78 research outputs found
Migratory behaviour and holding habitats of adult river lampreys (Lampetra fluviatilis) in two Finnish rivers
The effect of environmental factors on migratory activity of adult river lampreys entering
the Kalajoki and Perhonjoki, rivers in Finland, for spawning was studied using correlation
and regression analyses. Telemetric tracking of 60 individuals was utilized to study the
migratory patterns and holding habitat requirements of adult river lampreys. The increases
in the river discharge, wind forcing towards the river mouth and speed and magnitude of
river water cooling had positive effects on the numbers of lampreys entering the rivers
whereas the increase in the illumination intensity of the moon had a negative effect on their
migration activity. Radio-tagged lampreys typically passed slow-flowing river sections as
well as steep riffles during one night, and were holding in runs, glides and the lowermost
section of riffles. Substratum dominated by large boulders (> 256 mm) was preferred
during winter holding behaviour. The migratory activity of lampreys released in low
( 16 °C) river water temperatures was low. Lampreys tended to halt
next to illuminated bridges, and we suggest that this behaviour markedly shortened migration
distances. The passage efficiency through a natural-like fish ramp in the low-head
barrier was 100%. The results can be utilized in mitigation actions like river restoration,
transplanting of adults, and improving passage and water flow regulation.peerReviewe
Collapse and recovery of the European smelt (Osmerus eperlanus) population in a small boreal lake — an early warning of the consequences of climate change
Genetic-based evaluation of management units for sustainable vendace (Coregonus albula) fisheries in a large lake system
The goal of the processing industry, trade and consumers is to get eco-labelled freshwater fish products from sustainable fisheries into the market as soon as possible. The fourth largest natural lake system in Europe, the Saimaa lake system supports a fishery for vendace (Coregonus albula). Certification of the fishery requires an understanding of population structure to help determine the number and spatial extent of management units. In this study, we analysed the genetic diversity of local vendace populations in the Saimaa lake system and aimed to identify the conservation and management units of vendace. Within the Saimaa, the genetic divergence between local populations of vendace was weak and their genetic divergence did not follow an isolation by geographic distance pattern. Vendace has potential to disperse effectively within and between local populations in different lake basins. Even if we observed subtle genetic divergence within our study systems, available information showed no significant evidence that the local populations had unique evolutionarily significant traits. The local populations of the Saimaa lake system seem to have similar life history and morphological traits as in the whole Central Finland lake district. The conservation of genetic diversity seemed not to require basin-specific actions and we conclude that management of local vendace populations of Saimaa as one management unit is advisable
Kyrönjoen yläosan vesistötöiden vaikutus ja Kyrönjoen tila vuosina 1975-2003
Kyrönjoki (F = 4920 km², MQ = 43 m³/s) virtaa laajojen tasaisten peltolakeuksien läpi. Joki tulvii herkästi, minkä vuoksi vesistöalueen tulvasuojelu on ollut laajamittaista: vuonna 2003 valmistui Kyrönjoen yläosan tulvasuojelu, johon kuului jokivarren pengerrys noin 24 km matkalla, 22 tulvapumppaamon rakentaminen sekä aliveden aikaista vedenpintaa nostavan Malkakosken padon rakentaminen.
Kyrönjoen pääuoman virtaamia, veden laatua sekä kala-, rapu- ja nahkiaiskantoja sekä vesistötöiden vaikutuksia näihin on tarkkailtu vuosina 1975-2003. Kyrönjoen tilaan vaikuttavat vesistörakentamisen lisäksi lyhytaikaissäännöstely, virtaamien voimakas ja nopea vaihtelu, voimakas haja- ja pistekuormitus sekä varsinkin alueen happamien alunamaiden kuivatuksen aiheuttamat happamuusongelmat. Kyrönjoki on tummavetinen ja rehevöitynyt joki, jota luonnehtivat suuret virtaaman vaihtelut ja alajuoksua kohti pahenevat happamuusongelmat. Happamuus ja sameus ovat voimakkaimmillaan tulva-aikoina, kun taas rehevöitymisongelmat korostuvat kesän alivirtaamakausina. Kasvillisuudessa, pohjaeläimistössä, kalastossa sekä rapu- ja nahkiaiskannoissa näkyvät rehevöitymisen, happamuuden sekä rakenteellisten muutosten vaikutukset.
Heikoimmillaan veden laatu ja ekologinen tila oli 1970-luvulla, jolloin pistekuormitus oli voimakasta ja happamien maiden kuivatus laajimmillaan. Näistä ajoista joen ekologinen tilanne on hiljalleen parantunut, mikä näkyy esimerkiksi pohjaeläinlajiston runsastumisena. Vuosittaiset vaihtelut ovat kuitenkin suuria ja joen ekologista tilaa voidaan edelleenkin pitää melko heikkona.
