American Eels Habitat and Extinction - Research Paper Example

American Eels Habitat and Extinction The American eel, or Anguilla rostrata, is found mainly on the eastern coast of North America.It has a snake like body with a head almost similar to that of a snake. Only its tail give it an appearance of a fish. In other words, it is difficult to segregate it from snakes. It is brownish in color at the top and yellowish at bottom. One of the peculiarities of these eels is the regular basis of migration. In other words, they may not stay in a particular location for longer periods. They like to travel from rivers to river since it like fresh water very much. It stays major portions of tis life in rivers or fresh water sources and visit ocean mainly for spawning or laying eggs. A female eel can lay eggs as much as four million every year. However, after the egging period is over, it will suffer immediate death. Lafontaine et al. (2008) have pointed out that “Since the 1980s, the American eel (Anguilla rostrata Lesueur) fisheries have declined dramatically in the Lake Ontario–St. Lawrence River watershed providing evidence of a large decline in population of this species (Lafontaine et al., p.185). American eels are decreasing in number over the last few decades because of various reasons such as climate changes, global warming, water pollution etc. Even though, the decline of eels have been noticed as early in the 1960’s, the problem became intensified in the 80’s and 90’s. Eel landing started to decline considerably during the latter parts of the twentieth century, especially 1980 onwards. The decrease in the number of eel landing was calculated based on the catch per unit effort (CPUE) effort. This paper analyses the importance habitat and the reasons of endangerment of American eels. American eels are playing a vital role in marinating the eco system, especially the marine life. They clean up the eco system by eating dead fishes, insects etc. Eels are one of the tastier marine food items and therefore fishermen catch it using different methods. American eels have a complex life cycle and any changes in the environment or eco system can affect them drastically. American eels spawn somewhere in the Sargasso Sea east of the Bahamas and south of Bermuda. Eggs and larvae become entrained in ocean currents and are transported to continents. The Antilles Current and Caribbean Current likely carry larvae toward northern South America, Central America, the Gulf of Mexico, and the Caribbean islands. The Antilles Current may also carry larvae toward the Gulf Stream, which transports eels toward North America’s eastern seaboard or on lengthy oceanic voyage into the North Atlantic region including Iceland and Greenland. Even more amazing than the largely passive transport of eels toward the continent is the active migration of silver eels back to the spawning area as many as 30-40 years later (American Eels, p.2) “Possible causes of the decline are numerous and not mutually exclusive. They include dam-related effects, habitat loss, chemical contamination, fisheries, and global climate change” (Lafontaine et al., p.186). Cote et al (2009) have also supported the arguments put forward by Lafontaine et al. In their opinion, “the causes of anguillid eel decline are numerous and include barriers to migration and hydro-turbine mortality, habitat loss and alteration, fishing, parasitism, pollution, as well as environmental change in the Sargasso Sea and Atlantic Ocean circulation” (Cote et al., p.1935). Hedger et al. (2009) have also supported the ideas of Cote et al and Lafontaine et al. “Worldwide populations of anguillid eels are declining, possibly as a result of climatic oscillations experienced at sea such as the North Atlantic Oscillation, fishing pressure, obstructions to migration, hydroturbine mortality, pollution, competition from non-native species and parasites” (Hedger et al, p.1295) It should be noted that hydroelectric power projects are increasing day by day because of the severe energy crisis facing by America and other countries. In order to exploit the river water for power production, dams were constructed in majority of the prominent American rivers and that also at different locations. Hydroelectric dams prevent the smooth flowing of fresh water through such rivers. It should be noted that eels require fresh water for its existence. Hydroelectric dams will interrupt the smooth flow of water which is necessary to make the river water fresh. The accumulation of pollutants in the dams may cause immense damages to the habitat of eels. Chemical contamination is another major threat for the existence of American eels. Majority of the American manufacturing units dumping industrial wastes into the streams and rivers and these fresh water resources are getting more and more polluted as time goes on. Eels need extremely pure water for its survival. Climate change is another major threat over the survival of eels. Atmospheric temperature is rising because of global warming. The normal temperature of the river water is increasing as a result of global warming and atmospheric temperature rise which is dangerous to the survival of eels. Climatic seasons are also varying very much because of global warming problems. Earlier, winter, summer, spring