Preliminary Comparisons of Day and Night Habits of Freshwater Fish in Ontario Lakes

Abstract

Observations by SCUBA in Georgian Bay and Algonquin Park, Ont., indicate fish have specific habits of diurnal, crepuscular, and nocturnal activity in freshwater lakes. Of 21 species investigated, 17 either schooled or aggregated in the daytime, but only one (Osmerus mordax) schooled at night. The number of fish apparent at night in shallow water was greater than in the daytime primarily because of the influx of offshore species and lack of cover for resting diurnal species. Color changes parallel those reported in tropical oceans; at night a barred or mottled pattern was assumed by some fish resting on the bottom and bold daytime horizontal patterns faded. The parallel evolution of these color patterns in fresh and salt water suggests a strong evolutionary pressure for prey animals to disguise body shape when at rest at night, and that bold color patterns are disadvantageous when swimming at night.

Effect of light on juvenile walleye pollock shoaling and their interaction with predators

“…For visually oriented species, decreased activity may lower energetic costs during periods when fish are not actively feeding (Neilson & Perry 1990, Sogard & Olla 1996. Decreased activity may also facilitate the maintenance of congregations when there is insufficient light for visually mediated shoaling (Emery 1973). In addition to this modest light/dark effect, there was also a strong diel pattern of swimming speed, characterized by peak speeds during the early morning, which decreased through the day and then decreased further to uniformly low levels during the night.…”

“…Although other senses, such as the lateral line system, may play an important role in the spatial and angular orientation of individuals within a school (Partridge & Pitcher 19801, it is unlikely that in the wild many species are capable of schooling in the absence of sufficient light. Thls impression is supported by observational (Emery 1973, Helfman 1979 and bioacoustical studies which generally show that shoals and schools disperse at night (Appenzeller & Leggett 1992, Brodeur & Wilson 1996. Since ambient light in marine and aquatic habitats may vary greatly according to depth, turbidity, season, lunar stage and cloud cover (McFarland 1986), the meaning of 'night', relative to light levels, 1s rather ambiguous.…”

“…However, fish may have evolved other behaviors that minimize their nocturnal vulnerability and perhaps facilitate the reformation of groups at dawn. Some fish species decrease their activity during the night (Emery 1973, Helfman 1993) to conserve energy and possibly to reduce conspicuousness to predators. For shoaling and schooling fish, this may also minimize group dispersal and decrease the time required for individuals to locate conspecifics and reform shoals or schools at dawn.…”

Spatial Patterning of Prey at Reproduction to Reduce Predation Risk: What Drives Dispersion from Groups?

“…In our simulations, we assumed that wolves primarily detected caribou by olfaction and/or audition because forest cover limits visual detection. Environmental effects on vision may also determine the spatial distribution of prey as it directly affects the benefit of early predator detection provided by groups (Pulliam 1973, Beauchamp 2014 (Emery 1973) and dolphins (Scott and Cattanach 1998).…”

Acoustic measures of lake community size spectra

“…This dispersal makes fish more easily detected (especially as single targets) by acoustic equipment. Fish also move between offshore and nearshore areas between day and night (e.g., Emery 1973). Masson et al (2001) found that at night, fish distributions were skewed towards the offshore, with a greater proportion of smaller bodied fish present compared with daytime surveys.…”