Fish That Stay Home.
Fishermen have long known that the growth rings of the tiny crystalline structure in the inner ear of a fish reveal the age of the creature much the way tree rings reveal the age of a tree. And biologists have found that the bones, called otoliths, also hold a wealth of other information about fish life histories. Now American and Australian scientists working in two oceans have studied otoliths to learn where larval fish go after they hatch. Their findings, which challenge the common assumption that young fish disperse widely, could have major implications for fisheries management.
"The basic paradigm didn't make sense to me," says biology graduate student Stephen Swearer of the University of California at Santa Barbara. "If a larva develops in open ocean and disperses away from the natal population, it's at great risk of not finding suitable adult habitat." He and his colleagues studied the bluehead wrasse (below) in the coral reefs of St. Croix in the U.S. Virgin Islands. Comparing trace quantities of metals in their subjects' otoliths and in the water at particular reefs, they found that significant numbers of the fish stay at, or return to, the sites where they were spawned.
At about the same time, scientists from James Cook University in Australia marked the otoliths of more than 10 million damselfish embryos at Lizard Island on the Great Barrier Reef. (The procedure involved immersing the embryos briefly in an otolith-staining dye that otherwise did not affect the fish.) That allowed the researchers to identify damselfish that later returned to the same site-and to conclude that as much as 60 percent of juveniles may return home.