Geology topics

G.W. Fleischer

Publications and source records attributed to G.W. Fleischer.

7 recordsLinked to original sources

USGS2007

Relative abundance, site fidelity, and survival of adult lake trout in Lake Michigan from 1999 to 2001: Implications for future restoration strategies

We compared the relative abundance of lake trout Salvelinus namaycush spawners in gill nets during fall 1999–2001 in Lake Michigan at 19 stocked spawning sites with that at 25 unstocked sites to evaluate how effective site-specific stocking was in recolonizing historically important spawning reefs. The abundance of adult fish was higher at stocked onshore and offshore sites than at unstocked sites. This suggests that site-specific stocking is more effective at establishing spawning aggregations than relying on the ability of hatchery-reared lake trout to find spawning reefs, especially those offshore. Spawner densities were generally too low and too young at most sites to expect significant natural reproduction. However, densities were sufficiently high at some sites for reproduction to occur and therefore the lack of recruitment was attributable to other factors. Less than 3% of all spawners could have been wild fish, which indicates that little natural reproduction occurred in past years. Wounding by sea lamprey Petromyzon marinus was generally lower for Seneca Lake strain fish and highest for strains from Lake Superior. Fish captured at offshore sites in southern Lake Michigan had the lowest probability of wounding, while fish at onshore sites in northern Lake Michigan had the highest probability. The relative survival of the Seneca Lake strain was higher than that of the Lewis Lake or the Marquette strains for the older year-classes examined. Survival differences among strains were less evident for younger year-classes. Recaptures of coded-wire-tagged fish of five strains indicated that most fish returned to their stocking site or to a nearby site and that dispersal from stocking sites during spawning was about 100 km. Restoration strategies should rely on site-specific stocking of lake trout strains with good survival at selected historically important offshore spawning sites to increase egg deposition and the probability of natural reproduction in Lake Michigan.

North American Journal of Fisheries Management↗

USGS2007

Shell-free biomass and population dynamics of dreissenids in offshore Lake Michigan, 2001-2003

The USGS-Great Lakes Science Center has collected dreissenid mussels annually from Lake Michigan since zebra mussels (Dreissena polymorpha) became a significant portion of the bottom-trawl catch in 1999. For this study, we investigated dreissenid distribution, body mass, and recruitment at different depths in Lake Michigan during 2001-2003. The highest densities of dreissenid biomass were observed from depths of 27 to 46 m. The biomass of quagga mussels (Dreissena bugensis) increased exponentially during 2001-2003, while that of zebra mussels did not change significantly. Body mass (standardized for a given shell length) of both species was lowest from depths of 27 to 37m, highest from 55 to 64 m, and declined linearly at deeper depths during 2001-2003. Recruitment in 2003, as characterized by the proportion of mussels < 11 mm in the catch, varied with depth and lake region. For quagga mussels, recruitment declined linearly with depth, and was highest in northern Lake Michigan. For zebra mussels, recruitment generally declined non-linearly with depth, although the pattern was different for north, mid, and southern Lake Michigan. Our analyses suggest that quagga mussels could overtake zebra mussels and become the most abundant mollusk in terms of biomass in Lake Michigan.

Journal of Great Lakes Research↗

USGS2005

Stock structure of Lake Baikal omul as determined by whole-body morphology

In Lake Baikal, three morphotypes of omul Coregonus autumnalis migratorius are recognized; the littoral, pelagic, and deep-water forms. Morphotype assignment is difficult, and similar to that encountered in pelagic and deep-water coregonines in the Laurentian Great Lakes. Principal component analysis revealed separation of all three morphotypes based on caudal peduncle length and depth, length and depth of the body between the dorsal and anal fin, and distance between the pectoral and the pelvic fins. Strong negative loadings were associated with head measurements. Omul of the same morphotype captured at different locations were classified to location of capture using step-wise discriminant function analysis. Jackknife correct classifications ranged from 43 to 78% for littoral omul from five locations, and 45–86% for pelagic omul from four locations. Patterns of location misclassification of littoral omul suggested that the sub-population structure, hence stock affinity, may be influenced by movements and intermixing of individuals among areas that are joined bathymetrically. Pelagic omul were more distinguishable by site and may support a previous hypothesis of a spawning-based rather than a foraging-based sub-population structure. Omul morphotypes may reflect adaptations to both ecological and local environmental conditions, and may have a genetic basis.

