Mary T. Negus

Bioenergetics Modeling as a Salmonine Management Tool Applied to Minnesota Waters of Lake Superior

Abstract Lake Superiors fish community has undergone dramatic changes since the mid-1950s, with major shifts in the forage base, invasion of exotics, and decline of lake trout Salvelinus namaycush. Predator species have been introduced, and many of these are maintained by stocking. The impact of these stocked fish on the forage base and the ability of the forage base to sustain projected stocking levels are unknown. Bioenergetics modeling is a particularly useful tool for coordinating data to answer questions about predator–prey dynamics, stocking quotas, and forage requirements. This study focused on the Minnesota waters of Lake Superior to gain perspective on the impact of fish stocked by Minnesota and to serve as a basis for future expansion of the analysis to all parts of the lake. The objectives of this study were to compile data on the major salmonines in Minnesota waters of Lake Superior for use in a bioenergetics model, to estimate salmonine predation on prey populations through modeling simulati...

Retention and Nonlethal External Detection of Calcein Marks in Rainbow Trout and Chinook Salmon

Abstract An osmotic induction method was used to apply calcein marks to Chinook salmon Oncorhynchus tshawytscha and the Kamloops strain of rainbow trout O. mykiss (both migratory strains used for stocking into tributaries of Lake Superior). Preliminary exposure to a saline solution followed by immersion in a 0.5% calcein solution encouraged rapid infusion of calcein into fish tissues. Four-month-old Chinook salmon were exposed to a 1.5% or 5.0% salt solution to evaluate tolerance of different salinities and effects on mark intensity and retention. Rainbow trout were marked at three ages (2 weeks, 3.5 months, and 16 months posthatch) to evaluate the effects of age at treatment on mark intensity and long-term retention (a 5.0% preliminary salt bath was used). External detection of marks in scales, head, and fin rays was accomplished with a hand-held detector. The marking technique we used was well tolerated by both Chinook salmon and rainbow trout, and marks persisted into adulthood for rainbow trout treate...

Bioenergetics Evaluation of the Fish Community in the Western Arm of Lake Superior in 2004

Abstract Lake Superiors fish community continues to change as a result of the recovery of populations of lake trout Salvelinus namaycush, the naturalization of introduced salmonids Oncorhynchus spp. and Salmo spp., declines in the populations of rainbow smelt Osmerus mordax, and the fluctuating recruitment of cisco Coregonus artedi. This study used bioenergetics modeling of the dominant predator fish in the western arm of Lake Superior in 2004 to provide a comprehensive picture of the relationship between predator demand and prey fish availability. The results, presented for nearshore and offshore areas and three geographically distinct ecoregions, indicate that the western arm is at or near its carrying capacity for predators. Estimated predator demand was about one-half the annual biomass plus production of coregonines but exceeded the biomass plus production of rainbow smelt, possibly because of underestimates of this species in shallow areas and recent shifts in predator diets. Lean lake trout were r...

Interactions between Stocked Walleyes and Native Yellow Perch in Lake Thirteen, Minnesota: A Case History of Percid Community Dynamics

Abstract Studies of interactions among percids are important for understanding the fish community consequences of using stocking as a management tool and for understanding the ecological role of percids in lakes where they are native species. Percid community responses to discontinuing, then resuming, the stocking of walleye Sander vitreus were monitored in Lake Thirteen, Minnesota, a north temperate lake with a long-term history of walleye fry stocking. Fish population assessments during 1986–2002 tracked changes in relative abundance, size structure, and growth rates of yellow perch Perca flavescens and walleyes in response to discontinued walleye stocking during 1989–1996. Large changes occurred in the size structure and relative abundance of walleyes. The effect of discontinued stocking was to decrease the abundance of younger age-classes of walleyes in the lake. Reduced predation on small yellow perch allowed their numbers to increase and led to reduced growth rates while stocking was discontinued. W...

Determination of Smoltification Status in Juvenile Migratory Rainbow Trout and Chinook Salmon in Minnesota

Abstract The progress of smoltification was quantified with an enzyme assay (gill sodium-potassium-activated adenosine triphosphatase, or “Na+, K+-ATPase,” activity) in nonnative populations of migratory salmonines that are stocked or naturally spawned in Minnesota tributaries of Lake Superior. This information was needed to develop stocking strategies that would maximize imprinting at intended locations and to determine the causes and consequences of early emigration in stream-reared fish. Species and strains tested included (1) chinook salmon Oncorhynchus tshawytscha during hatchery rearing and after stocking, (2) two strains of O. mykiss—steelhead (naturalized) and a Kamloops (hatchery) strain of migratory rainbow trout—during hatchery rearing and after stocking, and (3) stream-reared steelhead emigrants captured in smolt traps. The ATPase activity level that distinguished smolts from nonsmolts was 11 μmol Pi · (mg protein)−1 · h−1 for chinook salmon and 10 μmol Pi · (mg protein)−1 · h−1 for all groups...

