Restoring Piscivorous Fish Populations in the Laurentian Great Lakes Causes Seabird Dietary Change

Abstract

Ecosystem change often affects the structure of aquatic communities thereby regulating how much and by what pathways energy and critical nutrients flow through food webs. The availability of energy and essential nutrients to top predators such as seabirds that rely on resources near the water's surface will be affected by changes in pelagic prey abundance. Here, we present results from analysis of a 25-year data set documenting dietary change in a predatory seabird from the Laurentian Great Lakes. We reveal significant declines in trophic position and alterations in energy and nutrient flow over time. Temporal changes in seabird diet tracked decreases in pelagic prey fish abundance. As pelagic prey abundance declined, birds consumed less aquatic prey and more terrestrial food. This pattern was consistent across all five large lake ecosystems. Declines in prey fish abundance may have primarily been the result of predation by stocked piscivorous fishes, but other lake-specific factors were likely also important. Natural resource management activities can have unintended consequences for nontarget ecosystem components. Reductions in pelagic prey abundance have reduced the capacity of the Great Lakes to support the energetic requirements of surface-feeding seabirds. In an environment characterized by increasingly limited pelagic fish resources, they are being offered a Hobsonian choice: switch to less nutritious terrestrial prey or go hungry.

Colonial Waterbirds Nesting on Egg Island, Lake Athabasca, 2009

“…In light of growing economic development in this region, more frequent censuses of waterbird populations on Egg Island are recommended. Waterbirds, such as terns and gulls, are useful indicators of environmental quality and ecosystem change (Kushlan 1993;Hebert et al 1999Hebert et al , 2008. Egg size data for California Gulls were similar to those reported previously for that species in Alberta (Vermeer 1969).…”

Marine birds and plastic debris in Canada: a national synthesis and a way forward

“…There are large gull and cormorant colonies that are studied intensively in these regions (Hebert et al 2008), but ingested plastics or plastic nest incorporation data are not readily available. There are ingested plastics data from inland black-billed magpies (Pica hudsonia; Reebs and Boag 1987), so it is likely that inland waterbirds are also ingesting plastics with unknown impacts.…”

“…To assess plastic pollution in this region, different species, and perhaps protocols, need to be identified and developed. This is an area where expanded efforts in species that are widely distributed and already intensively studied (e.g., doublecrested cormorants (Phalacrocorax auritus) and herring gulls (Larus argentatus)) may be warranted (Hebert et al 2008). Although the physical properties of inland water bodies are different from oceans, a monitoring program to track marine debris would augment other lake clean-up and conservation (de Pinto et al 1986;Hartig and Thomas 1988).…”

“…Bolus collection from inland gull species (e.g., Lindborg et al 2012). There are several programs that study inland gulls (e.g., on the Great Lakes; Hebert et al 2008). Bolus collection is low impact, can be done for colonies where current study programs exist with little extra cost, and can be done at a variety of locations that represent degrees of exposure to urban areas.…”

Fatty acid composition and concentration of alternative food of Semipalmated Sandpipers (Calidrispusilla) in the upper Bay of Fundy, Canada

“…Although adapting to an available prey base may have short-term and seasonal benefits, allowing individuals to exploit whatever food source is present, there may be unknown long-term impacts. If alternate prey are of inferior quality and birds are faced with a Hobson's choice of consuming poor-quality prey or going hungry (sensu Hebert et al 2008), then the result can be declines in body condition and (or) reproductive endpoints, as has been observed with some gull and passerine species (Hebert et al 2002(Hebert et al , 2008Blight 2011;Twining et al 2016a). Insufficient prey quantity or reduced prey quality, combined with other stressors, may have important implications for migratory avian species (Klaassen et al 2012).…”