Nancy A. Auer

Response of spawning lake sturgeons to change in hydroelectric facility operation

Abstract Spawning of lake sturgeon Acipenser fulvescens was documented from 1987 to 1992 below the Prickett hydroelectric facility on the Sturgeon River, a tributary to Portage Lake, Michigan. Lake sturgeons were captured at the spawning site with dip nets during periods of reduced flow. A change in the spawning characteristics of the population was noted that corresponded to a change in the operation of the hydroelectric facility. In 1987 and 1988 the facility operated in a peaking mode, which resulted in large daily fluctuations in river flows. The years 1989 and 1990 were years of transition, and in 1991 and 1992 the facility released near run-of-the-river (ROR) flows. Under near-ROR flows, which were more natural, adult lake sturgeons spent 4–6 weeks less at the spawning sites, 74% more fish were observed, weights were greater due to a 68% increase in number of females, and fish had increased reproductive readiness. The change in flow regime was the result of a Federal Energy Regulatory Commission rel...

Population Characteristics and Movements of Lake Sturgeon in the Sturgeon River and Lake Superior

A 2.6-km reach of the Sturgeon River, containing two sets of rapids, is an important spawning site to a native population of lake sturgeon, Acipenser fulvescens, which ranges widely into southern Lake Superior. Similar spawning areas in other Great Lake tributaries may also be important to the protection and rehabilitation of lake sturgeon throughout this region. Information on range and habitat needs of this species, which is considered “threatened” in the State of Michigan, was obtained from the Sturgeon River spawning population from 1987 to 1995. Radio-tracking was employed to determine movements and habitat use by post-spawning lake sturgeon. Telemetry data from 25 fish were supplemented with data obtained through identification tag returns. During the study 925 lake sturgeon were handled; 86 returned to spawn 1 time and 12 returned 2 times. Spawning intervals for male lake sturgeon were commonly 2, 3, or 4 years; yearly spawning by males was never observed. Females returned to spawn after 3 to 7 years. From 1991 to 1995 the male:female sex ratio at the spawning site was 1.25 to 2.7. In 1990 13 of 18 adults fitted with transmitters moved out of the river within 9 days. Upon reaching Portage Lake nine individuals spent time in shallow (maximum depth, 6 m) Pike Bay. After 3 to 53 days (mean, 22) tagged fish moved into the deeper water of Portage Lake (maximum depth, 17 m) and ranged more widely. Three fish were located in Keweenaw Bay, Lake Superior by late August. Identification tag returns reveal that lake sturgeon traveled 70 to 280 km from the spawning site throughout southern Lake Superior.

Movement and Habitat of Juvenile Lake Sturgeon (Acipenser fulvescens) in the Sturgeon River/Portage Lake System, Michigan

ABSTRACT The Portage Lake/Sturgeon River system in Michigan contains one of the last self-sustaining stocks of lake sturgeon (Acipenser fulvescens) in the Great Lakes without barriers to impede natural movement of juveniles. We conducted visual surveys in the Sturgeon River and collected young-of-the-year and juvenile lake sturgeon from 1997 to 2000. Twenty-four fish, 9.8 to 28.8 cm total length (TL), were found predominately over pea gravel 16 to 26 km below the spawning site. With gillnets and trotline we collected an additional 24 fish (22–83 cm TL) and one sub-adult (103.5 cm TL) lake sturgeon in Portage Lake; four juveniles and the sub-adult were fitted with radio transmitters. Average daily linear movement of lake sturgeon varied from 0.3 to 1.6 km. Total linear distance traveled by sturgeon averaged 15.5 km over 83 days. Diel movements indicated that two juveniles moved into shallow (<5 m) inshore areas at night and into deeper (>7.5 m) offshore areas as light intensified.

Lake Sturgeon Spawning Habitat in the Big Manistee River, Michigan

Abstract Spawning sites of lake sturgeon Acipenser fulvescens were verified using egg collection mats in the Big Manistee River in northwestern lower Michigan. Photographs taken by a fixed-position underwater video camera were used to characterize the substrate at egg mat locations. A total of 3,913 lake sturgeon eggs were captured at two discrete spawning locations in 2003 and 2004. Spawning locations consisted of 34–44% cobble and 0.04–8% sand, and nonspawning locations consisted of 2–43% cobble and 0.16–7% sand. Shannon diversity indices describing substrate heterogeneity at spawning locations were statistically higher than those for nonspawning locations in 2003 (P = 0.002). Four spawning events (one in 2003 and three in 2004) were documented at water temperatures ranging from 11.1°C to 14.8°C and egg incubation periods ranging from 6 to 10 d. Depth at spawning sites was 1.5–3.0 m, average water velocity was 0.34–1.32 m/s, and near-substrate water velocity was 0.08–1.26 m/s. The topography of the Big ...

