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.

Highlights

  • The three-spined stickleback (Gasterosteus aculeatus, hereafter referred to as stickleback) is one of several aquatic invasive species in Lake Constance, one of the largest lakes in Central Europe

  • Sticklebacks first established in the littoral zone of Upper Lake Constance (ULC) in the 1940s [1], but by the end of 2012 had expanded from an exclusively shoreline habitat into the pelagic zone [2]

  • Sticklebacks effectively forage on whitefish eggs during all light conditions results were combined with population and fecundity estimates to calculate the theoretical number of whitefish eggs that could be consumed by sticklebacks in Lake Constance

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Summary

Introduction

The three-spined stickleback (Gasterosteus aculeatus, hereafter referred to as stickleback) is one of several aquatic invasive species in Lake Constance, one of the largest lakes in Central Europe. Whitefish primarily spawn during twilight and night [5] near the surface in the middle of the lake [5] and whitefish eggs sink relatively quickly (around 1 m min-1; [6]) to the bottom with depths up to 250 m [5], while freshwater sticklebacks are thought to feed in well–lit environments [7] and only forage in maximum depths of around 30 m [3].

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