Sonora blenny, whitetip smoothhound, Cortez stingray, Cortez skate, Gulf grunion, delta silverside, leopard grouper, sawtail grouper, Cortez damselfish, Gulf signal blenny, Cortez clingfish, slow goby, Guaymas goby, and shortjaw mudsucker, among others. Mammals include the vaquita porpoise, and the Gulf fishing bat.
The Gulf contains a so-called “disjunct” segment of its fish fauna fauna, which, although not strictly categorized as endemics, are biogeographically and evolutionarily interesting: several species occurring in the northern part of the sea are absent from its southern (more tropical) waters, but appear again in the cooler waters on the outer coast of the Baja California peninsula and extend northward to southern and central California, or even farther. Examples of such disjunctly distributed fishes are: leopard shark, bat ray, giant sea bass, spotted sand bass, California scorpionfish, Mexican rockfish, white sea bass, sargo, pink surfperch, California sheephead, rock wrasse, bay blenny, bluebanded goby, longjaw mudsucker, shadow goby, fantail sole, and diamond turbot, among others. The origins and relationships of this disjunct fauna have been of long-term interest to biologists and have been the subject of some recent studies (e.g., Bernardi et al. 2003, Jacobs et al. 2004).
Minke, sei, Bryde’s, blue, fin, gray, humpback and sperm whales; vaquita (critically endangered); totoaba; Gulf corvina; several species of large groupers (Mycteroperca spp. and Epinephelus spp.); several species of large snappers (Lutjanus spp.); some species of snooks (Centropomus spp.); and loggerhead, East Pacific green, leatherback and olive ridley sea turtles. Species such as silky shark, dusky shark, blacktip shark, lemon shark, Pacific sharpnose shark, broadnose sevengill shark, Pacific angel shark, several species of hound sharks (Mustelus spp.), scalloped hammerhead and smooth hammerhead sharks, diamond stingray, bat ray, longnose eagle ray, golden cownose ray, and California butterfly ray are presenting signs of overeploitation from artisanal shark and ray fisheries targeted at immature individuals. Offshore fisheries impact species with low fertility rate such as the pelagic thresher, bigeye thresher, great white shark and shortfin mako. Other species of concern include whale shark, white shark, small- and largetooth sawfish, and mantas (giant manta, smoothtail mobula, pygmy devil ray, and sicklefin devil ray).
A red algae (Ishige foliacea), Pacific giant oyster, and threadfin shad. Although there are not yet any documented impacts from introduced species in marine habitats in the Gulf of California, the introduction of domestic animals and pests to the Gulf´s islands have eliminated many birds, rodents and lizards from those ecosystems (Brusca et al. 2004).
Coastal lagoons, estuaries, esteros, deltaic systems, mangroves, seagrass beds, coral communities and (few) coral and (many) rocky reefs, rhodolith beds and hydrothermal vents; an important oceanic recruitment area for billfish species is located between Los Cabos and Puerto Vallarta; the Gulf of California contributes to approximately 50 percent of Mexico’s national fisheries production by volume.
Fisheries production has declined over the last decade. During President Fox’s Administration (2002–2006) a major development project (Escalera Nautica) was set in motion in order to increase coastal and maritime tourism to the Mexican Pacific, especially in the Gulf of California. Mega-resort/tourism/vacation properties developments, including new marinas for increased recreational watercraft, which are principally aimed at USA and Canadian residents and investors, are rapidly proceeding with little ecological oversight (e.g., Cabo San Lucas/Los Cabos, La Paz, Loreto, San Felipe, Puerto Vallarta/Nuevo Vallarta, Mazatlán, Guaymas/San Carlos, Puerto Peñasco).
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Physical and Oceanographic Setting
The Gulf of California is a long, narrow, semi-enclosed sea (approximately 1,000 km long and 150 km wide, spanning over nine degrees of latitude). It is bordered by the Mexican coastal states of Sonora, Sinaloa, and Nayarit to the east, the two states of the Baja California peninsula to the west, and the Colorado River delta (Sonora/Baja California) to the north. It is an exclusively Mexican sea, once influenced by a US watershed (the Colorado River). Deep basins (greater than 3,000 m at the entrance to the Gulf), steep slopes, both narrow and wide continental shelves, numerous islands, sandy bays and beaches, and coastal lagoons (mostly hypersaline) characterize the region. The Guaymas Basin has tectonic activity and hydrothermal vents, and supports specialized biotic communities that are based on the use of hydrogen sulfide instead of sunlight for energy. The Gulf of California’s shores vary from silty to sandy to rocky, with most of medium-size sands.
