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... We almost never directly observe what is going on beneath the surface of 70 percent of the planet, and yet US fishing rules and regulations demand that scientists predict how many fish are in a given sea.
So scientists and fishermen and everyone else rely on computer models that mimic what is known about fish. Into the models goes information like size, age, growth rate, how many fish will die of natural mortality (predation, disease, moving away from the area) and how many are taken in the fishery.
Lobsters lack body parts like ear bones that help to reveal the age of other species; as a result, modelers use lobster size instead. But even size can be misleading, because lobster growth rates also vary with temperature: the warmer the water, the faster they grow. And since most lobsters move around throughout the year and over the course of their lives, their growth rate does not stay the same.
Variable growth rates can have surprising effects. According to Dr. Yong Chen, a fisheries scientist at the School of Marine Sciences at the University of Maine, the lobsters that grow into the size that can be legally harvested during any given year can include individuals born over a seven-year time span. In other words, the lobster on your plate could be four years old and the one on your friend's plate could be eleven years old, even if they are both one-pound lobsters that were caught in the same trap.
These facts complicate computer models. Throughout the 1990s and early 2000s, the National Marine Fisheries Service model consistently underestimated the number of lobsters in the sea, and therefore overestimated the percentage being caught in the fishery each year, leading federal scientists to believe that overfishing was occurring in the Maine lobster industry. Yet year after year, catches went up and research surveys recorded higher and higher numbers of lobsters. Clearly the model wasn't working.
Fast forward to 2008: The Atlantic States Marine Fisheries Commission and the National Marine Fisheries Service officially adopted a completely new model that estimated the lobster population as "not overfished."
This transformation occurred largely thanks to the talent and tenacity of Dr. Yong Chen.
According to Chen, there are four main areas where his model improved on the prior version. "We included the inshore trawl data from Maine and other state surveys, in addition to federal survey data; we had better catch data to work with than before; we had more realistic biology built into our virtual lobsters; and we used a statistical approach that incorporates margins of error in our inputs (this approach uses Bayesian statistics)," he said.
But how do we know that the new model is right versus less wrong?