Vesistörakentaminen on aiheuttanut joen rakenteellisia muutoksia ja toisaalta voimakkuudeltaan vaihtelevaa, vuosikausia jatkunutta eroosiota. Pitkään jatkunut rakentaminen on pitänyt yllä jokiekosysteemin jatkuvaa stressiä, joka on hidastanut Kyrönjoen tilassa muuten tapahtunutta myönteistä kehitystä. Malkakosken yläpuolelle muodostunut allas näyttää odotetusti rehevöityneen. Vesistörakentamisen suurimmat vaikutukset ovat kuitenkin välillisiä: tulvasuojelu mahdollistaa happamien alunamaiden tehokkaan kuivatuksen ja viljelyn, mistä puolestaan seuraa vesistön happamoitumista. Kuivatusalueilta tuleva happamuus yhdessä lyhytaikaissäännöstelyn muuttaman virtaamarytmin kanssa aiheuttaa nopeaa ja vesieliöstölle haitallista happamuuden vaihtelua
Occurrence of two-year cyclicity, "saw-blade fluctuation", in vendace populations in Finland
The tendency towards two-year cyclicity is considered typical of many Fennoscandian vendace populations, especially in fluctuation of recruitment, based on time series of individual lakes. We used two robust indicators to identify and quantify two-year cycles in vendace population proxy time series at different life-stages - spawning stock biomass (SB), density of newly hatched larvae (LD) and recruitment (REC) - from 22 Finnish lakes. Then we applied Fisher's meta-analytical test to assess the adequacy of the evidence to support the hypothesis that vendace population dynamics include two-year cyclicity. The results supported this hypothesis for REC but not for SB or LD. Yet. the indicators and test are conservative and time-series of SB and LD are shorter than those for REC. The appearance of cycles in REC is associated with high post-recruitment mortality, consequently practically only one spawning per cohort. Cycles may be typical for the recovery period from low abundance period also. Still, some populations with moderate post-REC mortality and non-cyclic SB abundance exhibited cycles in REC. Such dynamics presuppose the existence of more complex regulation based on the interaction of different life stages
Recruitment variability in vendace, Coregonus albula (L.), and its consequences for vendace harvesting
Timo Marjomäki tutkii väitöskirjassaan muikun rekryyttimäärän (=vuosiluokan runsaus ensimmäisen elinvuoden syksyllä tai talvella) vuosien välisen runsaudenvaihtelun ominaispiirteitä ja syitä sekä tarkasteli vaihtelun vaikutuksia kalastukseen ja sen säätelyyn ja toisaalta kalastuksen heijastumista vuosiluokkavaihteluun.This thesis analyses the characteristics and causes of interannual variability in vendace recruitment and its consequences for, and interactions with, vendace harvesting. The interannual variability of prerecruit mortality was high. The daily mortality during the stage 1-3 weeks after hatching was about 10% and in stage 3 weeks - recruitment about an order of magnitude lower. Yet, the stagespecific total mortalities and their variability were of the same order of magnitude. Thus, both stages had potential for determination of the year-class strength. The variability was largely caused by factors external to the population. The synchrony found in the population dynamics of proximal lakes supported this conclusion. Sparse evidence of compensatory density dependence in mortality was found between hatching and recruitment, but good evidence for compensation was found when the whole period from spawning to recruitment was studied.Considerable model and parameter uncertainty concerning the spawning stock-recruitment relationship existed and methodological biases handicapped the analysis. High larval abundance was required to produce an abundant year-class indicating a positive association between the spawning stock and recruitment in low stock level. Symptoms were found of delayed density dependent mortality induced by a previous year-class causing two year cyclicity. However, tendency for two year cyclicity was also detected for a simulated vendace population under high mortality without delayed density dependence. Observations and conceptual modelling revealed that fulltime commercial fishers diminish interannual yield and income variability by increasing fishing effort during stock decline. Fishing was stopped when the revenue per unit effort went below a certain minimum level. Simulation showed that the strategy of moderately adjusting fishing effort gained compromises of almost as high annual revenue as a constant effort strategy but with lower annual variation and lower risk to spawning stock than the strategy aiming at constant revenue. Successful reduction of variability requires lower mean fishing effort than that producing maximal sustainable revenue. No detrimental effects on pelagic fish stocks associable with fishing were found in a case study comparing zones of a lake with different intensities of trawl fishing. The results thus support high compensation capacity in vendace population dynamics. Means for regulating the number of fishing enterprises based on stock productivity was considered to be a precondition for successful attenuation of yield and revenue variability. Threshold control to secure a spawning stock sufficient to ensure sustainable fisheries was also considered necessary
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