Larval sea lamprey (Petromyzon marinus) and northern brook lamprey (Ichthyomyzon fossor) were collected monthly from three streams in the Upper Peninsula of Michigan from May 1992 through May 1993 and larval sea lampreys were collected during summer months from sites throughout the Great Lakes basin. Organic detritus made up most of the diet ash-free-dry-mass (AFDM) throughout the year, averaging 97.79%, with algae (2.12%) and bacteria (0.09%) making up the remainder of the diet AFDM. Assimilation efficiency for AFDM averaged 72% during warmer months and 53% during cooler months (annual mean = 61%). Gut fullness (amount of AFDM in the anterior one-tenth of the intestine) was low (mean = 0.10 mg diet AFDM∙g−1 ammocoete). There were no significant differences in these measures between ammocoetes collected from the Upper Peninsula and those collected throughout the Great Lakes basin. From a laboratory-determined relationship between gut fullness and feeding rate, feeding rate in the field was estimated to be extremely slow, ranging from 4.2 to 5.5 mg diet AFDM∙g−1 ammocoete∙d−1. These observations indicate that larval lampreys efficiently utilize a diet of organic detritus during warmer months when stream temperatures and food quality are more favorable for feeding, digestion, and growth.

Abstract.-A thorough understanding of the early life history of lake sturgeon Acipenser fulvescens is critical for rehabilitation of this species. Recruitment of lake sturgeon is known to be variable, but the extent of that variation and mortality rates experienced by early life stages are unclear. The objective of this study was to quantify early life stage mortality and explore the variability in year-class strength by estimating total egg deposition and abundance of larval and age-0 juvenile lake sturgeon from the 2006 and 2007 year-classes in the Peshtigo River, Wisconsin. Egg mats, drift nets, and visual surveys were used to collect lake sturgeon eggs, larvae, and age-0 juveniles, respectively. Total egg deposition, larval abundance, and age-0 juvenile abundance were higher in 2007 than in 2006. The magnitude of difference ranged from 2 times for eggs to 11 times for age-0 juveniles. The rate of mortality from the larval stage to the age-0 juvenile stage was higher in 2006 (98.26%) than in 2007 (90.46%); overall mortality from the egg stage to the age-0 juvenile stage was also higher in 2006 (99.98%) than 2007 (99.93%). These results suggest that mortality rates for these life stages of lake sturgeon are high, and large variation in early life stage abundance may be common. Management strategies to reduce these mortality rates may increase recruitment and aid population recovery.

Efforts to restore lake sturgeon Acipenser fulvescens to former population levels in the Great Lakes will benefit from a thorough understanding of the species' early life history. The rehabilitation of this species will be aided by identifying nursery habitats in riverine environments through characterizing the habitat use and movements of age-0 fish. The objectives of this study were to determine the habitat preferences and movement patterns of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin, a tributary of Lake Michigan. Fish were captured from June through October 2002 and 2003 by means of wading, snorkeling, haul-seine, and backpack electrofishing surveys, and radio transmitters were attached to individuals larger than 74 g. For each capture and relocation site, habitat features were evaluated by measuring water depth, velocity, and temperature and by characterizing substrate type and macroinvertebrate assemblage. Age-0 lake sturgeon were collected and relocated at water depths less than 2 m over sand substrates and at current velocities less than 0.60 m/s. Capture and relocation sites were dominated by dipteran larvae, and the median macroinvertebrate density was lower at these sites than in the remainder of the study area. Macroinvertebrate diversity index values were also lower at capture sites than in the overall study area. Daily movements of age-0 lake sturgeon showed that fish exhibited greater activity after dark, whereas seasonal movement patterns were related to changes in water temperature, particularly during fall months as fish moved from the river to Green Bay. These results suggest that shallow, riverine areas with sand substrates, low current velocity, and a predominance of dipteran larvae should be protected as important nursery habitats in Great Lakes tributaries that support spawning populations of lake sturgeon.

