Charles C. Krueger

ANNUAL PRODUCTION OF MACROINVERTEBRATES IN THREE STREAMS OF DIFFERENT WATER QUALITY

Macroinvertebrate annual production was estimated in three Minnesota streams that differed in watershed geologic origin and in total alkalinity. Annual mean alkalinities (as CaCOt) in the Caribou River, Blackhoof River, and North Branch Creek were 34, 83, and 245 mg/L, respectively. Annual production by herbivore-detritivore invertebrates was lowest in the Caribou River (wet mass: 27.0 g/m2), intermediate in the Blackhoof River (36.9 g/m2), and highest in North Branch Creek (I 19.6 g/m2). Estimates of annual production by invertebrate carnivores followed the same pattern: lowest in the Caribou River (5.5 g/m2, intermediate in the Blackhoof River (6.5 g/m2), and highest in North Branch Creek (12.8 g/m2). These estimates of annual production were positively associated with alkalinity, nitrates, and fish standing stocks.

Predation by Alewives on Lake Trout Fry in Lake Ontario: Role of an Exotic Species in Preventing Restoration of a Native Species

Lake trout (Salvelinus namaycush) restoration efforts in Lake Ontario have resulted in an abundance of spawning fish of hatchery-origin but virtually no detectable natural recruitment. One explanation has been predation by non-native alewives (Alosa pseudoharengus) on lake trout fry. The purpose of this study was to determine if alewives could be important predators on lake trout fry. In the laboratory, fry behavior was examined to ascertain when fry would be present in the water column during a 24-hour period and to determine the acceptability of fry as food for alewives. In aquaria exposed to ambient light regimes, sac fry activity in the water column was much greater at night than during day-light hours (P < 0.001). In laboratory tanks, lake trout fry (15-34 mm) were aggressively eaten by alewives (118-175 mm). Field studies were conducted at Stony Island Reef, Lake Ontario in 1989-1993 to determine whether alewives and fry were present at the same time on the reef, if alewives fed when on the reef, and if alewives fed upon naturally-produced lake trout fry. Lake trout fry captured in traps indicated that sac and emergent fry were available as prey from the middle of April through the third week of May. The first capture of alewives in gillnets set adjacent to the fry traps was typically in early May and corresponded to the peak capture of sac fry in traps. Food was present in 86% of the 1,239 alewives captured after sunset over the 5-year period. Ten lake trout fry were found in 6 of the 62 alewives captured after sunset on 20 May 1993 at Stony Island Reef; no fry were found in alewife stomachs caught on other dates. Predation by alewives might have caused substantial mortality of lake trout fry from spawning areas in Lake Ontario where alewives were abundant and could also be an important source of mortality in similar areas of Lakes Michigan and Huron. Increased stocking of predatory salmonids to suppress the alewife could enhance survival of fry and speed restoration in Lake Ontario, but suppression seems unlikely under current strategies to manage the alewife as forage for non-native salmonids. In this context, lakewide goals should be re-focused on restoration in localized areas where alewives do not congregate during the spring and predation on lake trout fry would be minimal—such as at offshore shoals.

From clients to stakeholders: A philosophical shift for fish and wildlife management

Abstract Fish and wildlife management in North America has been experiencing a fundamental philosophical shift among professional managers and policy makers about who are the beneficiaries of management. This has been reflected in broadening notions of who should be considered in decision making; not just traditional clients who pay for and receive services of managers, but all stakeholders in fish and wildlife management. The term “stakeholder”; has emerged to represent any citizen potentially affected by or having a vested interest (a stake) in an issue, program, action or decision leading to an action. The stakeholder approach in management decision making recognizes a larger set of beneficiaries of management (including, in concept, future generations) than the traditional concepts of constituencies and clients, or customers, a term currently popular among fish and wildlife agencies. The stakeholder approach requires: (1) identification of important stakeholders, (2) flexibility in selection of method...

