All day-long: Sticklebacks effectively forage on whitefish eggs during all light conditions

Abstract

The three-spined stickleback Gasterosteus aculeatus invaded Lake Contance in the 1940s and expanded in large numbers from an exclusively shoreline habitat into the pelagic zone in 2012. Stickleback abundance is very high in the pelagic zone in winter near the spawning time of pelagic whitefish Coregonus wartmanni, and it is hypothesized that this is triggered by the opportunity to consume whitefish eggs. Field sampling has qualitatively confirmed predation of whitefish eggs by stickleback, but quantification has proven difficult due to stormy conditions that limit sampling. One fundamental unknown is if freshwater stickleback, known as visual feeders, can successfully find and eat whitefish eggs during twilight and night when whitefish spawn. It is also unknown how long eggs can be identified in stomachs following ingestion, which could limit efforts to quantify egg predation through stomach content analysis. To answer these questions, 144 individuals were given the opportunity to feed on whitefish roe under daylight, twilight, and darkness in controlled conditions. The results showed that stickleback can ingest as many as 100 whitefish eggs under any light conditions, and some individuals even consumed maximum numbers in complete darkness. Furthermore, eggs could be unambiguously identified in the stomach 24 hours after consumption. Whitefish eggs have 28% more energy content than the main diet of sticklebacks (zooplankton) based on bomb-calorimetric measurements, underlining the potential benefits of consuming eggs. Based on experimental results and estimates of stickleback abundance and total egg production, stickleback could potentially consume substantial proportions of the total eggs produced even if relatively few sticklebacks consume eggs. Given the evidence that stickleback can feed on eggs during nighttime spawning and may thereby hamper recruitment, future studies aimed at quantifying actual egg predation and resulting effects on the whitefish population are urgently needed.

Size matters? Species‐ and size‐specific fish predation on recently established invasive quagga mussels Dreissena rostriformis bugensis Andrusov 1897 in a large, deep oligotrophic lake

“…(cf. (Baer et al ., 2021) to gain the same amount of energy as they can generate from a much larger quagga mussel. In this context it is relevant that only ~50% of the energy contents of dreissenids can be utilized by a fish (Nagelkerke & Sibbing, 1996).…”

Stickleback mass occurrence driven by spatially uneven parasite pressure? Insights into infection dynamics, host mortality, and epizootic variability

“…In this study, sticklebacks are conspicuously present in the same areas as spawning pelagic whitefish, which was observed during November and December when the highest NPUE were recorded in the pelagic zone. The concurrent movement of the sticklebacks into the area where whitefish spawn, together with the information from recent studies which demonstrate that ULC sticklebacks are effective predators of whitefish larvae and can successfully forage on whitefish eggs (Roch et al 2018;Ros et al 2019;Baer et al 2021), offers a biological trait to explain the invasion of the pelagic zone. Consequently, these high-energy food sources could be a main driver for the observed spreading of sticklebacks into the pelagic zone in ULC.…”

“…In conclusion, the invasion of sticklebacks in the pelagic zone of ULC is unlikely to be driven by an uneven risk of infection by S. solidus or predation between the littoral and pelagic zones. The possibility to forage during the spawning time of whitefish on the high-energy food source "whitefish eggs", and later their larvae, seems to be a more likely driver of the invasion (Baer et al 2021). Furthermore, major adverse effects of S. solidus in ULC were confined mainly to post-reproductive adult sticklebacks.…”

“…However, the results of two recent studies (Roch et al 2018;Rösch et al 2018) imply significant effects of stickleback presence on pelagic whitefish Coregonus wartmanni (Bloch 1784), the previously dominant pelagic fish species and the main target of local fisheries (Baer et al 2017). The suspected reasons include interspecific competition for food leading to reduced growth and survival, and predation by sticklebacks on whitefish larvae and probably eggs, hampering recruitment (Ros et al 2019;Baer et al 2021). These observations coincide with a sharp decline in whitefish yield, from around 300-600 mt (metric tons) before stickleback invasion to less than 150 mt with stickleback presence in the pelagic zone (Roch et al 2018).…”

Turning summer into winter: nutrient dynamics, temperature, density dependence and invasive species drive bioenergetic processes and growth of a keystone coldwater fish

“…The most surprising invasion occurred in 2012, when three‐spined stickleback (present in the lake since the 1940s; Roch et al 2018) shifted from solely nearshore habitats to the pelagic zone and became hyperabundant zooplanktivores (Eckmann and Engesser 2019, Gugele et al 2020). This invasion was closely coupled with reductions in the abundance and size‐at‐age of the commercially and culturally important pelagic spawning whitefish, which is likely in part due to competition for zooplankton during the primary growing season (Eckmann et al 2002, Bretzel et al 2021) as well as potentially widespread egg and larvae predation by sticklebacks (Roch et al 2018, Baer et al 2021). The combination of lower productivity and potential competition for already limited food considerably reduced mean body weight‐at‐age of whitefish by 33.3% after the stickleback invasion in 2012, resulting in much lower catches and over 40% of professional fishers quitting (Baer et al 2017).…”