Stable isotope values and trophic analysis of invasive three-spined stickleback in Upper Lake Constance points to significant piscivory

Abstract

The three-spined stickleback Gasterosteus aculeatus was introduced into Lake Constance in the 1940s and occupied a limited range until late 2012. Since then the species has expanded from a solely littoral habitat in Upper Lake Constance, but now makes seasonal migrations into the pelagic zone. This behavioral change has been accompanied by a drastic increase in stickleback abundance. In order to integrate information about feeding of sticklebacks in Upper Lake Constance over two consecutive years, stomach content analysis was combined with seasonal stable isotope analysis on two types of tissue (muscle and liver). Isotope values were also obtained for zooplankton, whitefish larvae and eggs. We calculated the contribution of potential food sources for sticklebacks’ diet using a Bayesian mixing model (SIMMR). Furthermore, we determined stickleback trophic position, and δ15N and δ13C values were compared with those of other fish species of Lake Constance. The results of the Bayesian model as well as the stomach content analysis showed clear evidence of stickleback predation on fish eggs and larvae. Stickleback δ15N values were elevated during winter and comparable to those of piscivorous pike, while δ15N values of zooplankton were reduced, and those of whitefish larvae were similar to those of sticklebacks after accounting trophic fractionation of N isotopes. Trophic position calculations further identified sticklebacks as piscivorous, while the δ13C values of the liver and stomach content analysis suggests that a benthic-pelagic species pair may exist in Lake Constance. These findings support the hypotheses that sticklebacks in Lake Constance can display piscivorous feeding behaviour on sympatric fish species, most likely whitefish larvae and eggs.

Escaping malnutrition by shifting habitats: A driver of three‐spined stickleback invasion in Lake Constance

“…In ULC in the years after the invasion in 2012, similar patterns were observed when sticklebacks began to migrate to the spawning grounds of whitefish (Gugele et al, 2020). Lake Constance sticklebacks are routinely piscivorous (Gugele et al, 2023) and target whitefish larvae and eggs during and shortly after that species' spawning period (Baer et al 2021). In the present study, remains of fish eggs and larvae in the guts of stickleback were found in all seasons except autumn, but they were most abundant in spring.…”

“…The full extent of the ecological impact of this pelagic invasion is yet to be evaluated, but direct effects are apparent on the pelagic whitefish Coregonus wartmanni (Bloch 1784), once the dominant keystone pelagic fish species and the main target of local fisheries (Baer et al, 2017). These impacts include interspecific competition for food leading to reduced whitefish growth and survival, and predation by sticklebacks on whitefish larvae and probably eggs, hampering recruitment (Baer et al, 2021; DeWeber et al, 2022; Gugele et al, 2023; Roch et al, 2018; Ros et al, 2019; Rösch et al, 2018). These observations coincide with a sharp decline in whitefish fishery yield, from around 300–600 mt (metric tons) before stickleback invasion to less than 22 mt in 2022 (http://www.ibkf.org).…”