Empirical evaluation of predator-driven diel vertical migration in Lake Superior

Abstract

Recent studies on Lake Superior suggest that diel vertical migration (DVM) of prey (generalized Coregonus spp.) may be influenced by the density of predatory siscowet ( Salvelinus namaycush ). We empirically evaluated this hypothesis using data from acoustic, midwater trawl, and bottom trawl sampling at eight Lake Superior sites during three seasons in 2005 and a subset of sites in 2006. We expected the larger-bodied cisco ( Coregonus artedi ) to exhibit a shallower DVM compared with the smaller-bodied kiyi ( Coregonus kiyi ). Although DVM of kiyi and cisco were consistent with expectations of DVM as a size-dependent, predator-mediated process, we found no relationship between siscowet density and the magnitude of DVM of either coregonid. Cisco appear to have a size refuge from siscowet predation. Kiyi and siscowet co-occur in demersal habitat > 150 m during the day, where visual predation is unlikely, suggesting predator avoidance is not a factor in the daytime distribution of kiyi. Seasonal patterns of kiyi DVM were consistent with reported DVM of their primary prey Mysis relicta . Our results suggest that consideration of nonvisual foraging, rather than light-based foraging theory (i.e., the antipredation window), is necessary to understand the processes driving DVM in deepwater systems.

Predation risk and prey fish vertical migration in Lake Superior: Insights from an individual based model of siscowet (Salvelinus namaycush)

“…Patterns in DVM may also vary among years according to changes in composition and predator behavior . The pattern of DVM in coregonines is consistent among spatial areas of Lake Superior and does not appear to be associated with spatial variability in predator densities within a given year (Stockwell et al, 2010). Furthermore, siscowet (Salvelinus namaycush siscowet), kiyi (Coregonus kiyi), and Mysis (Mysis diluviana) appeared to be very closely linked in their movements, which supports the contention that food web linkages are tight among species in the pelagic food web of Lake Superior (Ahrenstorff et al, 2011;Gamble et al, 2011).…”

“…Furthermore, siscowet (Salvelinus namaycush siscowet), kiyi (Coregonus kiyi), and Mysis (Mysis diluviana) appeared to be very closely linked in their movements, which supports the contention that food web linkages are tight among species in the pelagic food web of Lake Superior (Ahrenstorff et al, 2011;Gamble et al, 2011). Nevertheless, there has been some debate as to whether predation alters kiyi behavior or whether kiyi vertical movements are driven solely by movements of their primary prey, Mysis (e.g., Stockwell et al, 2010).…”

Abundance, spatial distribution, and diet of endangered Hovsgol grayling (Thymallus nigrescens)

“…Although our zooplankton data were collected at a relatively coarse vertical resolution, it is apparent that most zooplankton show similar vertical migrations as grayling. The observed DVM trajectories of Hovsgol grayling are notably shallower (change in depth of~15 m) than the observed DVM trajectory of other species, such as amphipods in Lake Baikal (change of~100 m) (Rudstam et al 1992) and kiyi (Coregonus kiyi) in Lake Superior (change of~150 m) (Stockwell et al 2010;Ahrenstorff et al 2011), which may be due to the lack of predators in the pelagic areas of Lake Hovsgol. It is unclear why large Hovsgol grayling undergo similar vertical migrations as small individuals since they do not feed heavily on zooplankton resources.…”

Partial diel vertical migration in an omnivorous macroinvertebrate, Mysis diluviana

“…Non-random partial DVM of Mysis adds complexity to our understanding of DVM and necessitates more detailed description of benthic and pelagic distributions of Mysis to determine when and why individuals migrate. We propose that future studies of vertically migrating organisms account for potential partial migration by expanding sampling techniques to better represent non-migratory individuals (e.g., Shea & Makarewicz, 1989;Stockwell et al, 2010). Selective sampling techniques that do not account for the full distribution of the target species could bias abundance estimates (e.g., Stockwell et al, 2006).…”