Behavioral Thermoregulation of Brook and Rainbow Trout: Comparison of Summer Habitat Use in an Adirondack River, New York

Abstract The body temperatures of 15 hatchery-origin and two wild brook trout Salvelinus fontinalis and 11 hatchery-origin rainbow trout Oncorhynchus mykiss were monitored with internally implanted, temperature-sensitive radio transmitters from June through September 1997 in a fifth-order Adirondack river (New York). The fish were released into a 12-km reach that during summer had maximum temperatures near those that are lethal for salmonids. Body temperatures were compared between species and with river temperatures. In 1997, the maximum river temperature was 26.4°C, and the highest average daily temperature was 25.0°C. The brook trout were usually cooler than the main river flow because they used two of five tributary confluences or groundwater discharge areas in two pools within the main river. The temperatures of the brook trout from June through September were an average of 2.3°C cooler than the main flow of the river and differed significantly (P = 0.002) from those of the rainbow trout, which were ...

Review of Genetics of Lake Trout in the Great Lakes: History, Molecular Genetics, Physiology, Strain Comparisons, and Restoration Management

This paper reviews historical differences among native lake trout (Salvelinus namaycush) populations, genetic comparisons of populations, heritability of physiological traits, performance of strains after stocking, and the role of genetics in management. Differences among lake trout were historically recognized by aborignal people, Jesuit missionaries, and French voyageurs, and later by naturalists and biologists. Lean trout represented trout that typically spawned on shallow rocky shoals. Exceptions included river spawning populations in Lake Superior and stocks reported to spawn over beds of algae in Lakes Superior and Michigan. Siscowets had high fat content, were caught in deep water, and likely spawned year-round. Humpers resembled the siscowet but had thin ventral body walls, intermediate fat content, and small size at maturity. The siscowet form and different stocks of lean trout were reported from all the Great Lakes except Lake Ontario. Data from chromosomal banding, allozyme data, and mitochondrial DNA analysis confirmed that genetic differences occur among the three forms. Genetic data also provided evidence for distinctive populations within forms. Fat content, swimbladder gas retention, and developmental rates of eggs were different among some populations and appear to be heritable. Differences among strains after stocking have occurred in survival, dispersal from stocking location, depth distribution, and reproduction. Genetic considerations have been incorporated in species restoration plans but full use has not been made of available genetic information about lake trout. Reproductive performance of different strains should be a central focus in the evaluation of stocking programs. In Lake Superior, high priority should be given to the conservation of native stocks, the last remaining gene pools of Great Lakes lake trout. Goals for management should embrace a vision that restoration is accomplished only when some level of diversity has been re-established. Achievement of restoration should require the existence of naturally-reproducing, self-sustaining populations of different lake trout forms that use a variety of habitats.

Evidence of Natural Reproduction by Stocked Lake Trout in Lake Ontario

Seventy-five lake trout fry (Salvelinus namaycush) were captured in Lake Ontario using emergent fry traps. The capture of these fry provides the first evidence of sizable natural reproduction of hatchery-origin lake trout in Lake Ontario since stocking was begun in 1973. The average catch of lake trout fry per trap in Lake Ontario (0.04 fry/trap day) was similar to that reported from Lake Huron (0.02), but lower than the catch per effort reported from Lake Michigan (0.27) and Lake Superior (0.46). Suction sampling and trawling were also conducted in the same area where fry traps were set. No fry were captured using these methods.

An Ecosystem Perspective on Re-establishing Native Deepwater Fishes in the Laurentian Great Lakes

Herein we examine scientific questions related to successful re-establishment of native deepwater fish communities in the Laurentian Great Lakes, and we (1) propose a conceptual model for native deepwater fish communities; (2) review current research and identify research hypotheses for lake trout Salvelinus namaycush, pelagic ciscoes Coregonus spp., and sculpins (Cottus spp. and Myoxocephalus spp.); (3) pose research questions emerging at community and ecosystem levels; and (4) identify high-priority research topics related to population re-establishment. The conceptual model is based on a generalized life cycle nested within processes at the population, metapopulation, community, and ecosystem levels. The conceptual model assumes that variation in population abundance is a natural phenomenon and that biodiversity contributes to ecosystem stability. Key research topics related to lake trout re-establishment include understanding recruitment variation over space and time, identifying sources of early life history mortality, determining the level of genetic differentiation among morphotypes and populations, and comparing the life history and ecology of lean lake trout with those of other lake trout morphotypes. Key research topics related to re-establishing deepwater species of cisco include resolving uncertainties in species identifications, understanding processes maintaining distinctiveness among species, understanding processes leading to cyclic and erratic recruitment, and developing effective propagation methods. Key research topics related to re-establishment of sculpin species include comparing spawning ecology and early life history of each species, determining population structure, and evaluating the feasibility of live-transfer methods. Key research topics related to community- and ecosystem-level interactions include understanding large-scale directional influences on community function, expanding current views on ecological succession in large lakes, and determining the evolutionary role of diel vertical migration in phenotypic diversification of deepwater fishes. Finally, we propose that research in four topical areas are most pertinent to re-establishing native deepwater fishes: life history bottlenecks, population and metapopulation dynamics, matching fish phenotypes to stocking sites, and propagation and stocking methods.

