Interactions between native juvenile burbot (Lota lota) and the invasive spinycheek crayfish (Orconectes limosus) in a large European lake

Abstract

Freshwater crayfish are successful invaders in many ecosystems and as cryptic nocturnal species display a potential niche overlap with benthic nocturnal fish. In this study, we tested the effects of the invasive spinycheek crayfish ( Orconectes limosus ) on native young-of-the-year (YOY) and adult burbot ( Lota lota ) in Lake Constance. Using mesocosm experiments, we tested if shelter preferences of YOY and adult burbot and crayfish changed between single and mixed species treatments. To further study the role of crayfish as a stressor for burbot, we monitored the nocturnal behaviour of the species in mesocosms using passive integrated transponder (PIT) tag technology and subsequently determined the plasma cortisol levels in burbot after single and mixed species treatments. Spinycheek crayfish successfully repelled YOY burbot from their preferred daytime shelters into alternative, previously unselected shelters. Crayfish also affected the nocturnal behaviour of YOY burbot by eliciting avoidance behaviour and caused an increase in the plasma cortisol levels. While adult burbot did not display any changes between single and mixed species treatments, our results indicate negative effects of spinycheek crayfish on YOY burbot. We conclude that the frequently dense, invasive crayfish populations in lakes may negatively influence local benthic fish populations via their YOY cohorts.