Survival Traits of Naturalized, Hatchery, and Hybrid Strains of Anadromous Rainbow Trout during Egg and Fry Stages

Abstract Two strains of anadromous rainbow trout Oncorhynchus mykiss, naturalized steelhead and “kamloops” (not the pure Kamloops strain from British Columbia, hence not capitalized) currently inhabit the Minnesota waters of Lake Superior and may have the potential to hybridize. This could compromise the genetic integrity of the naturalized steelhead population. Both strains are supplemented by annual stocking, despite the fact that the steelhead population reproduces naturally. Egg viability and fry behavior experiments were undertaken to evaluate the potential for hybridization and to provide information for future management of the two strains. The kamloops eggs were slightly smaller, but sizes overlapped substantially with steelhead egg sizes. Mortalilty of kamloops eggs from spawning to hatching was greater than steelhead eggs. Steelhead fry exhibited a greater fright response (wariness) than kamloops fry when startled by movement over their tanks. Hybrid egg survival and wariness traits were interme...

Thermal Marking of Otoliths in Lake Trout Sac Fry

Abstract The ability to distinguish hatchery-produced lake trout Salvelinus namaycush from their wild counterparts is essential for evaluation of restoration efforts in Lake Superior. However, when early life history stages are stocked, conventional external marking procedures are inappropriate. The use of thermal marks in otoliths has become an accepted procedure for fry of Pacific salmon Oncorhynchus spp., but knowledge of the technique with lake trout fry is limited. This study adds to existing knowledge of thermal marking with insight into factors that affect lake trout. Several thermal marking regimes with lake trout sac fry were evaluated by varying the number, range, duration, and spacing of temperature pulses. Pulses produced individual bands on otoliths that together constituted the mark. Mark visibility varied within treatments, but in general, the highest quality marks were achieved when fry were subjected to pulses of 10°C or higher for 8 h or more on alternate days. These marks were visible o...

Rates of Intraperitoneal Temperature Change in Lake Trout Implanted with Archival Tags

Abstract The rates of change in the intraperitoneal temperature of lake trout Salvelinus namaycush weighing between 817 g and 2,230 g were examined in the laboratory. Nine lake trout implanted with archival tags were moved between three tanks containing different water temperatures. The intraperitoneal temperatures recorded by the archival tags lagged behind the external temperatures when these thermal changes were encountered, but the smallest fish shifted temperature about twice as fast as the largest fish. The rate of core temperature change can be described by Newtons law of cooling, which states that the rate of temperature change of an object is proportional to the difference between its own temperature and the ambient temperature. This time lag can provide ample opportunity for fish to make brief forays into water temperatures outside an optimal range, while experiencing minimal change in intraperitoneal temperature. The relationship between the rate of temperature change and body mass varies with...

Contribution of Lake Trout Stocked as Fry to an Adult Population in Lake Superior

ABSTRACT Lake trout Salvelinus namaycush fry treated with heated water to create thermal marks in their otoliths were stocked at Sves Reef in Minnesota waters of Lake Superior in 1994, 1995, and 1996. These fish began to reach maturity in 2000, and were vulnerable to annual assessment gill nets set at several locations along the Minnesota shoreline. Captured fish also included fin-clipped lake trout stocked as yearlings, and naturally reproduced (wild) lake trout. Otoliths from 3106 undipped lake trout were aged and examined for thermal marks from 2000 to 2007, of which 1152 were from the target year classes (1994–1996). Thermal marks were found in otoliths from 64 fish, or 5.6% of those in the target year classes, demonstrating that stocked fry contributed to the adult lake trout population in Minnesota waters. Although numbers of recaptured fish were too low to demonstrate statistically significant differences, higher recapture rates of marked fish at Sves Reef in fall and spawning assessments suggest that these fish may have imprinted at the stocking location and homed back to this area to spawn. Wild lake trout populations in Lake Superior may be approaching fully rehabilitated levels, but recovery in the lower Great Lakes has progressed more slowly, and evidence of success with fry stocking could benefit those populations.

Simulating Effects of Nonintrogressive Hybridization with a Stocked Hatchery Strain of Rainbow Trout on the Sustainability and Recovery of Naturalized Steelhead Populations in Minnesota Waters of Lake Superior

Abstract A model was developed to explore the impacts of nonintrogressive hybridization with a stocked hatchery strain of rainbow trout Oncorhynchus mykiss (Kamloops strain [KAM]) on the sustainability and recovery of naturalized steelhead (anadromous rainbow trout) populations in Minnesota tributaries of Lake Superior. The model was used to assess the extinction risk of Lake Superior steelhead over a 50-year period based on multiple KAM stocking scenarios, initial population sizes, and levels of assortative mating. No extinctions occurred in simulated steelhead populations regardless of initial size after a one-time introduction of KAM; however, the risk of extinction due to nonintrogressive hybridization increased dramatically for scenarios involving annual stocking of KAM. The level of assortative mating among KAM and steelhead greatly influenced the risk of steelhead population decline or extinction for all scenarios. Results of the model support the contention that nonintrogressive hybridization coul...