Although it is a west coast region, the moderating effect of the Pacific Ocean on the climate is greatly reduced by an almost uninterrupted chain of 1,000 to 3,000-m-high mountains along the Baja California peninsula. The climate of the region is therefore more continental than oceanic, a fact that contributes to the large annual and diurnal temperature ranges observed. Desert-like conditions (Sonoran Desert) are found at its northern end and most of the Baja California peninsula (annual rainfall less than 100 mm). Monsoon rainfall conditions are observed in the summer throughout almost the entire region (annual rainfall in the southeast increases to about 1,000 mm); and there is more precipitation on the eastern than on the western side of the Gulf of California. Total rainfall depends on the incidence of tropical storms. Hurricanes seasonally affect the lower Gulf and often extend farther northward, and winds are extremely variable. In general, the region exhibits more tropical/subtropical characteristics during summer and more temperate characteristics during winter, especially in its northern part.
As most river water has been impounded or diverted for use in agricultural and urban purposes, freshwater input by rivers is relatively small (Santamaría-del-Angel et al, 1994). The Gulf of California is an evaporative basin, and exchange with the open Pacific is minor. The Gulf has mainly three natural mechanisms that help nourish the region: wind-induced upwelling, tidal mixing, and thermohaline circulation (Alvarez-Borrego, 2002). Although a complex pattern, upwelling generally occurs off the eastern coast with northwesterly winds (“winter” conditions from December through May), and off the Baja California coast with southeasterly winds (“summer” conditions from July through October), with June and November as transition periods. After the upwelling events, which usually last only for few days, the water column stabilizes and phytoplankton communities bloom. Tidal energy dissipation is strongest in the upper Gulf and around the Midriff Islands. Tidal amplitudes, which may be large as 7 m in the northernmost Gulf, and tidal mixing have a net effect of carrying colder and nutrient-rich water to the surface. Generally, heat and salt are exported out of the Gulf into the open Pacific and, as a result of thermohaline balances, the inflowing deep water has a higher inorganic nutrient concentration than the outflowing surface water. On the other hand, El Niño (ENSO) events have a suppressing effect on the primary productivity of the Gulf. These events can cause reproductive and recruitment failure of organisms higher in the water column and on and around the islands due to suppression of primary production or changes in the planktonic community structure, or both (Alvarez-Borrego 2002). Wind-driven upwelling is better developed and extends over a greater distance along the east coast, than off the Baja California peninsula. Very low oxygen concentrations at intermediate depths (300 to 900 m) are characteristic of the Gulf waters.
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Biological Setting
The Gulf of California is mainly a subtropical system (but closer to a temperate system in its northern part during winter) with exceptionally high rates of primary productivity due to a combination of its topography, warm climate, and systems of upwellings. This high primary productivity supports large populations of Pacific sardine, thread herrings, and many species of anchovies (Anchoa, Anchovia, Cetengraulis, Engraulis) which are in turn the main food source of a whole array of piscivorous species, including squids, fishes, seabirds, dolphins and whales. The Gulf and its islands also serve as breeding areas for seabirds and marine mammals. For instance, much of the world’s population of the widely distributed Heermann’s gull, royal tern, brown pelican, long-beaked common dolphin, and California sea lion breed in the region. The region is also home to a whole suite of other species, from the yellow-footed gull to the Mexican rockfish, and from the Pacific seahorse to the blue whale. Waters of the Gulf are so rich as to support a small, largely reproductively isolated population of fin whale, Balaenoptera physalus, the year round; an anomalous situation for this (seasonally) highly migratory cetacean elsewhere (Urbán et al. 2005).
Overall, the Gulf of California supports a diverse fish fauna composed of 911 species, 821 of them bony fish and 90 of them cartilaginous fish species (L.T. Findley, pers. comm.). There are also almost 5,000 known macroinvertebrate species in the Gulf, which are estimated to be less than half of the actual biodiversity (Hendrickx et al. 2005). Throughout the Gulf, mollusks and crustaceans are the most diverse taxa of macroinvertebrates. Cetacean species diversity in the Gulf of California is very high and its 31 species (in 21 genera), which are present permanently or seasonally, represent 39 percent of world’s total cetacean diversity.
Hundreds of species are dependent upon the riparian and aquatic habitats of the Colorado River delta, even though these habitats have been deprived of a great deal of their natural freshwater input due the river’s impoundment for agricultural and urban purposes. The upper Gulf provides habitat for many marine endemic species such as totoaba, Gulf corvina, and vaquita—one of the most rare and endangered marine mammals in the world. It also acts as nursery habitat for many species, including shrimp, several species of corvinas and croakers, sharks, rays and others of commercial importance. Other species at risk in the Gulf of California include various species of sharks, rays, groupers, snappers, great whales—including minke, sei, Bryde’s, fin, gray, humpback, blue and sperm—and loggerhead, East Pacific green, leatherback and olive ridley sea turtles.
