Ann. Zool. Fennici 58: 243–253 ISSN 0003-455X (print), ISSN 1797-2450 (online) Helsinki 30 August 2021 © Finnish Zoological and Botanical Publishing Board

Vendace (Coregonus albula) in — what has changed in 50 years?

Erno Salonen

Natural Resources Institute (Luke), Saarikoskentie 8, FI-99870 Inari, Finland (e-mail: erno. [email protected])

Received 5 Oct. 2020, final version received 17 June 2021, accepted 18 Mar. 2021

Salonen, E. 2021: Vendace (Coregonus albula) in Lake Inari — what has changed in 50 years? — Ann. Zool. Fennici 58: 243–253.

Lake Inari is a subarctic, oligotrophic, regulated lake in northern Finland, connected via the (Pasvik) River to the Arctic Ocean. A new coregonid species, the ven- dace (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 weak- est 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.

Introduction Such fluctuations were observed in the invasive vendace population in Lake Inari (Finland) and The vendace (Coregonus albula) is not native to further downstream in the Paatsjoki watershed Lake Inari or the Paatsjoki (Pasvik) watershed. ( and ) (Salonen et al. 2007). A native coregonid is the dwarf densely-rakered In 1956, some vendace larvae escaped acci- European whitefish (reeska in Finnish) (Corego- dentally from an Inari fish farm into the Juutua nus lavaretus), which is similar to the vendace River, which flows to nearby Lake Inari. In both biologically and ecologically. Its gillraker 1964–1966, vendace was introduced into nearby count, however, is between 30 and 40, while Alajärvi (Fig. 1). According to local accounts the vendace gillraker count is over 40 (Salonen (J. Kyrö pers. comm.), newly hatched vendace 1992, and author’s own unpubl. data). In general, larvae were also stocked directly into the - an introduced or invasive species that became joki. The distance from Alajärvi along the Ivalo- established in a new environment may, even joki to Lake Inari is about 30 km. In some way, long after establishment, undergo substantial and perhaps by active swimming or drifting with unpredictable population fluctuations, including the current down the river, sufficient amount of also boom-and-bust cycles (Williamson 1996). larvae managed to enter the southernmost part of

Editor-in-charge: Timo Marjomäki 244 Salonen • ANN. ZOOL. FENNICI Vol. 58

24°E 27°E 30°E 33°E

70°N Arctic Ocean

Skrukkebukta

Vaggatem NORWAY Lake Inari i

69°N Inari fish atsjok farm KaitakosPa

Juutua ki power Ivalo i plan Ivalojok Alajärvi* t

RUSSIA Porttipahta

68°N Lokka

Kitine

n

Luiro

Kelujärvi*

67°N Iso-Venejärvi White Se Raudanjoki

Ounasjok Kemijärvi a

Sinettäjärvi* i

Kemijoki Kemijärvi Rovaniemi Fig. 1. Map of the study area with Lake Inari, watersheds, and possible 66°N founder lakes (Kelujärvi, Legend FINLAND Sinettäjärvi, Alajärvi) into Lakes and reservoirs which vendace were intro- Kemijoki watershed duced. Data on water- Baltic Sea Paatsjoki watershed sheds from the Finnish Rivers Flow direction Environment Institute, and 0525 0 100 km State border on lakes and reservoirs 65°N * possible founder lakes from The National Land 24°E 27°E 30°E 33°E Survey of Finland.

Lake Inari, where vendace were observed for the resource for predatory fishes in the lake, espe- first time in 1973. There, the species gradually cially for valuable salmonids (e.g., Salmo trutta), established a new fish population in Lake Inari which before vendace introduction preyed upon (Sergejeff 1985, Salonen et al. 2007), and about C. lavaretus (dwarf densely rakered whitefish; two decades later (between 1989 and 1995), reeska in Finnish) as well as three-spined (Gas- vendace was found downstream in the Norwe- terosteus aculateus) and nine-spined (Pungitius gian part of the Paatsjoki (Pasvik) watershed pungitius) sticklebacks (Toivonen 1966). On the (Amundsen et al. 1999, 2012). In 2013, a genetic other hand, the alien vendace became quite a study confirmed that the vendace in Lake Inari strong competitor for resources with native C. and in Vaggatem and Skrukkebukta in the Pasvik lavaretus (reeska) (Salonen et al. 2007). watershed (Norway) were both of Sinettäjärvi Here, I describe history of the vendace in origins from introduction/stocking in 1964–1966 Lake Inari. The material for this work comprised (Praebel et al. 2013). yearly vendace catches and catch sample data Between 1973 and 2021, vendace changed since the mid-1980s up to the present day. fisheries in Lake Inari, and became a new prey ANN. ZOOL. FENNICI Vol. 58 • Vendace in Lake Inari — what has changed in 50 years? 245

