November 4, 2010
Scientists Use Virtual Fishing to Test Options for Sustainable Management of Blue Crabs
Now that blue crabs in the Bay seem to be making a comeback, scientists are working with managers to find fishing practices that are both environmentally sustainable and the most economically viable.
Until recently, research was concerned only with biological limits on harvesting. Now researchers, like fisheries biologist Thomas Miller of the UMCES Chesapeake Biological Laboratory, are studying the dollars and cents of blue crab management. They are trying to understand the combined economic and biological impacts of different fishing practices on the long-term sustainability of the stock.
In a study funded by Maryland Sea Grant, Miller along with colleague David Bunnell, is exploring how to fish for blue crabs in ways that bring the most benefit to society.
The first step requires understanding how the blue crab population would behave without fishing pressure, Miller explains. To simulate this, the team developed a mathematical model to track the crab population and represent what happens in the absence of fishing. This was no easy feat, Miller says.
Because crabs undergo successive molts, rather than growing continuously, the stock cannot be tracked as a single entity. Instead, the model must follow the growth of individual crabs, explains Miller. In other words, scientists track all the biological events that happen to an individual crab on a daily basis throughout the year. This includes molting, releasing eggs, and mating.
The second step, says Miller, is to use the model to test the possible impact of alternative fishing policies on the blue crab stock. To obtain the most precise results, management agencies and stakeholders present scientists with different harvest options such as, season opening and closing dates, minimum sizes, and the period in which females can be harvested -- in exact terms. Scientists can then “fish” the computer stock to determine the expected long-term benefit of the different methods.
After analyzing their data, researchers report findings to management jurisdictions. However, they do not simply recommend the most sustainable option. Instead, Miller says agencies asked them to report based on the expected revenue that the fishery would generate. “The agencies wanted to know the results in terms of the total dollar amount,” he adds.
According to Miller, there was surprisingly little difference in the economic revenue that would come from the overall fishery but “substantial differences” in which part of the industry would see the benefit (for example, hard shell vs. soft shell fisheries).
Because there is no clear biological benefit of one harvesting method over another, it is up to the fisherman to determine which method offers the more attractive option. The question then becomes a socio-political one: does society want to promote one category of fishing over another?
Lynn Fegley, Assistant Director of the Estuarine and Marine Fisheries Division of the Maryland Department of Natural Resources (DNR), agrees that there is no easy answer.
She believes that the work scientists, like Miller and his colleagues, are doing is “critical stuff” -- tying market values and fluctuations to population dynamics in order to figure out how to maximize economic benefits. “Unfortunately,” she says “the model, as they have it right now, is not quite ready for us to transition into management.”
Since the scientist's model now includes economic variables, it is more applicable on the ground. However, management still needs to determine the ultimate economic goals for each crab fishery.
This is a huge challenge because there is such diversity among fisheries. All market categories have different values. For example, on Smith Island, a fishery might focus on peelers and soft crabs. In Baltimore, the focus might be on large, hard-shelled crabs that can be sold in baskets. On the Lower Shore, where crabs are picked and packaged, female crabs might take priority.
There must be some tradeoffs or we risk exploiting the crab. “You can’t really have it all,” Fegley says. Boundaries must be set based upon biological limits but will require a conversation about which methods they can utilize to their highest economic benefit. This conversation demands a large stakeholder component, particularly from fishermen themselves.
“If everyone is mad, you’re probably doing a good job,” she laughs.
In all seriousness, Fegley explains that the decision made by DNR is the product of a “very long and arduous process.” “It’s not perfect,” she says, “but it’s as equitable as we can get.”
Miller agrees that research alone cannot bring about a sustainable blue crab fishery but research can define the boundaries of what is possible. “Helping society have the discussion of what it wants, I think, is the next big challenge.”
Science Journalism Intern, Fall 2010