James N. Bowlby

Lake Trout Rehabilitation in Lake Ontario

Attempts to maintain the native lake trout (Salvelinus namaycush) population in Lake Ontario by stocking fry failed and the species was extirpated by the 1950s. Hatchery fish stocked in the 1960s did not live to maturity because of sea lamprey (Petromyzon marinus) predation and incidental commercial harvest. Suppression of sea lampreys began with larvicide treatments of Lake Ontario tributaries in 1971 and was enhanced when the tributaries of Oneida Lake and Lake Erie were treated in the 1980s. Annual stocking of hatchery fish was resumed with the 1972 year class and peaked at about 1.8 million yearlings and 0.3 million fingerlings from the 1985–1990 year classes. Survival of stocked yearlings declined over 50% in the 1980 s and was negatively correlated with the abundance of lake trout > 550 mm long (r = −0.91, P < 0.01, n = 12). A slot length limit imposed by the State of New York for the 1988 fishing season reduced angler harvest. Angler harvest in Canadian waters was 3 times higher in eastern Lake Ontario than in western Lake Ontario. For the 1977–1984 year classes, mean annual survival rate of lake trout age 6 and older was 0.45 (range: 0.35–0.56). In U.S. waters during 1985–1992, the total number of lake trout harvested by anglers was about 2.4 times greater than that killed by sea lampreys. The number of unmarked lake trout < 250 mm long in trawl catches in 1978–1992 was not different from that expected due to loss of marks and failure to apply marks at the hatchery, and suggested that recruitment of naturally-produced fish was nil. However, many of the obstacles which may have impeded lake trout rehabilitation in Lake Ontario during the 1980s are slowly being removed, and there are signs of a general ecosystem recovery. Significant recruitment of naturally produced lake trout by the year 2000, one interim objective of the rehabilitation plan for the Lake, may be achieved.

Lake whitefish and walleye population responses to dreissenid mussel invasion in eastern Lake Ontario

We reviewed responses associated with the invasion of dreissenid mussels by two eastern Lake Ontario fish populations and the fisheries they support. Resurging lake whitefish and walleye populations declined following dreissenid mussel invasion in the early 1990s. Impacts on whitefish were associated with the loss of a key diet item, Diporeia, and its replacement with diet items of lower energy value. Impacts featured a die-off, dispersal, declines in juvenile and adult condition and growth rates, delayed age-at-maturity, and several years of reproductive failure. Impacts on walleye were consistent with dreissenid driven ecosystem change, particularly, clearer water. The key response by the walleye population was a downward shift in recruitment levels. This shift appears to be due to a change in the stock-recruitment relationship caused by decreased survival during early life (i.e. egg to 4-months), and suggests that the carrying capacity for these early life stages has diminished. Currently, whitefish reproduction has resumed and walleye reproduction appears stabilized at a lower level. Recent (i.e. 2003 and 2005) whitefish year-classes were relatively large but the fish are growing slowly and annual survival rate is not yet known. The whitefish commercial harvest continues to decline in synchrony with the declining adult whitefish population. The walleye recreational fishery (i.e. effort and harvest) has stabilized at a smaller size consistent with lower walleye year-class strength.

The Impacts of Atlantic Salmon Stocking on Rainbow Trout in Barnum House Creek, Lake Ontario

ABSTRACT We compared the impacts of stocking age-0 Atlantic salmon (Salmo salar) at high and low densities, and no stocking on abundance and growth of age-0 rainbow trout (Oncorhyncus mykiss) in Barnum House Creek, Ontario during 1993 to 2005. A similar stream, Shelter Valley Creek, was chosen as an appropriate reference stream where age-0 Atlantic salmon were not stocked. The catches of age-0 rainbow trout in Barnum House and the reference stream were highly correlated (r = 0.96) during years when no stocking occurred; however, this relationship did not persist in years when Atlantic salmon were stocked. The catch of age-0 rainbow trout in Barnum House Creek was significantly lower under both high (P = 0.00026) and low (P = 0.011) density Atlantic salmon stocking treatments compared with the no stocking treatment. The catches of age-0 rainbow trout and age-0 Atlantic salmon were negatively correlated in Barnum House Creek (r = −0.63). The length of age-0 rainbow trout in Barnum House Creek was depressed significantly (P = 0.004), under the high intensity Atlantic salmon stocking treatment, but not under the low intensity treatment (P = 0.20). In contrast, the length of age-0 rainbow trout in Shelter Valley Creek was unchanged over the same period. Restoration stocking of Atlantic salmon in Lake Ontario tributaries may impact rainbow trout abundance and growth.