8500 gillnet winter seine trapnet trawl 8000

7500 7000 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000

Fig. 2. Sampled and aged Sampled and aged vendace (indiv.) 1500 vendace caught with dif- 1000 500 ferent fishing gear in Lake 0 Inari. Fish caught in 1986 were not analysed. 198 5 198 6 198 7 198 8 198 9 199 0 199 1 199 2 199 3 199 4 199 5 199 6 199 7 199 8 199 9 200 0 200 1 200 2 200 3 200 4 200 5 200 6 200 7 200 8 200 9 201 0 201 1 201 2 201 3 201 4 201 5 201 6 201 7 201 8 201 9

Material and methods sebago) until 2001 and lake trout (Salvelinus namaycush) until 2012. There are many white- Study area fish morphs in the lake, including two dwarf forms: densely-rakered (reeska in Finnish) and Lake Inari in northern Finland (68°57´N, sparsely-rakered (rääpys in Finnish) whitefish. 27°40´E) is a large (around 1100 km2) central They can be identified by their morphology lake in the Paatsjoki (Pasvik) watershed, drain- (jaws, number of gill rakers), and they also differ ing northeast into the Arctic Ocean, first through from each other in their ecology (food selec- Russia and then as a borderline watercourse tion and growth) (Toivonen 1966, Marttunen et between Russia and Norway (Fig. 1). The water- al.1997). shed has been regulated since the 1940s, and the uppermost power plant, Kaitakoski, regulates the water level of Lake Inari (annual level change Data ~1.5 m). The ice-free season in Lake Inari lasts from May–June to October–November (often Information on the catch statistics was collected December in large open-water areas). The lake from commercial, local subsistence- and recrea- is quite deep (max. depth 95 m, mean depth tional fisheries with regular yearly mail inquires. 14.4 m), clear and oligotrophic. Its Secchi-depth These were complemented by interviews and ranges from 3–4 m to 7–10 m in the southern and book-keeping (daily catch and effort records) in northern parts, respectively. The fish community connection with the obligatory monitoring pro- includes 13 species, with whitefish (Coregonus cedures related to Lake Inari water-level regula- lavaretus s.l.), brown trout (Salmo trutta), Arctic tion (see above). char (Salvelinus alpinus), grayling (Thymallus Before the 1990s, during the vendace boom thymallus), perch (Perca fluviatilis), pike (Esox years, vendace samples originated from the lucius) and burbot (Lota lota) being the most entire Lake Inari, and afterwards mostly from abundant native species. Minnows (Phoxinus the southern part of the lake. The sampling phoxinus) are the only cyprinid species in the was performed mainly by commercial fishermen lake (Salonen 2004). Large obligatory stocking using gill nets, winter seines, trawls and trap nets programmes including whitefish and piscivorous (e.g. Salonen 1998). The data on the vendace for species such as brown trout and Arctic char have the 1985–2019 period include of over 40 000 been carried out since the 1970s. In addition specimens. Especially high numbers of vendace to vendace, two other non-native species were were caught (sampled) in 1989 particularly by stocked: land-locked salmon (Salmo salar m. trawling (Fig. 2). In recent years, only around 246 Salonen • ANN. ZOOL. FENNICI Vol. 58

