On Tuesday, the research ship Bell M. Shimada made preparations to head out again. This time, scientists will survey coastal waters from Mexico to near Santa Barbara looking for sardines.Southwest Fisheries Science Center scientist Roger Hewitt, Ph.D., said forage fish like sardines are critical."They feed everything that we care about," he said.Sardines feed not only people which results in $12 million in commercial fishing revenue in 2010 but they also feed birds and mammals such as whales and sea lions which are cornerstones of tourism."Sardines are used as bait," said Hewitt.They help fuel the massive sport fishing industry, which brings in more than 250 million a year for San Diego, according to the United Anglers of Southern California, citing a 1985 study.The last coast-wide survey occurred in 2006 going from Baja California to British Columbia. Scientists will be using echosounding, which is similar to sonar."It can actually be used to find fish in the water column," said Sam McClatchie, the chief scientist.They also collect fish. Two huge trawling nets are attached to gigantic spools and hang off the back of the ship to catch adult sardines so scientists can check their size and health.The Shimada just returned after two weeks at sea after collecting plankton, which is what sardines eat. They also looked for sardine eggs but did not find many.In fact, over the last 10 years, the number of sardines has dropped by about 35 percent, according to scientists."We should always be concerned when we see a downward trend of fish," said McClatchie.Russ Vetter, director of the Fisheries Resources Division, said, "Not enough babies are being born."However, they are not sounding the alarm bells yet because sardines have bounced back before. Meanwhile, the scientists will do what they can to right the course of the small but important fish.The research vessel will head out on Wednesday for about three weeks.