Temporal and spatial patterns in pelagic trawl fish catches in Lake Winnipeg

Diet of walleye and sauger and morphological characteristics of their prey in Lake Winnipeg

“…A beam-trawl with 6 mm mesh size (stretched) at the cod-end was deployed for 30 min at varying depths (surface, mid or deep relative to station depth) at up to 65 predetermined stations throughout the North and South Basins ( Fig. 1; Lumb et al, 2012). Up to 30 walleye and 30 sauger (N200 mm fork length) were randomly subsampled from the available catch at each location.…”

“…The number of prey fish captured in gill-nets was usually low (b 30 of varying species) and, thus, sample sizes were augmented from the beam trawl samples collected aboard the M.V. Namao in spring (late May-early June), summer (mid-Julyearly August) and fall (mid-September-early October; Lumb et al, 2012). All prey fish caught were immediately frozen at −20°C until further analysis.…”

“…The North Basin is deeper (mean depth 13.3 m), colder (surface temperature during open water season, 15.2 ± 3.5°C), with lower turbidity (mean Secchi depth: 1.2 ± 0.6 m); whereas, the South Basin is shallower (mean depth 9.7 m), warmer (surface temperature during open water season: 17.0 ± 4.5°C) and has higher turbidity (mean Secchi depth: 0.6 ± 0.3 m; Brunskill et al, 1980). Over the last decade for which extensive data are available, forage fish species in the lake, including emerald shiner (Notropis atherinoides), rainbow smelt, cisco (Coregonus artedi), white bass (Morone chrysops), yellow perch (Perca flavescens) and young walleye, had a higher density in the South relative to the North Basin (Lumb et al, 2012). Emerald shiner is the most abundant pelagic forage fish species in the lake during the open water season and is almost exclusively found in the South Basin (emerald shiner: 3.9 g wet weight/1000 m 3 ; all pelagic forage fishes:~8 g wet weight/1000 m 3 ); whereas, rainbow smelt, a non-indigenous forage fish, is the second most abundant species in the lake during the open water season and is found almost exclusively in the North Basin (rainbow smelt: 2.2 g wet weight/1000 m 3 ; all pelagic forage fishes:~3.5 g wet weight/1000 m 3 ; Lumb et al, 2012).…”

“…Over the last decade for which extensive data are available, forage fish species in the lake, including emerald shiner (Notropis atherinoides), rainbow smelt, cisco (Coregonus artedi), white bass (Morone chrysops), yellow perch (Perca flavescens) and young walleye, had a higher density in the South relative to the North Basin (Lumb et al, 2012). Emerald shiner is the most abundant pelagic forage fish species in the lake during the open water season and is almost exclusively found in the South Basin (emerald shiner: 3.9 g wet weight/1000 m 3 ; all pelagic forage fishes:~8 g wet weight/1000 m 3 ); whereas, rainbow smelt, a non-indigenous forage fish, is the second most abundant species in the lake during the open water season and is found almost exclusively in the North Basin (rainbow smelt: 2.2 g wet weight/1000 m 3 ; all pelagic forage fishes:~3.5 g wet weight/1000 m 3 ; Lumb et al, 2012). Densities of forage fish species associated with bottom waters, such as troutperch (Percopsis omiscomaycus) and freshwater drum (Aplodinotus grunniens), are unknown (Lumb et al, 2012).…”

Lake Winnipeg: The forgotten great lake

“…In this special issue, the paper by Lumb et al (2012) provides a first analysis of temporal and spatial variations of fish assemblages in the lake during 2002 to 2008. They observed that the biomass in trawl catches was higher in the south than in the north basin of the lake.…”