J. Ellen Marsden

Round Goby and Mottled Sculpin Predation on Lake Trout Eggs and Fry: Field Predictions from Laboratory Experiments

The accidental introduction of round gobies (Neogobius melanostomus) into the North American Great Lakes has raised concerns about their potential impacts on local fauna. Gobies have similar habitat and spawning requirements to mottled sculpins (Cottus bairdi) and slimy sculpins (C. cognatus), and may already be displacing sculpins where the ranges of the species overlap. Like sculpins, gobies are capable of penetrating interstitial spaces to acquire food, and therefore may become predators of interstitially incubating lake trout eggs. Laboratory experiments were conducted to compare egg consumption rates and critical size (the minimum size at which a fish was capable of ingesting an egg) between round gobies and mottled sculpins. Predation by both species on lake trout eggs and fry was also examined in two grades of substrate (cobble and gravel). Mottled sculpins consumed larger numbers of eggs than round gobies of similar size, and were capable of ingesting eggs at smaller sizes than gobies. Both gobies and sculpins had lower foraging success on smaller substrates (gravel) than on cobble. Gobies are currently present at higher densities than sculpins in areas where they are established in the Great Lakes. The similar predation of lake trout eggs by round gobies and mottled sculpin and high densities the goby has achieved at some Great Lakes sites leads to the prediction that the round goby may negatively affect lake trout reproduction and therefore rehabilitation.

Progress Toward Lake Trout Restoration in Lake Michigan

Progress toward lake trout restoration in Lake Michigan is described through 1993. Extinction of the native lake trout fishery by sea lamprey predation, augmented by exploitation and habitat destruction, resulted in an extensive stocking program of hatchery-reared lake trout that began in 1965. Sea lamprey abundance was effectively controlled using selective chemical toxicants. The initial stocking produced a measurable wild year class of lake trout by 1976 in Grand Traverse Bay, but failed to continue probably due to excessive exploitation. The overall lack of successful reproduction lakewide by the late 1970s led to the development and implementation in 1985 of a focused inter-agency lakewide restoration plan by a technical committee created through the Lake Committee structure of the Great Lakes Fishery Commission. Strategies implemented in 1985 by the plan included setting a 40% total mortality goal lakewide, creating two large refuges designed to encompass historically the most productive spawning habitat and protect trout stocked over their home range, evaluating several lake trout strains, and setting stocking priorities throughout the lake. Target levels for stocking in the 1985 Plan have never been reached, and are much less than the estimated lakewide recruitment of yearlings by the native lake trout stocks. Since 1985, over 90% of the available lake trout have been stocked over the best spawning habitat, and colonization of the historically productive offshore reefs has occurred. Concentrations of spawning lake trout large enough for successful reproduction, based on observations of successful hatchery and wild stocks, have developed at specific reefs. Continued lack of recruitment at these specific sites suggests that something other than stotk abundance has limited success. Poor survival of lake trout eggs, assumed to be related to contaminant burden, occurred in the late 1970s and early 1980s, but survival has since increased to equal survival in the hatchery. A recent increase in lamprey wounding rates in northern Lake Michigan appears to be related to the uncontrolled build-up of lampreys in the St. Marys River a tributary of Lake Huron. If left uncontrolled, further progress toward restoration in the Northern Refuge may be limited.

Lake Trout Spawning Habitat in the Great Lakes — a Review of Current Knowledge

Abstract We review existing information on lake trout spawning habitat, which might indicate whether habitat is now a limiting factor in lake trout reproductive success. Lake trout spawning habitat quality is defined by the presence or absence of olfactory cues for homing, reef location with respect to the shoreline, water depth, proximity to nursery areas, reef size, contour, substrate size and shape, depth of interstitial spaces, water temperature at spawning time, water quality in interstitial spaces, and the presence of egg and fry predators. Data on factors which attracted native spawners to spawning reefs are lacking, due to the absence of historic data on egg deposition. No direct evidence of egg deposition has been collected from sites deeper than 18 m. Interstitial space and, therefore, substrate size and shape, appear to be critical for both site selection by adults and protection of eggs and fry. Water quality is clearly important for egg incubation, but the critical parameters which define water quality have not yet been well determined in the field. Exposure to wave energy, dictated in part by reef location, may maintain high water quality but may also damage or dislodge eggs. The importance of olfactory cues, water temperature, and proximity to nursery habitat to spawning trout is unclear. Limited data suggest that egg and fry predators, particularly exotic species, may critically affect fry production and survival. Although availability of physical spawning habitat is probably not limiting lake trout reproduction, changes in water quality and species composition may negatively affect early life stages. This review of habitat factors that affect early life stages of lake trout suggests several priorities for research and management.

