Abstract
How spawning stock size, environmental conditions and recruitment relate to each other is an essential question in understanding population dynamics of exploited fish stocks. We estimated the recruitment of Eurasian perch (Perca fluviatilis), one of the most important species in coastal fisheries in northern Baltic Sea, and examined the factors that determine perch recruitment success. We hypothesized that perch spawning population biomass and summer water temperature would increase perch recruitment, with potential density dependence, while the effect of the population size of pikeperch (Sander lucioperca) would be negative. Different forms of general stock–recruitment functions, with and without density dependence, and with and without water temperature and pikeperch population size as environmental factors were fitted to long-term (1981–2014) stock assessment data of perch and pikeperch in the Archipelago Sea, southwestern coast of Finland. Perch spawning stock biomass (ages 5–14), water temperature in June–July and pikeperch stock size (ages ≥ 1) at spawning year best explained variation in perch recruitment. The results supported the predictions: perch recruitment increased with spawning stock in density-dependent manner, pikeperch effect on perch recruitment was negative and summer temperature effect was positive suggesting environmentally affected competitive interaction between these two percids.
Highlights
Large fluctuations in the recruitment success are characteristic to many percids (Neuman et al, 1996) which creates an inherent challenge for their fisheries
Year class strengths of perch fluctuated widely especially in the 1980s and 1990s, with the peak recruitment years coinciding with warm summers (Fig. 3)
The spawning stock biomass of perch was at highest in 1993 and 2002, while the abundance of pikeperch increased during the study period, being at the highest in the end of the 1990s and in the early 2000s (Fig. 3)
Summary
Large fluctuations in the recruitment success are characteristic to many percids (Neuman et al, 1996) which creates an inherent challenge for their fisheries. Eurasian perch (Perca fluviatilis L.), hereafter perch, is a widely distributed, generalist freshwater species found in diverse aquatic environments including coastal brackish waters. Both perch and the confamilial pikeperch (Sander lucioperca L.) favour sheltered areas over open pelagic surfaces in the Baltic Sea (Veneranta et al, 2011; Kallasvuo et al, 2017), and both species spawn in inner bay areas characterized by low salinity, high temperature and significant vegetation cover (Kallasvuo et al, 2017). Because of similar environmental dependency, synchrony in year class fluctuations of perch and pikeperch has been reported (Lappalainen et al, 1996). Agonistic relationships between these two percids have been observed in catch-per-unit-of-effort data from many Finnish lakes, with Lake Oulujarvi being one of the best documented cases (Vainikka et al, 2017)
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