Influence of Climate Change on Eel Migration

Influence of mode careen on Eel Migration launchFresh pissing eel populations be experiencing a worldwide decline, mainly due to over seek, home ground loss, and barriers to migration (Bonhommeau et al. 2008). However, an increasing carcass of work advises that clime tack poses a epoch-making threat to eel enlisting, currently, and in the future (Bonhommeau et al. 2008, Knights 2003). This should be an important consideration for eel centering in virgin Zealand, and is partially explored in opulent and Hicks 2008 paper peeing temperature and upriver migration of methamphetamine hydrochloride eels in sore Zealand implications of climate change. Theecological, cultural and frugal important of eels saucy Zealand is home to three main species of anguillidfresh- pee eel, the endemic longfin eel (genus genus Anguilladieffenbachii), the shortfin eel (Anguillaaustralis), and the recently discovered Australian longfin (Anguillareinhardtii) (Jellyman 2009). Bothpopulations ha ve declined from commercial fishing and habitat degradation, but at that place is lots than concern for the longfin eel.Aside from being undivided to invigorated Zealand, longfins be more slow fathering and are more vulnerable to current environmental changes than shortfinsbecause of their habitat optences.Their geographical distribution and copiousness has declined over the pastdecades, prompting its ranking as an At Risk-Declining species by the newfoundZealand Threat Classification System (Goodman et al. 2014).The status of New Zealand eels are important to manystakeholders because both(prenominal) species have ecological significance and give ear asvaluable cultural and economic re roots (Jellyman 2007, terrific and Hicks2008). Eels play a critical role infresh urine ecosystems as the apex predator.As opportunist scavengers, they in addition serve to remove dead organisms, component part to reprocess nutrients rear into the system (Jellyman 2012). Because they can prey upon n untimely all former(a)freshwater fish, eels have the business leader to control new(prenominal) fish (and eel)populations, and nonetheless those of introduced species (Chisnall et al. 2003). As an endemic New Zealand species and thelargest freshwater eel found in the world, at that place is similarly much justification toprotect the longfin eel and preserve the unique biodiversity of the country. Eels are taonga (cultural treasure) to Maori (theindigenous people of New Zealand).Historically eels were an essential food source of Maori, and remain ansignificant component of Maori culture and beliefs (Jellyman 2007, Wright2013). Eels are integrated in theirwhakapapa (genealogy), mythology (eels are seen as spiritual guardians ofwaterways), and it is important for Maori kaitiakitanga (guardianship) to protect eelsso as to restore the mauri ( spiritedness force) of their rivers (Wright 2013).Both shortfin and longfin eels support commercial,traditional and recreational f isheries. Thecommercial eel constancy is not very large for New Zealand, with eel exportsbringing in revenues of $5 million annually (Jellyman 2012). Unfortunately, this commercial fishing industryhas still greatly contributed to eel decline locally, prompting demands to reduceor ban commercial fishing of longfins (Wright 2013). Eeldecline a vulnerable life history Part of the cause eels are so vulnerable is theirextraordinary semelparous life history. Matureeels emigrate to oceanic spawning grounds (the exact location still unknown, butsuspect to be northeast of New Caledonia) where they spawn and die (Jellyman2009). The larvae migrate back to NewZealand, and metamorphosise into glass, or unpigmented, eels. They arrive at the coast, with peak arrivalsin phratry and October, and migrate upstream through rivers and streams fromlate winter to early summer. afterwardsspending many years, some full points decades in freshwater, mature eels will somigrate back to their oceanic spa wning grounds, continuing the reproductive cycle(Jellyman 2009).Unfortunately, this life history means that (1) eel recruitment is exceedingly dependent on their fortunate upstream and downstreammigration, (2) they take a relatively long time to r distributively reproductive age, (3) theyonly breed once per lifetime, and (4) they have check habitat. All these factors have made it even easierfor humans to disturb eel populations. change magnitudesedimentation in wetlands, lakes and rivers has further diminished availablehabitat, especially for longfins who prefer clean, clear waters (Wright2013). The construction of hydroelectricdams largely inhibits eel movement upstream and downstream (Jellyman,2007). Much of the management effortsconcerning eels involves facilitating the upstream and downstream migration ofeels and other aborigine fishes using ladders, the temporary shutting down ofhydroelectric dams, physically transporting glass eels over dams, etc (Jellyman2007). eyepatch there are many localized threats to eelpopulations, it is also peremptory to consider long term, overarching threatsto eels populations. A think by tremendousand Hicks aimed to better understand the environmental factors influencing eelmigration, and the purposes of their study suggest that we may wish tounderline climate change on the growing list of eel threats (2008). decisionand methods of the