Imagine floating on the empty blue Pacific Ocean, nothing but water in every direction, sunrise to sunset. Yet under the surface swim thousands of great white sharks.

That's not a bad dream - it's actually what happens around this time of year several thousand miles off the coast of Baja California, about halfway to Hawaii. The king predators congregate in a huge area of the ocean nicknamed the White Shark Cafe.

But why the big sharks favor this remote spot remains a mystery. The area is sometimes called "the desert of the ocean," and Sal Jorgensen, a research scientist at the Monterey Bay Aquarium, says there is little observable life to sustain a food chain. While there, the sharks assume bizarre behavior, sometimes diving thousands of feet at intervals as short as 10 minutes.

Scientists believe the white sharks congregate to find food and to find a mate, hence the idea of a "cafe" - but only better research can determine whether the shark gathering is more "restaurant" or "motel."

"We know very little," Jorgensen said, joking that it seems like Burning Man for white sharks.

A lack of sensory equipment makes it hard for researchers to find out what's happening below the surface of the water. Most data for studying sharks, or any ocean phenomenon, are gathered by buoys (which are immobile), satellites (which are inexact, usually confined to surface measurements and not always in range) or scientists on ships (which are expensive and time-consuming).

Reshaping Research

This is where drones come in.

Autonomous craft are reshaping the way scientists study the ocean, and two Bay Area companies, Liquid Robotics and upstart Saildrone, funded by the Marine Science and Technology Foundation (founded by Google Chairman Eric Schmidt), have been making waves with their unmanned gliders and sailboats. Saildrone recently completed a voyage around Hawaii and back to the Bay Area with its autonomous sailboats. But now the group must prove its crafts can do more than simply get from point A to point B - like gather critical ocean data.

"The next stage is to demonstrate that we can do real, valuable science," said Saildrone lead researcher Richard Jenkins.

The startup, which has a workshop in a hangar on Alameda's old Navy base, attaches shark sensors to its craft's keel. Getting sensors under the surface is key. As the drone passes within range of the shark, the sensor picks up its acoustic tag and beams the data back to mission control. Without the drone, researchers have to wait until the tag pops off (usually about a year) and then retrieve it via ship, which can cost tens of thousands of dollars per day. Then researchers must assemble the animal's activities retroactively.

The hope is that with drones periodically transmitting data as they traverse the White Shark Cafe, or any other area of interest, observations occur in real time - and at far less expense. Jorgensen and Stanford marine biologist Barbara Block, who is working with Liquid Robotics and Saildrone, hope for better data, such as the animal's exact positions in the water column at certain moments, giving them a 3-D perspective. This indicates whether (and what) the sharks are hunting, potentially helping scientists understand the purpose of the Cafe, not to mention other migratory and feeding habits. Block hopes for similar discoveries with bluefin tuna and other pelagic fish, which inhabit the open ocean away from shore and sea floor.

"You'd think we know, but we don't," she said. "It's a very inaccessible world."

The Stanford group has tried to open some of that world to the public with the Shark Net app for iPhones, which lets anyone monitor and see pictures of tagged fish, but continuous information is tricky. "This is a great concept, but the data is not up-to-date," notes a top comment in the iTunes Store. "Would be a great app if it was kept current."

Keeping information current is only one challenge. Saildrone must also make sure its instrumentation remains accurate in the brutal marine environment, where heat and cold can warp calibration. Jenkins and Co. are working with the National Oceanic and Atmospheric Administration to fine-tune the sensors. Even a slight deviation can make an entire data set meaningless.

"Just because you collect a number, doesn't mean it's right," Jenkins said.

Florida State University oceanographer Ian MacDonald hopes the drones will provide data to better predict tropical storms. Satellites, he says, can only measure surface temperatures - but temperature below the surface is vital for researchers.

"Anything that will give us a better handle would be very important," he said.

And drones could also map areas previously tricky for ships. Saildrone's crafts only cut 6 feet under the water, so it can navigate shallow areas - meaning it could take far more nuanced pictures of the ocean floor and save on the fuel compared with the boats currently performing the task.

The drones cost almost nothing to operate and are relatively simple to control and monitor. Provide destination coordinates, and off it goes - the command software is simple enough to run in a Web browser and Jenkins occasionally monitors the craft from his iPhone (via a private website). The vessel has small solar panels to power the onboard computers and sensors, but the drone moves completely on wind power.

But the drones can't stay at sea forever. Despite protective paint and a streamlined design, algae and other sea life will eventually coat the craft and slow it down, meaning it has to come back to shore for cleaning and a tune up.

The drone's hull is shaped something like a big pelagic fish, but Jenkins says sharks haven't mistaken it for prey yet. In fact, when they've sailed near marine life, the animals don't make much fuss. Crafts with engines usually have them scrambling to get away. Because the drones are silent, Jenkins believes animals don't pay much mind, viewing them as pieces of fast-moving driftwood.

Detailed Data

This sort of detailed insight into the lives of sharks presents something of a double-edged sword. Researchers need to publish data so activists and governments know where to establish marine conservation zones. But that data also inform fisherman, many of whom disregard catch limits on threatened species or even brutalize animals by slicing off shark fins for soup and leaving them to die.

"We're always faced with this dilemma," said Jorgensen.

Yet, to add one more bullet to the list of tasks these machines could perform, Jenkins has worked with government agencies to test drones for patrolling protected fisheries and taking pictures of boats violating the rules. Those discussions are also in very early stages.

Drones haven't proven to be a panacea for answering marine science questions quite yet. But Block is hopeful.

"These are the modern-generation tools to study the ocean," she said.

©2014 the San Francisco Chronicle