Recruitment of sympatric vendace (Coregonus albula) and whitefish (C. lavaretus) is affected by different environmental factors

Abstract

Vendace and whitefish in Lake Osensjøen (boreal south-east Norway) were studied by means of gillnet test fishing and hydro acoustic acquisition . Vendace increased in number between 1998 and 2009 while growth and size at maturity decreased. The relative density of whitefish decreased in the pelagic habitat, whereas growth and size remained the same. Both species exhibited varying year-class strength. Whereas strong year-classes of both species became less frequent after 1980 than before this, this seemed to change after 2000, especially for vendace. Generalised additive models suggested a strong positive relationship between July/ August mean air temperature and year-class strength of both vendace and whitefish. Whitefish recruitment was also negatively affected by the new regulation regime implemented since 1981, and positively correlated with water level after hatching and by late ice off. The reason for the diverging impacts of environmental factors on the two species may be that vendace spawn in deeper waters that whitefish do. The results indicate that increasing summer temperatures benefit recruitment of both species, whereas low water level and early ice off will harm whitefish recruitment. Both trends are caused by climate warming. It may be speculated that increased density of the specialised plankton feeding vendace may affect the algal community through increased predation on herbivorous zooplankton and potentially affect the trophic state of the lake.

Water level regulation affects niche use of a lake top predator, Arctic charr (Salvelinus alpinus)

“…year-classes being observed when late winter drawdown is minor (Linløkken and Sandlund, 2016). Large winter drawdowns have been associated with reduced hatching success in Canadian reservoirs (Gaboury and Patalas, 1984) and likely explain reduced recruitment and relative abundance of charr in heavily regulated Govdajavri.…”

“…The unexpectedly high reliance of charr on littoral resources in heavily regulated Govdajavri might reflect an overall smaller population size as indicated by lower CPUE (Figure a, Table ), and a tentative reduction in both littoral and pelagic food resources following the start of regulation (Milbrink et al , ). In other words, a reduced population recruitment due to potential freezing of eggs during the spring low‐water period (Sutela et al , ; Linløkken and Sandlund, ) may compensate for reduced littoral production and explain why the remaining charr apparently find sufficient food resources from the heavily eroded littoral areas and do not shift to a predominantly pelagic or profundal niche.…”

“…In contrast, the mortality of charr is likely lower in unregulated Cazajavri, which facilitates development of a dense population of small slow‐growing individuals. Comparative survival studies using coregonids have indicated that egg survival is strongly associated with the water level minimum in late winter (Sutela et al , ), with strong year‐classes being observed when late winter drawdown is minor (Linløkken and Sandlund, ). Large winter drawdowns have been associated with reduced hatching success in Canadian reservoirs (Gaboury and Patalas, ) and likely explain reduced recruitment and relative abundance of charr in heavily regulated Govdajavri.…”

Climate Change and Monitoring of Temperate Lakes

“…Temperature trends alarmed scientists in the 1990s, and lake ecology was predicted to change if Figure 1. [40].…”

“…In the regulated and oligotrophic Lake Osensjøen in Southeast Norway, pelagic fish density, mainly whitefish and vendace, has been monitored by means of echo sounding since the 1980s, and during the first decade of this century, a pronounced density increase was observed, and a study was published in 2015 [40]. Year-class strength of both species was positively correlated with summer temperature, especially for vendace, as whitefish recruitment was also affected by the regulated water level (due to spawning sites at relatively shallow water).…”