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.