Marty presented this at App State back in 2013:
The study's researchers captured the hypoxia effects by reviewing the month-to-month price changes of various market sizes of shrimp. They compared that data to the periods when low-oxygen conditions were present.
In a telephone interview, Smith said researchers have known for years that low oxygen levels in water stresses individual fishery species such as shrimp, including causing them to grow less quickly. "That will concentrate more smaller individuals in the population, and they also tend to aggregate on the edges of the hypoxic areas," he said.
That creates what he calls a "burning building effect" that shrimpers use to their advantage. "The shrimp swim out of the hypoxic area but bunch up just outside, like if you were running out of a burning building to get clear but stay nearby," he said.
Shrimpers tend to fish in those locations as the effects of hypoxia occur. That results in the capture of both the smaller shrimp and the larger shrimp in greater numbers than if they were fishing in the hypoxia-affected areas.
The researchers monitored the price of different market sizes of shrimp between 1990 and 2010, from the largest shrimp category (1 to 15 shrimp per pound) to the smallest (50 to 67 per pound). "The price of large shrimp rises higher because fewer large shrimp are caught when there's a bad hypoxia year, so there's upward pressure," Smith said. "But they can also end up with even more small shrimp, causing the price of small shrimp to go down."
In the past, researchers attempted to measure the effects of hypoxia by tracking landings -- the number of shrimp caught -- at different locations along the coast. But that did not take into account the response of shrimpers to hypoxia: They fish for shrimp where species congregates, outside the hypoxic areas.
The new study looks at the prices of different size shrimp with an understanding of where they're caught and other factors that add to their purchase price. For instance, shrimpers who target shrimp outside hypoxic areas might be using more diesel fuel to reach the location. And when the the response of foreign markets to higher large shrimp prices is added in, hypoxia's effect on prices becomes more clear, Smith said.
The paper was published in PNAS. Here is the "significance" paragraph from the abstract page:
Coastal hypoxia is a growing problem worldwide, but economic consequences for fisheries are largely unknown. We provide evidence that hypoxia causes economic effects on a major fishery that was once the most valuable fishery in America. Our analysis is also a breakthrough in causal inference for coupled human-natural systems. Although establishing causality with observational data is always challenging, feedbacks across the human and natural systems amplify these challenges and explain why linking hypoxia to fishery losses has been elusive. We offer an alternative approach using a market counterfactual that is immune to contamination from feedbacks in the coupled system. Natural resource prices can thus be a means to assess the significance of an ecological disturbance.
Here is my favorite part of the paper: