The impact of overfishing in the Northwest Atlantic can easily be seen by looking at the current composition of its marine food web. Since 1900, and even more dramatically since 1950, large, predatory fish species (such as blue-fin tuna, Atlantic cod, and Atlantic halibut) who were once abundant in numbers, have had their populations decimated by overfishing. This has led to the collapse of those fisheries and the triggering of a trophic cascade. However, those species are not the only ones who have been impacted from the overfishing. As the larger species' populations collapsed, the populations of the smaller, prey fish, rapidly increased as they were "released from predation." This led to fisheries increasing the catch totals of smaller fish species; which subsequently contributed to their overfishing. This process is known as "fishing down the food web."
This has four immediate and significant effects on the marine food web itself. First, it starts to decrease the populations of those next tier, smaller, prey fish. Secondly, because the population of the prey fish significantly decreased; the dwindling, remaining population of predatory fish has then lost a significant part of its food source and their populations approach extinction. Third, as those top two levels of consumers in the food web start to disappear, it allows for the following level (even smaller fish and zooplankton) to overpopulate as they become "released from predation." Lastly, the severe decrease in the top and middle levels of a marine food web from overfishing, causes a food shortage for the top species predators who are not commercially fished. With this nutrient shortage, the food web becomes void of significant predatory species; regardless of whether they were sustainably fished, overfished, or not fished at all. This process can be a vicious cycle and dramatically alters the structure and biodiversity of the ecosystem.
This has four immediate and significant effects on the marine food web itself. First, it starts to decrease the populations of those next tier, smaller, prey fish. Secondly, because the population of the prey fish significantly decreased; the dwindling, remaining population of predatory fish has then lost a significant part of its food source and their populations approach extinction. Third, as those top two levels of consumers in the food web start to disappear, it allows for the following level (even smaller fish and zooplankton) to overpopulate as they become "released from predation." Lastly, the severe decrease in the top and middle levels of a marine food web from overfishing, causes a food shortage for the top species predators who are not commercially fished. With this nutrient shortage, the food web becomes void of significant predatory species; regardless of whether they were sustainably fished, overfished, or not fished at all. This process can be a vicious cycle and dramatically alters the structure and biodiversity of the ecosystem.