Preface to the Special Issue “Integrated Monitoring in the Valkea-Kotinen Catchment during 1990–2009 : Abiotic and Biotic Responses to Changes in Air Pollution and Climate”

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Hajakuormituksen vaikutukset järvien ja jokien kalastoon ja ekologiseen tilaan

Julkaisussa väärä ISBN-numero. Oikea ISBN-numero: 978-951-776-564-0

Population dynamics and growth of perch in a small, humic lake over a 20-year period — importance of abiotic and biotic factors

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Water quality of a small headwater lake reflects long-term variations in deposition, climate and in-lake processes

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Troubled by the humics — effects of water colour and interspecific competition on the feeding efficiency of planktivorous perch

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Responses of the fish community in a eutrophicated lake to long-term food web management assessed by multiple sampling methods

Fish community responses to long-term mass removal of planktivorous fish from eutrophicated Lake Tuusulanjarvi were examined during 1996-2018 by gill net test fishing, hydroacoustics with simultaneous trawling, virtual population analysis (VPA) and fish growth measurements. The gillnet catches of white bream and roach increased first while bream and bleak decreased but recovered in the early 2000s. Perch and pikeperch increased but ruffe decreased and remained low. According to hydroacoustics, pelagic fish biomass decreased. Smelt was the most abundant species at the beginning and the end of the monitoring period but bream dominated the fish biomass in most years. VPA calculations indicated a five- and threefold increase in the biomass of bream and white bream, respectively, during 2005-2011. Significant increases appeared in the growth of perch, bream and roach. Overall, the responses in the fish community structure and fish abundance to the food web management were slight and mostly masked by changes in reproduction and growth of fish and annual variability in environmental conditions such as temperature and water turbidity. Gillnet test fishing and echo sounding complemented each other well in monitoring the effects of management fishing. Where bream is one of the dominant species VPA is also recommended.peerReviewe

An evaluation of gillnet CPUE as an index of perch density in small forest lakes

Gillnets are commonly used for monitoring fish communities and assessing the ecological quality inEuropean lakes. However, the relationship between gillnet CPUE and fish abundance is not linear anddepends on several factors affecting the catchability of gillnets. We investigated the effects of high watercolour, naturally anoxic hypolimnion, water temperature and sex ratio on the catchability of perch Percafluviatilis in gillnets. Data were collected during 10 years in nine forest lakes in southern Finland. Suchlakes are very common in Finland. The density and size structure of perch populations were estimatedby mark and recapture method during spring and standard gillnet fishing (CEN, 2005. Water qualitySampling of Fish with Multimesh Gillnets. European Committee for Standardization, Brussels (EN 14757))in late summer. Perch CPUE was positively but non-linearly dependent on the perch density. Catchabilityincreased with water colour, water temperature, and the volume of the anoxic hypolimnion. The sex ratiowas also important because late summer gillnetting overestimates the proportion of female perch. If thefactors that affect the catchability of perch in gillnets are taken into account, gillnet CPUE using standardmethods can be used as rough index of fish density in small forest lakes.Peer reviewe