A three-year (2001-2003) monitoring effort of 14 northeastern Minnesota lakes was conducted to document relationships between water-level fluctuations and mercury bioaccumulation in young-of-the-year (YOY) yellow perch (Perca flavescens) collected in the fall of each year at fixed locations. Six of those lakes are located within or adjacent to Voyageurs National Park and are influenced by dams on the outlets of Rainy and Namakan lakes. One site on Sand Point Lake coincides with a location that has nine years of previous monitoring suitable for addressing the same issue over a longer time frame. Mean mercury concentrations in YOY yellow perch at each sampling location varied significantly from year to year. For the 12-year monitoring site on Sand Point Lake, values ranged from 38 ng gww(-1) in 1998 to 200 ng gww(-1) in 2001. For the 14-lake study, annual mean concentrations ranged by nearly a factor of 2, on average, for each lake over the three years of record. One likely factor responsible for these wide variations is that annual water-level fluctuations are strongly correlated with mercury levels in YOY perch for both data sets.

Beavers are increasingly viewed as ''ecological engineers,'' having broad effects on physical, chemical, and biological attributes of north-temperate landscapes. We examine the influence of both local successional processes associated with beaver activity and regional geomorphic boundaries on spatial variation in fish assemblages along the Kabetogama Peninsula in Voyageurs National Park, northern Minnesota, USA. Fish abundance and species richness exhibited considerable variation among drainages along the peninsula. Geological barriers to fish dispersal at outlets of some drainages has reduced fish abundance and species richness. Fish abundance and species richness also varied within drainages among local environments associated with beaver pond succession. Fish abundance was higher in upland ponds than in lowland ponds, collapsed ponds, or streams, whereas species richness was highest in collapsed ponds and streams. Cluster analyses based on fish abundance at sites classified according to successional environment indicated that four species (northern redbelly dace, Phoxinus eos; brook stickleback, Culaea inconstans; finescale dace, P. neogaeus; and fathead minnow, Pimephales promelas), were predominant in all successional environments. Several less abundant species were added in collapsed ponds and streams, with smaller size classes of large lake species (e.g., black crappie, Pomoxis nigromaculatus; smallmouth bass, Micropertus dolomieui; yellow perch, Perca flavescens; and burbot, Lota lota) being a component of these less abundant species. The addition of smaller size classes of large lake species indicates that dispersal of early life-history stages from Kabetogama Lake played a role in determining the species richness and composition of less abundant species in successional environments on the peninsula. Furthermore, collapsed-pond and stream environments closer to Kabetogama Lake had higher species richness than similar successional sites located farther from the lake. Cluster analyses based on fish abundance at sites classified according to drainage indicated that species composition among drainages was influenced both by the presence or absence of geological barriers to fish dispersal and the nonrandom distribution of collapsed ponds and streams. Based on these results, we present a hierarchical conceptual model suggesting how geomorphic boundaries and beaver pond succession interact to influence fish assemblage attributes. The presence of a productive and diverse fish assemblage in headwater streams of north-temperate areas requires the entire spatial and temporal mosaic of successional habitats associated with beaver activity, including those due to the creation and abandonment of beaver ponds. The ultimate impact of the local successional mosaic on fishes, however, will be strongly influenced by the regional geomorphic context in which the mosaic occurs.

We supplemented physical‐tagging data with genetic data to provide evidence for spawning‐site and natal‐site fidelity by two spawning populations of northern pike Esox lucius in Kabetogama Lake, Minnesota. A mark–recapture study supported previous reports that individual northern pike and other esocids tend to return to the spawning grounds that they used in previous years. Of 1,900 northern pike marked at two spawning sites in the first year of the study, 23% were recaptured on spawning grounds one to three times over the next 4 years. Of these recaptured fish, only 1.3% and 4.8%, respectively, of those marked at the two spawning sites were recaptured at the other site. Tag returns from anglers showed that the year‐round ranges for fish from the two sites overlapped, so that lack of dispersal could not completely explain the high fidelity to spawning sites. Significant allele frequency differences at five microsatellite DNA loci between the 1983 (P = 0.03) and 1985 (P = 0.002) spawning populations indicated low levels of gene flow between the populations. This reproductive isolation would only be expected if most individuals first spawn at the site of their own birth and subsequently return to that site. We therefore conclude that northern pike in Kabetogama Lake exhibit both natal‐site and spawning‐site fidelity. Management on the basis of discrete spawning populations within lakes may thus be appropriate for a larger number of species and locations than commonly practiced.

Information presented concerning the pallid sturgeon, Scaphirhynchus albus, was compiled from published and unpublished papers, from personal communications with numerous biologists, and from the results of a survey of 45 agencies and individuals. Pallid sturgeon occur in the Missouri River and the lower half of the Mississippi River and certain of their tributaries. Of the 250 pallids that were reported, approximately 76% were collected from the Missouri River in Montana and the Dakotas. Because of the rarity of this species, information on its life history is limited. Regression equations were developed for the length‐weight relationships of pallids from two Missouri River reservoirs. The apparent rarity of the pallid sturgeon and the lack of knowledge concerning it has prompted 9 of the 13 states within its range to classify it as either threatened or endangered or to give it some other special recognition. The Endangered Species Committee of the American Fisheries Society has also classified it as threatened throughout its range. Additional information is needed on its habitat requirements if it is to be protected from habitat destruction or modification.