Bryan A. Henderson

Restoration of Lake Trout in Parry Sound, Lake Huron

Abstract The purpose of this study was to explain how a series of management actions facilitated the restoration of lake trout Salvelinus namaycush in Parry Sound of Lake Huron. Since 1988, the relative abundance of wild spawning lake trout has increased in Parry Sound. Estimates of the spawning population (1994–1997) varied between 16,000 and 29,000 individuals. This increase in abundance was achieved by controlling sea lampreys Petromyzon marinus (1960), stocking yearling lake trout derived from the remnant stock (1981–1997), creating a refuge (1987), restricting harvest by reducing both angling seasons and possession limits (1981), and imposing a size limit for retention (1994). By 1997, the three criteria of successful restoration were achieved, that is, the average age of mature females was 1 year older than the age of first maturation, wild fish composed 50% of the spawners, and the abundance of wild lake trout had been stable or increased for three consecutive years. As a consequence, stocking of y...

Recruitment of Yellow Perch (Perca flavescens) Affected by Stock Size and Water Temperature in Lakes Erie and St. Clair, 1965–85

Two influences on recruitment of yellow perch (Perca flavescens) were considered: parental stock size and spring water temperatures. The data for this analysis were obtained from two sources. First, from samples of trawl catches (near bottom) from April to October (1965–85) in the western, central, and eastern basins of Lake Erie, and from Lake St. Clair and second, from gillnet catches from April to July in the three basins of Lake Erie (1978–86). The relative abundances (CPUE) of stocks in these study areas were as follows: western > St. Clair > eastern > central basin. Degree-days and mean water temperatures of the basins were ranked as follows: St. Clair > western > central > eastern basin. Rates of warming of water were greatest in the western basin, followed by St. Clair, central basin, and eastern basin. The rates of increase in water temperature (April to June) were positively related to average water temperatures and total degree-days (above 0°C. Only in the western basin of Lake Erie could the variations in recruitment to age 1+ be apportioned to the effect of parental stock size (12%) and water warming in the spring (51%). Recruitment at age 0+ (young-of-year(YOY)) was explained also by both warming rate (17%) and parental stock size (12%) for the samples from the western basin. The pooled data obtained from samples of catches in the gillnets indicated that only parental stock size (19%) determined the abundance of perch at age 1+ yrs-old. The relative abundance of yearlings was related to the abundance of YOY perch in the previous year in only the central and western basins (trawl sample). The dependence of recruitment on the density of the parental stock was evident from the regression of the ratio of recruits (age 1 +) to spawners on parental stock size in the combined trawl samples from Lakes Erie and St. Clair, and in the separate samples from the eastern and central basins of Lake Erie and Lake St. Clair. Similarly, recruitment at age 0+ (YOY) was also shown to be density-dependent in all but the western basin of Lake Erie. The coefficients obtained by regressing recruitment (0 +, 1 + years) on stock size were significant and less than 1 in the pooled sample from the western basin and St. Clair, indicating density-dependent recruitment.

Phenotypic differences in buoyancy and energetics of lean and siscowet lake charr in Lake Superior

At least two phenotypes of lake charr, Salvelinus namaycush, coexist in Lake Superior. A lean morph frequents the shallow inshore waters (< 50 m) and the fat morph (siscowet) occupies the deeper offshore waters (50–250 m). The objective of this study was to determine if the elevated lipid concentration of siscowets reduces the costs of swimming in deep water. First, we modelled the effects of body composition (lipids) on the costs of swimming by lake charr, and then compared these theoretical results with empirical evidence obtained from Cesium 137-based estimates of food consumption, gross energy conversion, and swimming costs (activity multiplier). The attributes of growth, energy content (kJ g-1), lipid concentrations, and Cesium 137 concentration (Bq g-1) were obtained from multimesh gillnet catches in eastern Lake Superior (1998 and 1999). The model showed that siscowet (fat) lake charr expended less energy than lean lake charr moving through the water column. Empirical evidence derived from Cesium 137 analysis confirmed that the activity multipliers of siscowets (fat) were less than those for lean charr. These findings support the view that the restoration of the fish community of the predominately deep water of the Great Lakes might be facilitated by the introduction of the fat phenotype.

Factors Affecting Recruitment and Mortality Rates of Rainbow Smelt (Osmerus Mordax) in Lake Erie, 1963–85

Abstract Recruitment of young-of-the-year (YOY)rainbow smelt ( Osmerus mordax ) per parent was nqt dependent upon water temperature (rate of warming and average temperature) during spawning, Glugea infestation, or parental stock-size. Only in the eastern basin of Lake Erie was recruitment to age 1 + years-old positively correlated with the YOY index in the preceding summer. Recruitment of age 1 + year-old smelt was not related to parental stock-size. Recruitment (age 1 + years-old) per spawner was inversely related to the abundance of age 1 year-old smelt present during the year of hatch in both the eastern and central basins of Lake Erie. This could be taken as evidence to support the hypothesis that the alternating dominance of year-classes (1963–74) was caused by cannibalism of YOY by age 1 year-old smelt. After 1974, alternating year-class-dominance was not evident; we considered three possible explanations for the absence of strong year-classes. First, the size at age declined in both basins during the study so that more age classes could have fed optimally on young-of-year (YOY), resulting in a poorer survival of YOY smelt. Second, the harvest of smelt increased greatly after 1974, particularly for yearling smelt, so that year-class strength measured by the abundance of yearlings was reduced by fishing. Third, predation on smelt by stocked salmonids probably increased after 1974 as the stocking rates increased. Adult total mortality rates (ages 2 and 3 years-old) were positively related to stock density providing some evidence for density dependent mortality of smelt. There was no evidence that the variations in adult mortality were associated with the incidence of Glugea .