150 samples per year were taken from catches by Alajärvi (Fig. 1). The vendace larvae which had winter seine and gillnets, as only these two types escaped in 1956 were from the Kelujärvi stock, of fishing still targeted vendace. and the vendace introduced in 1964–1966 were The catch per unit of effort (CPUE) for from the Sinettäjärvi stock. Both lakes are in the vendace were calculated from the records of Kemijoki watershed (waters flow to the Baltic the commercial winter seining (1996–2020, 1–2 Sea) 150–250 km south of Lake Inari (Serge- seine teams), and gillnet fishing (data provided jeff 1985, Mutenia & Salonen 1992) (Fig. 1). by local subsistence fishermen in yearly mail According to local accounts (J. Kyrö pers. inquires). Commercial fishermen caught vendace comm.), newly hatched vendace larvae were also using gillnets only very occasionally, and com- stocked directly into the Ivalojoki in the vicin- mercial trawling had practically ceased already ity of the bridge in the village of Ivalo. Those in the1990s after the vendace boom years. After- larvae had the same origin (Sinettäjärvi stock) wards, one or two commercial trawlers operated and, as the ones in Alajärvi, were also introduced until 2017, but only very occasionally (no reli- in 1964–1966. The distance from Alajärvi along able CPUE data). Starting in 1994, vendace sam- the Ivalojoki to Lake Inari is about 30 km. In ples taken from winter seine catches to evaluate some way, by active swimming or drifting with the year-class strength. the current down the river, sufficient amount of Random subsamples (30–50 indiv.) were larvae managed to enter the southernmost part taken from vendace catches to determine fish of Lake Inari. The first vendace were caught in total length (TL, mm), body weighed (g), as well Lake Inari in 1973 most likely with 15–17 mm as sex and maturity. The fish were aged mainly (knot to knot) reeska gillnets, as before that from scales, but as of the year 2000, otoliths reeska was the only species fished using such were also taken from ≥ 15 cm TL vendace. Here, gear. In the 1980s, when the vendace fishing vendace growth was determined based on the really began, the earlier reeska gillnets replaced actual average age-specific total length in winter by vendace gillnets and the small-scale reeska seine samples taken yearly in January–April. fishery transformed into a large-scale vendace Based on annual catch, sample data and the fishery (Toivonen 1966; J. Kyrö pers. comm). age distribution according to the fishing gear After the 1970s, the species gradually estab- used, I calculated the cumulative catch for every lished a new fish population in Lake Inari (Serge- year-class between 1983 and 2019 (data for jeff 1985, Salonen et al. 2007), and in the 1990s, 2013–2019 incomplete). Only age-groups from vendace were found downstream in the Norwe- one to seven were included because vendace gian part of the Paatsjoki (Pasvik) watershed older than seven years were very rare (< 5%) in (waters flow to the Barents Sea) (Amundsen et every type of sampled fishing gear. al. 1999). In 2013, a genetic study confirmed I also analysed the relationship between one- that the vendace in Lake Inari and in Vag- year-old vendace caught in winter seine (CPUE gatem and Skrukkebukta in the Pasvik watershed of 1-year-olds) and the cumulative catch (all (Norway) were both of Sinettäjärvi origins from types of fishing gear) for 1994–2012 using linear introduction/stocking in 1964–1966 (Praebel et regression. al. 2013).On the Russian side, vendace popula- tions are found in watersheds from which waters flow to the White and Barents Seas. Vendace in Results and discussion those populations may have also originated from translocations from other parts of the country Vendace introduction, current range and (Amundsen et al. 2012). future Regulation of Lake Inari for hydroelectric power generation in Russia and Norway has In 1956, some vendace larvae escaped acci- continued since 1941 (Mutenia & Salonen 1994, dentally from an Inari fish farm into the Juutua Marttunen et al. 1997). The water-level fluc- River, which flows to nearby Lake Inari. In tuation in the lake is approximately 1.5 m (e.g. 1964–1966, vendace was introduced into nearby Mutenia & Salonen 1994), which is moderate ANN. ZOOL. FENNICI Vol. 58 • Vendace in Lake Inari — what has changed in 50 years? 247

