It's the kind of cloudy, wet spring day that most people spend indoors. But the cold and wet doesn't matter as much when you're planning to spend your day under 36 meters of cold water.

That's what these scuba divers are doing, as they conduct surveys for REEF, the Reef Environmental Education Foundation, which monitors fish populations around the world.

The data helps researchers understand where fish live and in what kind of numbers. It even lets them compare populations of the same species in different parts of the world - for instance, how a sea slug in Washington state is doing compared to the same species in Japan.

Surveyor Janna Nichols has just emerged from the 9-degree water. Back on the boat, she takes off her mask and regulator and pulls out her survey. She goes down the list, marking off what she's just seen.

"Sunflower stars, definitely, many of those - saw a lot of those around," she reports to the other divers. "No sand dollars, no sea urchins. Black-eyed gobies were everywhere. I would say under 100 of them. And they were mating!"

Nichols started doing REEF surveys in the Caribbean when she began diving there nine years ago. When she realized what she could see back home in the chilly waters of Washington state, she became an avid diver and surveyor here. She now leads classes to teach fellow divers how to identify the marine life they see in this region.

Creating an underwater corps of census takers

Christy Pattengill-Semmens, the director of science for REEF, says the data these "citizen scientists" collect is taken very seriously by professional scientists. She explains that before the survey program started 16 years ago, not much was known about overall fish populations.

The idea for volunteer surveyors came about when two naturalists were writing an underwater field guide. They couldn't find even basic data about where the different species could be found or how abundant they were in each location.

"And they realized that there were thousands of scuba divers and snorkelers with their faces in the water every day. So they decided to capitalize on the power of those numbers of volunteers who are interested in the marine environment to get them to report information back into a centralized database."

The naturalists teamed up with researchers from the government's National Marine Fisheries Service and the private Nature Conservancy to develop fish and invertebrate surveys. Snorkelers and divers use those to track what they see underwater.

Semmens says since 1993, more than 120,000 surveys have been submitted for thousands of sites worldwide.

"And so the information as it grows through time is really becoming a good baseline to evaluate change through time. Especially in sensitive and protected areas such as a marine reserve, being able to evaluate how a fish population may change through time once it's protected as a no-take zone."

Tracking the decline of a species

Volunteer surveyor David Jennings is on REEF's Advanced Assessment Team - its most experienced surveyors. Last summer he joined the team's annual survey of the Olympic National Park Marine Sanctuary, in a remote part of Washington state's Pacific coastline.

"I was pretty excited because from what I'd read the rockfish populations there - [there's] a lot of diversity, a lot of really fun species [of rockfish] to see: tiger rockfish, chinas, vermilions, canaries. But when I got there," he recalls, "we did the surveys. I was actually was very disappointed in how few rockfish I saw."

Jennings was surprised to learn that even though the park is called a "sanctuary," fishing is still allowed there - even for some rockfish species that can live to 115 years old. He wanted to see how tiger and china rockfish populations in the sanctuary had changed over time. So he looked at the past six years of REEF survey data.

"One of the best sources was someone that wrote up a diving experience he had in 2002, where he talked about running into dozens of tigers and many chinas."

Jennings notes that in a week of diving in that area, he only saw two tiger rockfish and three chinas.

"So it was a very big contrast to what people had reported in the past."

Jennings gathered more survey data and took it to the Washington Department of Fish and Wildlife, the agency that sets fishing limits.

A valuable resource for fisheries management

Fisheries biologist Greg Bargmann is working on next year's catch limits for different rockfish species. He says the volunteers' surveying methods aren't as precise as the state's. But he recognizes that the REEF volunteers' rockfish data is more current and covers a wider area.

"The REEF survey shows a very dramatic decrease in abundance over the last five years. Our state surveys don't show that, but we have a lot of imprecision in our surveys, so we're relying on the REEF surveys to look for changes in population."

Washington state will issue new fishing guidelines for rockfish populations this summer, based in part on the efforts of divers willing to spend a rainy day underwater with a flashlight and a checklist.