Influence of egg predation and physical disturbance on lake trout Salvelinus namaycush egg mortality and implications for life‐history theory

Abstract

The influence of egg predators and physical disturbance on lake trout Salvelinus namaycush egg mortality was investigated in situ in Lake Michigan where recruitment is below detectable levels and egg predator abundance is high. Comparisons were made with Lake Champlain where recruitment is low and egg predator abundance is also low and with Parry Sound (Lake Huron) where recruitment is moderate and egg predators are in low abundance. A multi-density egg seeding method (100 to 5000 eggs m À2 ) was used to quantify the effect of physical disturbance and egg predation on egg loss. Wind fetch was used as an index of physical disturbance and comparisons across all locations and egg densities suggested that at sites with high wind fetch (>5 km), physical disturbance may be a greater source of egg loss than predation. When analyses were limited to those sites having a wind fetch of <5 km, the percentage of eggs recovered was found to be linearly related to predator density. The strength of this relationship was based largely on egg recovery at 500 and 1000 eggs m À2 because recovery at lower (100, 250 eggs m À2 ) and very high (5000 eggs m À2 ) densities was not significantly related to predator density. The reason for this is probably that at low egg densities, crayfish Orconectes spp., the major egg predator at most sites, had difficulty finding and consuming eggs and at high egg densities they became satiated. Egg loss was directly related to wind fetch for Lake Michigan and on average six-fold greater than for Parry Sound suggesting that without corresponding changes in fecundity and age structure, lake trout populations in large lakes like Lake Michigan are inherently less productive than those from enclosed inland waters.

Microhabitat association of Hemimysis anomala on fish spawning reefs in Grand Traverse Bay, Lake Michigan

“…These characteristics will provide uniform and less variable sizes of interstitial space thereby limiting access by interstitial predators (e.g., rusty crayfish Orconectes rusticus, round goby Neogobius melanostomus, and sculpins Cottus spp.) which are often abundant on shallow, rocky habitats Jonas et al, 2005;Fitzsimons et al, 2007). For example, smaller substrate size reduced predation pressure on lake trout eggs by excluding larger mottled sculpins Cottus bairdi from interstitial spaces (Biga et al, 1998).…”

Population‐level effects of egg predation on a native planktivore in a large freshwater lake

“…Empirical studies that have tracked the fate of incubating fish eggs have found that as many as 79-99% of eggs will succumb to some source of mortality before hatching (Johnson 1961;Rupp 1965;Fitzsimons 1995;, and threats beyond predation can be prevalent. For example, benthic eggs can be subjected to disturbance by winddriven currents that may cause them to be buried under shifting sediments (Fitzsimons 1995;Fitzsimons et al 2007), and cool water temperatures can extend incubation and possibly increase the risk of mortality (e.g., Rice et al 1987b). In the hypolimnetic waters of Lake Michigan where bloater eggs are incubating and temperatures are relatively stable yet cold, we suspect that predation would be the primary source of egg mortality, although disturbance by currents remains a possibility (Gottlieb et al 1989).…”

A mesocosm experiment investigating the effects of substratum quality and wave exposure on the survival of fish eggs

“…However, at high current velocities and energy fluxes that can be caused by storms or by ships passing close to a spawning site, waves may also depress egg survival at sites with clean spawning substratum. Highintensity waves have already been shown to be an important habitat factor influencing egg survival of shallow water spawning fish (Rupp 1965;Fitzsimons et al 2007). …”

“…The egg stage is a critical bottleneck for many fish species, and egg survival is a major factor affecting year class strength (Gafny et al 1992;Fitzsimons et al 2007;Probst et al 2009). Knowledge about biotic and abiotic factors mediating egg survival, therefore, is important for the management of fish stocks and fish population modelling.…”