300 gillnet winter seine trapnet trawl 280 260 240

) 220 200 180 160 140 120 100

Vendace catch (tonnes 80 60 Introduction into Alajärvi 40 First catch in Lake Inari 20 0 1964 1965 1966 1973 1983 1985 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 First observation in Lake Inari First observation in the Pasvik watershed in Norway Fig. 3. Vendace catches in Lake Inari as well as years of introduction and first observations in Lake Inari and the Norwegian part of the Pasvik watershed. compared with that in Kemijärvi, where the the species (Henttonen et al. 2017, Jeppesen et amplitude is seven meters. In the first dec- al. 2012). Thus in future, the vendace status in ades, however, water-level changes profoundly Lake Inari may by quite different than today. affected fish communities and fisheries in Lake Inari. For this reason, compensatory measures, such as large-scale fish stocking of brown trout, Fisheries and catches arctic char and whitefish, were introduced. Ven- dace that feed on pelagic zooplankton and spawn In the mid-1980s, trials with several new types of mainly in deeper zones (1.5–30 m; Heikkilä et fishing gear — gillnets, winter seines, trap nets, al. 2006, Karjalainen et al. 2021), however, seem and pair trawls (Mutenia & Ahonen 1990) — not to be affected but detailed studies are lack- began, mainly targeting vendace, but also aiming ing. at more efficient exploitation of the whitefish Introduced vendace became established in stocks. New methods of vendace fishing were Lake Inari within about 50 years. However, adopted very quickly, and in the boom year of if escapees from 1956 are taken into account, 1989 catches exceeded 300 tonnes. The bust the species history in the lake may cover over in the 1990s after just a five-year boom period 60 years. In Lake Inari, vendace live at the was equally rapid (Salonen 1998). Afterwards, northernmost edge of their range, and outside the catches stabilized at a low level and were their natural distribution area. Therefore, climate taken mainly using gillnets (nowadays typically change and hydrological conditions in the lake 18–22 mm) (Fig. 3). CPUE by winter seining are expected to affect this species as in Fin- increased in 2018–2020 reaching about a 200 kg land, the average annual mean air temperature per haul in spring 2020 (Fig. 4). In 2010–2019, increase for 2070–2099, compared with 1971– vendace CPUE in local subsistence gillnetting 2000, has been projected to be 3–6 °C (https:// during the spawning period varied between 1 www.climatechangepost.com/finland/climate- and 3 kg per net night, the best season being the change/). Warming will be more pronounced autumn in 2019 (Fig. 5). at higher latitudes, which will favour vendace Coregonids, mainly whitefish, comprised the recruitment in Lake Inari, while at more southern bulk of the Lake Inari catches during the 80-year latitudes, similar warming may be detrimental to period. Whitefish were overwhelmingly the most 248 Salonen • ANN. ZOOL. FENNICI Vol. 58

3 In Lake Inari, vendace individuals of around 10 years of age occur in the samples almost every year, and 13-year-old fish have also been 2 caught (author’s own data). This can be con- sidered unusual, as there are only few lakes in 1 Finland, where similar is observed (e.g. Lake Konnevesi; see Marjomäki et al. 2021b). Some vendace can also grow large: the two largest CPUE (kg per gillnet day) 0 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 vendace reported from Finland weighed 550 g Fig. 5. Vendace gillnet fishing (18–25 mm mesh size) (caught on 1 October 2004, length 400 mm) and CPUE in Lake Inari (data obtained from local fishermen 634 g (caught on 29 September 2020, length using questionnaires send by mail). 399 mm). In Lake Inari the vendace population and catch consist of several year-classes, which important species in 1935–1940, before the lake should keep the catches more stable than in most regulation, which started in 1941, and also in lakes, where only 2–3 year-classes exist at the recent years, especially in 2017 and 2018. same time. Owing to that, one poor year-class Salmonids (mainly brown trout), but also does not affect the population as it might. pike and grayling, are overall very significant In the Norwegian part of the Paatsjoki water- and valuable species in the lake being a signifi- shed, vendace of the same origin (Sinettäjärvi) cant part of the fish yields (Fig. 6). dispersed rapidly in the first decades after the first observation in 1989 (Amundsen 1999, Amundsen et al. 2012). As compared with that in Growth and age structure Lake Inari, the population in lakes Vaggatem and Skrukkebukta grew more slowly and attained In Lake Inari, vendace growth seems to be slow- much smaller lengths. Their mortality was also ing down. Until 2004, one-year-old vendace could higher, hence the populations consisted of much reached nearly 95 mm TL, but no more than younger fish which maturated both at a younger 70–80 mm after 2011 (Fig. 7). Similarly, three- age and at a smaller size than in Lake Inari. year-old vendace could reached ~180 mm TL the According to samples taken between 1991 and mid-1990s, but no more than about 130 mm after 2007, in Lake Vaggatem, over 90% of the ven- the year 2014 (Fig. 7). The two-year-old vendace dace at age 1+ (length < 10 cm) were sexually (data not shown) grew up to 150 mm TL in the mature, whereas in Lake Inari, only 20%–40% mid-1990s, whereas in the most recent years, indi- of the vendace at age 1+ (length > 12 cm) were viduals were shorter than 110 mm. mature (Amundsen et al. 2012).

