Nathan Cooley
J. Johnston
English 1B, Essay #1
06 February 06, 1,075 words
The One That Got Away
Since prehistoric civilizations first learned how to catch fish with spears, and later with nets, fishermen have chosen to keep the largest fish. The larger fish provide the most sustenance for the same amount of fishing effort, and provide the fisher with the most prestige. As a result, we as a species have intentionally been removing the biggest fish from the gene pool for centuries. These fish were big for a reason. They survived because they had the fittest genes. Genes which best suited their ever-changing environments. Aside from fit genes, larger fish usually produce the highest numbers of offspring, far more than smaller individuals (Gardner). Recently, scientists have begun to wonder if we are inadvertently breeding for smaller (and fewer) fish; unfortunately, their research does not look promising.
All of the scientific data available on this subject points in one direction: down. That is where the average sizes of some of our most economically important marine species are headed. Author Carol Gardner conducted research for her article “I Once Caught a Fish This Big,” in Science magazine, and she found that sizes are in decline for many important fishery species. North Sea cod, plaice (a flatfish), swordfish, multiple species of tuna, shark, and salmon, and Patagonian Toothfish (a.k.a. Chilean Sea Bass)(Nash), are all experiencing average size declines. So are many invertebrate species, such as crab (multiple species) and lobster. Take the Atlantic halibut for example. Once a thriving fishery with individual fish sizes up to 700 pounds, that industry has now collapsed and it is rare to catch a one hundred pound Atlantic halibut (Gardner).
Archaeological excavations in New England have uncovered otoliths from cod that were consumed over a thousand years ago. Otoliths are small bones in the head which help control the fish’s stability. Forming growth rings like those of a tree, otoliths are the most accurate means by which to calculate a fish’s age and size. These otoliths showed that for centuries the average length of cod eaten by locals was just over three feet. Then, just about eighty or a hundred years ago, the average began to drop dramatically. Now the average size of a North Sea Cod in the market is less than a foot (Gardner). Many ecologists and oceanographers speculate that this drop was caused by environmental factors such as a drop in water temperature or insufficient nutrients (“Fish”). This could definitely be a factor; however, it is not that simple.
Most of today’s fisheries are “size-selective.” That means that whether by law or by economic desirability, only the largest specimens are kept for market, while the smaller individuals are either avoided or tossed back. Size restrictions that are enforced by law ignore evolution (Conover/Munch)(“Fish”)(Kettlewell). These laws place minimum legal size restrictions on fish in an effort to allow juveniles a chance to reach sexual maturity. The truth of the matter is that the older, larger fish in a population are usually the most successful breeders, both in terms of competing for a mate and in the number of offspring produced, according to researchers at the Stony Brook Research Center in New York (Conover/ Munch). Consider this: It takes 212 four-year-old Red Snapper females, weighing a little over a kilogram each, to produce nine million eggs. Meanwhile, the same amount of eggs is produced by one ten-year-old female, weighing around twelve and a half kilos (Gardner). It certainly seems wiser, both economically (more fish to sell now), and environmentally (more fish to catch later), to avoid or release the bigger fish. Some fisheries have ways to avoid catching small individuals all together. The lobster and crab industries for example, have special openings in their traps to allow small individuals to go free (“Fish”). With only the smallest individuals left to propagate, the next generation will only possess the genes of the smaller fish. Thus, over generations, fish and other species will continue to shrink in size, “and smaller fish could become more prevalent in future stocks” (Kettlewell).
That is a difficult claim to support because of the lack of sufficient test data and “control” populations, but quality research has been done. Researchers David O. Conover and Stephan B. Munch at Stony Brook, spent over a decade on an experiment to test the effects of different size selection techniques on captive populations of fish. The species they chose was the Atlantic Silverside (Menidia menidia), a small fish on the East Coast. Selected for its similar characteristics to more valued species, Menidia has a high reproductive rate, small eggs (which means more can be produced), and pelagic larvae (free swimming in the open ocean). Menidia also practice a schooling behavior, and they spawn en masse (Conover/Munch).
The experiment began by collecting fertilized eggs from natural spawning grounds and then allowing them to reach maturity under realistic conditions, in a laboratory. Six separate populations (of a thousand fish each) were created in separate tanks and then harvested under specific guidelines. From two of the tanks only the largest 90% were harvested. These were the large-harvest populations. From another two tanks only the smallest 90% were harvested, making these the small-harvest populations. The remaining two tanks had 90% of their populations harvested at random, making them the control populations. This procedure was repeated until the fourth generation had matured.
At the end of the experiment their hypothesis was proven to be correct and published in the journal Science. The large-harvest populations produced the highest initial yield and the highest individual fish weight, but then steadily declined. The small-harvest populations had the lowest initial yield and the lowest weight, but increased rapidly. When the fourth generation was harvested the total yield of the small-harvest populations had more than doubled that of the large-harvest populations. More interestingly, the mean weight (average of the largest fish) of individuals in the small-harvested tanks was more than six times that of the large-harvested tanks (1.05g large-harvested, compared to 6.47g small-harvested, and 3.17 random-harvested) (Conover/Munch). The scientists concluded that “because fecundity increases with size, small-harvested lines evolved much higher reproductive potential than did large-harvested lines.” (Conover/Munch).
The disappearance of big fish cannot be blamed solely on global warming, pollution, or over-fishing. These are a small factors, but the main causes are our current size-selective practices and misguided management techniques. Many researchers agree that by establishing and enforcing minimum and maximum size restrictions, we will be able to bring back the big ones, as well as rebuild our dwindling fish populations (Conover/Munch) (Kettlewell).
The future of our fisheries is in our hands. From the congressman, to the fisherman, to the consumer, it is our shared responsibility. If we do not take action soon, the big one will get away, forever.
Works Cited:
Conover, David O., Stephan B. Munch. “Sustaining Fisheries Yields Over Evolutionary Time
Scales.” Science 05 July 2002: 94. Science AAAS. ProQuest. Coll. of the Redwoods Lib.,
Mendocino Campus. 2 Feb. 2006. http://proquest.umi.com/pqdweb?did=136855501&sid=3&clientld=14510&RQT=309&VName=PQD
“Fish She Is Very Small.” The Starving Ocean. 2 Feb. 2006.
http://www.fisherycrisis.com/smallfish.html
Gardner, Carol. “I Once Caught A Fish This Big.” Blue Planet Fall 2002:16-21. Environmental
Oceanography Syllabus spring 2006. Greg Grantham. 29-34.
Kettlewell, Jo. “Fish Policies ‘Ignore Evolution’.” 4 July 2002. BBC News Online. 2 Feb. 2006
http://news.bbc.co.uk/2/hi/sci/tech/2094580.stm
Nash, J. Madeleine. “The Fish Crisis.” Time 11 Aug. 1997: 65-67. Environmental Oceanography
Course Syllabus Spring 2006. Greg Grantham. 109-111.