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Estimation of vendace year-class strength with different methods in the subarctic lake Inari
Abstract
Vendace (Coregonus albula) is a new introduced species in the Paatsjoki river system and lake Inari; it has only got a 30- to 40-year history in the area. The strong vendace year-classes of the 1980s were followed by weak ones until 2000, when a stronger year-class emerged. Data on the vendace catch-at-age were collected from 1987 to 2001 and the year-class strengths (YCS) were estimated by the virtual population analysis (VPA). The YCS was estimated directly by survey trawling conducted annually in early fall aimed at 0+ fish and by seine netting in the following winter. Direct estimates were compared with VPA estimates. The trawl survey and winter seine data show that the YCS of vendace is discernible during the first year of their lifespan. As a practical application in fisheries management, these data can be used in adjusting of e.g. stocking of predatory salmonids.
... Whole lake and lake-basin densities of vendace -adults as well as juveniles -were obtained by calculating acoustic coverage weighted mean densities for the different subareas. Classification of vendace young-of-the-year juveniles was based on annual size-distributions in the trawl catches (Salonen, 2004) supported by age determination from scales and otoliths. Thus, lake specific size thresholds were used to distinguish between 0+ and >0+ fish. ...
... In L. Vänern the hydroacoustic results showed strong yearclasses in Dalbosjön in years 2000, 2003, 2004and 2011, and in Värmlandssjön in 1995, 1996, 2004, 2005 (Fig. 6) ...
... In L. Vänern the hydroacoustic results showed strong yearclasses in Dalbosjön in years 2000, 2003, 2004and 2011, and in Värmlandssjön in 1995, 1996, 2004, 2005 (Fig. 6) ...
... Similar examples of the high variation in vendace biomass observed in the present study have been widely reported in the literature (Viljanen, 1986, Salojärvi 1987, Valkeajärvi & Marjomäki, 2004, Viljanen et al. 2004, Salonen 2004. Similar decreases of vendace biomass were observed in Lake Inari, Finland, where fi shery catches of vendace dropped from 300 t in 1989 to less than 5 t in 2000 to 2001 (Salonen, 2004). ...
... Similar examples of the high variation in vendace biomass observed in the present study have been widely reported in the literature (Viljanen, 1986, Salojärvi 1987, Valkeajärvi & Marjomäki, 2004, Viljanen et al. 2004, Salonen 2004. Similar decreases of vendace biomass were observed in Lake Inari, Finland, where fi shery catches of vendace dropped from 300 t in 1989 to less than 5 t in 2000 to 2001 (Salonen, 2004). This decline was attributed to very poor recruitment that spanned over 10 years, similar to the present fi ndings in Lake Pluszne. ...
... This implies that by the end of the present study, the majority of individuals in the population were 10 years old. Although vendace are considered to be a short-lived species (Bernatowicz et al. 1975), observations of vendace older than 10 years have been reported in Russian, Norwegian and Finish lakes (Aass 1972, Dâtlov, 1980, Sanlund et al. 1991, Salonen, 2004. In addition, in Poland vendace of age 11 years have been caught in Lake Łańskie which is adjacent to the present study lake (Ciepielewski & Hornatkiewicz-Żbik 2006). ...
... In Lake Vaggatem, Norway, in the upstream part of the Pasvik watercourse, the invader rapidly became the dominant pelagic fish species ( Bøhn et al. 2004, 2008). Long-term investigations with annual sampling of vendace have been carried out in Lake Inari since 1985 (Salonen 1998(Salonen , 2004) and in Lake Vaggatem since 1991 ( Amundsen et al. 1999;Bøhn et al. 2008). Here we perform a combined analysis of these time-series in order to compare the population biology and life-history strategies of the source (Lake Inari) and colonist (Lake Vaggatem) populations of the invader species prior to and following the downstream invasion and establishment. ...
... The invasion of vendace from Lake Inari to the downstream Pasvik watercourse occurred in the late 1980s (Amundsen et al. 1999). At this time period, the source population in Lake Inari was at a peak abundance (Salonen 1998(Salonen , 2004Salonen et al. 2007), suggesting that a high number of individuals may have emigrated from the lake and downstream into the Pasvik watercourse. The invasion proceeded rapidly down the watercourse, apparently facilitated by a concurrent overflow of the dam constructions ( Amundsen et al. 1999). ...
