BUENOS AIRES, Argentina — Oil is spreading across the Gulf of Mexico — the result of the sinking of an oil rig last week. A spill of this magnitude so close to the wetlands, estuaries and national fisheries of south Louisiana is unprecedented.

Though it's unclear how badly wildlife along the Gulf Coast will suffer, the timing of the spill couldn’t be worse. This is peak spawning and nesting season for many species of fish, birds, turtles and marine mammals. Many species remain in set breeding areas during this time and there’s less instinct to move away from danger.

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Disturbances to nests, fish spawning grounds or key links in the food chain might have lasting effects on species already at risk, commercial fish stocks and the people who make a living harvesting them. Minor oil spills are relatively common on the Gulf Coast, but this one has biologists, wildlife agencies, conservation groups and fishermen particularly concerned.

Here’s a selection of animals at risk in the open water, along the coasts and in the wetlands.

1. North Atlantic bluefin tuna

The Great Bluefin Tuna, prized for sushi and sashimi, is one of the species most in danger of slipping into extinction. Traveling down across the Atlantic seaboard, bluefin tuna spawn in the Gulf of Mexico between mid-April and mid-June.



Bluefin tuna. (Keith Ellenbogen/Oceana)

2. Sea turtles

Five of the world’s seven sea turtle species live, migrate and breed in the Gulf region. Kemp's ridley is the world's most endangered species of sea turtle, and one of its two primary migration routes runs south of Mississippi. Loggerhead turtles, also endangered, feed in the warm waters in the Gulf between May and October.



Sea turtle. (Toru Hanai/Reuters)

3. Sharks

Shark species worldwide are in decline. The grassbeds south of the Chandeleur Islands are very close to the oil spill. These grasses are a known nursing area for a number of shark species, which are now beginning their spawning season in the Gulf. Whale sharks, the world’s largest fish, feed on plankton at the surface of the water and could also be affected.



Whale shark. (Stringer/Reuters)

4. Marine mammals — whales and dolphins

Oil spills pose an immediate threat to marine mammals, which need to surface and breathe. Not only does the oil pose a threat, but also the nasty toxins that the oil kicks off into the air. A resident pod of sperm whales in the spill area could be at risk along with pygmy sperm whales and dolphins.



Dolphins. (Yuriko Nakao/Reuters)

5. Brown pelican

The state bird of Louisiana, the pelican nests on barrier islands and feeds near shore. Brown pelicans only came off the endangered species list last year, but they’ve had a rough time in past seasons with storms. Their reproductive rates are low. Breeding season just started, and with eggs incubating the oil could pose a significant threat.



Brown pelican. (Bill Stripling/National Audubon Society)



6. Oysters

The coastal waters around the very tip of Louisiana’s boot-shaped coast are home to some of the most productive oyster farms in the country. Oils and hydrocarbons are toxic to oysters. Unfortunately, hydrocarbons can persist in coastal sediments for months or even years. Louisiana oyster farmers, many of whom barely scrape by with high fuel costs and global competition, could have trouble weathering the oil spill if their harvests are affected.

7. Shrimp and blue crab

Coastal marshes are key to the life cycle and development of Louisiana shrimp and blue crab — both staples of the local seafood industry. Inshore shrimp season will open in mid-May, while brown shrimp are in their post-larval and juvenile development stages.



Blue crab. (Jorge Silva/Reuters)

8. Menhaden and marsh-dwelling fish.

The young offspring of species such as mullet, menhaden and marsh-dwelling forage fishes are especially vulnerable at this time of year. Menhaden is a little fish you've probably never heard of, but people all over the world use it everyday. Menhaden fish oil and meat are used in everything from cosmetics to animal feed. Louisiana is one of the world’s biggest suppliers and the oil spill comes smack in the middle of menhaden spawning season.



Mullet fish. (Toshiyuki Aizawa/Reuters)

9. Beach-nesting and migratory shorebirds

Overdeveloped beachfronts all along the Gulf Coast from Texas to Florida have made life difficult for several species of plovers, sandpipers, terns and oystercatchers. Those that build their nests on the ground and feed on invertebrates are susceptible to oil on the beaches. Some migratory shore birds fly nearly the length of the Western Hemisphere and use barrier islands in the Gulf for key resting and refueling spots on their journey.



Plover. (Bill Stripling/National Audubon Society)



10. Migratory songbirds — warblers, orioles, buntings, flycatchers, swallows and others

About 96 species of neotropical songbirds make a 500-mile journey without a pit stop across the Gulf of Mexico. The next two weeks mark the height of their migration as they travel north from Central and South America to breed in North America. The smoke from controlled burns to mitigate the oil spill could affect the migration, but the impacts will be difficult to monitor.



Warbler. (Vasily Fedosenko/Reuters)

On a positive note, the sweet crude oil found in the Gulf is lighter and less toxic than other oils. It can be burned without refining it first and some ecosystems might be able to break it down over time.

Sources: Gulf Restoration Network; Tulane Institute on Water Resources Law and Policy; Louisiana Sea Grant Program; National Audubon Society's Louisiana Coastal Initiative; Louisiana Department of Wildlife and Fisheries.

Editor's note: This story has been updated to correct the spelling of pygmy sperm whales and to correct a reference to porpoises.