40 300 catch CPUE 35 250

) 30 CPUE (kg per haul) 200 25

20 150 Fig. 4. Vendace winter seine catches and CPUE 15 in Lake Inari; CPUE data 100 from 1988–1995 are miss- Vendace catch (tonnes 10 ing. At the maximum (in 50 1989) there were seven 5 winter-seine teams, but no more than one at the 0 0 3 7 end of the studied period

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 201 2014 2015 2016 201 2018 2019 2020 (2018–2020). ANN. ZOOL. FENNICI Vol. 58 • Vendace in Lake Inari — what has changed in 50 years? 249

500 coregonids (whitefish + vendace) others (grayling + pike + burbot + perch) 450 salmonids (brown trout + arctic char + lake trout + land-locked salmon) 400 ) 350

300

250

200

150 Catches in Lake Inari (tonnes

100

50

0 197 7 197 9 198 0 198 1 198 2 198 3 198 4 198 6 198 7 198 8 198 9 199 0 199 1 199 2 199 3 199 4 199 5 199 6 199 7 199 8 199 9 200 0 200 1 200 2 200 3 200 4 200 5 200 6 200 7 200 8 200 9 201 0 201 1 201 2 201 3 201 4 201 5 201 6 201 7 201 8 1935–1940 1950–1955 1960–1964 1966–1970 Fig. 6. Coregonid, salmonid and other fish species catches in Lake Inari. The total catch in the years 1935–1940 (before the lake regulation) equalled 250 tonnes. The highest total catch for the studied period was in the year 1989 equalled 560 tonnes. Yearly fish catches by species from Toivonen (1966, 1972), Salonen 1992 and Nivaet al. (2020).

100 One-year-old vendace 95 90 85 80 75

Total length (mm) 70 65 60 1988 1989 199 0 1991 199 2 199 3 1994 1995 1996 1997 199 8 1999 2001 2002 200 3 2004 2005 200 6 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 201 7 2018 2019

200 Three-year-old vendace 190 180 170 160 Fig. 7. Mean length 150 (±95%CL) for 1-year- 140 130 and 3-year-old vendace Total length (mm) 120 caught by winter seine 110 fishing (January-April) in 100 Lake Inari over the time 6 8 1 4 7 1997 1998 1999 2001 2002 2003 2004 2005 2006 2007 200 2009 2010 201 2012 2013 201 2015 2016 201 period from 1985 to 2019. 1985 1988 1989 1990 1991 1992 1993 1994 1995 199 2018 2019

In Lake Inari, the vendace can reach a greater 1990s. They were also rapidly growing speci- maximum size than elsewhere in Finland. In mens, with the oldest individuals being 7-years Iso-Venejärvi (lake in the Kemijoki watershed, old (Alanne 2004). 50 km north from Sinettäjärvi) many large ven- In Lake Vaggatem (Norway), growth of ven- dace (700–800 g) were caught in the 1980s and dace declined strongly in 1995–1998 (Amund- 250 Salonen • ANN. ZOOL. FENNICI Vol. 58

40 1985 (winter seine only) 70 1995 trawl trapnet 60 winter seine 30 gillnet 50

40 20 30 Percentage 20 10 10

0 0 2345 6 0+ 1 23456789101112 Age (years) Age (years) 70 2005 50 2019 trawl gillnet 60 trapnet winter seine winter seine 40 gillnet 50 e 40 30

30 Pecentag 20 20 10 10

0 0 0+ 1234567 12345678910 11 Age (years) Age (years) Fig. 8. Vendace age distribution in catches by different fishing gears used in Lake Inari. The samples were from the years 1985, 1995, 2005 and 2019. One-year-old vendace in winter-seine catches in 1985 catches were not analysed.