We explore the long-term developments in population biology and life history during the invasion and establishment of the fish species vendace Coreg-onus albula in a subarctic watercourse by comparing life-history traits and molecular genetic estimates between the source and the colonist population. The two populations exhibited highly contrasting life-history strategies. Relative to the source population, the colonist population was characterized by slower somatic growth rates, earlier sexual maturation at smaller individual size, higher mortality rates and a shorter life span. The two populations could also be significantly discriminated by the genetic markers. Limited founder effects were detected from heterozy-gote deficit and reduced allelic richness in the colonist population, but both populations were associated with relatively high genetic diversity. The study reveals that the invasion into a new environment induced large changes in life-history strategy, with typical r-selected traits being more prominent in the colonist than in the source population. We discuss the mechanisms that may explain the observed life-history differences between the source and the colonist population, and argue that the accelerated life history of the colonist population represents an adaptive pioneer strategy aimed at fast population increase during colonization and establishment.
... Järven ainoa särkikalalaji on mutu (Phoxinus phoxinus). Lisäksi järvessä elää kolmipiikkiä (Gasterosteus aculeatus) ja kymmenpiikkiä (Pungitius pungitius), jotka ovat merkittäviä ravintokaloja muun muassa taimenelle (Salonen 2004(Salonen , 2021. Järveen on istutettu myös muikkua (Coregonus albula), järvilohta (Salmo salar m.sebago) ja harmaanieriää (Salvelinus namaycush). ...
The operational environment of commercial fishing in the North is changing
due to climate change and other environmental and socio-economic drivers.
In this study, we combine the practitioner knowledge of commercial fishers
operating on the subarctic Lake Inari in northern Finland with long-term meteorological and hydrological observations from the region. Our interviews show that fishers have adopted various short-term strategies to cope with difficult weather conditions, among them flexibility in timing and location of fishing, as well as in catch species and gear. The livelihood is diversified both within and outside fishing to enhance the profitability. Responses of fishers to future uncertainties were varied and based on individual rather than community behavior. Four distinct longer-term adaptation strategies utilized by fishers differ in terms of the catch species, investments, and risk levels. Finally, we discuss the sustainability of the identified adaptation strategies, and the governance aspects of the livelihood.
... In doing so we assume that other density-independent or density-dependent factors not investigated here that may affect young vendace between the 0 year old and 1 year old stages do not decouple the relationship between these two stages. Most of the pre-recruit mortality occurs in the larval phase (Karjalainen et al. 2000) and young of the year vendace can serve as a predictor for year class strength at least in lakes (Salonen 2004), both of which factors indicate that this assumption is acceptable for the Bothnian Bay vendace. Furthermore, spawning stock biomass (SSB) was shifted back to the year of hatching as recruitment of vendace is produced from SSB in the previous year. ...
Fish populations inhabiting marginal areas are generally highly susceptible to environmental
variation and therefore show large fluctuations in recruitment. The commercially important, and usually
freshwater, vendace (Coregonus albula (L.)) occupying the brackish waters of the Bothnian Bay forms
one such marginal population and shows large annual variation in recruitment. Here, we investigate
the relative importance of fishing (trawling time), hydro-climatic factors and species interactions in
explaining the variability in vendace recruitment using three sets of models. A comparison of the best
models in the hydro-climatic model set and the fi shing model revealed that the hydro-climatic variables
were overall superior to the anthropogenic model in describing recruitment variability. Trawling time
and water temperature in winter combined with salinity explained 33 and 63.7% of the variation in
recruitment, respectively. The importance of water temperature and salinity, in combination with the
effects of trawling time, calls for catch levels to be set with caution in this vendace fishery.
... The first vendace were observed in Lake Inari in 1973. By the early 1980s, a vendace population had established throughout the lake (Mutenia and Salonen 1992), increasing to a peak abundance in 1989 (Salonen 1998Salonen , 2004 ). During this period a downstream invasion of vendace apparently occurred to lakes in the Pasvik watercourse, the outlet river from Lake Inari, where the species was observed for the first time in 1989 (Amundsen et al. 1999). ...
