Signaalvähk (Pacifastacus leniusculus) Eestis, liigi mõju jõevähile ning võimalikud tõrjemeetmed
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Kuupäev
2012
Kättesaadav alates
ainult raamatukogus, only in library
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Käesoleva töö eesmärgiks oli anda ülevaade signaalvähi (Pacifastacus leniusculus) levikust, arvukusest ja populatsiooni struktuurist Eesti veekogudes ning selgitada võõrliigi mõju meie jõevähi (Astacus astakus) asurkondadele. Lisaks oli eesmärgiks signaalvähi likvideerimise ja leviku takistamise võimaluste hindamine.
Uuringud näitasid, et Eestis kaks signaalvähi populatsiooni: Harjumaal Mustjões ja Saaremaal Riksu ojas. Mõlemasse veekogusse on signaalvähk toodud umbes 5 aastat tagasi. Signaalvähkide sissetoomine on veekogudest hävitanud jõevähi. Mõlemas veekogus esineb signaalvähki aga väga lokaalselt, mitte pikemal kui 500 m lõigul ning madalal arvukusel. Kokku püüti välja Mustjõest 13 ja Riksu ojast 111 signaalvähki. Riksu ojas oli katsepüükide keskmine saagikus kõrgeim 2010. a augustis – 0,2 vähki mõrraöö kohta. Püükide tagajärjel oli Riksu ojas saagikus 2011. a augustiks langenud neli korda. Katsepüügi saagikus vähenes oluliselt ka Mustjões. Selle põhjal saab järeldada, et intensiivse püügiga saab väiksel lõigul suguküpsete isendite arvukust ajutiselt oluliselt kahandada, mitte aga täielikult liiki välja püüda. Probleemiks on noorjärkude kättesaamine, mis ei õnnestunud ka peenesilmaliste mõrdadega. Riksu ojast ja Saaremaalt signaalvähi likvideerimise võimaluseks on signaalvähi poolt asustatud jõelõigu veevooluta jätmine.
Mustjõest, Riksu ojast ja ka Salatsi jõest püütud signaalvähkide pikkusjaotused olid sarnased. Seega, ka pikalt välja kujunenud signaalvähi populatsiooniga Salatsi jõest ei tulnud mõrda väikseid isendeid.
Vähikatku (Aphanomyces astaci) uuringud näitasid, et Eesti signaalvähiga asustatud veekogudes esineb vähikatku tekitaja, kuid mitte pidevalt. Ka Salatsi jõest püütud signaalvähkidel vähikatku tekitajat ei leitud. Tõenäoliselt ei ole kõik signaalvähid katku kandjad ja katkuseene zoospoorid vallanduvad perioodiliselt.
Inimeste teavitamiseks jõevähi kaitse vajadusest ja ohtudest on mõistlik kasutada ajakirjandust, tele- ja raadiokanaleid, kuna parvlaeval teostatud küsitlus näitas, et inimeste teadlikkus jõevähki ohustavatest teguritest on üsna kõrge ning teavet on saadud valdavalt meediakanalitest. Saaremaa külastajate puhul oleks ilmselt efektiivsem autoaknast nähtav suur tahvel Virtsu sadamas. Enamus inimesi on huvitatud kodumaise jõevähi püsimisest.
Edaspidi on vajalik jätkata püüke nii Mustjões kui Riksu ojas, et omada signaalvähi asurkondade seisundi kohta ajakohast infot ning hoida liigi arvukus võimalikult madal. Ka uutes veekogudes võõrliikide esinemise kahtlusi, millele viitab jõevähi kadumine, tuleb kindlasti kontrollida. Samuti vajab signaalvähi levik täpsustamist Salatsi jões ja selle Eestisse ulatuvates lisaharudes.
