January 8, 2014
The study spearheaded by FSU biology professor Joe Travis advocates that fisheries experts and managers consider how overfishing and environmental changes disrupt species interactions and alter ecosystems, including pushing some ecosystems past their tipping points.
“In order to succeed, fisheries management must focus on species interactions,” says Steneck, a professor based at UMaine’s Darling Marine Center in Walpole.
Historically, Steneck says, fisheries science has focused on population dynamics, sustainable yields and influences of biological and oceanographic processes on fisheries.
“By incorporating a more ecological approach, we argue that managers can better understand the dynamics of a fishery, and which species interactions, if affected, can push the ecosystems that house a fishery past its tipping point,” he says.
The loss of one major species from an ecosystem can have severe and unintended consequences because of the connections between that species and others in the system. These changes often occur rapidly and unexpectedly and are difficult to reverse, say the researchers.
“You don’t realize how interdependent species are until it all unravels,” says study co-author Felicia Coleman, director of Florida State University Coastal and Marine Laboratory.
One case study looks at the collapse of sardine and anchovy stocks — partially as a result of overfishing — in the 1970s in the Northern Benguela ecosystem off Namibia. Subsequently, the far less calorie-rich bearded goby and jellyfish flourished. African penguins and gannets that had preyed on energy-rich sardines and anchovies, have suffered, say the researchers. African penguins and gannets have declined by 77 percent and 94 percent, respectively.
In addition, Cape hake and deep-water hake production plummeted from 725,000 metric tons in 1972 to 110,000 metric tons in 1990, say the researchers, and the population of Cape fur seals has dramatically fluctuated.
In Europe, Steneck points to the Atlantic cod stock’s seeming inability to rebound from overfishing. Currently, the cod’s former prey, a small fish called sprat, has become hyperabundant to the point that it preys on larval cod.
Closer to home, the decimation of cod and other large predatory species also resulted in a proliferation of sea urchins. In the late 1980s, a sea urchin fishery subsequently developed and boomed, but by the mid- to late-1990s, overfishing had decimated that industry.
With sea urchin stocks depleted, the macroalgae eaten by sea urchins increased substantially. This, in turn, created an ideal habitat for crabs, which are major predators of sea urchins.
In the same ecosystem, Steneck says declines in soft-shell clams are due to an explosion of non-native green crabs. “All of these examples result from strong ecological interactions that are not captured in most fisheries management models,” he says.
While it’s easy to write off one such case study, Travis says taken all together, the paper is a compelling case that “tipping points are real, we’ve crossed them in many ecosystems, and we’ll cross more of them unless we can get this problem under control.”
Steneck agrees. “Our paper provides case studies from all over the world illustrating how a chain of events taken with an appreciation for species interactions can contribute to complex problems in fisheries management,” he says.
The study, titled “Integrating the invisible fabric of nature into fisheries management,” was published in the Dec. 23, 2013 issue of Proceedings of the National Academy of Sciences. Travis and Coleman say they hope the research accelerates changes in how fisheries scientists approach ecosystem problems and how fisheries managers integrate system issues into their efforts.
The researchers recommend that more effort be devoted to understanding links between species that set up tipping points in ecosystems and they advised managers be cognizant of data that indicates when a system could be approaching its tipping point.
“It’s a lot easier to back up to avoid a tipping point before you get to it than it is to find a way to return once you’ve crossed it,” Travis says.
Fishing experts generally understand how overfishing affects other species and the ecosystem as a whole but it “needs to be a bigger part of the conversation and turned into action,” Coleman says.
Seven other scientists from the University of Connecticut, University of California-Berkeley, University of California-Santa Cruz, University of Chicago, University of North Carolina at Chapel Hill and the Centre de Recherche Halieutique Méditerranéenne et Tropicale in France participated in the study.