sen et al. 2012). In Lake Inari, it grew faster class of 1989 was still quite strong in the catches during the two first studied decades than in of 1995 (Fig. 8; data for 1985, 2005 and 2019 the most recent ones (age groups 1–3 based on shown for comparison), and old individuals (≥ 7 winter seine data; Fig. 7). As growth of vendace years old) were frequently caught with every depends on population density (see e.g. Viljanen type of fishing gear. Overall, the strongest year- 1986), strong vendace year-classes may grow class was that of 1986, but judging from cumula- slowly due to e.g., intense competition for lim- tive catch (Fig. 9) also those of 1989 and 1984 ited food resources (Amundsen et al. 2012, Mar- were very strong. Throughout the 1990s, only jomäki et al. 2021a). weak year-classes were born. Later, the year- The vendace is in principle a planktivo- class 2005 produced the best catches (Fig. 9). rous species. However, large individuals (about The data from 2020 showed that the 2019 year- 1 kg weight) may be partly piscivorous. This class was the strongest during the 26 years of was observed for example in Lakes Onega and monitoring (Fig. 10). Ladoga in Russia (Reshetnikov & Lukin 2006) The winter seine CPUE (one-year-old in num- but not yet in Lake Inari. bers) and the cumulative vendace total catch were positively correlated (Fig. 11). The best year-class of 2005 (~14 000 recruits in the winter seine Year-class strength and variation CPUE) produced cumulative catch (1–7-year- olds) of 1.6 million in the 2006–2012, whereas the Strong vendace year-classes appeared in the weakest year-class of 1996 (only ~20 recruits in catches for many years. For example, the year- the winter seine CPUE) produced only about 0.15 ANN. ZOOL. FENNICI Vol. 58 • Vendace in Lake Inari — what has changed in 50 years? 251 6 6 13 x 10 5 8.5 x 10

) 4.5 6 4 3.5 3 2.5 Fig. 9. Cumulative catch 2 of vendace year-classes 1.5 1983–2012. Notice, that the year-classes of 1986 1 Vendace catch (indiv. x 10 and 1989 rise above the 0.5 figure scale. Data for 0 2013–2019 are incom- 1983 198 4 1985 198 6 1987 1988 198 9 1990 1991 199 2 1993 199 4 1995 199 6 1997 199 8 1999 200 0 2001 200 2 2003 200 4 2005 200 6 2007 2008 2009 201 0 2011 2012 201 3 201 4 201 5 2016 2017 2018 201 9 plete. Year class

34000 32000 30000 28000 26000 24000 22000 20000 18000 16000 14000 vendace 12000 10000 8000 6000 4000 Fig. 10. Winter seining 2000 CPUE (mean + 95%CL, Mean + 95%CL CPUE of 1-year-old 0

n = 26) in the southern- 1994 199 5 1996 199 7 199 8 199 9 2000 200 1 2002 2003 200 4 2005 200 6 2007 200 8 2009 201 0 2011 2012 201 3 201 4 2015 2016 201 7 201 8 201 9 most Lake Inari. Year class

1.8 strong year-class 2005 1.6 ) 6 1.4

1.2 y = 88.38x + 152224, 1 r2 = 0.76, n = 19, p < 0.05 0.8 Fig. 11. Relationship between the one-year- 0.6 old vendace year-class 0.4 strength (caught in winter Cumulative catch (indiv. x 10 seine fishing) and ven- 0.2 weak year-class 1996 dace total catch (all year 0 classes, all types of gear). 0 2000 4000 6000 8000 10000 12000 14000 16000 Data from 1994–2012 Number of one-year-old recruits million vendace in the cumulative catch in 1997– strong year-class for quite a long time. Strong 2003. According to the above, it can be expected fluctuations are typical for vendace also in its that the good year-class of 2019 may produce native range (e.g. Salojärvi 1987, Auvinen 1994). good catches in the future, up to the year 2025. In the case of Lake Inari, the reasons for this The vendace stock rose quite rapidly in the even dramatic stock variation were presumed to 1980s due to many abundant year-classes; 1983, include unfavorable weather conditions, fishing, 1984, 1986, and 1989, which remained the last and salmonid predation. 252 Salonen • ANN. ZOOL. FENNICI Vol. 58

