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Human History of Fishery Exploitation and Marine Trophic Dynamics

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Human History of Fishery Exploitation and Marine Trophic Dynamics

The World's Oceans cover approximately 70% of the Earth's surface; and has been an integral part of human history and development (Brett, Clausen). These large bodies of water are filled with marine life, and provide mankind with food as well as various ecological services. The vast resources and value of the world's oceans have been depended on by the human race virtually since its origin. In early history, marine vegetation and fish were harvested on a subsistence level. As mankind progressed, and populations increased, the nature of there relationship with marine environments shifted from a subsistence based practice to that of a commercial nature. Fish were no longer harvested on a level relative to the individuals and families it provided for, but became an industry tethered to supply and demand. This change altered the dynamics between man and the oceans when commercial fishing effectively became a "commodities market" (Brett, Clausen). Certain species carried higher values than others and fishing practices became exploitive as the supply was thought to be endless within the huge bodies of water. However, at the time marine ecology was little understood and thus sustainable fishing practices were ignored as well as the not yet realized affects the commercial fishing industry had on trophic dynamics. As commercial fishing developed and spread along with population increase, intensive extraction by industrial fisheries became normal. Increased demands were placed on the oceans and overfishing resulted in severe depletion of wild fish stocks. In Richard Ellis' book Empty Oceans, he states, "Throughout the world's oceans, food fishes once believed to be immeasurable in number are now recognized as greatly depleted and in some cases almost extinct. A million vessels now fish the world's oceans, twice as many as there were twenty-five years ago". Estimates have stated that at the current rate, we are on the path to reducing half of Earth's plant and animal species to extinction or critical endangerment by the end of the century (Brett, Clausen). Despite the conservation efforts and the acceptance of humanities role in the degradation of marine environments; the depletion of fish stock and stable marine ecosystems continue to progress. This is an issue of great importance because the activities of man are directly linked to the worlds oceans, and mankind is deeply reliant on the resources that come from stable ocean environments. Over our history in commercial fishing there has been irreversible damage done to the higher trophic level marine mammals. Analysis of Oceanic systems shows a serious image of the coevolution of human society and the marine environment and its species. Upper trophic level Marine Mammals have a history exploitation on perhaps an irreversible scale. Whales were hunted on a tremendous level starting from 800-1000 A.D. to the point of extinction until December 1996, when the International Whaling Commission (IWC) was established (Svedrup,Armbrust). At that time the IWC was tasked in the interests of commercial objectives in order to provide for whale conservation in the interest of developing a sustainable industry rather than to protect the environment or the species from extinction and the possible outcome within trophic dynamics if whale population were to fall under a certain level. In the 1970's sentiments towards whaling changed significantly to the point where in 1982 the IWC, in a moratorium, changed its stance on whaling to that of conservation when they essentially ended the commercial whaling industry by outlawing harvesting or hunting whales (Svedrup,Armbrust). The aim was for whale populations to recover to their earlier populations prior to the massive human predation that had gone on for centuries. However this was a more daunting task than expected and simply outlawing commercial whaling would not achieve the goal. Impediments towards restoring the previous whale populations were numerous. For example Whales have a large dependence on Krill for food supply; which at the time was massively exploited as a protein source and as an animal feed additive by humans, another obstacle is the limited number of mates available for reproduction due to such low population levels. Dolphins and Porpoises are also facing danger in the last two decades. In a 1990 United Nations sponsored symposium it was reported that more than 1 million of these mammals die each year, usually as a result of being unwanted by-catch of the existing commercial fisheries, which throw away the species that are not desired (Svedrup,Armbrust). The Mexican Porpoise and the Black dolphin of the Chilean coast are examples of marine mammals becoming endangered due to commercial by-catch. Not only has the development and expansion of commercial fishing led to the severe depletion and even extinction in some fisheries and species. Commercial fisheries that harvest fish in disregard for the ecosystem in which they operate, also can cause major disruptions in the food webs, interactions between the varying trophic levels, and the marine life interdependency within the previously stable ecosystem. In a stable ecosystem, derived of a multitude of marine species. Marine organisms interact amongst themselves as well as their environment to maintain the stability of the ecosystem they inhabit. Due to the human interference within the synergy of these complex ecosystems, multiple trophic and spatial scales can be disrupted when certain species are harvested for commercial use. These actions constantly decrease the natural processes and stability of the ecosystems. The impact of human activities on marine environments have been an area of conflict in recent history. Where demand requires certain fish, while harvesting those fish can cause a chain of events that destroy the original environment. Food webs are most commonly described in a pyramid organization. Photosynthetic phytoplanktons form the base of the food web because they generate the organic matter that is consumed by other organisms higher on the food web. Photosynthetic phytoplankton are an example of primary consumers. A variety of organisms in the Zooplankton category directly consume the phytoplankton, and are generally referred to as herbivorous zooplankton. These types of zooplankton are categorized as primary consumers. Carnivorous zooplankton in turn, feed on the former zooplankton classification, and are classified as secondary consumers (Strong,Frank). Normally the flow of energy and food between different species in the food web is fairly direct, in which smaller organisms are consumed by larger organisms. Each of the classifications represents a trophic level. All food webs consist of a series of interactions between different groups of organisms. However, some food webs are more complex. The differences occur relative to ecosystems location in a marine environment, which in turn affects the complexity of the food web.

