San José State University
Department of Economics
& Tornado Alley
of the Grand Banks
The fishing of the Grand Banks off the coast of Newfoundland by Portuguese or Spanish fishermen may have begun even before the voyages of Columbus. In any case by the 16th century there were hundreds of ships plying the sea lanes between Europe and the Grand Banks carrying home cargoes of codfish which became a major staple of the diets of the people of western Europe. The harvest of cod was enormous and probably seemed endless, but it did end abruptly in the 1990's after a 15 year attempt on the part of Canada to bring it back after a near collapse in the 1970's. In 1968 the cod catch from the Grand Banks was 810,000 tons; in 1974 it was 34,000 tons.
Part of the problem was the development of more effective methods for netting up codfish. The dimensions of drift nets became enormous. Not only did these large nets haul in large numbers of fish but when lost they were devastating to the cod population. Lost nets would catch fish by the gills and drift to the bottom of the sea where the fish would die. Scavenger fish would clean the nets of those dead fish whereupon the net would float away to snare another catch of fish and this cycle would continue until the nets rotted or were destroyed.
Fishing companies developed trawling ships which pulled a bag-like nets behind them sweeping up all the fish in their path. The otter trawlers increased the effective of the trawl nets by putting chains on the bottom edge. In the 1980's some fishing companies also developed rock hopper dredges, which were nets with bottom edges held up by large wheels. This allowed the cod fishers to net cod near the bottom of the ocean without the nets snagging on rocks and other obstructions.
The other technological development which increased the catch of cod was the electronic scanning devices that helped the fishermen locate the schools of codfish.
The Grand Banks are part of the continental shelf of North America lying under the relatively shallow depth of a hundred to three hundred feet of ocean water. Up until 1977 the Grand Banks were part of the open ocean where the ships of any country could fish without limit. In 1977 Canada along with all other nations of the world with coastal boundaries extended its national sovereignty from a three mile limit to a 200 mile limit. This created the opportunity to manage and preserve the fish populations of the Grand Banks. Canadian fisheries experts advised their government that the imposition of proper catch limits would allow the cod population to recover so that by the mid-1980's the annual catch could be increased to 500,000 tons. They estimated that the Total Allowable Catch (TAC) should be 16 percent of the cod population.
Adult female codfish lay eggs into the ocean water and these eggs rise to the surface and float there. If the eggs have been fertilized by the sperm male codfish inject into the ocean water the eggs will hatch. Female codfish produce from 2 to 11 million eggs per year so the potential for reproduction of the cod population is very great but there are many contingencies involved. First is whether the male and female codfish can find each other. When the density of codfish in an area of the ocean gets low the probability of the eggs being fertilized drops off precipitously. Then there is the danger of the fertilized codfish eggs being eaten by other creatures. Herring eat codfish eggs but the herring population is kept in check by the size of the mackerel population because mackerel eat herring. Thus the hatch of codfish depends indirectly on the size of the mackerel population.
After the new codfish hatch from the eggs they stay at the surface until they are about an inch long; then they swim to the bottom where their survival depends upon finding an area with rocks and other irregularities where they can hide from predators. The rock hopper dredges were devastating to the cod population because they fished the areas that previously had been the refuge for young cod.
Although both young and old female codfish produce eggs it is the eggs of the old females which have a better chance of hatching and produce baby codfish that have a better chance of surviving. Therefore it is not just the total population of female codfish that is important. The age distribution is important as well.
Since the policies of fisheries management allowed a certain fraction of the stock of codfish to be harvested the crucial matter was the determination of the stock. It is not obvious how any measurement of the number of wild creatures can be obtained. It is done through sampling, tagging, releasing and re-sampling.
A sample of the wild creatures are captured and tagged, say 100 specimens. These are released back into the wild population. After sufficient times has passed to allow the thorough mixing of the tagged specimens with the general population another sample is captured. The portion of the tagged specimens found in the second sample indicates what portion of the total population the first sample was. Suppose the proportion of tagged specimens in the second sample was ten percent. This means that the first sample was about ten percent of the total population. Thus the total population was 100 divided by ten percent or 1000 creatures.
There is the possibility that some of the tagged specimens died between the first and second sample. he survival rate can be estimated by taking a third sample. Suppose in a third sample taken after a period time equal to that between the first and second sample the proportion of tagged specimens were eight percent as opposed to the ten percent in the second sample. This means that the survival rate for one sampling period is 80 percent. This means that of the 100 tagged specimens there were only 80 which could have been captured in the second sample. Thus these 80 constituted 10 percent of the population at the time of the second sample and thus the total population at the time of the second sample would have been 800. This would also be the estimate of the population at the time of the first sample. specimens were eight percent as opposed to the ten percent in the second sample. This means that the survival rate for one sampling period is 80 percent. This means that of the 100 tagged specimens there were only 80 which could have been captured in the second sample. Thus these 80 constituted 10 percent of the population at the time of the second sample and thus the total population at the time of the second sample would have been 800. This would also be the estimate of the population at the time of the first sample.
There are special problems involved in sampling a fish population. Fish tend to congregate in schools. Even with any proclivity of fish to seek each other there would be concentrations of fish populations in the areas of the best feeding. Thus even when the codfish population of the Grand Banks was getting low there would be areas of high density of cod.
The supervision of the Grand Banks became the responsibility of the Canadian Department of Fisheris and Oceans (DFO). The DFO did random sampling of areas of the Grand Banks to estimate the total stock of cod fish. The DFO's estimates of cod population became a matter of political controversy. Fishermen, not understanding the concept of random sampling, objected to the DFO's estimate on the basis that the DFO had sampled in a lot of places where there were no fish instead of only sampling where there were a lot of fish.
The fishermen had other reasons to doubt the validity of the DFO's cod population estimates. When the DFO sent a government trawler to fish along side of private company trawlers the private trawlers caught several times more fish than the government trawler as a result of more effective use of the same sort of equipment. For example, the private trawlers were careful to keep the lines to the nets of equal length where as the government trawler did not which led to the net being skewed.
The DFO formulated a mathematical model of the cod fish population which they used to calculate the maximum sustainable yield (MSY). The U.S. government had a similar concept which was called optimal yield. These models were single species models that did not take into account the complexity of the fish eco-system. They were, in a word, defective.
In 1989 the DFO advised that the total allowable catch (TAC) of codfish should be 125,000 tons. The Canadian Minister of Fisheries thought this figure was too low and arbitrarily increased it to 235,00 tons. In the course of DFO management the TAC was often set by negotiation between the DFO, the fishing industry and politicians. The DFO, using their defective model, was setting setting the TAC too high. The politicians responding to pressure from the industry increased the TAC from the already too high figures. The net result was that in the last years of codfishing on the Grand Banks the catch was about 60 percent of the population instead of 16 percent. The collapse was catastrophic. In January of 1992 the DFO was advising that the TAC should be 185,000 tons. By June of 1992 the DFO was advising that the cod fishing should be stopped.
Orrin H. Pilkey and Linda Pilkey-Jarvis, in their book Useless Arithmetic: Why Environmental Scientists Can't Predict the Future summed up the case of the Grand Banks cod fisheries as follows:
It is accurate to say that in the case of the codfish debacle [the DFO] made one of the most important and far-reaching scientific blunders of the age. [page 9]
(To be continued.)
Orrin H. Pilkey and Linda Pilkey-Jarvis, Useless Arithmetic: Why Environmental Scientists Can't Predict the Future, New York, Columbia University Press, 2007.