Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon

Täplärapu (Pacifastacus leniusculus) on vieraslaji, mutta sitä on istutettu paljon suomalaisiin vesistöihin etenkin rapuruton hävittämien jokirapukantojen tilalle. Kalataloudellisesti täpläravun merkitys on nykyään huomattava. Täpläravun vaikutusta kalalajeihin on tutkittu vähän. Säkylän Pyhäjärvell...

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Päätekijä: Muuri, Tarmo
Muut tekijät: Matemaattis-luonnontieteellinen tiedekunta, Faculty of Sciences, Bio- ja ympäristötieteiden laitos, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylän yliopisto
Aineistotyyppi: Pro gradu
Kieli:fin
Julkaistu: 2015
Aiheet:
Linkit: https://jyx.jyu.fi/handle/123456789/48062
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author Muuri, Tarmo
author2 Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Bio- ja ympäristötieteiden laitos Department of Biological and Environmental Science University of Jyväskylä Jyväskylän yliopisto
author_facet Muuri, Tarmo Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Bio- ja ympäristötieteiden laitos Department of Biological and Environmental Science University of Jyväskylä Jyväskylän yliopisto Muuri, Tarmo Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Bio- ja ympäristötieteiden laitos Department of Biological and Environmental Science University of Jyväskylä Jyväskylän yliopisto
author_sort Muuri, Tarmo
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description Täplärapu (Pacifastacus leniusculus) on vieraslaji, mutta sitä on istutettu paljon suomalaisiin vesistöihin etenkin rapuruton hävittämien jokirapukantojen tilalle. Kalataloudellisesti täpläravun merkitys on nykyään huomattava. Täpläravun vaikutusta kalalajeihin on tutkittu vähän. Säkylän Pyhäjärvellä täplärapukanta on kasvanut nopeasti 2000-luvulla, mutta samalla myös siikapopulaatio on heikentynyt huomattavasti. Tässä tutkimuksessa selvitettiin täpläravun vaikutusta siikapopulaatioon vuosina 1998–2010. Täpläravut voivat käyttää kalojen mätiä ravinnokseen, ja suurissa tiheyksissä ravut saattavatkin saalistuksellaan vaikuttaa negatiivisesti siikojen mädin säilyvyyteen. Kohorttianalyysin avulla laskettiin siian eri ikäryhmien tiheys ja kalastuskuolevuus. Siian pyydyskohtainen yksikkösaalis laskettiin jakamalla saalis pyyntiponnistuksella. Biomassa-arvio laskettiin kertomalla yksilömäärät ikäryhmäkohtaisella keskimassalla. Kutukannan biomassa saatiin painottamalla kutakin ikäryhmää sukukypsien kalojen osuudella. Kutukannan, gonadosomaattisen indeksin ja mätimunien märkämassan avulla laskettiin populaation fekunditeettiarvio, johon poikasmäärä suhteutettiin ja saatiin siten arvio mädin talvisäilyvyydestä. Kutukanta–rekryytti-riippuvuutta tutkittiin tiheysriippuvuusmalleilla. Kyseiseen malliin lisättiin muuttujaksi täpläravun tiheyttä kuvaava yksikkösaalis. Tulosten perusteella ei voida sanoa täpläravulla olevan vaikutusta siian poikastiheyteen Säkylän Pyhäjärvellä tarkastelujakson aikana. Täpläravun tiheys ei vaikuttanut mädin talvisäilyvyyteen, joten täpläravut tuskin käyttävät merkittävästi siian mätiä ravinnokseen tai niiden saalistus ei lisää mädin kokonaiskuolevuutta. Jotta voitaisiin varmasti selvittää täplärapujen vaikutus mädin säilyvyyteen, tulisi Pyhäjärvessä tutkia kokeellisesti mätiin kohdistuvaa predaatiota sekä määrittää tarkemmin täpläraputiheys ja rapujen liikkuminen siian kutuaikana ja kutualueilla. Signal crayfish (Pacifastacus leniusculus) is an alien species but it has been stocked abundantly in Finnish lakes. It has been used to replace noble crayfish stocks which have been destroyed by crayfish plague. Nowadays signal crayfish catches have become economically very significant. Until now the effects of signal crayfish on fish species have been studied only a little. In Lake Pyhäjärvi, the signal crayfish stock has rapidly increased through the 21st century, while at the same time the whitefish stock has declined notably. In this study, the aim was to investigate whether the signal crayfish stock had an influence on the whitefish population during the study period from 1998 to 2010. Signal crayfish may feed on fish eggs and in dense stock crayfish population might have a negative effect on the survival of whitefish eggs. Density of whitefish individuals in the different age groups and fishing mortality was calculated by a cohort analysis. Catch was divided by fishing effort to get a catch per unit of effort. Estimation of the biomass of whitefish was calculated multiplying number of individuals in each age group by average mass of whitefish in that age group. Biomass of the spawning stock was estimated by weighing each age group with proportion of mature fishes. Estimate of the total fecundity of the whitefish population was calculated by multiplying the spawning stock density by the gonadosomatic index and wet mass of the fish eggs. Subsequently, the survival during the egg incubation was estimated according to the annual total fecundity estimates and larval density estimates. The spawning stock-recruitment model was then used to analyze the relationship between the densities of the crayfish and hatched whitefish larvae. CPUE of crayfish was included into the spawning stock-recruitment model. During the study period, the density of crayfish did not have an impact on the density of the hatched whitefish larvae in Lake Pyhäjärvi. The crayfish did not have an effect on winter survival of the fish eggs so crayfish probably don't prey significant amount of whitefish eggs or they don't increase total egg mortality. Collapse of the whitefish population can be derived from food competition especially with vendace. In order to investigate if the crayfish have an impact on whitefish egg survival in Lake Pyhäjärvi field experiments should be carried out, which specifies more accurately the predation and crayfish density at the spawning time and area of whitefish.
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spellingShingle Muuri, Tarmo Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon predaatio Akvaattiset tieteet Aquatic sciences Kohorttianalyysi 4012 täplärapu siika mäti vieraslajit Säkylä Pyhäjärvi
title Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
title_full Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
title_fullStr Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
title_full_unstemmed Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
title_short Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
title_sort täpläravun pacifastacus leniusculus vaikutus säkylän pyhäjärven siian poikastuotantoon
title_txtP Täpläravun (Pacifastacus leniusculus) vaikutus Säkylän Pyhäjärven siian poikastuotantoon
topic predaatio Akvaattiset tieteet Aquatic sciences Kohorttianalyysi 4012 täplärapu siika mäti vieraslajit Säkylä Pyhäjärvi
topic_facet 4012 Akvaattiset tieteet Aquatic sciences Kohorttianalyysi Pyhäjärvi Säkylä mäti predaatio siika täplärapu vieraslajit
url https://jyx.jyu.fi/handle/123456789/48062 http://www.urn.fi/URN:NBN:fi:jyu-201512113992
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