The impact of human activities on sharks in the northwest atlantic Essay
The impact of human activities on sharks in the northwest atlantic
The earth is a finite space. Everyone and everything on it must share its vast yet limited resources, and the actions of one species effects many, if not all, others. Over time, we have come to realize that human activities are having disproportionately negative effects on the global environment. An excellent example of this within the marine biome can be seen in analyzing shark populations of the Northwest Atlantic. In their study, “Collapse and Conservation of Shark Populations in the Northwest Atlantic” (2003), Julia K.
Baum, et al. traced the changes in the populations of eight shark species from 1986 to 2000 (two species were only recorded from 1992 onward). They looked at the areas comprised of the “Caribbean, Gulf of Mexico, Florida East Coast, South Atlantic Bight, Mid Atlantic Bight, Northeast Coastal, Northeast Distant, Sargasso/North Central Atlantic, Tuna North/Tuna South. ” In this region, they noted an 89% decline in the hammerhead shark population over a period of 14 years.
Similarly, white sharks declined 79%, tiger sharks 65%, and thresher shark populations declined by 80% between 1986 and 2000. In fact, each of the eight species saw a population decline over the course of the study. The study concludes that “The magnitude of the declines estimated…suggests that several sharks may also now be at risk of large-scale extirpation. ” The study goes on analyse the causes of such drastic decline over such a short period of time.
Citing overfishing as a significant culprit it claims, “In the past half century, as fishing fleets expanded rapidly in the open ocean, have large marine predators been subject to this intense exploitation. ” Overfishing however is not a new phenomenon, and has indeed been a factor in depleting populations of marine species historically as well. In his 2001 colloquium paper, “What was natural in the coastal oceans? ” Jeremy B. Jackson cites 19th century overfishing in cause “live coral abundance declined to 1-2% cover from values of 50% or more” in the 1908s.
He claims that while this was noted in the 1980s it is the result of historical trends by determining, “Coral communities did not change noticeably until the epidemic mortality of Diadema antillarum in the 1980s because ecological redundancy of herbivores obscured the potential effects of the loss of large herbivorous fishes for well over a century. Macroalgae were not able to overgrow corals until the last major herbivore was lost from the system.
” The ramifications for sharks and other carnivorous species as is significant because declining herbivore populations means there is a food scarcity and thus will result in a decline in predator populations as well. The Baum study notes that their finding of “large and rapid declines…are in addition to substantial historical reductions. Overexploitation of elasmobranchs (sharks, skates, and rays) is known to have already nearly eliminated two skate species from much of their ranges. ” They then engage in a discussion of appropriate measures that could be adopted to counteract the declines their study revealed.
They particularly examine marine reserves an “increasingly popular tool for marine conservation and resource management worldwide” (2002). Using “simple models to analyze the implications of large-scale marine reserves for shark conservation. They ran each of these models with two likely scenarios “(i) after the closure, fishing effort is displaced and changes such that the same total swordfish quota is caught (“constant-quota scenario”); or (ii) fishing effort is displaced but remains constant overall (“constant-effort scenario”). ”
Surprisingly, the study found that “marine reserves can indirectly cause harm if fishing effort is merely displaced. ” They found that while closing one region of the study area benefited some species of that region, it had the potential to harm other species both within the closed region and in other regions of the Northwest Atlantic. Their findings suggest that “if marine reserves are to be effective, their placement is of critical importance, and conservation initiatives must explicitly consider impacts on the whole community of species.
” They concluded that “emphasis on single-species conservation, without controlling effort, simply shifts pressure from one threatened species to another and may actually jeopardize biodiversity. ” This scenario would be much like that of 19th century overfishing in that its results would be indirect and thus their effects might immediately be masked but could show up to be catastrophic in the long-term.
A more recent study further indicated that ensuring species survival would require a 40-80% reduction in fishing mortality, and that “rapid recovery of community bio-mass and diversity usually occurs when fishing mortality is reduced. ” This recovery was noted to be “more variable for single species, often because of the influence of species interactions. ” Thus, the study concluded that multi-species management must be targeted toward the needs of the most sensitive rather than the most robust species in the system.
Finally, in order to most effectively aid in the recovery of predator species of the Northwest Atlantic, the effort must include “reductions in fishing effort, reduction in bycatch mortality and protection of key areas to initiate recovery of severely depleted communities” (Myers & Worm, 2005). Analysis the potential outcomes of any activity is significant because all human activity, not just actions determined to have a negative effect such as fishing, affects the environment.
Even activities whose goal is to benefit another species can have unforeseen ramifications, some of these could even result in further harm to the species or environment they are seeking to aid. Rather than merely rushing to the conclusion that marine regions should be designated as reserves, it is important to examine not only the effects on one species, but look to the larger biome and scrutinize the impact that one variable is likely to have on countless other factors with which it interacts directly and indirectly.
Within the finite space of the earth, any one action regardless of its intent is likely to reverberate throughout the environment and especially be felt within a specific region or biome. Thus, humans must consider all of there actions when working with the marine biome so as to ensure the least possible harm to its species and the larger world in general.
References Baum, J. K. , Myers, R. A. , Kehler, D. G. , Worm, B. , Harley, S. J. , & Doherty P. A. (2003).Collapse and Conservation of Shark Populations in the Northwest Atlantic, Science, 299 (5605), 389-392. Halpern, B. S. and Warner R. S. (2002). Marine Reserves Have Rapid and Lasting Effects, Ecology Letters, 5, 361-366. Jackson, J. B. C. (2001).
What Was Natural in the Coastal Oceans? , Procedures of the National Academy of Science U. S. A. 98, 5411-5418. Myers, R. A. , & Worm, B. (2005). Extinction, Survival or Recovery of Large Predatory Fishes, Philosophical Transactions of the Royal Society B: Biological Sciences, 360 (1453), 13-20.
University/College: University of California
Type of paper: Thesis/Dissertation Chapter
Date: 21 April 2017
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