Dispersion of vendace eggs and larvae around potential nursery areas reveals their reproductive strategy

Abstract

Depending on their reproductive strategy, different fish species aim to aggregate or disperse eggs and larvae in their reproductive habitat. Many pelagic species disperse their eggs widely around the potential nursery areas. Larval dispersion or aggregation affects population sub‐structuring, which has important implications in fisheries management and conservation of the natural spatial diversity in populations. The dispersion of larval vendace (Coregonus albula) was quantified in two oligotrophic Finnish lakes, and effects of density and environmental variables on the inter‐annual variation in the larval distribution were examined by analysing spatial abundance data from the lakes from 1999 to 2017. A 3‐D hydrodynamic egg distribution model was used to simulate the larval transport after hatching. Vendace larvae dispersed lake‐wide to both littoral and pelagic zones but, in some littoral hot spots, more larvae aggregated year after year. However, in years of high larval number, the densities increased not only in the hot spots, but generally at all sampling plots. An overall increase in abundance was observed at all sampling sites. The simulations of the egg distribution model supported the hypothesis that the dispersion of the eggs occurs by spawners, i.e. by spawning at several different spawning sites, which are located all around the lake. The dispersion of vendace eggs and larvae can be seen as a bet‐hedging strategy in space and time since in boreal oligotrophic large lakes with fragmented morphology, weather and other environmental factors in spring during hatching varies from year to year spatially in unpredictable manner. Lake‐wide larval dispersion suggests that the subpopulations of adjacent lake deeps may swap considerable amounts of individuals during early life and may not be closed units. Conservation of particular habitats seems unnecessary for Finnish vendace populations where large potential spawning areas in lakes are available.

Vendace (Coregonus albula) Disperse Their Eggs Widely during Spawning

“…In 2018, 50 samplers were lowered to the bottom at one spawning plot (plot 11) and in 2019, 500 samplers were placed in 20 sampling plots. Of those plots, 15 were selected from 20 regular and randomly located littoral larval-vendace monitoring plots (Karjalainen et al 2019). Five regular monitoring plots (3,12,13,17,19) were excluded and replaced with 5 extensive sampling plots (30,35,43,71,73).…”

“…Lambert and Ware (1984) suggested a "continuum of reproductive strategies with 'bet hedging' at one extreme and an 'all at once' egg release at the other". Karjalainen and Marjomäki (2018) discovered that autumn-spawning vendace (Coregonus albula) is a batch spawner which seems to have the bet-hedging reproductive strategy in space and time, where larvae and presumably also eggs are allocated widely into different habitats around lakes (Karjalainen et al 2019). In long-term monitoring of vendace larvae in Finnish lakes, it was found that only 4%-15% of the random sampling plots in the littoral zone did not contain vendace larvae, and the simulation results from an egg distribution model supported the hypothesis that the spawning of vendace in Lake Southern Konnevesi occurs in littoral and sub-littoral zones across the entire lake (Karjalainen et al 2019).…”

“…Karjalainen and Marjomäki (2018) discovered that autumn-spawning vendace (Coregonus albula) is a batch spawner which seems to have the bet-hedging reproductive strategy in space and time, where larvae and presumably also eggs are allocated widely into different habitats around lakes (Karjalainen et al 2019). In long-term monitoring of vendace larvae in Finnish lakes, it was found that only 4%-15% of the random sampling plots in the littoral zone did not contain vendace larvae, and the simulation results from an egg distribution model supported the hypothesis that the spawning of vendace in Lake Southern Konnevesi occurs in littoral and sub-littoral zones across the entire lake (Karjalainen et al 2019). In boreal, oligotrophic, large lakes with fragmented morphology and complex shoreline, weather-induced conditions (winds, currents, water level, water temperatures, ice conditions), water quality and predation between spawning in autumn to hatching in spring vary spatially unpredictably from year to year.…”

Monitoring and Modelling of Butyltin Compounds in Finnish Inland Lake

“…Different BTCs are represented as particles with differing properties. Same particle module without degradation chain has been used when estimating the reproducing strategies of larvae in surface waters (Karjalainen et al 2019).…”

Effects of warming winter embryo incubation temperatures on larval cisco (Coregonus artedi) survival, growth, and critical thermal maximum

“…Most coregonines spawn nearshore in late-autumn, embryos incubate under ice, and hatch in spring near ice-out, when rising spring water temperatures trigger hatching (Karjalainen et al, 2021, 2019, 2015; Stockwell et al, 2009). Increases in air temperature and water temperatures of seasonally ice-covered lakes are projected to be greatest during the winter and spring, respectively, in response to climate change (Christensen et al, 2007; Ozersky et al, 2021; Schindler et al, 1990; Winslow et al, 2017).…”