First documentation of spawning by deepwater sculpins in the Great Lakes and potential impacts of round gobies

Abstract

Deepwater sculpins Myoxocephalus thompsonii, formerly fourhorn sculpin M. quadricornis (marine form), inhabit all five Great Lakes. Deepwater sculpin is prey for lake trout Salvelinus namaycush and feeds on benthos. Populations have been declining with possible reasons being oligotrophication, quagga mussels (Dreissena bugensis), predation, and impacts of round goby Neogobius melanostomus competition or predation on eggs. Deepwater sculpins are thought to spawn during winter based on gravid females and appearance of larval fish in spring, but a male guarding a nest has not been documented. We used remotely operated vehicle technology during December 2015, March 2017, and March 2021 in 70–191 m in Grand Traverse Bay, Lake Michigan to identify the distribution of deepwater sculpins, round gobies, and nests with a guarding male. Round gobies were much more abundant (observations/hr = 139) in water < 125 m than were deepwater sculpins (11/hr), while in water > 166 m, deepwater sculpins were much more common (39/hr) than at shallow sites. At deep sites, round gobies were more abundant (51/hr) than deepwater sculpins (39/hr). On 16 March 2021 in 190 m of 1.9 C surface water we discovered several presumptive, unoccupied nests, but one nest in a depression next to a branch contained a deepwater sculpin and a clump of eggs. This is first evidence of where and how deepwater sculpins spawn. We also documented round gobies in the same area with one within 2 m of the nest, creating the possibility for consumption of eggs potentially affecting their long-term survival.