Abundance and Distribution of Benthic Invertebrates, with Emphasis on Diporeia, along the Keweenaw Peninsula, Lake Superior

Abstract The benthic invertebrate community in Lake Superior is an important component in the fisheries food web. Among the Great Lakes, only Lake Superior contains populations of Diporeia spp. that have not been reduced or extirpated in the last 20 years. The objectives of this study were to determine the abundance and distribution of benthic invertebrates along the Keweenaw coast, and to investigate the reproductive ecology of Diporeia . The benthic community was sampled monthly from 1998 to 2000, using a ponar dredge along three transects with distinctly different bathymetry. Each transect contained shelf, slope, and profundal depth regions. Diporeia was the most abundant invertebrate, accounting for 48% of the invertebrate community, while chironomids composed 21.3%, oligochaetes 18.7%, and sphaeriids 8.4%. Only chironomids showed a statistically significant change in monthly density, being more abundant in September than earlier or later in the year. Diporeia and Sphaeriidae were most densely distributed along the slope, and the distribution of chironomids and oligochaetes was even more specific within the slope region, with peak densities occurring at 50 meters on all three transects. Diporeia reproduced when the water temperature was 4°C or colder. Along the shelf, Diporeia released their young in May, whereas in the slope and profundal regions young appeared in June and September, suggesting two periods of reproduction, late spring and summer. In the shelf area Diporeia grew at a faster rate than those offshore. There was a linear correlation between the length of female Diporeia and the number of eggs carried, similar to what has been shown for the other Great Lakes. The benthic invertebrate community peaks in abundance in the slope region of Lake Superior along the Keweenaw Peninsula. This region may provide important habitat and nutrients for other organisms in the Lake Superior food web

Changes in the Zooplankton of Onondaga Lake: Causes and Implications

ABSTRACT The zooplankton assemblage of ionically polluted, culturally eutrophic Onondaga Lake was monitored over the 1979–1989 interval, and compared to surveys conducted in 1968 and 1978. A major shift in the assemblage was apparent by 1987, soon after the closure (1986) of an industrial discharger of ionic (Cl; Na+ and Ca2+) waste. Species richness increased from 8 to 18 common species, and more efficient grazers, large-bodied cladocera and the calanoid copepod Diaptomus sitihides, became dominants. Until 1987, a single cyclopoid copepod, Cyclops vernalis, was the dominant component of zooplankton biomass. The most likely cause for the shift in the zooplankton assemblage of the lake is the reduction in salinity, and attendant precipitation of calcium carbonate, associated with the closure of the industry. Improved clarity in the lake, manifested largely as intervals of dramatic increases described as ‘clearing events’, observed annually since 1987, has been attributed to die shift to more efficient graz...

Inshore-offshore Distribution of Larval Fishes in Lake Superior off the Western Coast of the Keweenaw Peninsula, Michigan

We surveyed the larval fish community in Lake Superior off the western coast of the Keweenaw Peninsula, Michigan, as a first component in understanding how the Keweenaw Current affects larval fish distribution and survivorship. On transects at Ontonagon, Houghton, and Eagle Harbor, we collected larval fishes with a 1-m diameter plankton net towed through surface and deep (below metalimnion) waters at an inshore location (1 km from shore) and an offshore location (5–9 km from shore) during day and night in 1998 and 1999. The most abundant larvae caught were lake herring (Coregonus artedii), rainbow smelt (Osmerus mordax), burbot (Lota lota), deepwater sculpin (Myoxocephalus thompsoni), and spoonhead sculpin (Cottus ricei). Lake herring was generally most abundant at the surface during the day, while the other four species avoided the surface by day but not at night. Overall, larval fish density was greater inshore than offshore, with exceptions for particular locations and seasonal periods (1.24x for lake herring, 12.93x for rainbow smelt, 1.27x for burbot, 1.25x for deepwater sculpin, and 4.26x for spoonhead sculpin). Differences in the sizes of larvae between inshore and offshore locations, in conjunction with density patterns, suggest a seasonal inshore to offshore movement. Despite the presence of the Keweenaw Current, the overall distribution patterns of larval fishes follow those of previous studies conducted in the Great Lakes, but with lower densities.