Comparison of Catches in Mono- and Multifilament Gill Nets in Lake Erie

Abstract The purpose of this study was to compare the number, age, sex, and size offish caught in mono- and multifilament gill nets used to assess populations in Lake Erie, The results of this study could be used to adjust estimates of catch per unit of effort if there were a change from multifilament to monofilament gill nets. More yellow perch Perca flavescens (ratio of catches in mono- and multifilament gill nets = 2.04/1), white bass Morone chrysops (2.78/1), white perch Morone americana (2.07/1), freshwater drums Aplodinotus grunniens (2.93/1), walleyes Stizostedion vitreum (1.92/1), and white suckers Catostomus commersoni (1.23/1) were caught in monofilament gill nets. Only rainbow smelt Osmerus mordax and silver chub Macrhybopsis storeriana were more catchable in multifilament nets. There was some evidence that white perch and freshwater drum saturate monofilament gill nets more than multifilament nets. Age, size, and gender compositions of the catches were similar for both gears. Previously, catch...

Yellow Perch (Perca Flavescens) Growth and Mortality Rates in Lake St. Clair and the Three Basins of Lake Erie, 1963–86

Growth and mortality rates differed among the three stocks of yellow perch (Perca flavescens) examined in Lake Erie from 1978 to 1985 in samples obtained from multi-mesh gillnets set in May and July. Growth rates were significantly greater in the central basin than in either the western or eastern basins for yellow perch sampled from four year-classes (1976–79). The lowest growth rates were found among yellow perch from the western basin in the May and July sampling periods. Pooling each age class from 1978 to 1985, we showed that perch from the central basin were usually larger at age. These differences in size at age and growth rates were not explained satisfactorily by differences in population density and water temperature among the basins but could be attributed in part to differences in primary production and fish community structure. Size at age in trawl samples tended to decline in all basins of Lake Erie and Lake St. Clair, particularly in the late 1970s and 1980s, and in the western basin and Lake St. Clair. We suggest that this decline in size may have been caused by both a decrease in primary productivity and the increase in the abundance of white perch (Morone americana). From estimations of total mortality rates derived from cohort catch curves (ages 3–6, 1975–79 year-classes) and annual changes in relative abundance, we concluded that total mortality (Z) was positively correlated with commercial fishing effort (western> central> eastern)

Yield of Yellow Perch in Lakes Erie and St. Clair: Community Associations

Abstract Commercial catches of yellow perch Perca flavescens in the Canadian gill-net fishery of Lake Erie declined in the 1970s, even though fishing effort increased and mesh size decreased between 1970 and 1975. Multiple stepwise regression of annual catch (kg) on effort (km gill net), recruitment by year-class, total fish community biomass, and weight at age 3 showed that only recruitment explained a significant portion of the variations in catches in the eastern basin, and only weight was important in the western basin. Year-class strength declined in the late 1960s and 1970s; catches from both experimental and commercial gear provided some indication of improvement by the 1980s. Although recruitment was associated with variations in the abundance of some species in four fish communities (Lake St. Clair and the three basins of Lake Erie), there was no evidence that any common groups of species were regulating recruitment. Fish community structures were similar (discriminant function analysis) in the e...

Progress Toward the Rehabilitation of Lake Trout (Salvelinus namaycush) in South Bay, Lake Huron

ABSTRACT Our objective was to evaluate the status of lake trout Salvelinus namaycush rehabilitation in South Bay, Lake Huron. Standardized surveys were conducted to quantify natural recruitment, annual mortality, and the contribution of wild- versus hatchery-origin lake trout. Some indicators suggest a high level of natural recruitment. The spawning population was comprised of multiple ages, and the mean age of spawners (8.4 years for females, 7.9 years for males) was at least 1 year older than the age at 50% maturity (5.8 years). Estimated annual total mortality rates (0.20–0.25) and sea-lamprey induced mortality rates (0.02) were less than maximum allowable values. The proportion of wild-origin fish captured was high among spawners but varied among sampling programs (42% in fall trap nets, 70% in fall gill nets, and 88% in summer gill nets). A strong year class (1997) could be tracked from 2001 to 2005. Few fish were captured from early (< 1996) or later (1999–2002) year classes. Possible explanations for low natural recruitment during these later years include declining spawning habitat quality caused by low water levels and/or invasion of non-native mussels (Dreissena spp.) and/or direct or indirect effects of alewife (Alosa pseudoharengus).

Changes in the Georgian Bay fish community, with special reference to lake trout (Salvelinus namaycush) rehabilitation

We describe and explain some of the changes in the fish community as reflected by the catches of the commercial fishery, and evaluate the efforts to restore the trout (Salvelinus spp.) in Georgian Bay. The changes in the fish community were caused in part by excessive fishing for lake trout (S. namaycush), lake whitefish (Coregonus clupeaformis) and deepwater ciscoes (Coregonus spp.), and the introduction of new species such as sea lamprey (Petromyzon marinus), alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax) and salmonids (Oncorhynchus spp.). The most striking changes were the near extinction of the lake trout, reductions in lake herring (Coregonus artedii), deepwater ciscoes and lake whitefish, and the increase in abundance of smelt and alewife. In an effort to replace the loss of yield from the cold-water habitat, a fast growing and early maturing hybrid trout (splake [S. namaycush × S. fontinalis]) and its backcross to lake trout were selectively bred for stocking in Georgian Bay. Splake did poorly because of low survival immediately after planting. The survival of backcross after planting was better, but adult mortality was still high. Adult survival of backcross improved considerably after restrictions were placed on the commercial fishery in 1984. The first naturally produced backcross larvae were collected in 1985.