Derek H. Ogle

Diet and Feeding Periodicity of Ruffe in the St Louis River Estuary, Lake Superior

Abstract Ruffe Gymnocephalus cernuus, a percid native to Europe and Asia, is established in the Lake Superior drainage and could have negative impacts on native fish through competition for forage and predation on fish eggs. We investigated the diet of ruffes in the 4,654-ha St. Louis River estuary in May–October 1989–1990 and the feeding periodicity of ruffes in two adjacent habitats during five 24-h periods in summers 1990–1991. Ruffes were primarily benthophagous. Age-0 ruffes fed mostly on cladocerans and copepods in early summer and midge larvae (Chironomidae) in late summer and fall. Adult ruffes less than 12 cm fed mostly on midges and other macrobenthos but also consumed large numbers of microcrustaceans. Adult ruffes 12 cm and larger fed mostly on midges, burrowing mayflies Hexagenia spp., and caddisflies (Trichoptera). Ruffes consumed few fish eggs. Adult ruffes in deeper waters and all age-0 ruffes fed throughout the day as indicated by weight patterns of stomach contents. However, adult ruffes...

A Synopsis of the Biology and Life History of Ruffe

The ruffe (Gymnocephalus cernuus), a Percid native to Europe and Asia, has recently been introduced in North America and new areas of Europe. A synopsis of the biology and life history of ruffe suggests a great deal of variability exists in these traits. Morphological characters vary across large geographical scales, within certain water bodies, and between sexes. Ruffe can tolerate a wide variety of conditions including fresh and brackish waters, lacustrine and lotic systems, depths of 0.25 to 85 m, montane and submontane areas, and oligotrophic to eutrophic waters. Age and size at maturity differ according to temperature and levels of mortality. Ruffe spawn on a variety of substrates, for extended periods of time. In some populations, individual ruffe may spawn more than once per year. Growth of ruffe is affected by sex, morphotype, water type, intraspecific density, and food supply. Ruffe feed on a wide variety of foods, although adult ruffe feed predominantly on chironomid larvae. Interactions (i.e., competition and predation) with other species appear to vary considerably between systems.

Ruffe Length–Weight Relationships with a Proposed Standard Weight Equation

Abstract Ruffe Gymnocephalus cernuus length–weight data from 141 data sets were obtained from a variety of waters across Europe and the Laurentian Great Lakes for summarization and development of standard weight (Ws ) equations. The mean slopes of the length–weight relationships from all populations and for all percentiles except the 95th percentile were not different from 3.0, suggesting that ruffe growth is generally isometric. The Ws equations developed using the regression line percentile, linear empirical percentile (EmP), and Froeses methods exhibited length-related biases. The quadratic EmP Ws equations for the 75th and 50th percentiles did not exhibit length-related biases and thus can be used to compute the relative weight of ruffe. The EmP 75th percentile Ws equation was log10(Ws 75) = −2.5800 + 0.6210·log10(total length, TL) + 0.6073·[log10(TL)]2, and the 50th percentile Ws equation was log10(Ws 50) = −3.3524 + 1.3969·log10(TL) + 0.4054·[log10(TL)]2 when constrained to ruffe between 55 and 205...

A technical note on seasonal growth models

The growth of many organisms is seasonal, with a dependence on variation in temperature, light, and food availability. A growth model proposed by Somers (Fishbyte 6:8–11, 1988) is one of the most widely used models to describe seasonal growth. We point out that three different formulae (beyond numerous typographical errors) have been used in the literature referring to Somers (Fishbyte 6:8–11, 1988). These formulae correspond to different curves and yield different parameter estimates with different biological interpretations. These inconsistencies have led to the wrong identification of the period of lowest growth rate (winter point) in some papers of the literature. We urge authors to carefully edit their formulae to assure use of the original definition in Somers (Fishbyte 6:8–11, 1988).

Predation on ruffe by native fishes of the St. Louis River Estuary, Lake Superior, 1989-1991

Abstract The ruffe Gymnocephalus cernuus, an exotic Eurasian percid, recently became established in the St. Louis River estuary, Lake Superior, after accidental introduction. Management actions (catch regulations and stockings) were enacted in 1989 to increase the density of top-level predators in the estuary, and thus to increase predation on ruffe. We conducted a field and laboratory study to determine if, and to what extent, native piscivores consume ruffe. Stomachs of 3,669 predators were examined in 1989–1991. Ruffe occurred in 6.7% of burbot Lota lota, 5.8% of bullheads Ictalurus spp., 4.7% of smallmouth bass Micropterus dolomieu, 2.6% of northern pike Esox lucius, 2.6% of black crappies Pomoxis nigromaculatus, and 1.3% of yellow perch Perca flavescens (4.5% after 1989) captured during the 3-year study. No ruffe were found in 967 stomachs of walleyes Stizostedion vitreum examined. Ruffe were 22.7%, of the diet (by weight) of bullheads (during the only year bullheads were captured) and 0.1–17.9% of t...

