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Antarctic krill
Antarctic krill play a central role in the Southern Ocean ecosystem and also support a major fishery.
Photo: British Antarctic Survey

February 13, 2006

Major grants fund research on California steelhead and Antarctic krill

By Tim Stephens

Two new grants will support research projects at UCSC that address important management issues affecting steelhead trout populations along the California coast and krill populations in the Southern Ocean.

Juvenile steelhead
Born in fresh water, this juvenile steelhead (called a parr) will eventually migrate downstream toward the ocean as a smolt, mature into an adult in the ocean, and then return to spawn in the stream where it was born.
Photo: Morgan Bond

Marc Mangel, professor of applied mathematics and statistics, is a principal investigator on both projects, which bring the tools of mathematical and theoretical biology to bear on practical problems in conservation and fisheries management.

The steelhead project, funded by a $1 million grant from the CalFed Bay-Delta Program, is led by Mangel and Susan Sogard, chief of the ecology branch at the National Marine Fisheries Service (NMFS) Santa Cruz Laboratory. The researchers will investigate how juvenile steelhead respond to environmental factors in rivers and streams before they migrate to the ocean. The three-year study will provide crucial information to water managers about the effects of water conditions on threatened steelhead populations.

The CalFed Bay-Delta Program is a collaborative state-federal effort to implement a long-term, comprehensive plan to restore the ecological health of the San Francisco Bay and the Delta formed by the Sacramento and San Joaquin Rivers. One of its goals is to help the recovery of salmon, steelhead, and other fish populations in the Bay-Delta system.

Mangel also received a $750,000 grant from the Lenfest Foundation at the Pew Charitable Trusts to investigate the implications of climate change for populations of Antarctic krill in the Southern Ocean. Antarctic krill are abundant shrimplike crustaceans that play a central role in the Southern Ocean ecosystem and also support a major fishery. Climate change is expected to affect krill populations, and Mangel's project aims to predict what those effects will be.

"Our work will try to predict how krill will respond to climate change, how their predators will respond, and what that means in terms of the quotas for the krill fishery," said Mangel, who directs the Center for Stock Assessment Research (CSTAR) at UCSC.

Both projects will involve graduate students and postdoctoral researchers affiliated with CSTAR, a collaboration between the NMFS laboratory and UCSC to train researchers in the quantitative tools and basic science needed in fisheries management.

In the case of steelhead, the researchers want to understand the factors that lead juvenile steelhead to adopt different life-history pathways. There is great variation in steelhead life histories--most migrate to the sea after spending two years in freshwater, but some go to sea after only one year, while others wait three or four years.

The decision to migrate is determined by the interaction of genetic and environmental factors, Mangel said. "These fish have a genetic program that is cued by the environment, and we're trying to understand that interaction," he said.

Because life in the stream is riskier than in the ocean, the timing of migration affects how many juvenile steelhead are likely to survive to adulthood and eventually return to their native streams to spawn.

"If we can understand how environmental factors such as water flow, water temperature, and food availability affect when they migrate down to the ocean, then we can predict survival rates and provide advice to water managers on how certain water management practices will affect the fish," Mangel said.

Genetically distinct populations of steelhead live in the streams along the Central Coast and in big inland rivers, such as the Sacramento and San Joaquin Rivers. All of these populations are listed as threatened under the federal Endangered Species Act. Part of the research project will involve field studies to compare different populations.

"Those populations live in very different kinds of environments, and we would expect them to be different in their responses to environmental factors," Mangel said.

Mangel will use the data from laboratory and field research to develop quantitative models that can be used to predict the effects of different water regimes on steelhead populations. For the krill project, the focus will be on mathematical modeling using existing sources of data.

"There is an enormous amount of data on Southern Ocean krill and their predators. One exciting aspect of this work is using data that has been collected by others to test and refine the models," Mangel said.

Mangel has been involved in research on the krill fishery since 1986 and served on U.S. delegations to the international commission that regulates the fishery. The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) was signed in 1982 amid concerns that an increase in krill catches in the Southern Ocean could have serious effects on populations of krill and the animals that feed on them.

Now the concern is over the effects of climate change on the krill and the rest of the Southern Ocean ecosystem. Changes occurring in the Antarctic region include the hole in the ozone layer in the upper atmosphere, increasing water temperatures, and changing patterns of sea-ice formation in winter.

"It's not clear how these things will affect the krill population and the rest of the ecosystem," Mangel said. "We need to use mathematical models to look at this, because if we wait to see what happens it will be too late."

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