Species invasions can have wide-ranging biological and socio-economic effects and are generally unwanted by legislation. Identification of the source population as well as the ecology and genetics of both the invader population and the receiving community is of crucial importance. The rapid invasion of a small coregonid fish vendace (Coregonus albula) in a major northern European subarctic watercourse has resulted in a labile ecological situation in the receiving community. The ecological impact of the invasion has been thoroughly documented, but the genetics of the invasion remains to be explored. We analyzed the genetic diversity and divergence patterns among the two possible source populations from southern Finnish Lapland and three colonists populations within the Inari-Pasvik watercourse using ten microsatellite loci in order to (i) identify the most likely source of the invasion, (ii) reveal the dispersal pattern and genetic structure of the secondary expansion, and (iii) to investigate whether the initial introduction and the secondary expansion were associated with founder effects. We revealed that repeated translocation of vendace from Lake Sinettäjärvi into a tributary lake of L. Inari in 1964-1966 is the most plausible source for the invasion. Both the initial introduction and the secondary expansion were found not to be associated with significant founder effects. The secondary expansion followed a stepping stone pattern and the source and colonist populations of this expansion have undergone rapid genetic divergence within a period of 15-35 years (ca. 8-17 generations). The rapid divergence may be contributed to lack of gene flow among the source and colonist populations due to the extensive hydroelectric damming in the watercourse. Multiple introductions and substantial genetic variation in combination with the boom-and-bust population development of the species thus likely counteracted the founder effects as well as fueled the rapid establishment and expansion of this species within the Inari-Pasvik watercourse.
... Vendace is a relatively small, short-lived species with a plastic life history strategy (Bøhn et al. 2004;Gregersen et al. 2011). Maximum length and age are reported to be 25-30 cm and 5-7 years, respectively, in the majority of lakes (Schultz 1992;Bøhn et al. 2004), although fish older than 10 years have been found in single lakes (Salonen 2004). Age at maturation is between 2 and 5 years, with males usually reproducing earlier than females (Sandlund 1992;Bøhn et al. 2004). ...
Systematic comparisons of the ecology between functionally similar fish species from freshwater and marine aquatic systems are surprisingly rare. Here, we discuss commonalities and differences in evolutionary history, population genetics, reproduction and life history, ecological interactions, behavioural ecology and physiological ecology of temperate and Arctic freshwater coregonids (vendace and ciscoes, Coregonus spp.) and marine clupeids (herring, Clupea harengus, and sprat, Sprattus sprattus). We further elucidate potential effects of climate warming on these groups of fish based on the ecological features of coregonids and clupeids documented in the previous parts of the review. These freshwater and marine fishes share a surprisingly high number of similarities. Both groups are relatively short-lived, pelagic planktivorous fishes. The genetic differentiation of local populations is weak and seems to be in part correlated to an astonishing variability of spawning times. The discrete thermal window of each species influences habitat use, diel vertical migrations and supposedly also life history variations. Complex life cycles and preference for cool or cold water make all species vulnerable to the effects of global warming. It is suggested that future research on the functional interdependence between spawning time, life history characteristics, thermal windows and genetic differentiation may profit from a systematic comparison of the patterns found in either coregonids or clupeids.
Long-term monitoring of the planktivorous vendace (Coregonus albula) in Pyhäjärvi,
a lake in SW Finland, revealed periods characterised by different types of population
regulation. In 1971–1989, the vendace stock was strong and exhibited a two-year
cycle. In 1990–1999, extreme weather conditions and predation resulted in recruitment
failures, after which overfishing kept year-classes small. From 2000 onwards, the twoyear
oscillations were re-established at a lower level. Here, we show that the two-year
cyclicity prevalent in the 1980s was consistent with the hypothesis of asymmetric
competition between adults and juveniles. Food consumption by juveniles of strong
year-classes retarded growth and weakened condition of the co-occurring adults,
resulting in less abundant year-classes. In 2000–2018, the role of intraspecific competition
diminished due to interspecific competition from increased populations of other
planktivorous fish, preventing vendace from attaining higher abundance. Elevated
temperature probably confounded the effects of competition, but its direct role was
masked by simultaneous gradual eutrophication and fish assemblage changes.
Lake Inari is a subarctic, oligotrophic, regulated lake in northern Finland, connected via the Paatsjoki (Pasvik) River to the Arctic Ocean. A new coregonid species, the vendace (Coregonus albula), was introduced into the watershed in the 1960s and gradually established a population in the lake becoming part of its ecosystem. The annual vendace catch in 1989 reached 300 tonnes, while during the following 25 years the vendace catches declined stabilizing at a very low level. Vendace introduction radically changed the fishing practices within a short time, and its population became firmly established in the lake. It benefited both fisheries and predatory fishes, especially salmonids. The vendace year-class strength varied greatly between 1983 and 2019. According to winter seine CPUE data, the strongest year-classes were up to 100 times greater than the weakest ones. Winter seine CPUE of one-year-old fish correlated positively with catches in the coming years. The growth data for the period 2015–2021 revealed a decrease in the youngest vendace age-groups.