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Human Activities and Impacts
Although the Gulf of California is thought to be a resilient large ecosystem, due in part to its coastal wetlands and submarine topography/surface wind patterns that cause the upwelling of nutrients; factors such as overfishing, river water diversions, sedimentation, pollution, and aquaculture installations (mainly shrimp farms) have been altering the region’s ecosystems. The decrease of fresh water input from the Colorado River has drastically changed the ecological conditions of what used to be an estuarine system, important for fish reproduction. It is now an area of high salinity, and many ecological processes occurring in the once brackish waters have been diminished or altered, including changes in life history patterns of important species such as totoaba (Rowell et al. 2008).
Fishing in the Gulf is of prime importance to local communities and to Mexico in general, but current fishing levels have exceeded maximum sustainable levels in most commercial fisheries. Apart from several species of sharks, rays, and mantas, commercially fished species in the Gulf of California include: blue, brown and whiteleg shrimps; swimming or blue crabs; several species of clams, murexes and pen shells; jumbo squid; northern anchovy; Pacific sardine, round herring, and middling and deepbody thread herrings; Gulf, sawtail, broomtail, leopard, goliath, and star-studded groupers, Gulf coney, spotted and flag cabrillas, and spotted, goldspotted and parrot sand basses (all from the Serranidae Family); amarillo, colorado, spotted rose, Pacific dog, Pacific red, and whipper snappers and barred pargo (Family: Lutjanidae); Gulf, shortfin, striped, and orangemouth corvinas, and bigeye croaker (Family: Sciaenidae); almaco, green, black, Pacific crevalle and yellowtail jacks, along with blackblotch pompano and jack mackerel (Family: Carangidae); roosterfish (Family: Nematistiidae); dolphinfish or dorado (Coryphaenidae); striped mullet (Mugilidae); skipjack, black skipjack, bigeye, yellowfin, and Pacific bluefin tunas, as well as Pacific chub mackerel, wahoo, and Gulf and Pacific sierras (Family: Scombridae); sailfish and black, Indo-Pacific blue and striped marlins (Istiophoridae); dappled flounder, Cortez halibut and fantail sole (Paralichthyidae); finescale and orangeside triggerfishes (Balistidae); and bullseye puffer (Tetraodontidae). For many years, the use of hook-and-line type gears was able to support a healthy fishery—one that depended on long life spans and decades of egg and larval production by fishes in an ecosystem subjected to relatively little fluctuation and environmental perturbation. As stocks declined in abundance, fishermen have moved to other gear and to newly targeted species. With higher rates of fishing mortality and the escalation of gear types to gillnets, trawls and longlines, a fairly rapid reduction in total standing stocks, changes in species dominance, and the loss of older age classes of larger fish followed. It is believed that the region’s stocks will soon decline to levels that will not produce maximum sustainable yield. The totoaba, a large and endemic fish of the northern Gulf of California—for which a legal fishery no longer exists—along with other apex predators of the Gulf of California that appear to have declined to very low levels, and declining stocks of highly migratory species (marlins, sailfish, tunas), may be examples or perhaps harbingers of such a dreadful prospect. Overfishing, the loss of ecologically important species via bycatch mortality, and the widespread destruction of bottom habitats by shrimp trawlers, all contribute to the worsening situation. A formerly large fishery for sea cucumbers collapsed in recent years due to overfishing to supply oriental markets. The continuing excessive mortality of large pelagic predators and the shift in biomass dominance to planktivorous species could have substantial and possibly irreversible effects on the ecological structure and function of the region, triggering a broad expansion of ctenophores (comb jellies), squids (for which a new fishery, again for oriental markets, is developing for one of the larger species recently abundant), and small pelagic fishes (sardines, anchovies, etc.) (NOAA 2002).
The Baja California peninsula, until recently known for its remoteness, is becoming increasingly populated along several Gulf shores, where the coast is otherwise dotted with many fishing villages. Urban development, in general, has not been a major threat to the region. However, during President Fox’s administration (2002–2006) a mega-development project (Escalera Nautica) was planned and set into motion. With the planned construction of several new coastal marinas and support installations, and the renovation of existing facilities at some port towns and cities, the project is aimed at luring 1.6 million recreational boat owners to the Gulf of California; this coastal development may increasingly threaten the ecology of the region.
Level II and Level III Descriptions
Level II captures the break between neritic (near shore) and oceanic areas and is determined by large-scale physiography (continental shelf, slope, and abyssal plain, as well as areas of oceanic islands and major trenches, ridges and straits). This level reflects the importance of depth as a major determinant of benthic marine communities as well as the importance of major physiographic features in determining current flows and upwelling. Like Level I, it extends from the coasts to the EEZ.
Level III captures differences within the neritic realm and is based on more locally significant variables (local characteristics of the water mass, regional landforms, as well as biological community type). Level III is limited to the continental shelf, since only this area has sufficient information for finer-scale delineation.
Level II and Level III Ecoregions
Other Marine Ecoregions
Marine ecoregions are areas of general similarity in terms of physiographic, oceanographic and biological characteristics, which fall within the Exclusive Economic Zones of the North American countries. There are 24 marine ecoregions in North America.
