Each spring, many of Florida's winter migrants -- including American robins, goldfinches and a stream of motor homes -- head north. So do rare North Atlantic right whales.

But the whales are only one of many species that participate in a vast and complex trans-Atlantic migration that never ceases.

Driven by the need to eat and reproduce, and influenced by the deep, warm current of the Gulf Stream, seasonal water temperature fluctuations and other factors scientists don't fully understand, an amazing variety of creatures circulates past Volusia and Flagler counties.

Those include seabirds, whales, sharks, rays, fish, sea turtles and eels.

A few species, like the right whale, pass close enough to touch (but don't; it's illegal). Others, such as whale sharks, may move far seaward of the Gulf Stream. The mix of species ranges from the largest animal on Earth -- the blue whale -- to the smallest, microscopic creatures at the bottom of the food chain.

"If you were a regular beachgoer and you could see through the water all year long, it would be fascinating," fisheries biologist Grant Gilmore said.

For animals, migration is all about energy, said Bonnie Ponwith, director of the Southeastern Fisheries Science Center. Everything they do is based on an energy budget.

The first priority of the animals is generating enough energy to keep their hearts beating and their gills flapping, Ponwith said. Animals devote their remaining energy to discretionary activities, such as chasing better food, procreating or moving around.

They migrate because they find it energetically advantageous to make the long excursions, she said. It might enable to them to have more calves or produce more eggs.

"The benefit of that excursion outweighs that cost," she said. For a female whale, it might be finding the exact water temperature to have that calf, so instead of burning calories to stay warm she generates enough milk to feed the calf.

"Or, on the flipside, the whale makes that long journey to cold water where the density of food is higher so she can make the journey south next year to have another calf."

Ponwith finds unanswered questions about migration "utterly fascinating."

"Do they go by themselves, or as a crew? Do they use landmarks ... or are they using the magnetism of the Earth to guide those migrations?"

From shore, Michael Brothers of Volusia County's Marine Science Center often spots unusual birds that make brief appearances during some of the world's longest migrations. Several times a year, he takes a group of birdwatchers to sea to scout for ocean-going birds.

When you get out 100 miles, "you really start to see some neat things," Brothers said. "That's where we see whale sharks, marlin, tuna, flocks of sooty terns and bridled terns."

Professional fishermen who spend most of their lives on the ocean get a closer look at migrating animals than most.

"You never know what you're going to see out there," said local fishing captain Paul Nelson, who has fished the Atlantic commercially since he was6. "You can see something new every day."

That can become an unforgettable experience. Nelson clearly remembers his first encounter with one of the ocean's most fearsome animals -- a great white shark -- on his uncle's fishing boat.

"I was 11 and fishing on the Little Dolphin. When it came out of the water and opened its mouth, he was right at us.

"He moved his jaws back and forth and cut right through the (15-gauge stainless) wire," Nelson said. "They're pretty impressive."

WHALES: Giants roam Gulf Stream

Many Volusia and Flagler residents look forward each winter to the arrival of the endangered North Atlantic right whales.

Female right whales, often accompanied by juveniles, travel to Florida and Georgia coastal waters to give birth. Lucky observers can see them from shore as they breach, blow and frolic in the waves.

However, nearly a dozen additional whale species can be found roaming the ocean at varying distances from the Volusia-Flagler coast during their annual migrations.

Right whales swim along the Continental shelf, said Keith Mullin, who conducts marine mammal assessments for the National Fisheries Service. But when the shelf ends and water depth drops to more than 600 feet, beaked whales, sperm whales and others join the migration.

"If it's in the ocean, it's in the Gulf Stream," said Steve McCulloch, a program manager at Harbor Branch Oceanographic Institute in Fort Pierce. He once took a call from someone surprised to see a killer whale in the Bahamas.

"It's rare, but they are there," he said. "It's part of a natural annual migration these animals conduct within the Gulf Stream waters."

Scientists do not yet understand the migrations of many whale species, but Mullin said information they do have is fascinating.

