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Titill
en

Survival of Atlantic Puffins (Fratercula arctica) in Vestmannaeyjar, Iceland during different life stages

Útgáfa
Janúar 2012
Útdrættir
  • Fjallað er um nokkra þætti í stofnvistfræði lunda í Vestmannaeyjum. Í fyrsta kafla er fjallað um varpárangur í sjö lundavörpum í þremur eyjum í Vestmannaeyjum árin 2008-2009. Varpárangur var lélegur bæði árin en nokkuð breytilegur á milli þeirra þriggja eyja sem rannsakaðar voru en varpárangur var metin 14.3% (n=203) 2008 og 20.1% (n=149) 2009. Varptími dróst á langinn og stóð yfir í um 64 og 55 daga eða fram til 11. september (SD=3.9) og 14. september (SD=4.8) að meðaltali. Þetta telst seint í samanburði við meðal-dagsetningu merkinga á fleygum pysjum frá 1959 til 2007: 26 Ágúst (SD=10). Sú dagsetning byggir á merkingagögnum sem aflað var af tveimur merkingamönnum, Óskari J. Sigurðssyni og Sigurgeiri Sigurðssyni (d. 1994) á Heimaey en merkingar Óskars ná aftur til ársins 1953. Í öðrum kafla er þessum merkingagögnunum lýst, tímasetning og staðsetning endurheimta eru skoðuð með tilliti til aldurs og farið er yfir forsendur reiknilíkana á lífslíkum og frekari útreikninga. Af 37.319 merktum pysjum, bæði fleygum og ófleygum milli 1959 og 2007 voru 5512 (14.8%) endurheimtar, að langmestu leiti í gegnum veiði en aðeins 193 náðust aftur verpandi. Eitthvað var um sleppingar veiðimanna á merktum fuglum sem hefði annars ekki verið sleppt sem orsakar skekkju auk þess sem áreiðanleiki slíkra endurheimta minnkar. Af þeim fuglum sem endurheimtir voru dauðir úr veiði í Vestmannaeyjum voru 74.7% yngri en fjögurra ára þ.e. á fimmta aldursári. Flestir þeirra endurheimtust á fjórða aldursári eða 36%. Miðað við að endurheimtur í veiði dragast mikið saman eftir 5 ára aldur samhliða aukningu fugla sem fundust verpandi í fyrsta skipti á svipuðum aldri má renna líkum að því að flestir lundar hefji varp á bilinu frá fimmta til sjöunda aldursárs. Langflestar endurheimtur eru innan Vestmannaeyja en einungis 77 fuglar af þekktum aldri fundust utan Vestmannaeyja, þar af einungis þrír fuglar í öðrum byggðum á Íslandi. Einungis tveir fuglar voru endurheimtir á öðru aldursári í veiði en annars eru allar endurheimtur fram að þriðja aldursári erlendis frá, að langsmestu leiti frá Nýfundnalandi. Fuglar merktir sem varpfuglar (n=5825) endurheimtust aftur á móti að mestu leiti verpandi aftur og allir í Vestmannaeyjum. Í þriðja kafla er lífs- og endurheimtulíkur varpfugla í Stórhöfða metnar með CJS-líkani. Fjögura þátta mátgæðismat (e. Goodness of fit test) sýndi fram á töluverð “flökku-fugla áhrif” (e. transience effect) sem tekið var tillit til í líkanagerð til útreikninga á lífslíkum. Besta líkanið gerði ráð fyrir að lifun breyttist ekki milli ára en endurheimtulíkur og hlutfall flökku-fugla breyttust milli ára. Lífslíkur voru metnar 87.3% (95% CL 86.4% - 88.2%) en meðal endurheimtulíkur voru 9% (SD=0.05 N=50). Þessar lífslíkur eru lægri en lífslíkur lunda beggja vegna Alantshafsins. Einnig er stuttlega fjallað um æskileg viðfangsefni lundarannsókna í framtíðinni og þýðingu niðurstaðanna og hvað megi vinna frekar úr þessum gögnum.

