Growth of pikeperch in relation to lake characteristics: total phosphorus, water colour, lake area and depth

The growth of pikeperch Sander lucioperca was studied in 41 lakes in central Finland. The backcalculated average total length of 3 year-old pikeperch was used as an indicator of growth. The growth correlated positively with total phosphorus and water colour and negatively with lake area and depth. The reason for differences in growth may be differences in the amount of suitable food, foraging success or temperature dynamics in different lakes.

Use of stable isotope analysis to evaluate the possible impact of fish migration on a lake biomanipulation

1. A lake restoration project involving mass fish removals was started to improve further the water quality of a lake recovering from severe eutrophication. The effectiveness of such biomanipulation as a lake management option could be compromised if removed fish are rapidly replaced by large-scale immigration from a connected lake. 2. Stable isotope analysis (SIA) was used to examine the migrations of perch (Perca fluviatilis L.) and roach (Rutilus rutilus (L.)) between two connected lakes in central Finland, Jyvasjarvi and the larger Paijanne. Baseline δ15N signatures in primary consumers were significantly higher in Jyvasjarvi and this difference was reflected further up the food chain i…

Dispersion of vendace eggs and larvae around potential nursery areas reveals their reproductive strategy

Depending on their reproductive strategy, different fish species aim to aggregate or disperse eggs and larvae in their reproductive habitat. Many pelagic species disperse their eggs widely around the potential nursery areas. Larval dispersion or aggregation affects population sub‐structuring, which has important implications in fisheries management and conservation of the natural spatial diversity in populations. The dispersion of larval vendace (Coregonus albula) was quantified in two oligotrophic Finnish lakes, and effects of density and environmental variables on the inter‐annual variation in the larval distribution were examined by analysing spatial abundance data from the lakes from 19…

Kalavarojen kestävä käyttö : suunnittelu ja toteutus

Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish

Fish are known for their high phenotypic plasticity in life-history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade-offs in phenotypic plasticity between life-history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long-term incubation experiments. The wild parental fish originated from four separate populat…

Empirical Estimation of Accumulation-Induced Change in Gill Net Catchability: Mind the Observation Errors

We analyzed cumulative catches for 24 h gill net exposures divided into 4*6 h, 2*12 h and 1*24 h soak time treatments to estimate the reduction in its catchability due to accumulation of fish. The effects of loss of catch during net lifting, disturbance effect and fouling were eliminated as far as possible to reveal the true effect of accumulation. First we applied simple nonparametric and parametric tests in comparison of treatments. As expected, considerable reduction in catchability took place along with the increase in soak time, indicated by significantly lower total 24 h catches from longer soaks in comparison with shorter ones. The reduction was more pronounced for roach than for per…

Negligible effect of hypolimnetic oxygenation on the trophic state of Lake Jyväsjärvi, Finland

Hypolimnetic oxygenation by pumping oxygen-rich surface water to the hypolimnion (HLO) is a commonly used tool for the restoration of nutrient-loaded dimictic lakes. However, in recent years its effectiveness has been questioned. In this case study we evaluated monitoring data covering a period of 23-years to show that, although experimental cessation of HLO drastically changed the lake's temperature and dissolved oxygen regimes, it did not significantly affect its trophic status. Thus, we recommend that the limited financial resources available are better directed towards further lowering the lake's external phosphorus load than continuing HLO. peerReviewed

A validated bioenergetics model for ruffeGymnocephalus cernuusand its application to a northern lake

A bioenergetics model was constructed for ruffe Gymnocephalus cernuus, and the model was used to estimate the food consumption of a native G. cernuus stock in Pyhajarvi, a large mesotrophic lake in south-west Finland. The parameters for the bioenergetics model were determined through laboratory experiments conducted at several temperatures between 5 and 22° C for different sized G. cernuus (from 6 to 27 g). The model was verified and validated with independent laboratory growth experiments. The validated model was applied to field data from Pyhajarvi to estimate the food consumption of G. cernuus and its effects on the zoobenthos community during the years 2002–2004. The total annual food c…

Keski-Suomen taimenseuranta vuonna 2015

Sisävesien talouslajien saalispotentiaali Suomessa

Feeding ecology and behaviour of pikeperch, Sander lucioperca (L.) in boreal lakes

