Jõevähi sugupoolte vahekord katsepüükides ja seda mõjutavad tegurid
Laen...
Kuupäev
2013
Kättesaadav alates
ainult raamatukogus, only in library
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Käesoleva bakalaureusetöö eesmärgiks oli uurida jõevähi sugupoolte jaotust katsepüükides ning seda mõjutavaid tegureid.
Jõevähk (Astacus astacus) on Eesti suurim ja ainuke selgrootu, kelle püsimajäämine looduses nõuab aina enam inimeste sekkumist. Inimtegevuste ja haiguste tulemusena on looduslikud vähkide asurkonnad piirkonniti hõrenenud või täielikult hävinud. Teadmised sugupoolte varieeruvustest ja seda mõjutavatest faktoritest annavad eelise asurkondade populatsiooni suurendamisel.
20. sajandi keskpaiku oli Eestis sugupoolte vahekord jaotunud võrdselt või näitas väikest emaste ülekaalu (Järvekülg, 1958). Abrahammsoni (1966; 1971) katsepüükides, mis viidi läbi Rootsis ja Norras omasid vastupidiselt Järvekülje (1958) andmetega isaste ülekaalu. Nimetatud 1958., 1966. ja 1971. aasta seirepüükide andmeid saab võrrelda tänapäevaste andmetega, et vaadelda, kas sugupoolte jaotustes on toimunud muutusi. Kui muutused on olemas, siis välja tuua põhjused, miks need esinesid.
Uurimistöös on kasutatud EMÜ VLI kalakasvatuse osakonnas loodud vähipüükide andmebaasi, mis sisaldab katsepüükide ja harrastuspüükide andmeid. Töös analüüsitud püügid viidi läbi maist oktoobrini. Perioodiliselt vaadeldi emaste osakaalu aastaaegade ja kuude lõikes. Püüke, mis sisaldasid 50 isendit, oli 413.
Veekogud, kus erinevate püügipiirkondade emaste osakaalud oli sarnased (11-20%) või väga sarnased (0-10%), moodustasid 87% kogu valimist. Kuna emaste osakaal veekogu erinevates piirkondades oli nii väike, andis see põhjuse uurimaks emaste osakaalu sõltuvust piirkonnast, sesoonist, veekogu tüübist ja mõõduliste vähkide osakaalust.
Suurima emaste osakaaluga periood oli august - emased moodustasid 44% püügis olevatest isenditest. Juulikuu püükides oli emaste osakaal augusti omast 3% võrra madalam (41%). Kõige madalam oli septembri kuu emaste osakaal 39 protsendiga. Piirkondlikult oli kõige suurem emaste osakaal Lõuna-Eestis teostatud katsepüükides (46%). Emaste osakaal oli väikseim saartel (41%) ja mujal Eestis (37%). Mõõduliste isendite ja emaste vahel esines nõrk korrelatiivne seos (r - 0,0161). Uurimustöö raames selgus, et emaste osakaalud on jaotunud võrdselt vahemikes, kus mõõdulised jõevähid moodustasid 0-30% ja 61-100% püügis olevatest isenditest.