Observations of vendace (Coregonus albula (L.)) distribution, abundance and biology in Lake Pluszne, Poland, made using hydroacoustics and trawling between 2001 and 2010 are presented. Since 2002, the numerical density of vendace has decreased continuously, while their mean length and weight have increased. Young-of-year vendace were sampled only in 2001 when a strong year class recruited and their subsequent absence indicates that natural reproduction after 2001 has been hampered. The average condition of individual vendace over this time period was low compared with the condition observed in the 1960s. Observed changes in the vendace population were related to worsening hydrological conditions associated with increased eutrophication of the lake.
In northernmost Finland, in lake Inari (1100 km2) and the reservoirs, Lokka and Porttipahta (total 630 km2), commercial fishing is significant for its economical and social aspects. Local European whitefish (Coregonus lavaretus) is the most important catch species. Two new coregonids were introduced: vendace (Coregonus albula) in the Inari area in the 1950s, and peled (Coregonus peled) into the reservoirs in the 1970s. Later these species have naturally succeeded in reproduction. In lake Inari, the commercial fishery originated in the 1930s and in the reservoirs in the 1980s. Essential for the development of the commercial fishery was the modern infrastructure, established in the 1980s, when the stocks of vendace and peled became dense. The commercial fishery took up trap netting and trawling, in addition to gillnetting. The number of commercial fishermen increased and the commercial coregonid catches peaked at 350 tonnes in both areas. After the collapse of the vendace and peled stocks, European whitefish has maintained the commercial fishery. Today, in all about 50 commercial fishermen supply the market with high-quality coregonids.
Density of young-of-the-year (YOY) peled (Coregonus peled) in late summer trawling was used to estimate their forthcoming year-class strength (YCS) in two northern reservoirs, Lokka and Porttipahta. We applied virtual population analysis (VPA) in estimating year-class strength. A good correlation was found between YOY density and YCS of peled. In contrast, the density of YOY whitefish (C. lavaretus) did not reliably reflect their YCS. Annual number of trawling tows in 1991-2001 averaged 23 per reservoir. Precision (SE ̄-1) of the annual replicate samples averaged 0.33 and 0.31 for peled and whitefish, respectively. This level of precision was sufficient for detecting the large, often order-of-magnitude differences between annual mean YOY densities. As a practical application in fisheries management, YOY densities in survey trawling can be used in adjusting of stocking density and fishery of peled in the reservoirs studied.
The population dynamics, especially recruitment, of vendace (Coregonus albula) in lake Konnevesi were analysed from a time series of three decades from 1971 onwards. Recruitment success was highly variable, with no clear relationship between spawning stock and recruitment. Furthermore, no regular recruitment failure from large spawning stocks that would imply over-compensation was detected. Since 1982, an 11-year period of very poor year classes occurred despite the spawning stock and larval density being at high enough levels to produce abundant year-classes in the beginning of this period. A comprehensive recession appeared at the same time in other vendace stocks in southern Finland. In lake Konnevesi, perch (Percafluviatilis) stock increased rapidly during the vendace recession. High summer temperatures were revealed to strengthen the perch stock, especially in the 1980s, as indicated by CPUE data with a lag of two years. Perch probably delayed the recovery of vendace and it is also likely that its predation affected the dynamics of the vendace stock even in the beginning of the recession. We suggest that predation pressure as a whole was an important factor for the onset and duration of the vendace recession.
Tiivistelmä: Erip. Finnish fisheries research ; no 15, s. 49-58. Ilm. myös erillisenä. Diss. -- Helsingin yliopisto.
Forecasting potential yield may be important for adequately managing intensive commercial fisheries in highly productive lakes. Between 1986 and 1995, a small midwater trawl was used in November/December at night to assess population density and age structure of Lake Hallwil whitefish (Coregonus suidteri) in eutrophic Lake Hallwil, Switzerland. Acoustic data were recorded on the same day and night using dual beam technology. Year-class strength was calculated by virtual population analysis, based on catch statistics and age data of the commercial catch. Year-class strength varied highly between years. The number of young-of-the-year Lake Hallwil whitefish caught by standardized one-night trawling effort showed close correlation with year-class strength. Acoustic data corresponded well with pelagic fish abundance but not so well with size frequency distribution and biomass. Potential Lake Hallwil whitefish yield in subsequent years can be inferred from year-class strength assessed by the two methods, and using data on growth and size-at-harvest. Altogether, midwater trawling, combined with acoustics, was found to be an effective tool for forecasting year-class strength and yield of coregonids in small to middle-sized eutrophic lakes.