Kuhakannat ovat parin viime vuosikymmenen aikana vahvistuneet. Samalla myös tiedontarve kuhan perusekologiasta on kasvanut. FK Tapio Keskisen väitöskirjassa tutkittiin kuhan merkitystä järvien kalayhteisöissä. Erityisesti rehevissä järvissä kuha on tärkeä petokala.Telemetrialähettimellä merkittyjä kuhia seurattiin Päijänteen vesistössä. Osa kuhista oli paikallisia liikkuen vain parin kilometrin säteellä, kun taas osa vaelsi pisimmillään yli parikymmentä kilometriä. Kesäaikaan kuhat suosivat kahta erillistä elinympäristöä: virtaavia, lämpötilakerrostumattomia alueita ja lämpötilakerrostuneita selkävesiä. Kuhat hakeutuivat lämpimimpään tarjolla olevaan veteen vuorokaudenajasta riippumatta. Va…

Tutkimus ja seuranta

Kalavarojen käyttö ja hoito pysyvät kestävällä pohjalla, kun päätökset perustetaan mahdollisimman luotettavaan ja ajantasaiseen tietoon. Tietoa tarvitaan toiminnan kaikissa vaiheissa, mutta erityisesti silloin, kun asetetaan tavoitetilaa ja osatavoitteita sekä myöhemmin, kun on aika arvioida toimenpiteiden tuloksellisuutta. Tässä luvussa esitellään alueelliseen käyttöön soveltuvia tiedonhankintamenetelmiä sekä annetaan ohjeita aineistojen keruuseen ja tulosten tulkintaan. nonPeerReviewed

Features of intercohort cannibalism of Vendace (Coregonus albula(L.)) under laboratory conditions

Cannibalism in Vendace (Coregonus albula (L.)) was studied under laboratory conditions by exposing Vendace eggs (100) or newly hatched larvae (20) to an older individual in aquaria. Predation on the eggs was not detected whereas both biting and ingesting of newly hatched larvae were observed in 23% of older Vendace individuals. Small individuals (<100 mm in total length) were significantly more likely to attack larvae than larger individuals. Differences were also found in attack rates between individuals. The rate ranged from no attacks to attacks towards every larva exposed to the cannibalistic individual. These results confirm that intercohort cannibalism is neither an exceptional nor a …

Kalastuksen ohjaus

Impacts and adaptation options of climate change on ecosystem services in Finland: a model based study

At a global level, it is estimated that nearly two-thirds of ecosystem services have been degraded in just fifty years. The additional stresses imposed by climate change will require extraordinary adaptation. This paper synthesises main result of a large Finnish project studying the vulnerability of key ecosystem services to climate change and the possibilities for the individual sectors to adapt to these changes. The project based its work on data and infrastructures of nine intensively studied areas belonging to the Finnish LTER (Long-Term Ecological Research) network. The methods developed and used included remote sensing, derivation of impact scenarios, dynamic modelling, laboratory exp…

Diet and prey size spectrum of pikeperch in lakes in central Finland

The stomach content of pikeperch Sander lucioperca was studied in 24 lakes in central Finland. The most important prey species was smelt Osmerus eperlanus then perch Perca fluviatilis. The proportion of cyprinids as prey increased with pikeperch total length (LT) and lake phosphorus content. Prey L T and pikeperch L T correlated positively, but the prey-to-predator size ratio correlated negatively with pikeperch L T .

Upstream migration activity of cyprinids and percids in a channel, monitored by a horizontal split-beam echosounder

A 200 kHz digital echosounder (HTI) with two split-beam transducers was aimed horizontally to monitor the upstream migration activity of fish, from 24 April to 28 June, in Aijalansalmi channel (mean width 35 m, length 700 m, and maximum depth 5 m) from large mesotrophic Lake Paijanne to small eutrophic Lake Jyvasjarvi. This study was part of a larger project which aims to analyse the movement of commercially unimportant fish species and reduce the abundance of these fish in L. Jyvasjarvi. Catch samples were collected with a trap net located immediately upstream from the acoustic beams. The most common species in the catch were roach (Rutilus rutilus), perch (Perca fluviatilis), bream (Abram…