Fishing or the environment – what regulates recruitment of an exploited marginal vendace (Coregonus albula (L.)) population?

Lack of panmixia of Bothnian Bay vendace - Implications for fisheries management

“…Vendace (Coregonus albula) is a small salmonid fish that belongs to Eurasian cisco complex (Coregoninae) (Mehner et al, 2021;Sendek, 2021). This species inhabits deep and oligotrophic lakes in Western and Northern Europe (Vuorinen and Lankinen, 1978;Sendek, 2021;Karjalainen et al, 2022) and also occurs in the Baltic Sea, in brackish waters of the Bothnian Bay (Bergenius et al, 2013) and in the eastern part of the Gulf of Finland (Sendek, 2012). The southward distribution of vendace in the Baltic is limited by the increased salinity but it also occurs in estuaries.…”

“…The upper salinity range of vendace is about 2 to 3 PSU (Lehtonen, 1981) and the Bothnian Bay salinity levels can increase to over 3 PSU in the southern part. Vendace is a shortlived species and can reach maturity already in their first year of life (Bergenius et al, 2013). Vendace spawns from October to December in river estuaries and shallow coastal areas (Lehtonen, 1981) and is known for its strong and unpredictable stock fluctuations caused by large fluctuations in recruitment (Karjalainen et al, 2000).…”

“…Vendace spawns from October to December in river estuaries and shallow coastal areas (Lehtonen, 1981) and is known for its strong and unpredictable stock fluctuations caused by large fluctuations in recruitment (Karjalainen et al, 2000). Besides spawning stock biomass, hydro-climatic factors, in particular winter temperature and salinity, have shown to be important variables influencing the temporal variability of recruitment of vendace in the Bothnian Bay (Bergenius et al, 2013). Furthermore, Bergenius et al (2013) demonstrated that recruitment variability in Bothnian Bay vendace is determined by density-independent factors (Karjalainen et al, 2000;Marjomäki, 2003).…”

“…Besides spawning stock biomass, hydro-climatic factors, in particular winter temperature and salinity, have shown to be important variables influencing the temporal variability of recruitment of vendace in the Bothnian Bay (Bergenius et al, 2013). Furthermore, Bergenius et al (2013) demonstrated that recruitment variability in Bothnian Bay vendace is determined by density-independent factors (Karjalainen et al, 2000;Marjomäki, 2003). The role of trophic factors influencing vendace abundance in the Bothnian Bay have significantly changed with the increasing number of seals in the Bothnian Bay since the beginning of the 90s.…”

“…The yearly consumption of vendace by seals is larger than the Finnish and Swedish landings combined (Lundström et al, 2014). The vendace in the Swedish part of the Bothnian Bay is mainly fished with pair bottom trawling for its roe, but also a smaller part of the fillets is sold for consumption (Bergenius et al, 2013). The main fishery takes place within the Luleå, Råneå and Kalix archipelagos during five weeks (as maximum) in September and October before spawning.…”