  • en

    The aims of this study are to explore survival and the relevant demographic variables of the Puffin population in Vestmannaeyjar, Iceland. It is divided into three chapters combining results from current research projects and part of a long term ringing series. Findings are then compared to findings from published literature on the species.
    Chapter 1
    Breeding success was estimated in seven colonies on three islands in Vestmannaeyjar archipelago in 2008 and 2009 as a part of an ongoing monitoring project. In 2008 total hatching success was 73.4% (n=203) but 19.5% (n=149) of the chicks survived until end of the study. In 2009 total hatching success was 40.9% (n=137) and 53.6% (n=149) of the chicks survived. This resulted in relatively low observed breeding success of 14.3% (n=29) and 20.1% (n=30) in 2008 and 2009, respectively. The overall breeding success was similar between years but varied between colonies within both years or between years within individual colonies. The rearing period was prolonged to 64 and 55 days in 2008 and 2009 and lasted on average until 11. September (SD=3.9) and 14. September (SD=4.8), respectively. In comparison, the 49 year average fledgling (ringing)-date 1959-2007 was 26 August (SD=10). These prolonged rearing periods suggest that food shortage limited chick growth rates and are congruent with the low nest survival. This low success is thought to be related to poor feeding conditions which have been attributed to recruitment failure the Sandeel population Ammodytes spp., which historically has been the main food source of Puffins of the South coast of Iceland. In an apparently prolonged Sandeel collapse it is important to maintain monitoring even though such work is difficult due to the Puffin’s underground nesting habit. Firstly we should do so because of international responsibilities, since the Vestmannaeyjar archipelago harbours a relatively large proportion of the world’s population. Secondly we bear a moral obligation since the puffin is the most exploited game species in Iceland. Thirdly the species is important to the country’s image and is a popular tourist attraction.
    Chapter 2
    Between 1959 and 2007 two ringers in Vestmannaeyjar archipelago ringed 43,144 Puffins, mostly nestlings and fledglings but also breeders and non breeding adults. Of 5825 breeders 1427 were recaptured alive during breeding and a further 147 were recovered through harvest all within the archipelago. Of 37.319 individuals ringed either as fledglings or nestlings 5512 (14.8%) were subsequently encountered mostly through harvest. There is though some negative bias on kill-rate as well as possible marker oversight caused by hunters releasing ringed birds, preserving them only because they are ringed. Of 4149 dead recoveries 74.7% were killed before sixth calendar year (CY) but most, 36.0% in the fourth CY. The subsequent drop in proportion of harvest after the fourth CY corresponds to individuals starting to breed in their fifth CY as is further supported by age distribution of 193 individuals of known age caught breeding in Stórhöfði which indicates that Puffins start breeding aged 5 CY to 7 CY. All ringed breeders subsequently encountered were without exception retrieved within the archipelago. Only 77 birds of known age were encountered outside Vestmannaeyjar, of which only two were encountered elsewhere in Iceland. Birds encountered aged 1-2 CY (n=45) were with few exceptions recovered during winter near Newfoundland and only two were recovered through harvest in Vestmannaeyjar.
    Chapter 3
    Survival rates for a harvested breeding population of Atlantic Puffins are reported from a single colony in Vestmannaeyjar Archipelago using data from 5825 individuals, ringed from 1959-2007. Using CJS multinomial modelling approach accounting for heterogeneity in survival rates with Pradel’s (1997) TSM model for transience, the highest ranking model included constant resident survival rates of 87.3% (95% CL 86.4% - 88.2%) while recapture rates were time dependent but low or on average 9% (SD=0.05 n=50). These survival estimates are quite low compared to survival rates amongst non-harvested Puffin populations from both sides of the Atlantic although comparable to short periods of low survival in the East Atlantic. The low survival rates in Vestmannaeyjar may be a result of harvesting or the method of capture-recapture employed (instead of the widely used capture-resighting).

Birting
3.2.2012


Skrár
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