Kyle Van Houtan, a marine ecologist at Duke University and a researcher for the National Oceanic and Atmospheric Administration, has spent the last few months scouring libraries, Web sites and private collections for Hawaiian restaurant menus dating as far back as the late 1800s. Why menus? Van Houtan and his colleagues are trying to learn about fish species abundance during the early and mid-20th century—a period for which there are few solid records but plenty of potentially informative souvenirs.

“Nowadays everybody travels, but in the early 20th century, going to Hawaii was really special, and people kept everything, from matchbooks to menus,” Van Houtan says. He and his colleagues hope that the menu census will give scientists a better idea of what healthy Hawaiian fish populations should look like. “It’s helpful to understand long-term changes when you want to assess population health,” he explains. “This means that you sometimes have to be creative when you are looking for data.”

Although menus aren’t usually part of the ecologist’s toolkit, Van Houtan argues that the disappearance of popular reef fish from Hawaiian menus, such as certain species of goatfish Native Hawaiians call “weke” and “kumu,” is indicative of a broader and poorly understood trend in Hawaii: the impact of early tourism and agricultural development, with its attendant polluting runoff. “Hawaii was governed differently back then,” he says, adding that record keeping was largely absent between 1902 and 1948, eleven years before Hawaii’s statehood, “so there is a gap in commercial fishery data that we need to fill.”

According to the data gathered from menus, populations of small near-shores fishes declined markedly after 1948. Swordfish, tuna and other larger species on the other hand, suddenly became much more widely available in restaurants, thanks in part to improvements in fishing technology. Yet even today, if you ask older Hawaiians about “weke”—a goatfish catchall that can designate anything from yellowfin goatfish to bandtail goatfish—“many will get nostalgic,” Van Houtan recounts. That means “the decline didn’t occur because of changes in people’s tastes in seafood,” he says. “The demand was there, but the fish weren’t.”

The lists of restaurant dishes were also helpful in uncovering the reasons for turtle population declines during the first half of the 20th Century. “We were surprised that turtle meat didn’t really appear in the menus,” Van Houtan says. Evidently, tourism was not to blame for the turtle decline. Rather, the primary trade in turtle meat likely took place at local fish markets.

The importance of the new study, recently published in Frontiers in Ecology and the Environment, is in providing an “accurate target for ecological recovery,” Van Houtan says. He also thinks that using menus is a good way to grab people’s attention and raise awareness. “It’s a lot more intuitive than computer modeling,” he says. And now that the news about the study is spreading, people from all over the U.S. have been getting in touch with Van Houtan to send him their antique menus, bolstering the argument that alternative sources of information should not be overlooked simply because the data points happen to come poached, grilled or served in a meunière sauce.