Carcass deposition to suppress invasive lake trout causes differential mortality of two common benthic invertebrates in Yellowstone Lake

Abstract

Invasive species require management to mitigate their harmful effects on native biodiversity and ecosystemprocesses. However, such management can also have negative, unintended consequences on non-target taxa,ecosystem processes, and food web dynamics. In Yellowstone Lake, invasive lake trout (Salvelinus namaycush)have caused a decline in the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population. Tosuppress the invader, lake trout carcasses are deposited on the species’ spawning sites, causing embryo mortalityby reducing dissolved oxygen as they decay. The non-target effects of carcass deposition are unknown, but benthicinvertebrates may be sensitive to reductions in dissolved oxygen. Benthic invertebrate taxa have varying hypoxiatolerances; caddisflies of the family Limnephilidae are hypoxia sensitive whereas the amphipods Gammarus lacustrisand Hyalella azteca are hypoxia tolerant. Both taxa are widespread and abundant in Yellowstone Lake andcomprise a large proportion of fish diets, and changes in their abundances could therefore alter food web dynamics.We conducted an in situ experiment to determine if carcass deposition causes mortality in these two benthic invertebratetaxa. The probability of mortality for caddisflies was 3.15 times higher in carcass treatments compared tocontrols, while amphipod mortality did not change in response to carcass treatment. Amphipods, which contributemost significantly to fish diets, are unlikely to be reduced in response to carcass deposition, which is confined to asmall fraction of the lake where lake trout spawn, limiting the possibility for lake-wide effects. We conclude thatcarcass deposition is unlikely to alter the availability of invertebrates as a food source for fish in Yellowstone Lake.

Aerial Application of Organic Pellets Eliminates Lake Trout Recruitment from a Primary Spawning Reef in Yellowstone Lake

“…However, the ingredients in the pellets (vitamin E, phytoestrogen, and soybean oil) reduced the growth of primary producers, possibly offsetting the increased growth caused by nutrients (Lujan et al 2022). The probability of mortality of limnephilid caddisflies was more than three times higher in organic (carcass) treated spawning reefs than in control reefs, whereas mortality of the amphipods Gammarus lacustris and Hyalella azteca did not differ (Briggs et al 2021). Amphipods are abundant and make up a large proportion of fish diets in Yellowstone Lake (Glassic et al 2021;Glassic 2022).…”

“…The probability of mortality of limnephilid caddisflies was more than three times higher in organic (carcass) treated spawning reefs than in control reefs, whereas mortality of the amphipods Gammarus lacustris and Hyalella azteca did not differ (Briggs et al. 2021). Amphipods are abundant and make up a large proportion of fish diets in Yellowstone Lake (Glassic et al.…”

Fish carcass deposition to suppress invasive lake trout through hypoxia causes limited, non‐target effects on benthic invertebrates in Yellowstone Lake

“…We examined responses of hypoxia‐sensitive taxa because they may be particularly susceptible to the low‐oxygen conditions that cause mortality in lake trout embryos (Poole et al., 2020; Thomas et al., 2019). Ephemeroptera and Trichoptera taxa can experience mortality due to low oxygen conditions in less than 4 days (Nebeker, 1972), and in an experimental setting, carcass treatment in Yellowstone Lake increased mortality in captive Trichoptera within 3 days (Briggs et al., 2021). Carcass treatment in our experiment reduced DO concentrations below 3.4 mg/L, a threshold known to cause mortality in lake trout embryos, for multiple days at both sites (Koel, Thomas, et al., 2020).…”

“…Carcass treatments may differentially affect the abundance and biomass of benthic invertebrate taxa depending on their physiological characteristics (Dolédec et al., 2011). Hypoxic or anoxic conditions may result in mortality, or reduction in growth or reproduction, in sensitive invertebrate taxa (Briggs et al., 2021; Connolly et al., 2004; Nebeker 1972). Sessile taxa may be particularly susceptible to mortality in response to carcass treatment due to an inability to move away from unfavourable conditions caused by carcass decay, such as reduced DO and increased fungal and bacterial growth (Fenoglio et al., 2010; Poole et al., 2020).…”

Combination of Acoustic Telemetry and Side‐Scan Sonar Advances Suppression Efforts for Invasive Lake Trout in a Submontane Lake

“…Changes in chemical composition (i.e., dissolved oxygen concentration) and phytoplankton, macroinvertebrate, and higher-trophic-level species abundance and community structure due to nutrient additions could also have negative effects at the ecosystem level (Beeton 1964;Capblanq 1990;Smith et al 2006). For example, embryo suppression treatments in Yellowstone Lake induced localized changes in macroinvertebrates except amphipods; however, due to the small treatment area, embryo suppression treatments would have little effect lakewide (Briggs et al 2020). Monitoring the relative abundances of vertebrate and invertebrate species may be necessary because of the physical differences between Swan and Yellowstone lakes (i.e., total lake area [m 2 ], basinwide volume of water, and hydraulic residence time).…”