Phenotypic Diversity of Lake Trout in Great Slave Lake: Differences in Morphology, Buoyancy, and Habitat Depth

Abstract Little is known about the phenotypic diversity of lake trout Salvelinus namaycush in large North American lakes outside the Laurentian Great Lakes. This study tested the hypothesis that phenotypic diversity in Great Slave Lake, Northwest Territories, Canada, is associated with water depth, as was observed during similar studies of lake trout in Lake Superior. We describe the association of body size with color, buoyancy, and morphology; compare these phenotypic traits among depth strata; and establish whether lake trout phenotypes occur as discrete groups. Phenotypic diversity increased among fish longer than 43 cm standard length. In water less than 50 m deep, large lake trout (≥43 cm) were light in color, buoyantly heavy, and streamlined and possessed short pectoral fins. In water deeper than 50 m, large lake trout were dark in color, buoyantly light, and deep bodied (less streamlined) and had long pectoral fins. Without assigning descriptions to individuals before the analysis, we identified t...

Dynamics of Reproduction by Hatchery-Origin Lake Trout (Salvelinus namaycush) at Stony Island Reef, Lake Ontario

Natural recruitment from hatchery-origin lake trout in the Great Lakes has been minimal, except in Lake Superior and a few limited areas in Lake Huron. Quantitative studies of survival between egg deposition and fry emergence were conducted on a spawning reef in the eastern basin of Lake Ontario to determine variables associated with poor reproduction of hatchery-origin lake trout. Thirty to 90 mesh bags were buried in the substrate of Stony Island Reef in 1990, 1991, and 1992 to collect eggs and fry. Bags were retrieved on three dates over the six month period between the end of spawning and fry emergence. Mean egg abundance in the substrate increased significantly (P < 0.01) from 700 m−2 in 1990 to 3,572 m−2 in 1991 and 3,355 m−2 in 1992. Change in egg abundance probably resulted from an increase in the proportion of Seneca strain spawners, rather than an increase in the total number of adults in the eastern basin. Mean embryo survival from spawning to late November or early December was 45% (range, 27–57%), approximately 7.5% (range, 7.4–7.5%) to mid–April, and about 3% (range, 1.8–3.9%) to the time of emergence in mid-May. Much of the early mortality of fertilized eggs was probably due to physical shock caused by water currents during storms. Mortality later in development was caused by predation and possibly poor incubation quality of substrate along the base of the reef due to sedimentation. A life history model for lake trout in Lake Ontario was developed and parameters set with the levels of fertilization and egg-to-fry survival rate estimated in this study. Other parameters were estimated from stocking rates and previous studies. Model output indicated that the current lake trout population has the potential to produce over 1.2 million age-1 fish annually. No evidence exists for this level of recruitment in Lake Ontario. Natural recruitment may be limited by a low proportion of eggs incubating in suitable substrate and/or low survival of fry to age-1. These problems could be due to a combination of 1) a limited amount of spawning habitat, 2) ineptitude of some strains to locate or recognize spawning habitat, 3) disease-related mortality during the swim-up life stage, and 4) mortality from fish predation shortly after swim-up. Managers need to reconsider current strategies and time requirements necessary to achieve restoration goals and objectives for lake trout in Lake Ontario.

Ontogenetic niche shifts and resource partitioning of lake trout morphotypes

Resource polymorphisms are widely observed in fishes; however, ontogenetic contributions to morphological and ecological differences are poorly understood. This study examined whether ontogenetic c...