The purpose of the present thesis was to provide an overview of the spread, multiplicity and population structure of signal crayfish (Pacifastacus leniusculus) in Estonian waters and to explain the influence of introduced species to the population of our native crayfish. Another purpose was to assess the possibilities to eliminate and block the spread of signal crayfish. Research has revealed that there are two signal crayfish populations in Estonia, which locate in the River Mustjõe in Harju County and in the Riksu Stream in Saaremaa. Signal crayfish has been brought to both waters approximately 5 years ago, which has destroyed the population of native noble crayfish (Astacus astacus) by now. In both waters signal crayfish occurs locally, not on a longer section than 500 metres, and in low numbers. 13 signal crayfishes from the River Mustjõe and 111 from the Stream Riksu were caught during the catches. In the Riksu stream, the average catch per unit effort was highest in August 2010 – CPUE = 0,2. Due to the trial catches, the yield dropped 4 times by August 2011. The yields of the trial catches dropped significantly also in the river Mustjõe. The prey decreased remarkably during catches, which indicates that intensive catching enables to decrease the number of mature individuals, however, not eliminate the species completely. The biggest problem is to catch the young, which was impossible even with very fine nets. One possibility to eliminate the signal crayfish from the River Riksu in Saaremaa is to leave the section of river that has been located by the crayfish without watercourse. The length distributions of the crayfish caught from the river Mustjõe, the Riksu stream and from the river Salaca, were similar. Thus, even from an old population of river Salaca, the small individuals were not caught by trap. The research of crayfish plague (Aphanomyces astaci) revealed that crayfish carries the infection, but not all the time. The crayfish plague was not found from the individuals caught from the river Salaca. However, all signal crayfishes are not the infection carriers and the zoospores of fungus release periodically. The inquiry that was submitted on ferry revealed that the awareness of the factors which endanger native crayfish is high and the main information source had been media. Therefore, it is reasonable to use press, TV and radio channels in order to inform people of the necessity to protect native crayfish and understand the related dangers. A large board in the Port of Virtsu would probably be effective to the visitors of Saaremaa. The majority of people are interested in the persistence of native crayfish. In order to have an accurate overview of signal crayfish populations, catches in the River Mustjõe and the Stream Riksu must be continued. Also, all doubts that are related to introduced species in Estonian waters (disappearance of native crayfish) have to be checked. The spread of signal crayfish needs to be specified in the River Salaca and its branches in Estonia.
The purpose of the present thesis was to provide an overview of the spread, multiplicity and population structure of signal crayfish (Pacifastacus leniusculus) in Estonian waters and to explain the influence of introduced species to the population of our native crayfish. Another purpose was to assess the possibilities to eliminate and block the spread of signal crayfish. Research has revealed that there are two signal crayfish populations in Estonia, which locate in the River Mustjõe in Harju County and in the Riksu Stream in Saaremaa. Signal crayfish has been brought to both waters approximately 5 years ago, which has destroyed the population of native noble crayfish (Astacus astacus) by now. In both waters signal crayfish occurs locally, not on a longer section than 500 metres, and in low numbers. 13 signal crayfishes from the River Mustjõe and 111 from the Stream Riksu were caught during the catches. In the Riksu stream, the average catch per unit effort was highest in August 2010 – CPUE = 0,2. Due to the trial catches, the yield dropped 4 times by August 2011. The yields of the trial catches dropped significantly also in the river Mustjõe. The prey decreased remarkably during catches, which indicates that intensive catching enables to decrease the number of mature individuals, however, not eliminate the species completely. The biggest problem is to catch the young, which was impossible even with very fine nets. One possibility to eliminate the signal crayfish from the River Riksu in Saaremaa is to leave the section of river that has been located by the crayfish without watercourse. The length distributions of the crayfish caught from the river Mustjõe, the Riksu stream and from the river Salaca, were similar. Thus, even from an old population of river Salaca, the small individuals were not caught by trap. The research of crayfish plague (Aphanomyces astaci) revealed that crayfish carries the infection, but not all the time. The crayfish plague was not found from the individuals caught from the river Salaca. However, all signal crayfishes are not the infection carriers and the zoospores of fungus release periodically. The inquiry that was submitted on ferry revealed that the awareness of the factors which endanger native crayfish is high and the main information source had been media. Therefore, it is reasonable to use press, TV and radio channels in order to inform people of the necessity to protect native crayfish and understand the related dangers. A large board in the Port of Virtsu would probably be effective to the visitors of Saaremaa. The majority of people are interested in the persistence of native crayfish. In order to have an accurate overview of signal crayfish populations, catches in the River Mustjõe and the Stream Riksu must be continued. Also, all doubts that are related to introduced species in Estonian waters (disappearance of native crayfish) have to be checked. The spread of signal crayfish needs to be specified in the River Salaca and its branches in Estonia.
Kirjeldus
Märksõnad
signaalvähk, võõrliigid, jõevähk, populatsioonid (biol.), levik (biol.), arvukus, vähipüük, vähikasvatus, vähikatk, veekogud, Eesti, magistritööd