etc like seasons came only at a particular period of time in an year. However, at present raining and drought happening quite unexpectedly and one among the victims would be the eels. Oscillations taking place in the oceans can also affect the habitat of eels The North Atlantic Oscillation index and inflow of North Atlantic water into the North Sea were negatively correlated with eel abundance, with a lag of 11 years. Increased currents towards the North Atlantic during high North Atlantic Oscillation years may send larvae into the subpolar gyre before they are ready to metamorphose and settle, resulting in low recruitment in the northern part of the distribution area for these years. The Skagerrak time series was compared with glass eel recruitment to freshwater in the Netherlands (Den Oever glass eel time series), and similar patterns were found revealing a cycle linked to changes in oceanic factors affecting glass eel recruitment. The recent decline of eels in the Skagerrak also coincided with previously documented shifts in environmental conditions of the North Sea ecosystem (Durif et al). Surface pressure of water at different place could be different because of climatic changes. In some places, the surface pressure could be more and in some other places it could be less because of the temperature differences. In other words, when temperature increases, pressure decreases and when temperature decreases pressure increases. As the pressure gradient steepens between waters at different locations, strength of the winds and oceanic currents could also be changed. It should be noted that eels are laying eggs in oceans and therefore oceanic oscillations or fluctuations can affect the spawning and hatching process. Another reason cited for the declining of American eels is the changes in sex ratio among American eels growing in different rivers. According to Cote et al. (2009), “It was found that young A. rostrata from Mira River (MR, Cape Breton, Nova Scotia, Canada, an area where both males and females occur) grew faster than those from Grande- Rivi`ere-Blanche” (Cote et al, p.1934). The exact reasons for such growth variations are still unknown even though there are some hypotheses. Regardless of the relative role of environmental v. genetic basis of phenotypic variation, there is still little consensus about the proximate factors, as well as developmental timing of sex differentiation in anguillid eels. Some studies have been proposed that different habitat preferences and environmental characteristics may influence sex distribution and differentiation. Density is also generally believed to play an important role in determining sex whereby high density has generally been reported to produce males. On the other hand many other studies have been concluded that while the exact mechanisms remain to be elucidated, there seems to be growing evidence that sex differentiation as well as habitat preference and survival are at least partially linked directly or indirectly to growth (Cote et al., p.1936) In any case, it is agreed by majority of the scholars that sex is definitely associated with the growth pattern of American eels. It is proved beyond doubt that slow growing eels may become females and they will attain much higher sizes than the rapidly growing male eels. The differences in growth pattern has affected the sex ratio among American eels. In other words, male eels grow much faster than female eels and therefore they may face problems in getting mating partners at the right time. Thus, different developmental characteristics among male and females eels staying in different American rivers are causing many threats to the survival of eels in America. To conclude, American eels are one the verge of destructions because of various reasons such as climate changes, water pollution, construction of hydroelectric dams, oceanic oscillations, changes in sex ratio etc. Eels are spending majority of its life span fresh waters and industrial waste dumping in fresh water sources is a big threat for their survival. Eels are extremely vulnerable to environmental changes and any small changes in the environemnt can cause huge damages to American eels. Works Cited “American Eels”. Web. 15 November 2011. Cˆot´ C. L., Castonguay M., Verreault G. and Bernatchez L. “Differential Effects of Origin and Salinity Rearing Conditions on Growth of Glass Eels of the American eel Anguilla rostrata: Implications for Stocking Programmes”. 2009. Journal of Fish Biology (2009) 74, 1934–1948. doi:10.1111/j.1095-8649.2009.02291.x, EBSCOhost. Durif1, Caroline M. F, Gjøsæter Jakob and Vøllestad Asbjørn L. “Influence of Oceanic Factors on Anguilla anguilla (L.) Over the Twentieth Century in Coastal Habitats of the Skagerrak, Southern Norway. Web. 15 November 2011. Hedger R. D., Dodson J. J., Hatin DCaron. F. and Fournier D. River and Estuary Movements of Yellow-stage American eels Anguilla Rostrata, Using a Hydrophone Array”. 2009. Journal of Fish Biology (2010) 76, 1294–1311 doi:10.1111/j.1095-8649.2010.02561.x, Lafontaine Yves, Gagnon Pierre & Coˆte´ Bernard. Abundance and Individual Size of American Eel (anguilla rostrata) in the St. Lawrence River Over the Past Four Decades. Hydrobiologia. Springer. June 15, 2010. EBSCOhost. Read More