Journal of Fish Biology↗

USGS2004

Landscape scale measures of steelhead (Oncorhynchus mykiss) bioenergetic growth rate potential in Lake Michigan and comparison with angler catch rates

The relative quality of a habitat can influence fish consumption, growth, mortality, and production. In order to quantify habitat quality, several authors have combined bioenergetic and foraging models to generate spatially explicit estimates of fish growth rate potential (GRP). However, the capacity of GRP to reflect the spatial distributions of fishes over large areas has not been fully evaluated. We generated landscape scale estimates of steelhead ( Oncorhynchus mykiss ) GRP throughout Lake Michigan for 1994-1996, and used these estimates to test the hypotheses that GRP is a good predictor of spatial patterns of steelhead catch rates. We used surface temperatures (measured with AVHRR satellite imagery) and acoustically measured steelhead prey densities (alewife, Alosa pseudoharengus ) as inputs for the GRP model. Our analyses demonstrate that potential steelhead growth rates in Lake Michigan are highly variable in both space and time. Steelhead GRP tended to increase with latitude, and mean GRP was much higher during September 1995, compared to 1994 and 1996. In addition, our study suggests that landscape scale measures of GRP are not good predictors of steelhead catch rates throughout Lake Michigan, but may provide an index of interannual variation in system-wide habitat quality.

Lake Michigan↗

USGS2002

Mitochondrial DNA variability among Lake Baikal omul Coregonus autumnalis migratorius (Georgi)

Omul, Coregonus autumnalis, are a commercially important coregonine fish from Lake Baikal, Siberia, Russia. In Lake Baikal, three morphotypes recognized by fishery experts occupy different zones in the lake: they are referred to as "littoral," "pelagic," and "benthic". Expressed character divergence was supported by whole-body morphometric analysis, but it is not known whether discrete genetic differences accompany the observed morphological variation. This study was designed to assess the genetic variation of three different omul morphotypes sampled from different locations in Lake Baikal that were segregated by morphotype in multivariate analysis. We surveyed genetic variation with restriction fragment length polymorphism analysis of specific gene loci amplified with the polymerase chain reaction. Sequence variation was localized in the mitochondrial control region. Though no discrete genetic markers were found, there is evidence of reproductive segregation by geographic location that corroborates geographic variation in morphological characters.

Advances in Limnology↗

USGS2002

Population dynamics of bloaters (Coregonus hoyi) in Lake Michigan, 1973-1998

Past research has demonstrated that the recruitment pattern of Lake Michigan bloaters (Coregonus hoyi) was best represented by a Beverton-Holt function during 1977-1983. In this present study, we re-assessed relations in bloater recruitment and investigated trends in sex ratio and mean length at age as they related to recent changes in bloater abundance. Bloaters were collected from 1973 to 1997 during lake-wide bottom-trawl surveys and in western Lake Michigan from 1980 to 1998 during graded-mesh gill-net surveys. Length, weight, age, sex, and maturity of bloaters were recorded. The relative abundance of females in the population increased throughout the past 10-15 years to more than 80% in 1997. Relative abundance of females in the population was inversely related to overall abundance during periods of increasing female dominance. Female dominance may be related to an increasingly older population, which resulted from low recruitment, and to the greater longevity of female bloaters. Mean length at age decreased steadily in the 1980s with increased bloater abundance. Bloater recruitment was density dependent and followed a Ricker-type stock-recruitment relation. Future research will focus on identifying other factors that influence bloater recruitment such as the effect of female dominance.

Advances in Limnology↗

USGS1999

Comparative ecology of exotic invaders and ecologically equivalent species of hydrobionths in the Great Lakes of the world: Results of Russia-USA cooperation

This paper presents brief fragments of the results of joint Russia-US research conducted through the cooperative project entitled, 'Comparative ecology of exotic invaders and ecologically equivalent species of hydrobionths in the Great Lakes of the world: Lake Baikal and the Laurentian Great Lakes.' The project was executed under the Agreement on Scientific Cooperation between the Institute of General and Experimental Biology (formerly Buryat Institute of Biology) of the Siberian Branch of the Russian Academy of Sciences and the Great Lakes Science Center of the U.S. Geological Survey.

Conference Paper↗