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The computer screen displays a lobster trap distribution map of the Maine coast, developed in Yong Chen's lab.

Illustration by Carrie Graham


Taking Stock
UMaine marine scientist's models of fisheries population dynamics aid resource management

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Fifteen years ago, a lobsterman who agreed with a government scientist was a rare if not impossible find. Number crunching by regulatory agencies showed that lobsters were overfished, while the men and women hauling traps in the Gulf of Maine were harvesting record numbers of crustaceans. Everyone was using a different source of information and nothing made sense. Disagreement led to mistrust, some bitter words and overall discontent in the world of lobsters.

Was the lobster population healthy or not?

For answers, the University of Maine and Maine Department of Marine Resources (DMR) turned to Yong Chen.

"My work is like being an ecological detective," says Chen, a fisheries population dynamics researcher who came to UMaine in 2000 from Memorial University of Newfoundland. "You collect data from wherever you can and try to create a story about why species numbers are changing. From there, you can estimate what kind of impact fishing would have on a population."
Chen has analyzed fish populations in Canada, Australia and China, but the stock assessment needs in the northeastern U.S. are different, he says.

"In many ways, they were behind the times," he says. "On the West Coast, in Australia, they were using newer technology and methods. And there was this history of problems because the assessment of lobster kept predicting overfishing. So I came at the right time, because people were ready for something new."

Counting lobsters is no trivial matter. Lobster is one of the most valuable fisheries in the U.S., generating $350 million each year, and Maine's 7,000 license holders bring in about 75 percent of all the lobsters landed in this country.

Chen's first task was to identify potential problems with the existing stock assessment. One concern was that the model used only one source of survey data, which didn't include the range of lobster sizes and ages.

Many marine stock assessments are age-based, taking into account the proportion of older and younger fish in a given population. But lobsters, like most invertebrates, do not have the ear bones and scales that record growth over the years.

Chen developed a new computer model based on lobster size that accounted for many factors, including seasonal patterns and lobster
biology. Different management scenarios can be plugged into the model to predict results of different fishing activities, such as v-notching.

Before, v-notching (the practice of fishermen marking reproductive female lobsters with a v-shaped notch in their tails and not keeping any such marked lobsters in their catch) was undocumented and unsupported by the government and fisheries scientists. Chen's models have helped confirm that v-notching has made a difference in the lobster fishery by protecting reproductive stocks, says Carl Wilson, a DMR lobster biologist.


Fisheries population dynamics is a complex and sophisticated field. In the Northeast, only two or three people are familiar with these models and use them on a routine basis, says Larry Jacobson, a biologist with the National Marine Fisheries Service.

Whether modeling population dynamics of lobsters, Jonah crabs, seaurchins, sea cucumbers, groundfish or marine worms, Chen must work with limited surveys conducted by the state and federal governments, and the catch reported by harvesters. The more information Chen has about a species and its environment, the better he can build his computer model, but there is always some negative space. To fill in the gaps, he uses various statistics that let him assume certain situations.

The lobster stock assessment model developed by Chen, Wilson, Jacobson and postdoctoral researcher Minoru Kanaiwa endured rigorous review for years before the Atlantic States Marine Fisheries Commission adopted it for the 2008 lobster assessment. Chen's tool will be used to assess all the lobster stocks in the United States.

Because the model is so complicated, Chen is developing a user-friendly version for biologists and fishermen. Ph.D. student Michael Errigo is doing further testing, funded by a three-year fellowship from the National Marine Fisheries Service, the National Sea Grant College Program and UMaine.

The rigors of Chen's field and his work require that people trust him. "What Yong and his lab have been able to do, in a remarkably unconfrontational way, is to introduce new methods and ways to evaluate how we assess lobster stocks. He is cutting edge in his field," says Wilson.

For Chen, the key is in working closely with managers and biologists, and attending government meetings to get input. He also maintains a global perspective as an adjunct professor at both Central China Agricultural University and Shanghai Fisheries University, and a visiting professor at National Taiwan University. He served as a consultant to the United Nations, studying the impacts of the Gulf War on the fisheries of the Middle East.

"Trust-building is a long process, but it works," he says.


More models are needed for more fisheries, which will require more experts like Chen. But with a shortage of well-trained people with technical fisheries expertise, one of Chen's critical responsibilities is in preparing the next generation of marine scientists in fisheries dynamics, says Jacobson.

Students tend to prefer marine biology or even economics to population dynamics, which requires knowledge of biology (How long do lobsters live? How often do they mate?), ecology (How do lobsters interact with other species? What are the migration patterns?), statistics (What is the probability of a given population in a given time frame?), math (What is the formula for exponential population increases?), computer science (Can I write a computer program that will calculate all of the above?), and policy (What do the outcomes need to look like so the government can decide on their regulations and fishermen can keep their jobs?).


Today, Chen has nine graduate students in his lab, many who are working with DMR and fishermen while pursuing their research. Chen also regularly meets with DMR staff and many DMR employees take his course in fisheries population dynamics.

In turn, DMR provides Chen with data collected in its trawl surveys and landings reports from fishermen, which he uses to develop models and assessments that he hands back to the agency.

"He's really interested in the nuts and bolts of fisheries science, and he understands that fishermen need good models and assessments," says Linda Mercer, resource management director with DMR. "He's enthusiastic about new methods. He seems pretty undaunted by the needs we've thrown his way, species after species."

Chen designed the first-ever stock assessment for Maine's sea urchins, and he was the first to study the population of sea cucumbers - a species that has the potential to become a new fishery without much knowledge of the animal's biology. A sea cucumber model to estimate population and biomass will allow DMR to determine if the fishery can be expanded, and get more people fishing, says Mercer.

Sheril Kirshenbaum worked on the sea cucumber project as a graduate student pursuing dual degrees in marine policy and marine
biology.

"The emerging fishery provided invaluable experience," says Kirshenbaum, who graduated in 2005 and is now an ocean and coastal policy research associate at the Nicholas Institute for Environmental Policy Solutions at Duke University.

"I was involved in understanding the population dynamics of a fascinating species, while exploring real-world socio-economic and political implications. Science informs policy, and this was the ideal setting to learn to communicate between worlds."

by Catherine Schmitt
September-October, 2008

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