Divers have a tendency to dream big. Our dreams include diving in faraway, exotic locations, swimming with and photographing all sorts of magnificent creatures — especially some of the ocean’s largest critters. Dolphins, manta rays and whales are likely on a diver’s big animal “bucket list.” However, it is not surprising that the animal occupying the top spot on many divers’ lists is an apex predator. A shark. “The” shark. And by “the” shark, I mean the great white shark. 

California Diving News
There are a handful of places throughout the world where cage divers can see white sharks. For California divers, one of the best places in the world to dive with great whites is practically in our own backyard. That place is about 180 miles offshore of Ensenada, which is 87 miles south of San Diego. In the past 10 years Guadalupe has emerged as a leading destination for great white shark encounters, with as many as a dozen different animals routinely seen during a normal five-day trip, and the sharks have grown accustomed to divers, often hanging out amongst the cages for extended periods. The underwater visibility is excellent, routinely exceeding 100 feet. And water temperatures are relatively mild, averaging in the high 60s/low 70s F. 
Due to the distance from shore, this is obviously not a day trip. Several well-appointed live-aboard boats offer regularly scheduled charters during summer months, usually late July through late October.
About Guadalupe Island
The island is volcanic in nature, covered with towering cliffs, cinder cones, and plugs. It has a kind of rugged beauty that makes it the perfect backdrop for experiencing the raw beauty of an apex predator like the great white shark. The color in the cliffs defies words. Adentro (inner) Island, a rock at the extreme southern tip of the island, glows orange in the morning sun, and the cliffs above Spanish Bay show off colorful strata from thousands of years of lava flows.
The island vegetation is rather sparse due to centuries of foraging by wild goats, although the natural flora is slowly coming back since most of the goats have been eliminated. Offshore, the waters are teeming with thick schools of fish, green sea turtles, Guadalupe fur seals, California sea lions, elephant seals, and lobster. The only human inhabitants of Guadalupe are a small Mexican Navy Base at the south end of the island and a fishing village close by.
The earliest human visitors came to the island to hunt seals and sea lions. They took all they could find. However, a few Guadalupe fur seals and northern elephant seals escaped the hunters, presumably by retreating into small caves. The caves of Guadalupe are directly responsible for these two species surviving the threat of extinction at the hands of seal hunters.
Decades ago long-range tuna boats from San Diego visited the island for trophy yellowfin and bluefin tuna, yellowtail jacks, and the occasional marlin. Then divers discovered the island. These early explorers were mostly spearfishermen, but a few underwater photographers also came along. These trips had a certain level of risk since white sharks sometimes took large tuna from the fisher’s spear. This lead to natural discovery of the island by shark divers, and the first commercial expedition occurred in 2001.
The Great White
The great white shark (Carcharodon carcharias) is the largest of the toothed sharks. It can grow up to 21 feet long and weigh over 5,000 pounds. The sharks found at Guadalupe Island average about 14 feet in length. 
A male white shark reaches sexual maturity at around age 10. A female white shark may take up to 15 years to reach sexual maturity. Almost nothing is known about great white shark mating and reproduction. It is known that females are ovoviviparous, which means eggs develop and hatch in the uterus and pups continue to grow until birth. Gestation is approximately an 11-month period.
The great white was once thought to live about 30 years, but its true lifespan is estimated to be more than twice that. 
White sharks are what I call “warmer blooded” animals. Instead of maintaining their body at a constant temperature like mammals, their metabolism keeps them about 20°F above the sea temperature. This feature allows them more energy for bursts of speed — they can reach speeds of up to 35 mph — but increases their food requirements. White sharks need calories, and fat is the most compact source of energy. White sharks seek out fatty prey. Young white sharks feed mostly on other sharks and rays and are believed to switch to marine mammals as they grow. They are known to hunt otters, harbor seals, sea lions, and feed on whale carcasses. Year-old elephant seals may be the ideal food for adult white sharks: they are the right size to be subdued by a moderate-sized shark; they have lots of fat, and are relatively unobservant. Big, fat, and dumb — perfect prey. While at Guadalupe the sharks feed on tuna in the early season and then switch to elephant seals as winter approaches when the colder water drives tuna south and elephant seals come to the island to breed.
Scientists estimate there are at least 250 white sharks along North America’s west coast and perhaps as many as 2000. White sharks spend August through December feeding at a few sites, notably the Southeast Farallon Island, Año Nuevo Island, Tomales Point, and Guadalupe. They then head out to sea; either to Hawaii or to a spot scientists call the White Shark Café, about halfway between Baja California and Hawaii. No one knows why these sharks travel so far, but researchers theorize they are engaging in mating activities.