Experimental Evidence That Captured Rusty Crayfish (Orconectes rusticus) Exclude Uncaptured Rusty Crayfish from Entering Traps

ABSTRACT Baited modified minnow traps are often used to collect rusty crayfish (Orconectes rusticus), an invasive species in many areas of North America. However, the use of baited traps as a collection gear for decapods has received considerable scrutiny. We designed a tank-experiment to determine if captured rusty crayfish exclude uncaptured rusty crayfish from baited traps. We found that significantly more crayfish were captured in traps where captured crayfish were immediately removed (experimental tanks) than in traps where crayfish were not immediately removed (control tanks). In addition, more small crayfish were captured in the experimental tanks. These results are consistent with a hypothesis that large and aggressive previously captured rusty crayfish exclude other, generally smaller, rusty crayfish from the trap.

The Intersection of Community and Place in an Outdoor Orientation Program

This study investigated outcomes of a college outdoor orientation program that utilized 3, 4, 5, and 12-day adventure based trips. Sense of community and sense of place were measured using a one-sample pre/post-test design (n = 118). Paired sample t-tests were implemented to explore differences and, in general, students reported significant changes following participation. Students demonstrated increases in the number of their friends, trusted individuals, and 6 of the 7 factorial components measuring sense of community and sense of place (p < .05). The importance of community and place is discussed, highlighting suggestions and implications for future consideration in outdoor orientation programming.

Diet of Larval Ruffe (Gymnocephalus cernuus) in the St. Louis River Harbor, Lake Superior

The diet of larval (3-17 mm total length) ruffe (Gymnocephalus cernuus) is described from samples collected in 1994 at two locations in the St. Louis River Harbor, a tributary to Lake Superior. Copepoda, Daphnia spp., and Bosmina longirostris dominated the diet of larval ruffe in the St. Louis River Harbor. Larger Copepoda and Daphnia spp. occurred more often and in larger numbers as ruffe total length increased, whereas smaller Bosmina longirostris occurred less often and in smaller numbers as ruffe total length increased. Ruffe from Whaleback Bay consumed Daphnia spp. rarely and in very small numbers whereas ruffe from Allouez Bay consumed Daphnia spp. often and in large numbers. A general decrease in Copepoda and increase in Daphnia spp. occurred in the second and third weeks of June for ruffe from Allouez Bay, but not Whaleback Bay.

Check Formation on the Scales of Hatchery-Reared Lake Trout Prior to and Soon after Release into Lake Superior

Abstract We investigated two assumptions about scales of hatchery-reared lake trout Salvelinus namaycush stocked as yearlings into Lake Superior: (1) only one check is formed during hatchery life and (2) a “stocking check” forms when the fish are released. We examined four scales from each of 176 fish prior to release from five hatcheries and 55 fish soon after release. Prior to release, 91 % of the lake trout had only one check. This percentage was 81–100% for individual hatcheries. Evidence for a stocking check was observed only on fish whose scales had grown substantially between release and subsequent recapture. All measures of variability were less and check conspicuousness was greater for fish raised in hatcheries with seasonal cycles of temperature and photoperiod than for those reared with nearly constant water temperatures and darkness. We conclude that the assumption of only one check prior to stocking was not grossly violated when several scales from the same fish were interpreted and that ther...

Evaluating the physical removal of ruffe (Gymnocephalus cernuus) with bottom trawling

The ability to reduce a population of ruffe (Gymnocephalus cernuus) with intense repeated bottom trawling was examined at two locations in Chequamegon Bay of Lake Superior. Trawling significantly depleted the population at the Kakagon River site but not at the Second Landing site. At least 93% of the estimated population of ruffe was removed from the Kakagon River site, but ruffe re-established in the area within 1 year. The relative success of short-term reduction at the Kakagon River site was likely due to habitat and biological characteristics that led ruffe to congregate in large numbers. Physical removal does not appear to be an effective way to effect long-term removal of ruffe.