Sperm whales, for example, are champion divers, Mullin said. "They'll typically dive for 40 to 50 minutes."

Scientists believe female and juvenile sperm whales remain in the tropics and sub-tropics, while mature males leave.

"As they get older they migrate further and further north. They end up in colder waters where the feeding is better," Mullin said. "Then once they're sexually mature, they migrate back."

Studies of humpback whales show they travel from Canada and Greenland south to Silver Bank off the Dominican Republic.

"A huge number of them from all over the North Atlantic converge on the Caribbean to breed," Mullin said.

Scientists argue over why that movement takes place. It could be to seek warmer water for their young or it could be to avoid killer whales, which frequent colder water.

Other whales may migrate in east-west patterns across the Atlantic.

Little is known about the migration of the rare blue whale, but scientists believe it may travel south in the Atlantic. Historic records show blue whale strandings in the Gulf of Mexico and a blue whale was killed in the Caribbean at the entrance to the Panama Canal in January 1922. Cornell University scientists using acoustic recording equipment east of New York Harbor reported that they recorded a male blue whale in January 2009, about 70 miles off the south shore of Long Island and another whale far off into the distance.

Grant Gilmore, a Florida fisheries biologist who specializes in acoustics, said the whales can communicate across great distances in the ocean because they use low-decibel sounds and swim to depths where sound can be transmitted "hundreds if not thousands of miles."

SHARKS: Great whites venture here

A diverse assortment of sharks and rays off the Florida coast changes with the seasons.

In the winter, northern sharks, such as great whites, venture south chasing food that moves with colder water, while tropical species migrate north in spring and summer. Many, including basking sharks, whale sharks and others, have been seen east of Daytona Beach.

Scientists learn more about shark movement through tagging experiments. More than 200,000 animals, including 52 species, have been tagged in studies dating back to 1964, said Greg Skomal, a senior biologist with the Massachusetts Department of Fish and Game.

Skomal tagged five great white sharks off Cape Cod last September. Three of the five tags surfaced off the Florida coast since January. The tags record water temperature, depth and light levels, which scientists use to calculate a shark's probable movements.

Skomal said the three great whites remained in New England until September and then traveled south. The tag from one 12-foot-long shark began transmitting data on Jan. 15 about 50 miles east of Jacksonville. Another shark surfaced 30 miles north of that point on Feb. 4. A third surfaced about 80 miles south of the first shark -- east of Daytona Beach -- on March 1.

The sharks stayed over the continental shelf while traveling south, Skomal said, moving up and down between the ocean floor and surface almost daily. The sharks spent more than 90 percent of their time in water depths less than 150 feet.

One shark entered the Gulf Stream off North Carolina in early November and dove to depths of more than 1,500 feet daily for about 10 days.

Skomal will continue to study the tag information. He said the shark's close association with the shelf may reveal more about mating and feeding habits. Tags from the remaining two sharks could still surface.

Great whites might follow whales south to try to feed on newborn whale calves, said Dr. John Carlson, a shark biologist with the National Marine Fisheries Service in Panama City.

"The calves swim slowly and mom has used up all her energy. She may not be able to get away or defend her calf," Carlson said. And, they may glide down to lower depths to save energy as they migrate.

In earlier studies, Skomal tagged basking sharks, the world's second-largest shark species. One surfaced well offshore east of Daytona Beach.

Once thought to remain in the northern ocean, the basking shark completes long-scale migrations from hemisphere to hemisphere.

Scientists surmise that's for "mating and pupping," said George Burgess, director of the shark research program at the University of Florida.

Basking sharks swim at depths up to 3,000 feet for several weeks or even months, and move as far south as Brazil. Burgess said they remain in deeper water and do not come in along the shore.

One of the more interesting species found offshore, Carlson said, is the endangered saw fish, a cross between a shark and a ray that continues to mystify scientists. Florida is the only place they are found in the United States.

FISH: Species search for ideal nursery

Fishermen who spend their lives on the sea gauge the change of seasons by the varieties of fish they find in the Atlantic Ocean.