Depending on location, after the first level carnivorous consumers, second level carnivorous consumers and third level carnivorous consumers follow, which are comprised of different types of fish depending on location. For example in coastal regions Herring may represent second level carnivorous consumers. Fishing exploitation can result in what is called a Trophic Cascade where the food web is disrupted by the removal of either the bottom level producer or the top-level consumer (Strong,Frank). If a top-level producer is removed it is referred to as a top-down cascade, and bottom-down cascade in the instance of a removal of a bottom level producer. Trophic Cascades have can completely throw off the stability of an ecosystems synergy. An example of a top-down cascade as a result of fishery overexploitation of cod on Canada's Scotian Shelf on the Eastern coast. Within this ecosystem it is estimated that in 1505 there were 7 million tonnes of Cod swimming within the area by the time the Cod moratorium was announced in 1992 there were only 22,000 tonnes left from the overexploitation of the fishery (Strong,Frank). Even after the fishery was closed for more than a decade the Cod stocks have failed to rebound due to the affect of its removal over the course of the fisheries harvesting. As a result of the drastically lower levels of cod, the populations of small fishes and large invertebrates including the Northern Snow Crab increased dramatically, the population of large plant eating zooplankton decreased as well because of the lack of a higher trophic level consumer, phytoplankton increased a great deal as well, and seal populations increased exponentially. Another example is in the complex cascade effects of kelp forests. In 1968, the rocky floor of St. Margaret’s Bay, Nova Scotia, was completely covered by a dense kelp forest and urchin biomass. The urchin biomass in most cases averaged 150g/meter squared, however there were several areas where the urchin biomass was much higher and where kelp had been entirely removed leaving coralline barrens. At first these were small and temporary but became progressively larger until the point where most of the kelp beds were completely destroyed. This was a result of another Top-down cascade where the overfishing of lobster (Strong,Frank). Without an abundance of Lobster to eat the Urchins, they were free to feed on the kelp forests until they were destroyed.

Despite the prevailing knowledge that action must be taken to restore currently and previously exploited fisheries, commercial value has been a powerful presence to combat. The friction between the market for fish and the need for restoration has produced an array of areas of declining, collapsed, and rebuilding fish stocks and ecosystems around the world. Management actions both by public organizations and government order have accomplished measurable reductions in exploitation in some areas of the world. However a significant portion of fish stocks remain in danger. A major problem in effective reductions is the lack of jurisdiction in the open ocean as well as governments that openly oppose any efforts to restore fisheries. Even Whaling is still prevalent in countries such as Japan, Norway, and Iceland who have ignored the pleas made almost unanimously by countries on Earth (Worm et al). Already it has been maintained that the damage done will affect selective fisheries for decades and even centuries to come. The main hurdle for a more efficient commercial fishing industry is jurisdictional lines that hinder the ability for an overall rule. The peril caused by trophic cascades have caused problems that do not only extend to the Earth's oceans. Phytoplankton and other photosynthetic marine organisms are a critical part of the World oxygen supply, absorbing carbon dioxide and producing oxygen. The worlds oceans and there inhabitants have a direct correlation to humanity and its survival. Fishery Exploitation and Trophic Cascades are just part of the issues that are effecting the world oceans. Harvard Professor Edward O. Wilson coined the acronym HIPPO to describe the ways that biodiversity is currently being threatened. H standing for Habitat destruction, I for Invasive Species, P for pollution, P for population growth of human communities, and O for over-harvesting (Worm et al). There are an array of issues facing the Oceans stability, and the only way to combat it on a successful level is for a uniform approach.

Works Cited

Clark, Brett, and Rebecca Clausen. "The Oceanic Crisis: Capitalism and the Degradation of Marine Ecosystem." Monthly Review 60.3 (2008): 91. Print.

Strong, Donald R., and Kenneth T. Frank. "Human Involvement in Food Webs." Annual Review of Environment and Resources 35.1 (2010): 1-23. Print.

Sverdrup, Keith A., and E. Virginia Armbrust. An Introduction to the World's Oceans. Dubuque, IA: McGraw-Hill, 2009. Print.

Worm, B., R. Hilborn, J. K. Baum, T. A. Branch, J. S. Collie, C. Costello, M. J. Fogarty, E. A. Fulton, J. A. Hutchings, S. Jennings, O. P. Jensen, H. K. Lotze, P. M. Mace, T. R. Mcclanahan, C. Minto, S. R. Palumbi, A. M. Parma, D. Ricard, A. A. Rosenberg, R. Watson, and D. Zeller. "Rebuilding Global Fisheries." Science 325.5940 (2009): 578-85. Print.

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