Life history, distribution, and production of Diporeia near the Keweenaw Peninsula Lake Superior

ABSTRACT Benthic amphipods are a keystone species in food webs of marine and freshwater systems. The amphipod in the phylogroup Diporeia found in the Great Lakes has historically been a dominant member of the benthic community and is critical to the fisheries food web. This study investigates water depth, life stage, sex, production, lipid content, and gut fullness as influences and outcomes of Diporeia distribution in Lake Superior. Samples were collected at 2- to 3-week intervals from May to October 2003 from ten stations along one transect in Lake Superior near the Keweenaw Peninsula of Michigan to determine seasonal trends in abundance and condition. Diporeia comprised, on average, 52% of the benthic macroinvertebrate community. Abundance and productivity of Diporeia is greatest within the slope region (depths of 30 to 125 m) with estimated biomass and annual P/B (production/biomass) values of 0.57 and 0.73 g/m2 for this habitat. Young-of-the-year Diporeia were the most abundant life stage in the shelf in the spring while adults were most abundant in the slope and profundal regions in fall. The greatest mean percent gut fullness occurred in September and October while the least full and empty gut occurrences were observed in June and July. The slope of the length-weight relationship for Diporeia in Lake Superior is lower (less biomass per unit length) than that observed for lakes Huron, Michigan, and Ontario. The greatest lipid content was 41% DW in July at 20 m with the overall average lipid content of Diporeia from Lake Superior in 2003 at 32% with a decline observed from September to October. The description of Diporeia abundance, distribution, and life history presented here for Lake Superior, and compared with that of other Great Lakes, will be of use in support of studies of lower food web bioenergetics.

Chemical Suitability of Substrates for Walleye Egg Development in the Lower Fox River, Wisconsin

Abstract Site suitability for egg development was assessed for walleyes Stizostedion vitreum in the Fox River, Wisconsin. Water chemistry at the sediment-water interface was compared with criteria for walleye egg hatch success (oxygen and hydrogen sulfide) and chronic toxicity (free ammonia). Reduced concentrations of dissolved oxygen and elevated concentrations of ammonianitrogen and hydrogen sulfide occurred above some sand and all soft muck substrates. The chemical oxygen demand (COD) of the surficial sediments was a useful surrogate variable for identifying the chemical suitability of spawning sites; locations with a surficial sediment COD less than 40 mg O2/g dry weight were considered suitable. A comprehensive surficial sediment survey of the lower Fox River below the DePere Dam showed that optimal walleye spawning habitat (gravel-cobble substrate) is rare (less than 3% of the area) and that 75% of the suboptimal (sand and muck) substrate is chemically unsuitable for walleye egg development. We conc...

Genetic assessment of straying rates of wild and hatchery reared lake sturgeon (Acipenser fulvescens) in Lake Superior tributaries

ABSTRACT Natal philopatry in lake sturgeon (Acipenser fulvescens) has been hypothesized to be an important factor that has lead to genetically distinct Great Lakes populations. Due to declining abundance, population extirpation, and restricted distribution, hatchery supplementation is being used to augment natural recruitment and to reestablish populations. If hatchery-reared lake sturgeon are more likely to stray than naturally produced individuals, as documented in other well-studied species, outbreeding could potentially jeopardize beneficial site-specific phenotypic and genotypic adaptations. From 1983 to 1994, lake sturgeon propagated using eggs taken from Lake Winnebago adults (Lake Michigan basin) were released in the St. Louis River estuary in western Lake Superior. Our objective was to determine whether these introduced individuals have strayed into annual spawning runs in the Sturgeon River, Michigan. Additionally, we estimated a natural migration rate between the Sturgeon River and Bad River, Wisconsin populations. Presumed primiparous lake sturgeon sampled during Sturgeon River spawning runs from 2003 to 2008 were genotyped at 12 microsatellite loci. Genotypic baselines established for the Sturgeon River (n = 101), Bad River (n = 40), and Lake Winnebago river system (n = 73) revealed a relatively high level of genetic divergence among populations (mean FST = 0.103; mean RST = 0.124). Likelihood-based assignment tests indicated no straying of stocked Lake Winnebago strain lake sturgeon from the St. Louis River into the Sturgeon River spawning population. One presumed primiparous Sturgeon River individual likely originated from the Bad River population. Four firstgeneration migrants were detected in the Sturgeon River baseline, indicating an estimated 3.5% natural migration rate for the system.