Predation on emergent lake trout fry in Lake Champlain

Abstract

The rehabilitation of extirpated lake trout ( Salvelinus namaycush) in the Great Lakes and Lake Champlain has been hindered by various biological and physiological impediments. Efforts to restore a lake trout fishery to Lake Champlain include hatchery stocking and sea lamprey control. Despite these management actions, there is little evidence of recruitment of naturally-produced fish in annual fall assessments. Spawning occurs at multiple sites lake-wide in Lake Champlain, with extremely high egg and fry densities, yet sampling for juvenile lake trout has only yielded fin-clipped fish. To investigate this recruitment bottleneck, we assessed predation pressure by epi-benthic fish on emergent fry on two spawning reefs and the subsequent survival and dispersal of fry in potential nursery areas. Epi-benthic predators were sampled with 2-h gillnet sets at two small, shallow sites in Lake Champlain throughout the 24-h cycle, with an emphasis on dusk and dawn hours. In total, we documented seven different species that had consumed fry, with consumption rates from 1 to 17 fry per stomach. Rock bass and yellow perch dominated the near-shore fish community and were the most common fry predators. Predator presence and consumption of fry was highest between 19:00 and 07:00. Predators only consumed fry when fry relative abundance was above a threshold of 1 fry trap − 1 day − 1 . We used an otter trawl to sample for post-emergent fry adjacent to the reef, but did not capture any age-0 lake trout. Due to the observed predation pressure by multiple littoral, species on shallow spawning reefs, lake trout restoration may be more successful at deep, offshore sites.