Salonen, E. 1998. The vendace stock and fisheries in Lake Inari. Boreal Env. Res. 3: 307–319. ISSN 1239-6095 Vendace (Coregonus albula) has a short history (30–40 year) in Lake Inari, being intro-duced into the watercourse in the 1950s and 1960s. The growth of the stock was slow at the beginning, but increased rapidly in the 1980s due to three strong, successive year classes in 1983, 1984 and 1986. All these years, and also in 1989, summers were quite warm and the water temperature favourable after the ice-break. The peak stock size was recorded 1987, and after that, there was a slump. In the middle of the 1990s, the stock size had stabilized to a very low level compared with the situation in the end of 1980s, and the vendace stock concentrated mostly in the southern parts of the lake. The vendace fishery flourished for less than five years. The peak year concerning fisheries and catches was 1989 with a vendace catch of nearly 3 kg ha –1 and a total catch of about 5 kg ha –1 , rather high figures in subarctic northern regions. After 1989, the vendace catch de-creased rapidly. It seemed that the fishing effort of some years (1989 and 1990) was so heavy that the spawning stock size gradually decreased to a level, where the revival was difficult. Unfavourable weather conditions with cold summers at the beginning of 1990s, and, at the same time, quite hard pressure of predation by abundantly stocked salmonids on vendace contributed together to the fact that only very scanty year-classes were born. This, in turn led to a collapse of the vendace stock in the 1990s.
Year-class variation and growth of the vendace (Coregonus albula (L.)), the most important commercial freshwater fi sh species in Finland, was assessed in Suomunjärvi from 1974-2001 seine and gill net catches. We estimated the relative abundances and growth of the individual year-classes. The year-classes 1980, 1985, 1990, and 2000 were strong. There were often oscillations of year-class strengths, although the period of oscillation was not regular. Strong year-classes dominated catches for almost as long as they were present in the lake. The strongest year-class was about 300 times greater in size than the weakest. The growth of the year-classes varied considerably; the difference in growth rate between the strongest and weakest year class was about 2.5-fold. Comparison of the growth of a year-class with its strength showed a marked negative correlation ( p < 0.001). The size of the whole stock (CPUE data) also had a negative effect on yearly growth ( p < 0.005).
In northernmost Finland, in lake Inari (1100 km2) and the reservoirs, Lokka and Porttipahta (total 630 km2), commercial fishing is significant for its economical and social aspects. Local European whitefish (Coregonus lavaretus) is the most important catch species. Two new coregonids were introduced: vendace (Coregonus albula) in the Inari area in the 1950s, and peled (Coregonus peled) into the reservoirs in the 1970s. Later these species have naturally succeeded in reproduction. In lake Inari, the commercial fishery originated in the 1930s and in the reservoirs in the 1980s. Essential for the development of the commercial fishery was the modern infrastructure, established in the 1980s, when the stocks of vendace and peled became dense. The commercial fishery took up trap netting and trawling, in addition to gillnetting. The number of commercial fishermen increased and the commercial coregonid catches peaked at 350 tonnes in both areas. After the collapse of the vendace and peled stocks, European whitefish has maintained the commercial fishery. Today, in all about 50 commercial fishermen supply the market with high-quality coregonids.
Many recent studies have stressed density-dependent regulation mechanisms in oscillating vendace (Coregonus albula) populations. Long-term studies on the population dynamics of vendace have been hampered by the difficulty of obtaining reliable estimates of year-class sizes. Data collected from Lake Pyhäjärvi (Southwest Finland) during 1971–91 allowed relatively accurate analysis of vendace abundance changes. In the winters of 1979–91, daily catch statistics were collected from professional fishermen. Species, age, and size composition were analysed from regular catch samples. We estimated the size of the vendace population from the decrease in the CPUE during 10 winters. For the remaining 10 years, estimates were based on the relationship between the numbers of a year-class in autumn and mean individual growth rate. A 2-yr cycle was the most conspicuous feature of the data implying density-dependent regulation. We suggest that in Lake Pyhäjärvi the basic model producing a persistent 2-yr cycle is the asymmetrical food competition between age groups.
The density of pelagic vendace stock in a deep Finnish lake (110 km2) during the period 1984–1992 was estimated by five methods. Relative fish density estimates (virtual population analysis, depletion method, catch-per-unit-effort, hydroacoustics and length of 1-year-old vendace) were able to show the direction of change in density. All density estimates for 1 + vendace had a strong negative correlation with the length of 1-year-old vendace of the same cohort. The VPA and depletion methods resulted in similar numerical estimates at high stock densities. The estimates differed at low densities. Hydroacoustics produced lower estimates than the other absolute methods, especially in the years when 1+vendace dominated. The length-density index predicted the catch of 1+vendace in the following season (r2=0.78, n=8, P=0.004) and hydroacoustic density estimates predicted the total vendace catch (r2=0.87, n=6, P=0.006).