The decrease in the spawning stock in the January and 3 February 2021 included mostly 1990s took place at a time when the already the strong vendace 2019 year-class (now two- declining stock had been subject to quite inten- year-old) with some addition of the 2020 year- sive fishery (Salonen 1998). However, all ven- class. The coming years will reveal the fate of dace year-classes in the 1990s were very poor the excellent 2019 year-class, and other potential and their catches were only a fraction of those changes in the vendace population in Lake Inari. when year-classes were strong (Salonen 1998). The strongest year-classes of 1986 and 1989 pro- duced around a hundredfold more catch than the Acknowledgements weakest ones (1991 and 1993; see Fig. 9). At the same time, the trawl fishery declined after only a Greatest thanks go to professional fishermen Juha, Arvo and few years, from 16 to 2 trawl pairs in 1989–1990 Olavi Kyrö who provided fish samples, and Juha Kyrö who provided catch and CPUE statistics. I also thank the staff of and 1996, respectively (Salonen 1998). RKTL and LUKE who participated in the data collection and Due to major changes in both the vendace fish handling in the laboratory. Special thanks go to Ahti Mute- stock and fishing in the beginning of the 1990s, nia (dec.) who organized the first studies of vendace, Heimo survey trawling in Lake Inari was carried out in Pukkila who took care of the large-scale collection of vendace 1993–2001, with the aim to evaluate the abun- samples from the fishermen, Kirsi Leppänen who aged ven- dace at the end of 1980s and in the 1990s, and Sari Raineva dance of one-summer-old (0+) vendace, the ear- who handled and aged vendace samples for the last 20 years. liest life stage that could be quantified (Salonen 2004). A 12-meter-deep pelagic trawl with a cod-end mesh size of 8 mm was used in six areas of the lake (Nanguvuono, Ämmänhiekka, Ukon- References selkä, Kaikunuora, Partakko and Roiro). Until Alanne, M. 2004: Iso-Venejärven muikun kasvu ja ravinnon- 1999, trawl CPUEs of 0+ vendace were very low, kulutuksen arviointi bioenergeettisen mallin avulla. — followed by slight increase in 2000 (Salonen M.Sc. thesis, University of Jyväskylä, Finland. 2004). The survey also indicated that fish densi- Auvinen, H. 1994: Intra- and interspecific factors in the ties (0+ and older fish) differed among the lake dynamics of vendace (Coregonus albula L.) populations. — Finnish Fisheries Research. 15: 49–58. areas: the survey catches were much higher in Amundsen, P.-A., Staldvik, F. J., Reshetnikov, Y. S., Kashu- the southernmost part than in the northern parts lin, N., Lukin, A., Bøhn, T., Sandlund, O. T. & Popova, (Salonen 2004). Yearly catch statistics (author’s O. A. 1999: Invasion of vendace (Coregonus albula) in unpubl. data) and some occasional trawl hauls a subarctic watercourse. — Biological Conservation 88: along with echo sounding searches for vendace 405–413. Amundsen, P.-A., Salonen, E., Niva, T., Gjelland, K. O., schools (J. Kyrö pers. comm.) revealed that Praebel, K., Sandlund, O. T., Knudsen R. & Bøhn, T. during the short boom period in 1987–1991, ven- 2012: Invader population speeds up life history during dace spread across the entire lake, but later the colonization. — Biological Invasions 14: 1501–1513. fish seemed to concentrate in the southern part of Heikkilä, J., Huuskonen, H. & Karjalainen, J. 2006: Loca- the lake. Our annual winter seine samples were tion of spawning grounds of vendace (Coregonus albula (L.)): implication for dispersion of newly hatched larvae. taken from the best southernmost vendace areas — Verhandlungen des Internationalen Verein Limno- of the lake. logie 29: 1725–1728. Survey trawling for 0+ vendace in autumn Henttonen, H. M., Nöjd, P. & Mäkinen, H. 2017: Environ- followed by winter seine sampling of one-year- mental-induced growth changes in the Finnish forests old individuals (i.e., same year-class) next winter during 1971–2010 — an analysis based on National Forest Inventory. — Forest Ecology and management confirmed that the 2000 year-class was the first 386: 22–36. strong one for a long time (Salonen 2004). Jeppesen, E., Mehner, T., Winfield, I. J., Kangur, K., Sarvala, Recent winter seine surveys revealed a very J., Gerdeaux, D., Rask, M., Malmquist, H. J., Holmgren, strong vendace year-class of 2019 (CPUE about K., Volta, P., Romo, S., Eckmann, R., Sandström, A., 20 000 recruits; Niva et al. 2020) predicting Blanco, S., Kangur, A., Ragnarsson, S. H., Tarvainen, M., Ventelä, A.-M., Søndergaard, M., Lauridsen, T. L. & even higher catches than those of the highly pro- Meerhoff, M. 2012: Impacts of climate warming on the ductive year-class 2005 (depending on the actual long-term dynamics of key fish species in 24 European fishing effort). Winter seine samples taken on 20 lakes. — Hydrobiologia 694: 1–39. ANN. ZOOL. FENNICI Vol. 58 • Vendace in Lake Inari — what has changed in 50 years? 253