experimentIn their study, August and Hicks investigated theupstream migration of glass eels in the Tukituki River, in Hawke Bay, NewZealand (2008). The purpose of their experimentwas to see how environmental variables affected the get of migrants, and tosurvey the species art object, size, condition and pigmentation of themigrants (2008).They conducted this survey in the rivers lower tidalreaches by trapping glass eels most nights from September to late November in2001, and until early December in 2002.Eels were trapped using a date net, with mesh screens on either sides topreve nt eels from moving past the net.Fishing began an min originally sunset, and every 45 minutes, glass eelsand bycatch were removed from the net, counted and recorded. A subsample of glass eels was removed fromthe catch each night so the train of pigmentation and species could beidentified in the lab later. Fishingended each night when the glass eel catch decreased over three sequentialtrapping periods. August and Hicks also measuredwater temperature at the have site and river mouth, river flow 10kmupstream from the sampling site, wind, barometric pressure, and solarradiation. compendium of covariance(ANCOVA) was used to analyze associations mingled with the number and length (dailymeans of complete length for each species) of migrants and the environmentalvariables, separated by species and year.Studyresults and backchatIn thorough, the inquiryers caught 50,287 eels in 2001and 19,954 in 2002, and they do not discuss reasons for this balance in eelnumbers. Out of the envir onmentalvariables measured, they found that river water temperature, sea watertemperature and river flow were most associated with glass eel catch, thoughriver and sea water temperatures were highly correlated. Maximum eel numbers were found when riverflow was low or ordinary (less than or equal to 22 m3 s-1),with fewer numbers at higher(prenominal) flows. Migrating glass eels seemed to prefer moderate river temperatureswater temperatures below 12C and above 22C seemed to almost or completely suppresseel migration. August and Hicks createda habitat suitability curve and proposed 16.5C as the optimaltemperature for upstream migration of New Zealand glass eels (2008). This relationship between may exist becausewater temperature can facilitate (or hinder) the swimming ability of fish, bothby bear upon the metabolism of the fish and the kinetic viscosity ofwater. laze mannequin, which has been historically associatedwith glass eel invasions, was sometimes associated with peak eel runs into thestream. However, they found that moonphase was confounded by other variables, namely water temperature and tidalcurrents, and suggest that these factors, rather than the moonlight itself, maybe the mechanism driving eel invasions during well(p) and new moons. This observation, while limited to theTukituki River, may assistant to clarify the lunar association with eel migrationsglobally. In both years, their catch was mainly shortfins (91%in 2001 and 93% in 2002), which is consistent with observations that shortfinsdominate the North Island east coast.However, this finding could be valuable for eel management sinceshortfin dominance may be reflect the sylvan development of the area andresult from their superior tolerance to increasingly boggy waters. They acknowledge some shortcomings of the study,including the fact that glass eel recruitment likely began beforetrapping. They did not estimate trapefficiency, though visual observations suggested that no more than 5% o f themigrating glass eels escaped entrapment.Significanceof their findings go glass eel recruitment may be associated withvarious environmental factors, water temperature was the most strongly linkedfactor out of the measured variables.This study thus supports the surmise that water temperature is a cue forthe start and intensity of the New Zealand upstream eel migration. This has been observed for Anguillarostrata (American eels ) (Marin 1995), Anguilla anguilla (Europeaneels) (Edeline et al. 2006), and even observationally for Anguilla japonica (Japaneseeels) (Chen and Chen 1991), but had notbeen thoroughly explored in New Zealand eels.Nevertheless, this study contributes further documentation oftemperature thresholds for eel migrations, and puts forth an optimaltemperature for New Zealand migrations.In finding linkages between water temperature and lunar phases, theirwork may also help to clarify the supposed relationship between the moon andeel invasions globally. Their findi ng ofpeak migrations during spring tides is consistent with previous studies(Jellyman 1979), and demonstrates how eels use flood tides to succeed passiveupstream movement. Findings from Jellyman et al.s 2009 study in the Waikato River system contradictedthe results of August and Hicks study.While Jellyman et al. also found that temperature had a significantrelationship with the migration strength, their largest migrations occurred atmuch cooler temperatures, between 12.6 and 13.1C. These temperatures are well below August andHicks optimum temperature of 16.5C , and undermined their hypothesis thattemperatures below 12C would suppress migrations. These variations in the eel responses to temperaturecould result from the Waikato study site being further inland than August andHicks study. Aside from using differentriver systems