UC Davis marine biologist Laura Rogers-Bennett is searching for the best way to preserve California's vanishing abalone populations. Two challenges confront her team: tracking the rare, ocean-dwelling mollusks, and determining how scarce conservation dollars should be spent to save them.

"When conservation funds are limited, we have to make decisions about where best to put our resources," said Rogers-Bennett, a research associate with the campus's John Muir Institute of the Environment.

Her team has spent five years assembling data to describe the life histories of two abalone species. Although both red and white abalone were hurt by overfishing, limited red abalone fishing is still allowed in Northern California. In contrast, the number of white abalone shrank so drastically that, in 2001, it became the first endangered marine invertebrate.

To understand the life cycles of red and white abalone, the team combined measurements on current populations with archived data collected during the 1970s and 80s, when populations were larger. With this information, they built detailed images of the animals' growth, reproduction and survival patterns.

Now, with mathematical matrix models, they are using that information to predict which conservation strategies will be most cost-effective.

The key to the models' success will be the level of demographic detail they provide. Human demographic data is given by age group, whereas for abalone, demographic questions are based on size classes.

"For example," Rogers-Bennett said, "the red abalone fishery has a size limit -- animals less than seven inches can't be fished. With our models, we can ask whether that limit protects the size classes that contribute most to population growth."

Rogers-Bennett notes that a similar strategy improved sea turtle conservation in Florida. Florida biologists found it was better to spend money saving big, old female turtles with high egg-laying potential than to use money raising turtle hatchlings.

"Mathematical modeling lets us ask very practical conservation and restoration questions," Rogers-Bennett said. "We can find out which management measures have an impact on population growth."

Rogers-Bennett's modeling work is being funded by a California Sea Grant. She is an employee of the California Department of Fish and Game and conducts her research at the Fish and Game unit at the UC Davis Bodega Marine Laboratory.

Laura Rogers-Bennett, (707) 875-2035, rogersbennett@ucdavis.edu (Rogers-Bennett returns from the field to her office on Aug. 29.)

• Bodega Marine Laboratory