Karjalainen, J., Tuloisela, M., Nyholm, K. & Marjomäki, T. Praebel, K., Gjelland, K. O., Salonen, E. & Amundsen, J. 2021: Vendace (Coregonus albula) disperse their eggs P.-A. 2013: Invasion genetics of vendace (Coregonus widely during spawning. — Annales Zoologici Fennici albula (L.)) in the Inari-Pasvik watercourse: revealing 58: 141–153. the origin and expansion pattern of a rapid colonization Marjomäki, T. J., Auvinen, H., Helminen, H., Huusko, A., event. — Ecology and Evolution 3: 1400–1412. Huuskonen, H., Hyvärinen, P., Jurvelius, J., Sarvala, J., Reshetnikov Y. & Lukin A. 2006: Modern state of the diver- Valkeajärvi, P., Viljanen, M. & Karjalainen, J. 2021a: sity of Coregonids from Onega Lake and the problems Occurrence of two-year cyclicity, “saw-blade fluctua- of their species identification. —Journal of Ichthyology, tion”, in vendace populations in Finland. — Annales 46: 694–708. Zoologici Fennici 58: 215–229. Salojärvi, K. 1987: Why do vendace (Coregonus albula L.) Marjomäki, T. J., Valkeajärvi, P. & Karjalainen, J. 2021b: populations fluctuate? — Aqua Fennica 17: 17–26. Lifting the vendace, Coregonus albula, on the life table: Salonen, 1992: Inarijärven kalataloudellinen käyttö- ja hoi- survival, growth and reproduction in different life- tosuunnitelma. Nykytila. — RKTL, kalantutkimusosasto, stages during very high and low abundance regimes. — Helsinki. Annales Zoologici Fennici 58: 177–189. Salonen, E. 1998: The vendace stock and fisheries in Lake Marttunen, M., Hellsten, S., Puro, A., Huttula, E., Nenonen, Inari. — Boreal Environment Research 3: 307–319. M.-L., Järvinen, E., Salonen, E., Palomäki., Huru, H. & Salonen, E. 2004: Estimation of vendace year-class strength Bergman, T. 1997: Inarijärven tila, käyttö ja niihin vai- using different methods in the subarctic Lake Inari. — kuttavat tekijät. — Suomen ympäristö 58: 1–197. Annales Zoologici Fennici 41: 249–254. Mutenia, A. & Ahonen, M. 1990: Recent changes in the Salonen, E., Amundsen, P.-A. & Bøhn, T. 2007: Boom fishery on Lake Inari, Finland. — In: van Densen, W. L. and bust development by invading vendace (Coregonus T., Steinmetz, B. & Hughes, R. H. (eds.), Management albula) in the subarctic Inari–Pasvik watershed (Finland, of freshwater fisheries. Proceedings of a symposium Norway and Russia). — Advances in Limnology 60: organized by the European Inland Fisheries Advisory 331–342. Commission, Göteborg, Sweden, 31 May to 3 June 1988: Sergejeff, K. 1985: Muikku Inarijärvessä. — Suomen kalas- 101–111. Pudoc, Wageningen. tuslehti 92: 50–51. Mutenia, A. & Salonen, E. 1992: The vendace (Coregonus Toivonen, J. 1966: Lausunto veden säännöstelyn vaiku- albula L.), a new species in the fish community and fish- tuksista Inarijärven kalakantoihin ja kalastukseen. — eries of Lake Inari. — Polish Archives of Hydrobiology RKTL, kalantutkimusosasto, Helsinki. 39: 583–591. Toivonen, J. 1972: Veden säännöstelyn vaikutus Inarijärven Mutenia, A. & Salonen, E. 1994: Rehabilitation of fisher- kalakantoihin ja kalastukseen. Täydentävä lausunto. — ies of regulated Lake Inari, northern Finland. — In: RKTL, kalantutkimusosasto, Helsinki. Cowx, I. G. (ed.), Rehabilitation of freshwater fisheries: Viljanen, M. 1986: Biology, propagation, exploitation and 280–288. Fishing News Books, London. management of vendace (Coregonus albula L.) in Fin- Niva, T., Salonen, E., Raineva, S., Savikko, A., Vaajala, M. & land. — Archiv für Hydrobiologie Beihefte Ergebnisse Siitari, S. 2020: Inarijärven ja sen sivuvesistöjen kalata- der Limnologie 22: 73–97. loudellinen velvoitetarkkailu 2019. — Luonnonvara- ja Williamson, M. 1996: Biological invasions. — Chapman & biotalouden tutkimus 107/2020: 1–44. Hall, London.