Decline of Yellow Perch in Southwestern Lake Michigan, 1987–1997

Abstract The abundance of yellow perch Perca flavescens in southwestern Lake Michigan declined severely in the 1990s, after state and federal agencies noted a lakewide paucity of age-0 yellow perch in 1989. Regulations were changed in 1995 to reduce recreational and commercial fishing harvests, and commercial fisheries were closed lakewide in 1997. To document changes in the yellow perch population and to evaluate possible causes of the decline, we examined data collected annually in the Illinois waters of Lake Michigan during 1987–1997. Larval yellow perch were collected with plankton nets, age-0 yellow perch were collected with bottom trawls, and adult yellow perch were collected with fyke nets and gill nets. Age-0 yellow perch were rare or absent after 1988; however, larval abundance did not decline severely until after 1993. The presence of larvae and the almost complete absence of age-0 yellow perch in 1989–1993 suggest that overfishing was not initially responsible for the decline. The length at age...

Exotic Species in Lake Champlain

ABSTRACT The Lake Champlain basin contains substantially fewer exotic species (N=48) than the Great Lakes (N>180), in part due to its isolation from commercial traffic. Exotic species have been introduced by authorized and unauthorized stocking, bait buckets, use of ornamental plants, and through the Champlain and Chambly canals that link the lake to the Hudson River, Mohawk River, Erie Canal, and the Great Lakes. Several species, such as water chestnut and zebra mussels, have had severe ecological, economic, and nuisance effects. The rate of appearance of new species increased in the 1990s, potentially as a result of increasing activity in the basin, improved water quality in the Champlain Canal, and increased sampling. Efforts to slow the introduction of new species have focused on public education and legislation to reduce bait bucket introductions and quarantine undesirable plants; however, the major remaining vector for introductions is the Champlain Canal. An estimated 20 species have entered the lake via canals, of which at least 12 used the Champlain Canal, and numerous species in the connected drainage systems could still enter via this route; some are already in the Erie Canal. Most recently (2008), the Asian clam was discovered two locks below Lake Champlain. The Lake Champlain canals also function as a conduit for exotic species exchange between the Hudson River, St. Lawrence River, and Great Lakes. The potential for future introductions could be reduced by a biological barrier on the Champlain Canal, and additional emphasis on public education.

Spawning Substrate Preferences of Yellow Perch along a Sand–Cobble Shoreline in Southwestern Lake Michigan

Abstract Yellow perch Perca flavescens in small lakes generally spawn in nearshore areas on rooted macrophytes and submerged brush; however, such materials are absent near many wave-swept shorelines of the Great Lakes. We examined substrate selection by spawning yellow perch in southwestern Lake Michigan. Adult yellow perch were sampled using fyke nets during 1994–1998 at nine sites near Lake Bluff, Illinois. Substrate type at these sites was either cobble, sand, or mixed cobble and sand. Relative densities of yellow perch were higher at sites with cobble substrate than at sites with sand or mixed substrates in all but one year of the study. We conclude that, in areas devoid of vegetation or woody debris, the distribution of spawning yellow perch is nonrandom with respect to substrate type. Information about spawning-site characteristics may permit fishery managers to protect spawning yellow perch by establishing refuges. Substrate type should also be considered when permitting habitat alterations, such a...

Comparison of Otolith and Scale Ages for Yellow Perch from Lake Michigan

The age composition of the yellow perch (Perca flavescens) population in Lake Michigan is assessed annually by five management agencies, but all agencies do not use the same structure to estimate ages. The reliability of the most commonly used structure, scales, has not been formally evaluated for this population. We compared ages estimated by three readers from scales and sagittal otoliths for 150 yellow perch from southwestern Lake Michigan. The maximum age of yellow perch determined from scales and otoliths was 12. Otoliths had better precision (reproducibility) and usually had more annuli than scales for all three readers. Scale ages were usually younger than otolith ages when otolith ages were ≥ 7. Chi-square tests revealed significant differences (P < 0.05) between the age distributions determined from scales and otoliths for two of the three readers. We recommend use of otoliths for aging Lake Michigan yellow perch greater than 150 mm in length because of greater precision, easier readability, and detection of more annuli.