The International Union for Conservation of Nature (IUCN) list the great white as a vulnerable species. The Convention on International Trade in Endangered Species (CITES) in Appendix II lists the great white as a “species that are not necessarily threatened with extinction, but may become so unless trade in specimens of such species is subject to strict regulation in order to avoid utilization incompatible with the survival of the species in the wild.”
The growing popularity of shark tourism is helping dispel the myth that, “the only good shark is a dead shark,” a phrase made popular by the 1975 film Jaws. Those who spend money on shark diving expeditions help reinforce the fact that sharks are actually worth more alive than dead. 
The Experience
Shark trips to Guadalupe are typically five days in length. It takes a day to get to the island and another to get back, allowing for three full days of cage diving. Some live-aboard charter boats depart from San Diego but must clear port in Ensenada before traveling on to Guadalupe. Other boats leave from Ensenada, Mexico but their staff escorts guests from San Diego to Ensenada by air-conditioned bus. Shark boats typically anchor near the north point of the island at Prison Beach, the site of an abandoned Mexican prison. 
Dive boats often have more than one cage in the water at a time; usually one or two cages are at the surface, while another is lowered to a depth of about 30 to 40 feet. Rather than wearing a conventional scuba setup, divers do not wear tanks. Or fins. Instead, they stand in the cages and breathe from hookah regulators, which means unlimited air, for plenty of bottom time on each encounter. This also means you do not have to be a certified diver to enjoy the surface cages! 
Because you can expect long bottom times (and thus plenty of shark action), it’s a good idea to add a little more exposure protection — at least a 5- or 7-mm suit, with hard-soled booties, a hood, and gloves. Or even a dry suit if you’ve got one. Most of the dive boats offer a pretty good selection of suit rentals, but inquire ahead of time just to make sure they can accommodate your needs.
I probably don’t even need to mention the fact that you should bring an underwater camera. I mean, after all, you’ll be face-to-face with great white sharks. Believe me, it’s kind of a big deal, so if you don’t already have at least a simple to use point-and-shoot underwater camera, be sure you sort this out ahead of time.
Now, for the actual encounter. Some sharks are very shy and cautious, and spend much of their time hanging out below or behind the cage. Others are more confident and will take hang baits 5 to 10 feet from the cage. Others are absolutely fearless and slowly swim inches from the cage, eyeing the divers within. They also have personalized hunting styles. Some will slowly and cautiously approach the hang baits; others will lurk in the depths, and charge the bait from below with great speed and violence.
Each shark also has its own unique appearance. Some are sleek and clean with a flawless complexion. Others are scared by time and violent encounters with prey and other sharks. Adult female sharks usually have bite mark scars right behind the head, since during mating the males hold on to females with their teeth. Many of the male sharks have nasty bite marks around the head, back and gills, presumably by other white sharks. Sharks of both sexes can have paired puncture or cut marks around their mouth, characteristic of elephant seal bites.
You don’t get to be very old by being bold and reckless; you grow old by being cautious and restrained. The sharks divers observe from the cages are neither excited nor frenzied, and the notion of a shark as a crazed killer is quickly dispelled when you observe them from the safety of a cage. Curious, inquisitive, and graceful are perhaps the most accurate description of these sharks.
Sharks have an image problem. On one hand those who do not know them very well think of them as indiscriminate, savage killers; while those who have spent time with them in the water think of them quite differently. Silent, fluid, curious, graceful, sleek are the words often used to describe them. My own personal opinion is that white sharks are among the most fascinating subjects I have ever encountered. I have truly been in awe of their magnificence.
If a personal encounter with a great white shark is on your “big stuff list,” I suggest you book a trip to Guadalupe. 
“Do I Need To Be A Certified Diver?”
The short answer is no. Some charter operators allow those who are not scuba certified to dive in the cages — at the surface only. Only certified divers are allowed in submerged cages. Those who are new to scuba must complete an intro course with one of the boat’s dive instructors. The course provides the basics, including how to breathe from and clear the hookah regulator, equalization and ear clearing, and how to clear a flooded mask. Ask your charter operator if they offer this option. 
The following businesses offer  great white shark expeditions to  Guadalupe Island:
Great White Adventures
Great White Sharks  of Guadalupe
Islander Charters
Nautilus Explorer Live-aboard
Solmar V Live-aboard
California Diving News