A major sailfish migration, for example, peaks here in October, as the large billfish head to the Florida Keys for the winter, said David Nelson, a Port Orange fishing captain.

Sailfish are one of many species that spend at least part of their time off the Florida shore.

Fish have "a huge diversity of migration patterns," said Dean Grubbs, a research scientist at Florida State University. He's particularly impressed by the complexity of some of the patterns.

In the case of many fish, such as tunas, the entire migration is tied to getting their larvae to areas where conditions are right for development, Grubbs said. Tuna migrate to locations, "not because they're particularly great habitat for the adults, but because they're in very specific areas so oceanographic conditions are perfect for the eggs.

"The eggs will get transported to areas where the hatching larvae will be in warmer water with lots of food for development."

One study found that gag grouper swim from North Carolina to Florida to spawn and then return, said Grant Gilmore, a fisheries biologist and owner of an aquatic research firm in Vero Beach. The grouper depend on the ocean currents to distribute their eggs along the Atlantic Coast. If the grouper remained in North Carolina to spawn, Gilmore said their eggs would wind up far north in ocean currents too cold for survival.

Several fish species travel great distances, far more than many people realize, Gilmore said.

Electronic tagging studies on marlin, for example, showed that the fish move among the oceans, traveling between the Pacific, Atlantic and Indian Oceans.

In Gilmore's snook studies, he found the fish travel at average speeds of 3 - 4 mph.

"People had no idea how mobile some of these animals are," he said.

Tagging studies done during a nine-year period by the Tuna Research and Conservation Center, a collaboration between Stanford University and the Monterey Bay Aquarium, found that bluefin tuna move thousands of miles in the Atlantic. The studies also found the 150- to 900-pound tuna sometimes drop to depths exceeding 3,000 feet.

BIRDS: From 'every corner' of ocean

Of all the animals that migrate past the Volusia and Flagler coasts, sea birds are seen more easily than others.

"We have such a wonderful vantage point where we're seeing birds coming from every corner of the Atlantic Ocean," said Michael Brothers, a bird expert and manager at the Marine Science Center of Volusia County.

Birds move from the Arctic to the Antarctic and almost every point in between.

"The idea that migration is these birds coming from up north is a really simplified idea of what's going on," Brothers said. "The whole idea of how these birds are moving around is mind-boggling."

On expeditions far out into the ocean, avid bird-watchers can witness any number of these birds in flight.

At other times, migratory fowl can be seen right on the beach, especially with a pair of good binoculars. Occasionally, even rare birds wash up on the beach, exhausted and stranded. If they're alive, the sick stragglers are taken to the science center's Mary Keller Seabird Rehabilitation Sanctuary and nursed back to health.

While some sea birds fly in from the Caribbean, others come from farther away. The Cory's shearwater, for example, nests on islands off the northwest coast of Africa and circumnavigates the Atlantic, passing Florida and the northern U.S. coast before circling over Europe and back to the African coast.

Greater shearwaters share a similar migration path. Flying from a remote group of islands between South Africa and South America, they fly along the coasts of South and North America on their way to Canada's Bay of Fundy, Brothers said. Then they move south through the Central Atlantic to the west coast of Africa and back across to South America.

The diminutive Wilson's storm petrel and the Arctic tern travel the greatest distances. The storm petrel nests on islands off the coast of Antarctica and travels north throughout the Atlantic Ocean.

The Arctic tern follows a similar path in reverse, but conducts the longest annual migration in the world. It makes a round trip from the Arctic to the Antarctic each year, traveling up to 43,000 miles.

In December, an international research team published a report in the Proceedings of the National Academy of Sciences, documenting the terns' mega-migration. The research showed the terns, which weigh about 4 ounces, make the equivalent of three trips to the moon and back during their lives.

The study's authors said terns take full advantage of prevailing global winds to reduce the energy demands of their long flight.

"That's an insane amount of travel," Brothers said. "We actually get to see those birds in the spring when they're traveling along the coastline."