Sea Lamprey Control in Lake Champlain

Abstract In 1990, the United States Fish and Wildlife Service (USFWS) and state agencies initiated an 8-year experimental sea lamprey ( Petromyzon marinus ) control program on Lake Champlain to reduce parasitic phase sea lamprey and increase sport fish survival and growth. Twenty-four 3-trifluoromethyl-4-nitrophenol (TFM) treatments were conducted on 13 tributary systems, and nine Bayluscide treatments were conducted on five deltas. Most tributaries received two rounds of treatment, 4 years apart. Trap catches of spawning-phase sea lamprey in three monitored tributaries declined by 80–90% from 1989 to 1997, but nest counts were reduced by only 57% during the same period. Sixteen of 24 TFM treatments reduced ammocoetes to less than 10% of pre-treatment levels. Eight of nine Bayluscide treatments resulted in mean ammocoete mortality rates over 85% in caged test animals. Nontarget effects were noted among amphibians, mollusks, macroinvertebrates, native lamprey, and other fishes, and were higher for Bayluscide treatments than TFM. Recovery of delta taxa occurred within 4 years after treatment. Wounding rates on lake trout and Atlantic salmon were reduced in the Main Lake basin. Catches-per-unit-effort (CPUE) and estimated angler catch of lake trout increased. A moderate (25%), statistically significant increase in survival of 3–4 yr lake trout was noted. Returns of Atlantic salmon (Salmo salar) to tributaries increased significantly after treatment, and there was an estimated 3-fold increase in returns to the Main Lake sport fishery. Angler catches of brown ( Salmo trutta ) and rainbow trout ( Oncorhynchus mykiss ) were higher in 1997 than in 1990. Economic analysis of the program indicated a 3.5:1 economic benefit: cost ratio. Results indicate that the experimental control program was successful, and provide justification for continuing sea lamprey control on Lake Champlain.

Differences in Reproduction among Hatchery Strains of Lake Trout at Eight Spawning Areas in Lake Ontario: Genetic Evidence from Mixed-Stock Analysis

The restoration of self-sustaining populations of lake trout to the Great Lakes has involved stocking multiple hatchery strains of lake trout. To determine whether reproductive success varied among strains, embryos and fry from three sites in the eastern basin and four sites in the western basin of Lake Ontario were genetically characterized with allozyme electrophoresis at 18 polymorphic loci. These data and data from previous studies were used to estimate by mixed-stock analysis (MSA) the strain composition of parents that contributed to the embryo and fry mixture samples. In the eastern basin of Lake Ontario, the parental contributor to embryos and fry at three of the four spawning sites was primarily the Seneca strain (73–95%); Superior/Killala and Manitou strains contributed to a lesser extent (0–13%) and the Clearwater and Jenny strains were nearly absent from the estimates (< 2%). Strain contributions at the fourth eastern spawning area were different: Seneca–10%, Superior/Killala–43%, Manitou–43%, Clearwater–2%, and Jenny–1%. In the western basin, parental contributors to embryos were similar at three spawning sites; Seneca and Superior/Killala each contributed 33–48% with the balance divided among the other three strains. At the fourth western spawning area, the Seneca strain was absent, and contributions from the Clearwater, Manitou, and Superior/Killala strains each varied between 15 and 44% depending upon the year. Differences in strain composition among lake trout embryos from spawning sites 10–50 km apart and the temporal consistency of strain compositions at two sites where embryos or fry were collected over 3–7 years indicated that the criterion adult fish used to select spawning sites varied among strains. The Superior/Killala strain consistently contributed less than lake-wide stocking rates predicted, but the Seneca strain usually contributed more. Contributions from the Jenny, Manitou, and Clearwater strains were inconclusive because of low expected and observed values. The Seneca strains greater overall contribution indicates that stocking more of the Seneca strain may increase the potential for natural reproduction. The minimal contribution of the Seneca strain at two of the eight spawning sites, however, suggests that other strains should continue to be stocked to make use of spawning habitat not used by the Seneca strain.

Lake Trout Reproduction in Lake Champlain

Abstract Native lake trout Salvelinus namaycush were driven to extirpation in Lake Champlain in the early 1900s. Possible causes include overharvest, predation on adults by sea lamprey Petromyzon marinus, and predation on fry by rainbow smelt Osmerus mordax. Efforts to restore a lake trout fishery began in 1972 when a coordinated stocking program was initiated. Attempts to control sea lamprey populations began in 1990. Despite these management actions, reproduction by stocked fish has not resulted in large, naturally produced year-classes. This is the first formal study to quantitatively assess the level of natural reproduction by lake trout in Lake Champlain. In 2000–2002, we located 14 potential lake trout spawning sites and evaluated the habitat characteristics and level of spawning activity at each site. Passive egg collectors revealed that eggs were deposited at 8 of 14 sites, egg abundance ranging from 1.9 to 9,623 eggs/m2. In 2001 and 2002, lake trout fry were collected in emergent fry traps at thr...