with capablenessly very different ranges of temperatures, thismeant that the eels sampled by Jellyman et al. were older and may respond to environmentalfactors differently. Implicationsfor climate change addicted the predictions that climate change will lead torising ocean temperatures, August and Hicks speculate that heating plant temperatureswill cast outly impact glass eel recruitment.However, in the article, they do not discuss or predict in circumstance howrising water temperatures will impact eel migration, such as effectuate on thetiming or numbers of migrants. Theymaintain that the generality of the negative effects of high watertemperatures on glass eel invasionsremains to be substantiate (August andHicks 2008), which is a reasonable statement given the limited scope of theirstudy. However, the proceeds of thisarticle could have been strengthened by analyzing, in more detail, thepotential threat climate change poses to eels.This paper also lacked a word of honor of whether eelscould adapt to the projected increases in ocean temperatures. These ocean temperature rises are expect tobe relatively gradual, with warming in New Zealand between 0.7-5.1C, with a best estimate of 2.1C, by 2090 (Ministryof the Environment, 2008). TheJellyman et al. 2009 study may actually turn in evidence that eels are alreadyadapting to warming ocean temperatures.When they compared migration catch information between a 30 year interval, theyfound that the main migration period occurred several weeks earlier. This suggests that eels may be compensatingfor increasing temperatures by migrating earlier in the season (Jellyman et al.2009). By shifting their migration times,or even by other adaptations in their physiology, eels may avoid thedetrimental effects of climate change.However, there is also the danger that as temperatures warm, the windowof temperatures suitable for migration will grow smaller and smaller, whichcould still lead to declines in recruitment.Moreover, it is already clear that eel recruitment has decreased both inNew Zealand and globally, so it is unlikely that adaptation will kick eels tocompletely escape the effects of climate change. Climate change may also be more strongly affecting eelrecruitment through food availability, rather than through temperatureincreases. One appraise of continentalwater conditions and the decline of American, European and Japanese eels foundcorrelations between eel recruitment and sea surface temperature anomalies(Knights 2003). They hypothesized thatglobal warming trends will negatively impact eel recruitment by inhibitingspring thermocline mixing and nutrient circulation(Knights 2003). Changes in the resultingfood availability may be a significant endorser to the worldwide eeldecline. Despite several studiesinvestigating the impact of large weighing machine oceanic warming trends, we still verymuch lack an intelligence of how much climate change will, and is currently,playing a role in eel populations. Implications for Eel ManagementThis study was beneficial byinforming the population composition of eels (specifically species and size) inthe Haw ke Bay region. Knowing the sizeof migrations in 2001 and 2002 can allow ecologists to measure the health ofeel populations in the future by using this information as a point forcomparison. This population informationalso gives preference managers some sense of what to expect from mature eelpopulations in the future. Understanding howenvironmental variables affect eel recruitment can help eel managers predictmigrations with greater preciseness and to understand why they are witnessingcertain trends in eel populations. By helping managers make predictions for whenpeak glass eel migrations will occur, this study can help inform ideal times toturn off hydroelectric dams or invest more efforts into eel transfers over upstreamobstacles. Even though this study makes an important step towardsconsidering how ocean warming will affect eel recruitment, its ability toadvance our understanding of eels and climate change is extremely limited. Further experimental studies are indispensable toin vestigate the temperature preferences of eels and the effects of temperature. Even then, studies researching the effects ofwarming temperatures on eels are inherently limited because they cannotconsider species responses and adaptations on a timescale relevant to climatechange. Regardless, given our worldwideeel decline, and evidence that climate change may already be impacting eelpopulations, its clear that more research is needed to investigate the currentand future threat of climate change for eels. decisivenessThe August and Hicks study advanced our understandingof the abiotic factors controlling glass eel migrations in New Zealand. They found a strong association betweenmigrations and water temperature, which raised concerns that rising ocean temperatureswill negatively impact eel recruitment.While their predictions about the effects of climate change are largelylimited by the scope and nature of the study, their findings demonstrate theneed for further research on climate chan ge and eels. Such research is especially imperative giventhe context of local and global declines in eel recruitment andpopulations. countersignatureCount 2,434Works CitedAugust, S. M., & Hicks, B. J.(2008). 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