The interactions of abiotic and biotic factors influencing perch Perca fluviatilis and roach Rutilus rutilus populations in small acidified boreal lakes

Four small, acidified boreal lakes, all sustaining populations of perch Perca fluviatilis, roach Rutilus rutilus and pike Esox lucius, were studied in four successive years. Three lakes were moderately acidified (mean pH of 5·61–5·83), while the fourth was more acidic (mean pH of 5·16) and had a sparse population of R. rutilus. Perca fluviatilis density was higher in this lake (1004 ha−1) than in the other three (355–717 ha−1), where R. rutilus dominated in terms of numbers (981–2185 ha−1). Large, potentially predatory, P. fluviatilis were most abundant in the lake with clearest water, and these seemed to have a negative effect on P. fluviatilis density. Perca fluviatilis mean mass was negatively correlated with R. rutilus biomass and was highest in the most acidic lake with the sparse R. rutilus and the highest P. fluviatilis density. Perca fluviatilis mass correlated positively with pH in two lakes (with the highest fish biomass), suggesting that low pH affected P. fluviatilis mass negatively. Perca fluviatilis growth correlated positively with summer (July to August) air temperature in the lake with sparse R. rutilus, thus differing from P. fluviatilis and R. rutilus growth in the other three lakes. The mean age of P. fluviatilis was generally lower than that of R. rutilus and was lowest in the two lakes with the highest fish biomass, indicating that adult mortality was affected by density-induced factors

Recent improvement of fish populations in the Jarfjord Mountains in northern Norway due to reduced surface water acidification

Appendix 10/15 of the publication "State of the environment in the Norwegian, Finnish and Russian border area 2007" (The Finnish Environment 6/2007)

Arctic charr (Salvelinus alpinus) re-established in a formerly acidified and highly dilute mountain lake under declining acidic deposition

Arctic charr in Lake Ronvatn, a mountain lake in southern Norway was re-established through stocking. The population went extinction during the early 1980s due to acidification, when the lake was highly acidified with a mean pH of 5.2-5.4 with occasional declines to 4.3-4.7. However, from the mid to late 1990s, the pH and acid-neutralising capacity (ANC) of the lake rose to 5.8-5.9 and 13-15 µeq L-1, respectively. The lake is extremely dilute with a mean conductivity and calcium concentration of 7.7 µS cm-1 and 0.35 mg L-1, respectively. The lake was stocked with 250 Arctic charr from a neighbouring lake between 1998 and 2000. These introductions were highly successful, as test-fishing in 2004, 2008 and 2012 revealed a relatively dense population of Arctic charr, and the presence of several young age groups. Water quality has remained stable since the late 1990s, or has slightly improved

Distribution of non-native brook trout (Salvelinus fontinalis ) across Norwegian waterbodies – is it an invasive species?

Non-native brook trout (Salvelinus fontinalis MITCHILL, 1815) was introduced into Norway in 1883. However, it was not until the late 1970s that this acid-tolerant salmonid species was stocked into many acidified lakes that many populations became established. In 2004, all brook trout stocking in Norway ceased. In this study, we surveyed the distribution of brook trout in Norwegian water bodies. A totally of 202 self-sustaining populations were identified, mostly in unregulated lakes (n=101), streams (n=71) and also to some extent in reservoirs (n=25). Only four populations were found in inland rivers, and one population in a river with Atlantic salmon (Salmo salar L.). Localities with brook trout covered a wide range of altitudes and sizes. Analyses of time-series catches in sympatric populations of brown trout (Salmo trutta L.) and brook trout from 12 lakes (1997-2012) revealed a strong decline in brook trout stocks. A similar development in abundance has also emerged from other studies in recent years. Generally, lake-dwelling brook trout is regarded as a low-risk species with respect to invasiveness. However, brook trout/brown trout interactions may be habitat-specific, as brook trout may dominate in small and relatively cold streams.publishedVersio

Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range

Qvenild T, Fjeld E, Fjellheim A, Hammar J, Hesthagen T and Lakka H-K. 2021. Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range. Fauna norvegica 41: 50–88. The Arctic tadpole shrimp Lepidurus arcticus has a circumpolar distribution and the Scandes (Fennoscandian Mountains) marks its southernmost limit in Europe. Within this area, 391 natural and 88 regulated lakes with L. arcticus have been identified, of which 87% are above the treeline. The lakes hosting L. arcticus decrease in altitude from south to north, which results from its temperature preferences. The majority of the locations are at a lower lake air temperature than 11°C which is equivalent to a water temperature near 14°C. This is assumed to be near the upper thermal threshold for L. arcticus. In lakes that exceed this average summer water temperature (1 July – 15 September), sustainable populations seem to be rare. In warmer lakes, life cycle mismatches are assumed to explain the absence of L. arcticus, most likely by affecting the embryo and juvenile stages. The distribution appears to be dichotomous, with one large northern area north of 65°N and one separated southern “island”. Only two locations of L. arcticus are known for the area between latitudes 62.88 and 64.39°N. In this part of the Scandes, the lakes are likely too warm to host L. arcticus as most of them are situated below 700 m a.s.l. This may also be the case in the northernmost region, north of 70°N, where only 11 populations are recorded. Most of the lakes in this area typically occurs below 400 m a.s.l. L. arcticus populations are sensitive to fish predation, and dense fish populations may be another stressor limiting its distribution. In contrast to water bodies in the High Arctic where L. arcticus only exists in shallow, fishless ponds, in the Scandes they co-exist with fish in 97% of the findings. Global warming has already modified the environment of the Scandes, and populations of L. arcticus are at threat in many of the small and shallow water bodies at low altitudes

Metadata of European lake fishes dataset

Here we provide the metadata for an overview on fish species presence/absence in 1943 Palearctic (Europe + Turkey) lakes and reservoirs. The data have been obtained by standardized multi-mesh gillnet fishing, primarily to fulfill the requirements of the European Water Framework Directive (WFD). The species list encompasses about 100 species, a few of them split into subspecies. The database has been accumulated for the purpose of intercalibration of the evaluation systems for the WFD, and has systematically been used for research in the EU project WISER

Overvåking av langtransporterte forurensninger 2009. sammendragsrapport

Rapporten presenterer sammendrag av resultatene for 2009 fra tre overvåkingsprogrammer: “Overvåking av langtrans­portert forurenset luft og nedbør”, ”Overvåkingsprogram for skogskader” (OPS) og “Program for terrestrisk naturovervåking” (TOV). The report presents results for 2009 from three national monitoring programmes on long-range transboundary air pollution

Fangstutbytet og bestandstilhøva hjå auren i Tesse-magasinet i Jotunheimen i åra 1979-2017. NINA Rapport 1407. Norsk institutt for naturforskning

