NEW BEDFORD, Mass. — April 10, 2011 – The term “overfishing” carries far more metaphoric weight than practical meaning, according to Dr. Brian Rothschild, Montgomery Charter Professor of Marine Science at the University of Massachusetts Dartmouth School for Marine Science and Technology. In “The Overfishing Metaphor,” a paper recently published for the American Institute of Fishery Research Biologists, Dr. Rothschild issues a bold challenge to a long established paradigm, arguing that outmoded benchmarks are hindering real-life fisheries management.
“The golden metric is whether stocks are overfished or not,” explains Rothschild. In other words, is the rate of fishing incompatible with sustaining future healthy fish populations? The answer to this question is determined by calculations — through various mathematical formulas that attempt to relate the magnitude of an entire fish stock to fishing mortality — to determine if that number is greater than a pre-determined maximum yield. “But those determinations are being based on models created 50 or more years ago and do not consider the nuances of the latest science. Theoretically, fisheries are supposed to be managed with the best available science.”
In the first part of his paper, Dr. Rothschild explains how quantitative theories from the 1940s and 1950s helped foster the belief that practical definitions of overfishing could be developed from mathematical models linking fishing mortality and population abundance. But for a number of reasons, the resulting models prove to be insufficient, as Dr. Rothschild points out. He writes that they, for one, do not in general correspond with real data, and they are difficult to interpret.
“[T]hese deficiencies result in applications that do not describe the dynamics of fish populations,” writes Dr. Rothschild. “A consequence of this is that stock abundance and fishing mortality are not always tightly coupled, reflecting that the theories of fishing can only be considered to be metaphorical representations of the relationship between fishing mortality and fish population abundance and, as such, associated definitions of ‘overfished/overfishing” are also metaphorical. … [T]hat there is no unique definition of overfishing …, and different overfishing standards are applied to different stocks, make it difficult to interpret overarching ‘mission accomplished’ claims about the success or lack of success of fisheries management.”
Dr. Rothschild also adds that because environmental information is not adequately considered in the models that inform existing policy, claims of overfishing as a culprit are hard to qualify.
The collapse of the cod stock complex in the northwest Atlantic from 1984 to 1994 serves as a telling example. Overfishing was largely thought to be the culprit for the collapse. But, as Dr. Rothschild points out, a moratorium on fishing subsequent to the collapse didn’t result in recovery, as one might expect. That’s because, while overfishing may have exacerbated the decline of the fishery, it was never the primary cause. Dr. Rothschild lists other observations that reflect a widespread deterioration of environmental productivity for the cod complex: the fact that the natural mortality rate (independent of fishing) was significantly increased; growth rates had declined; the fish were exhibiting changes in their diets; and other fish species associated with cod were also exhibiting declines in abundance, growth and condition. But none of these, though, were taken into any meaningful account.
“Our current system clearly isn’t working,” says Dr. Rothschild. “We are being made to fit real data into a model that just won’t allow it to fit.”
What Dr. Rothschild proposes as an alternative is radically and refreshingly simple: to measure fish stock abundance by frequently measuring rate of capture. “If stocks get too small, we can slow fishing down. If stocks get too big, we can speed it up,” he says. This places the focus on obtaining optimum yield rather than depending on poorly defined criteria such as “overfished” and “overfishing.”
Dr. Rothschild explains. “Right now we have a research vessel that conducts random sampling twice a year for 30 minute tows, seeing what they catch at random spots in the ocean,” he says. “They have to not only determine what species they catch but the age structure to determine population demographics. Then they determine the growth rate. Then they estimate catch, and so on. Then they assemble all of these various data into these mathematical equations, which can be very time-consuming. By the time they get answers, the dynamics in the ocean may be totally different and inconsistent with their findings. Nature abhors a vacuum.
“Instead,” says Dr. Rothschild, “we can put impartial monitors on fishing boats to get more direct and regular data that will reflect more of the actuality in the sea and would shift the focus from maximum yield to optimal yield. This would provide more specific information that would enable the determination of ideal fishing targets that would help prevent overfishing or underfishing, which is not even meaningfully considered now, even though it represents important ecological – and economic — significance.”
If his proposal is not yet ready for policy-makers, Dr. Rothschild’s ideas are getting the attention of his peers. “Brian's recent investigations of the overfishing concept demonstrate why he is considered one of the premier fisheries scientists in the world and in the history of our field,” says Steve Cadrin, Director of the NOAA/UMass Cooperative Marine Education and Research Program at the University of Massachusetts Dartmouth School for Marine Science and Technology. “He applies a scholarly approach to understanding the theoretical basis of overfishing, and sees current problems from an enlightened perspective.”
Read Dr. Rothschild's paper "The Overfishing Metaphor".