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<p>Fishless lakes can be particularly valuable for aquatic insects and their avian predators. In Scotland’s Flow Country, a peatland World Heritage Site, abundant waterbodies support important waterbird populations. These include UK red-listed common scoters <i>Melanitta nigra</i>, which select lakes having low brown trout <i>Salmo trutta</i> populations. Scoters and four other invertivorous waterbird species have responded positively to trout population reductions. Here we investigated 10 small lakes, comparing four considered trout-free, to six with trout present. We surveyed waterbirds and adult mayflies, stoneflies, alderflies and caddisflies. We investigated whether these aquatic insects, and insectivorous waterbirds, were more abundant at trout-free lakes. Lakes were surveyed three times annually for five years. We collected insects by sweep-netting, and surveyed waterbirds using direct observations and camera traps. Across species, insect and waterbird counts tended (weakly) to be higher at trout-free lakes, but responses varied among species. Counts were better modelled including the interaction between species and trout status. This showed that trout-free lakes had higher counts of four insect species, including the nationally-scarce caddisflies <i>Limnephilus nigriceps</i> and <i>Molanna albicans</i>, and two waterbird species, including common scoters, which had counts 2.9 times higher at trout-free lakes (cls 1.2–6.8). One insect species was more common at trout lakes. Six key invertivorous waterbird species of the Flow Country protected site, analysed together, had counts 2.5 times higher (cls 1.1–6.1) at trout-free lakes than trout lakes. Our results support an increased focus on researching and conserving trout-free lakes.</p>

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Small peatland lakes with or without trout: comparing their aquatic insects and insectivorous waterbirds

  • 期刊论文

  • 发表日期：

    2026年7月12日

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  • Mark H. Hancock,
  • Anna Grozelier,
  • Chris Bingham,
  • Robert D. Hughes

摘要

Fishless lakes can be particularly valuable for aquatic insects and their avian predators. In Scotland’s Flow Country, a peatland World Heritage Site, abundant waterbodies support important waterbird populations. These include UK red-listed common scoters Melanitta nigra, which select lakes having low brown trout Salmo trutta populations. Scoters and four other invertivorous waterbird species have responded positively to trout population reductions. Here we investigated 10 small lakes, comparing four considered trout-free, to six with trout present. We surveyed waterbirds and adult mayflies, stoneflies, alderflies and caddisflies. We investigated whether these aquatic insects, and insectivorous waterbirds, were more abundant at trout-free lakes. Lakes were surveyed three times annually for five years. We collected insects by sweep-netting, and surveyed waterbirds using direct observations and camera traps. Across species, insect and waterbird counts tended (weakly) to be higher at trout-free lakes, but responses varied among species. Counts were better modelled including the interaction between species and trout status. This showed that trout-free lakes had higher counts of four insect species, including the nationally-scarce caddisflies Limnephilus nigriceps and Molanna albicans, and two waterbird species, including common scoters, which had counts 2.9 times higher at trout-free lakes (cls 1.2–6.8). One insect species was more common at trout lakes. Six key invertivorous waterbird species of the Flow Country protected site, analysed together, had counts 2.5 times higher (cls 1.1–6.1) at trout-free lakes than trout lakes. Our results support an increased focus on researching and conserving trout-free lakes.