Vähikasvatuse ja ka loodusliku vähivarude seisukohast on oluline, et jõevähkide sugupoolte osakaal ei varieeruks. Emaste võrdne või suurem osakaal veekogus tagab asurkonna populatsiooni kasvu - isased on võimelised paarituma mitme emasega, emased saavad läbida lõimetishoolt aastas ainult korra. Et sugupoolte varieeruvusi ühtlustada võib looduslikesse veekogudesse sisse tuua vähimajanditest püütud emaseid. Emaste osakaalu suurendamisega luuakse asurkonnal võimalus kindlustada ja suurendada jõevähkide 45 populatsiooni. Tuginedes uurimustööle võib öelda, et isegi emaste ümberasustamine vähimajandist looduslikku veekogusse ei pruugi emaste osakaalu katsepüükides tõsta, sest isaseid satub püüki rohkem nende agressiivsuse tõttu
The purpose of the given bachelor’s thesis was to investigate the variability of the sexes of crayfish and the causes of that. It was researched, whether the distribution of sexes depends on the region, period, type of the waterbody and the percentage of the sized specimen. Water bodies, where the catches were taken in different areas, had similar (11-20%) or very similar (0-10%) proportion of females, accounting for 87% of the total sample. The small variability in different spots of the same body of water gave a reason to investigate the influence of region, season, type of the waterbody and the percentage of the commensurable crayfish to the percentage of females. The period with the highest rate of females crayfish was August (44% of the specimen). During July, the amount of females was 3% lower, at the rate of 41%. The month with least females was September (39%). Lower amount of females in July and September was probably influenced by mating and maternity. By region, the highest rate of females appears in Southern Estonia (46%). The percentage of females was lower on the islands (41%) and in the rest of Estonia (37%). The periodic dependence of the sexes was probably caused by the quiddities of different waterbodies. In rivers, the mating and maternity takes place in a different time due to lower water temperature. The variations in different regions might have been a result of the small amount of samples (33 catches on the islands, 4 in Southern Estonia and 7 in the rest of Estonia). There was a weak correlational relationship between the commensurable specimen and the females (r – 0,0161). The percentage of females was equal within different intervals of the commensurable crayfish. In the catches, where the commensurable crayfish made up 0% to 30% and 61% – 100% of the specimen, the percentage of females varied only by 1%. Even though the relationship between the females and the commensurable specimen was very weak, the percentage of males within the commensurable specimen was still higher. It is important for the crayfish farming that the proportion of the crayfish sexes would not vary. There should be an equal or slightly dominant distribution of female crayfish in waterbodies because it contributes to the population growth – the males are able to mate with a number of females. In order to balance the variability of sexes in the bodies of water, the proportion of males and females must be regulated during re-colonization. Increase of the females is a prerequisite of ensuring and increasing the crayfish population. Based on the findings of the research, however, it can be argued that the re-colonization of the female population might not show an increase of the females in the catches due to the fact that the males are more aggressive and therefore end up in the catches more often. In the future there should be artificial waterbodies. The data from these artificial waterbodies should include the water temperature and ecological indicators. In case these conditions can be fulfilled, one should not speculate on the variability of the sexes and the research could be based on firm data.
The purpose of the given bachelor’s thesis was to investigate the variability of the sexes of crayfish and the causes of that. It was researched, whether the distribution of sexes depends on the region, period, type of the waterbody and the percentage of the sized specimen. Water bodies, where the catches were taken in different areas, had similar (11-20%) or very similar (0-10%) proportion of females, accounting for 87% of the total sample. The small variability in different spots of the same body of water gave a reason to investigate the influence of region, season, type of the waterbody and the percentage of the commensurable crayfish to the percentage of females. The period with the highest rate of females crayfish was August (44% of the specimen). During July, the amount of females was 3% lower, at the rate of 41%. The month with least females was September (39%). Lower amount of females in July and September was probably influenced by mating and maternity. By region, the highest rate of females appears in Southern Estonia (46%). The percentage of females was lower on the islands (41%) and in the rest of Estonia (37%). The periodic dependence of the sexes was probably caused by the quiddities of different waterbodies. In rivers, the mating and maternity takes place in a different time due to lower water temperature. The variations in different regions might have been a result of the small amount of samples (33 catches on the islands, 4 in Southern Estonia and 7 in the rest of Estonia). There was a weak correlational relationship between the commensurable specimen and the females (r – 0,0161). The percentage of females was equal within different intervals of the commensurable crayfish. In the catches, where the commensurable crayfish made up 0% to 30% and 61% – 100% of the specimen, the percentage of females varied only by 1%. Even though the relationship between the females and the commensurable specimen was very weak, the percentage of males within the commensurable specimen was still higher. It is important for the crayfish farming that the proportion of the crayfish sexes would not vary. There should be an equal or slightly dominant distribution of female crayfish in waterbodies because it contributes to the population growth – the males are able to mate with a number of females. In order to balance the variability of sexes in the bodies of water, the proportion of males and females must be regulated during re-colonization. Increase of the females is a prerequisite of ensuring and increasing the crayfish population. Based on the findings of the research, however, it can be argued that the re-colonization of the female population might not show an increase of the females in the catches due to the fact that the males are more aggressive and therefore end up in the catches more often. In the future there should be artificial waterbodies. The data from these artificial waterbodies should include the water temperature and ecological indicators. In case these conditions can be fulfilled, one should not speculate on the variability of the sexes and the research could be based on firm data.
Kirjeldus
Märksõnad
jõevähk, sugupooled, vähipüük, vähikasvatus, Eesti, bakalaureusetööd