February 18, 2002 Ocean movements linked to recruitment of juvenile rockfish By Kristin Cobb Ocean currents have dramatic effects on the populations of fish that inhabit rocky reefs along the California coast, including commercially important rockfish. Newborn fish larvae spend several months drifting at the whim of the ocean currents before making their way back to nearshore reefs. But the patterns of their dispersal and return have eluded scientists for years. Now, UCSC researchers have made a critical connection between a specific movement of ocean waters and the influx, or recruitment, of young fish to local populations in Monterey Bay. The gopher rockfish is one of the species being studied by PISCO researchers. Photo: Giacomo Bernardi "When you are planning protected marine fisheries, you need to know where the fish are going and when they are coming back," said Margaret Dekshenieks, assistant professor of ocean sciences. Linking a physical event in the ocean with a biological one was a major breakthrough for her research team, she added. Dekshenieks is studying larval dispersal and recruitment as part of the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO), a marine science research consortium involving UCSC, UC Santa Barbara, Oregon State University, and Stanford University. PISCO focuses on understanding the nearshore ecosystems of the West Coast of the United States. Marine biologists Mark Carr and Peter Raimondi lead the PISCO team at UCSC. The team's latest discovery was an interdisciplinary effort: Dekshenieks and postdoctoral researcher Curt Storlazzi served as the physical oceanographers, and Carr, Raimondi, and graduate student Arnold Ammann provided the biology. The team presented its findings at the 2002 Ocean Sciences Meeting in Honolulu on February 11. The researchers linked the recruitment of juvenile rockfish to patterns in the upwelling of deep ocean waters that occurs along the California coast. During the summer in Monterey Bay, winds from the northwest blow warm surface waters offshore and stir up deep, cold water nearshore; this is called upwelling. Roughly every 10 to 12 days, the winds shift and the upwelling subsides; this is called a relaxation event. During these relaxation events, warm water moves back to the coastline, bringing with it an influx of certain species of juvenile rockfish. Storlazzi identified upwelling and relaxation events by monitoring sea temperature and current velocity, recorded at Hopkins Marine Station, and wind data gathered by an offshore weather buoy. He correlated relaxation episodes with the recruitment of rockfish to local kelp beds, which is being tracked by Carr, an associate professor of ecology and evolutionary biology. Carr said that the team's discovery has wider implications for predicting how fish populations will change over time and how they will respond to natural variability in the environment. "This gives us more insight into the physical mechanisms that contribute to rockfish recruitment both within a single year and also with respect to larger-scale climatic events," Carr said. Carr's group had previously discovered that certain species of rockfish recruit preferentially during El Niño, a weather pattern that suppresses upwelling and causes the winds to shift. The species of rockfish that recruit during El Niño are the same ones that Storlazzi found to recruit during relaxation events. Because El Niño events are occurring more frequently and more intensely than in the past, this has implications for rockfish, Carr said. In the future, this information may also help resource managers distinguish whether fish populations are changing due to human impacts, such as water pollution and fishing, or due to natural changes in the environment, Carr said. Carr and Storlazzi said that the team's next step is to figure out where the rockfish larvae go when they are dispersed offshore and how their spatial distribution is determined by the interaction of biology and physical events. This would help scientists to protect rockfish everywhere they go, not just where people catch them, Storlazzi said. Return to Front Page