http:/www.meeloun.com 留学生论文专业定制代写网站留学生Essay写作气候变化对鳗鱼迁移的影响IntroductionFreshwater eel populations are experiencing a worldwide decline,mainly due to overfishing,habitat loss,and barriers to migration(Bonhommeau et al.2008).However,an increasing body of work suggests that climate change poses a significant threat to eel recruitment,currently,and in the future(Bonhommeau et al.2008,Knights 2003).This should be an important consideration for eel management in New Zealand,and is partially explored in August and Hicks 2008 paper:“Water temperature and upstream migration of glass eels in New Zealand:implications of climate change.”The ecological,cultural and economic important of eelsNew Zealand is home to three main species of anguillid fresh-water eel,the endemic longfin eel(Anguilla dieffenbachii),the shortfin eel(Anguilla australis),and the recently discovered Australian longfin(Anguilla reinhardtii)(Jellyman 2009).Both populations have declined from commercial fishing and habitat degradation,but there is more concern for the longfin eel.Aside from being exclusive to New Zealand,longfins are more slow growing and are more vulnerable to current environmental changes than shortfins because of their habitat preferences.Their geographical distribution and abundance has declined over the past decades,prompting its ranking as anAt Risk-Decliningspecies by the New Zealand Threat Classification System(Goodman et al.2014).The status of New Zealand eels are important to many stakeholders because both species have ecological significance and serve as valuable cultural and economic resources(Jellyman 2007,August and Hicks 2008).Eels play a critical role in freshwater ecosystems as the apex predator.As opportunist scavengers,they also serve to remove dead organisms,helping to recycle nutrients back into the system(Jellyman 2012).Because they can prey upon nearly all other freshwater fish,eels have the ability to control other fish(and eel)populations,and even those of introduced species(Chisnall et al.2003).As an endemic New Zealand species and the largest freshwater eel found in the world,there is also much justification to protect the longfin eel and preserve the unique biodiversity of the country.Eels are taonga(cultural treasure)to Maori(the indigenous people of New Zealand).Historically eels were an essential food source of Maori,and remain an significant component of Maori culture and beliefs(Jellyman 2007,Wright 2013).Eels are integrated in their whakapapa(genealogy),mythology(eels are seen as“spiritual guardians of waterways”),and it is important for Maori kaitiakitanga(guardianship)to protect eels so as to restore the mauri(life force)of their rivers(Wright 2013).Both shortfin and longfin eels support commercial,traditional and recreational fisheries.The commercial eel industry is not very large for New Zealand,with eel exports bringing in revenues of$5 million annually(Jellyman 2012).Unfortunately,this commercial fishing industry has still greatly contributed to eel decline locally,prompting demands to reduce or ban commercial fishing of longfins(Wright 2013).Eel decline:a vulnerable life historyPart of the reason eels are so vulnerable is their extraordinary semelparous life history.Mature eels migrate to oceanic spawning grounds(the exact location still unknown,but suspected to be northeast of New Caledonia)where they spawn and die(Jellyman 2009).The larvae migrate back to New Zealand,and metamorphosise into glass,or unpigmented,eels.They arrive at the coast,with peak arrivals in September and October,and migrate upstream through rivers and streams from late winter to early summer.After spending many years,sometimes decades in freshwater,mature eels will then migrate back to their oceanic spawning grounds,continuing the reproductive cycle(Jellyman 2009).Unfortunately,this life history means that(1)eel recruitment is highly dependent on their successful upstream and downstream migration,(2)they take a relatively long time to reach reproductive age,(3)they only breed once per lifetime,and(4)they have limited habitat.All these factors have made it even easier for humans to disturb eel populations.Increased sedimentation in wetlands,lakes and rivers has further diminished available habitat,especially for longfins who prefer clean,clear waters(Wright 2013).The construction of hydroelectric dams largely inhibits eel movement upstream and downstream(Jellyman,2007).Much of the management efforts concerning eels involves facilitating the upstream and downstream migration of eels and other native fishes using ladders,the temporary shutting down of hydroelectric dams,physically transporting glass eels over dams,etc(Jellyman 2007).While there are many localized threats to eel populations,it is also imperative to consider long term,overarching threats to eels populations.A study by August and Hicks aimed to better understand the environmental factors influencing eel migratio