Correlates of lake use by breeding common scoters in Scotland

Abstract

ABSTRACT1. Many populations of sea-ducks, which typically winter at sea but breed on fresh water, are declining. Numbers of common scoters Melanitta nigra (L.) breeding in Scotland halved between 1995 and 2007, despite most breeding sites having special conservation status. To identify potential conservation measures, a 3-year study was conducted, investigating correlates of lake use by scoters.2. At 26 scoter breeding lakes, food abundance (macroinvertebrates) and foraging habitats (substrates, water depth) were measured, and their associations with scoter lake use explored using multi-model inference. Correlates of macroinvertebrate abundance (water quality, fish abundance) were also investigated.3. Averaged over 3 years (2009 -2011), these lakes held 26.7 (SE 6.3) females, around half the Scottish breeding population. Scoters occurred more often at lakes having abundant large-bodied invertebrates and extensive shallow water. Lakes where the average weight of the largest invertebrate in each sample exceeded 4 mg had 9.2 times (females) or 27 times (broods) more scoter records than other lakes. Lakes where water depths (10 m from the shore) averaged less than 1.3 m had 2.5 times (females) or 12 times (broods) more scoter records than other lakes.4. The abundance of large-bodied invertebrates was greater where small fish species (mostly three-spined sticklebacks Gasterosteus aculeatus) were more common and brown trout Salmo trutta were scarcer.5. Results suggest two approaches to scoter conservation. At lakes used for hydro-electricity generation, water level regimes that provide extensive shallow water should be tested to see if these benefit scoters. At lakes used for trout fishing, trout reduction by increased angling should be trialled, to see if this increases large-invertebrate abundance and scoter use.

From a research study to a conservation partnership: Developing approaches to restoring common scoter populations

“…Instead, they suggested that adaptive management might work best in addressing smaller, more tractable problems, ‘in simple systems in which existing data suggest the causal relationships, and where contrasting management regimes can be introduced to test the hypothesized relationships’ (Rist et al, 2013, p. 14). Our situation is quite similar to this, with our single‐species focus and current management trials that are based on previous research, including the lake selection study of Hancock et al (2016). An adaptive management focus on one species or a specific guild within an ecosystem can nevertheless bring multiple wider ecological and ecosystem services benefits (King et al, 2009).…”

“…Like most sea ducks, common scoters winter at sea but breed in freshwater habitats, and feed by diving for invertebrate prey. The scoter lake‐use study published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) (Hancock, Robson, Smith, & Douse, 2016) investigated correlates of lake use in the two remaining scoter breeding concentrations in Scotland. In the West Highlands, scoters breed at large (~300–1,300 ha) valley‐bottom lakes managed for hydropower generation (within the Great Glen scheme; Scottish and Southern Energy [SSE], 2005).…”

“…These results were interpreted as reflecting the effects of prey abundance (large invertebrates), prey availability (shallow water), and competition for invertebrate prey (brown trout). In their AQC article, Hancock et al (2016) discussed ways in which the results could be used to develop conservation measures, highlighting different possible approaches in each of the two main breeding areas. In the West Highlands, where lake levels are regulated for hydropower generation, the article discussed the possibility of improving the availability of shallow water habitat by adjusting water level management regimes.…”

“…Through this partnership, supported by scientific evidence — including, but not limited to, the AQC lake‐use publication (Hancock et al, 2016) together with our knowledge of lake management, we worked to develop conservation interventions that might reverse common scoter population declines. We found that the different circumstances in the two main breeding areas (West Highlands, Flow Country) necessitated a different approach in each area.…”

“…At these lakes, we considered whether the regulation of water levels might allow us to favour scoter conservation. The lake selection paper (Hancock et al, 2016), and subsequent foraging studies (Hancock et al, 2019), had shown that shallow water was likely to be a particularly important habitat element. Meanwhile, more recent detailed WWT‐led work (Burrell et al, 2014; Hilton et al, 2020) at the two most important lakes had shown that some low‐lying islands, surrounded by shallow water, could be key nesting locations important to chick production in some years when compared with nests on the mainland.…”