Hesthagen, T. 2018. Fangstutbytet og bestandstilhøva hjå auren i Tesse-magasinet i Jotunheimen i åra 1979-2017. NINA Rapport 1407. Norsk institutt for naturforskning. Tesse har sidan 1941 vore regulert i fleire tinn. Den siste reguleringa 1963 innebar ei reguelring på ca. 12,4 meter. Da vart Veo vart overført til Tesse via Smådøla. Den er sterkt breførande, og Smådøla vart øydelagt som gyteelv, kominert med kanalisering i den nedre delen. Tesse dekkjer eit areal på 1426 hektar ved høgste regulerte vasstand (HRV). Aure er einaste fiskeslaget. Denne rapporten oppsummerer fangstutbytet på stågarn (35 millimeter) og oter frå båt i åra 1979-2017. Fram til og med 2006 er også avkastinga berekna. Regulanten har vore pålagt å setja ut fisk. Fram til 1979 vart det årlege utsettingar på 10 000 einsomrig settefisk av framand stamme. På den tida var ikkje settefisken merka (finneklipt). I åra 1980-1986 vart det sett ut både stadeigen og framand fisk med 17800-28000 individ pr. år. Sidan 1987 har det berre vore sett ut stadeigen fisk. I 1988-1989 vart det ikkje sett ut fisk i det heile, og berre eit llite antal i 1990. Frå 1996 og fram til og med 2014 vart det i hovudsak sett ut eitårig fisk, som ut frå størrelsen tilsvara 10 000 einsomrige individ. Sidan 1980 har det meste av settefisken vore finneklipt. Gjennomsnittleg fangstutbyte på stågarn i åra 1979-2006 var 2377 kilo (690-4878). Det gjev ei avkasking på 1,67 kilo pr. hektar. Etter Tsjernobylulykka våren 1986 avtok fangstinnsatsen ein del. Seinare tok fisket seg gradvis opp att, spesielt utover på 2000-talet. Gjennomsnittleg fangst pr. garnnatt i antal og vekt var respektive 1,09 fisk og 365 gram (1979-2017). Det var ein klar auke i fangst pr. garnnatt over tid. Gjennomsnittleg vekt hjå fisk på 35 millimeter stågarn var 323 gram. Størrelsen avtok frå 327-336 gram i åra 1979-1981 til 294-299 gram i åra 1986-1988. Seinare låg vekta i fleire år på ca. 350-390 gram, men gjekk ned til 301-334 gram i åra 2006-2009. Det har også vore ei negativ utvikling i kondisjon og tilvekst. Fangstane i juni og fram til midten av juli har vore høgast i år med låg vasstand. Dette kjem av at det vassdekte arealet er mindre ved låg vasstand, slik at tettheita av fisk blir høgare. For variasjonen i totalt årleg fangst-utbyte på garn var fangstinnsatsen (antal garnnetter) den beste forklaringsvariabelen med 39 prosent. I tillegg bidrog vasstand i veke 29 (16.-22. juli) med ytterlegare 13 prosent. Den merka settefisken frå 1980 kom i haustbar størrelse på 35 millimeter garn etter fire år, og utgjorde 36 prosent av fangsten. Andelen auka til 56 prosent fram til 1990. Sidan har innslaget av settefisk gått gradvis attende, og i åra 2001-2017 låg den på 6-29 prosent. Andelen settefisk i haustbar størrelse auka med talet på settefisk fem år tidlegare. Det var likevel ingen samanheng mellom andelen settefisk og fangst pr. garnnatt. Oterfisket frå båt gav eit utbyte på 27,5 fisk pr. tur, med ei snittvekt på 249 gram. Gjennomsnittleg årleg utbyte var 3200 individ (1045-6985) og 796 kilo (260-1739). I tillegg kjem ca. 90 kilo på landoter. Gjennomsnittleg utbyte på stågarn og oter blir såleis 3263 kilo, eller 2,29 kilo pr. hektar. Det største utbytet i seks påfølgjande år var i snitt 4686 kilo, eller 3,29 kilo pr. hektar (2000-2005). Fisket på Tesse har halde seg bra etter reguleringa på 12,4 meter. Fisken ernærer seg no i stor grad av krepsdyr i dei frie vassmassane, og den naturlege rekrutteringa er stor nok til å halde oppe eit utbytet på to-tre kilo pr. hektar. Fiskeproduksjon var likevel mykje høgare før reguleringa. I ei periode på seks år tidleg på 1930-talet var gjennomsnittleg årleg utbyte ca. 9000 kilo. Dette gav ei avkasting på 7,4 kilo pr. hektar basert på arealet ved normal vasstand. Det kan ha vore nær det maksimale for vatnet sin bereevne. Utbytet i dag er truleg noko lågare enn det bestanden kan tåle. Fisket kan såleis halde fram på noverande nivå, og det er heller ingen trong til å starte opp att utsettingane