No abstract

The availability of lotic spawning, staging, and nursery habitats is considered a major factor limiting the recovery of Lake sturgeon (Acipenser fulvescens) in Lake Michigan. Despite efforts to better understand the population biology and habitat use of remnant Lake sturgeon stocks, little information exists on the quantity, quality, and spatial distribution of habitats for riverine life stages. We applied georeferenced habitat information on substrate, water depth, and stream gradient to a Lake sturgeon habitat suitability index in a geographic information system to produce spatially explicit models of life stage-specific habitat characteristics in the Menominee River, Michigan-Wisconsin; the Peshtigo, Oconto, and lower Fox rivers, Wisconsin; and the Manistique River, Michigan. High-quality Lake sturgeon spawning habitat associated with coarse substrates (‚2.1 mm) and moderate-to high-stream gradients (‚0.6 m/km) comprised 1-6% of the available habitat in each system. Staging habitat characterized by water depths greater that 2 m located near potential spawning habitat comprised an additional 17-41%. However, access to a majority of these habitat types (range 30-100%) by Lake sturgeon from Lake Michigan is currently impeded by dams. Highquality juvenile Lake sturgeon habitat associated with finer substrates, lower stream gradients, and a broad range of water depths (i.e., 0.5-8 m) was relatively ubiquitous throughout each system and comprised 69-100% of the available habitat. Our study suggests that efforts to rehabilitate Lake sturgeon populations should consider providing fish passage and creating supplemental spawning habitat to increase reproductive and recruitment potential.

Few studies have examined the seasonal movement patterns, habitat use, and home range of flathead catfish Pylodictis olivaris in lotic systems throughout the northern United States. We used ultrasonic telemetry on 39 flathead catfish (range, 430-1,132 mm total length) in the lower St. Joseph River, Michigan, to increase our understanding of these behaviors in northern populations of flathead catfish and to provide important information for the development of appropriate management strategies in this system. Transmitters were surgically implanted into the peritoneal cavity of selected individuals captured by means of low-voltage AC electrofishing during 2002 and 2003. Habitat use of flathead catfish was dominated by large woody debris and riprap at water depths less than 3 m during all seasons except winter, when fish utilized main-channel pool habitats associated with coarse substrates at water depths greater than 4 m. Flow rates at fish locations were not significantly different among seasons (range, 0.1-0.7 m/s). The mean seasonal movement distance and home range of flathead catfish were greatest during spring (1,045 and 1,513 m, respectively) and fall (1,146 and 1,296 m, respectively), when fish transitioned between summer and winter habitats, while movement distance and home range during summer months averaged 218 and 596 m, respectively. No movement was observed during the winter season. Our study results indicate that seasonal differences exist in the movement patterns, habitat use, and home range of flathead catfish in the lower St. Joseph River and that the availability of structure and main-channel pool habitats are important considerations in the management of this species.

Populations of lake herring Coregonus artedi in Lake Superior have exhibited high recruitment variability over the past three decades. To improve our understanding of the mechanisms which influence year-class strength, we conducted a 225-d laboratory experiment to evaluate the effects of body size, physiological condition, energy stores, and food ration on the winter survival of age-0 lake herring. Small (total length [TL] range ϭ 60-85 mm) and large (TL range ϭ 86-110 mm) fish were maintained under thermal and photoperiod regimes that mimicked those in Lake Superior from October through May. Fish in each size-class were maintained at two feeding treatments: brine shrimp Artemia spp. ad libitum and no food. The mortality of large lake herring (fed, 3.8%; starved, 20.1%) was significantly less than that of small fish (fed, 11.7%; starved, 32.0%). Body condition and crude lipid content declined for all fish over the experiment; however, these variables were significantly greater for large fed (0.68% and 9.8%) and small fed (0.65% and 7.3%) fish than large starved (0.49% and 5.7%) and small starved (0.45% and 4.8%) individuals. Final crude protein and gross energy contents were also significantly greater in large fed lake herring (17.6% and 1,966 cal/g), followed by small fed (17.1% and 1,497 cal/g), large starved (15.4% and 1,125 cal/g), and small starved (13.2% and 799 cal/g) fish. Lake herring that died during the experiment had significantly lower body condition and energy stores relative to those of the surviving fish. These results suggest that the depletion of energy stores contributes to greater winter mortality of small lake herring with limited energy uptake and may partially explain the variability in recruitment observed in Lake Superior.

Genetic relationships among lake whitefish ( Coregonus clupeaformis ) spawning aggregates in Lake Michigan were assessed and used to predict a stock or management unit (MU) model for the resource. We hypothesized that distinct spawning aggregates represented potential MUs and that differences at molecular markers underlie population differentiation. Genetic stock identification using 11 microsatellite loci indicated the presence of six genetic MUs. Resolved MUs corresponded to geographically proximate spawning aggregates clustering into genetic groups. Within MUs, analyses suggested that all but one delineated MU was a stable grouping (i.e., no between-population differences), with the exception being the Hog Island – Traverse Bay grouping. Elk Rapids was the most genetically divergent population within Lake Michigan. However, low Fst values suggested that moderate to high levels of gene flow occur or have occurred in the past between MUs. Significant tests of isolation by distance and low pairwise Fst values potentially led to conflicting results between traditional analyses and a Bayesian approach. This data set could provide baseline data from which a comprehensive mixed-stock analysis could be performed, allowing for more efficient and effective management of this economically and socially important resource.