Fish community structure in the Bay of Quinte, Lake Ontario: The influence of nutrient levels and invasive species

Intensive, long-term sampling in the Bay of Quinte with multiple gears (i.e. gill nets, bottom trawls, trap nets and boat electrofishing) allowed examination of the fish community and major fish populations in the context of key stressors up to 2009. Excessive nutrient input and hyper-abundant non-native fish species, White Perch and Alewife, shaped the depreciated fish community of the 1970s. After implementation of phosphorus input control measures and simultaneous winter-kills of the hyper-abundant non-native fish in the late 1970s, Walleye recovered and served to restore a predator-prey balance to the fish community by the late 1980s. However, in the absence of a significant recovery of submerged aquatic vegetation (SAV) in littoral areas, off-shore species (e.g. Alewife and White Perch) still tended to dominate; even in littoral areas. Following establishment of Dreissenid Mussels in the mid-1990s, water transparency increased and SAV increased significantly in littoral areas. This pivotal event led to a shift in the fish community that included an overall decline in Walleye, an increase followed by a decrease in Yellow Perch, and dominance by centrarchids (i.e. Bluegill, Pumpkinseed, Black Crappie and Largemouth Bass) in the nearshore. Round Goby invaded in 1999, proliferated and became important in the diet of piscivores by 2003. The current species assemblage, including the piscivores, is diverse and indicative of a healthy fish community.

Distribution and movement of Bay of Quinte Walleye in relation to temperature, prey availability and Dreissenid colonization

The spatial and seasonal distribution of walleye were surveyed with gillnets in the Bay of Quinte and Lake Ontario during 1992–2008. Walleye movements were determined with tagging in the Bay of Quinte and Lake Ontario surrounding Prince Edward County during fall 1998–2003, and with recaptures from angling and other fisheries in Lake Ontario and the St. Lawrence River during 1998–2003. Immature walleye (age <4 yr) were abundant in the upper Bay of Quinte from April to November, moved small distances down the bay during summer, and were less frequently observed in Lake Ontario. Mature walleye (age >4 yr) were found in the upper Bay of Quinte during spring, and farther down the bay during summer. Older mature walleye (age-7+) were observed in eastern Lake Ontario during summer. The tagging data were consistent in showing that older fish moved down the Bay of Quinte toward Lake Ontario during summer. During fall mature walleye moved back up the Bay of Quinte either from Lake Ontario or the lower bay. Immature and mature walleye moved farther up the Bay of Quinte during fall to spring, again with older walleye tending to move longer distances. Walleye migration between the Bay of Quinte and Lake Ontario during spring and fall was consistent with avoiding warm temperature in the upper bay, and foraging on alewife in the lower bay and Lake Ontario during summer and young-of the-year fishes such as gizzard shad during fall. The distribution of walleye between the Bay of Quinte and Lake Ontario did not change after dreissenid colonization.

The fish community of Hamilton Harbour, Lake Ontario: Status, stressors, and remediation over 25 years

Hamilton Harbour is a large (21 km2) protected harbour located at the western end of Lake Ontario that was designated as an Area of Concern in 1985 by the International Joint Commission. As part of the designation, the fish community was deemed “impaired.” One of the long-term goals of the Hamilton Harbour Remedial Action Plan is to rehabilitate the fishery to a state, at least in part, to what it was prior to the degrading effects of industrial and municipal pollution, habitat loss, and invasive species. Since the Area of Concern designation, the nearshore fish community has been monitored regularly via a federal boat electrofishing program (1988–2013) and more recently, by a trap net program (2006–2012). During the study period, the harbour underwent significant physical and biological change which was related to both lake-wide (e.g. Dreissenids) and localized harbour events (e.g. habitat restoration). The fish community was assessed temporally using two indices of ecosystem health, the Great Lakes Index of Biotic Integrity and Proportion of Piscivore Biomass, and species-specific catch trends at unaltered sites or sites modified by habitat restoration. Early on, the fish community was dominated by tolerant species characteristic of degraded, eutrophic environments and piscivore abundance was low. The fish community responded positively to ecosystem actions during the first decade that improved water quality, increased physical habitat and reduced invasive species, but further progress was confounded by the interactions with other factors in the last decade that included new invasive species and a decline in water quality. Fish community assessments in the last decade, using both the indices found that the fish community was still impaired and dominated by non-native and pollution tolerant species. The Index of Biotic Integrity was a suitable indicator of ecosystem health strengthened by a consistent assessment with the Proportion of Piscivore Biomass index. A science based refinement of the existing Index in the future would benefit the ability to assess nearshore fish assemblages in the context of conservation goals.

Verifying Identification of Salmon and Trout by Boat Anglers in Lake Ontario

Abstract We estimated how well anglers with varying levels of fishing experience identified six salmonid species during creel surveys of the boat angler fishery in Canadian waters of Lake Ontario (1995 and 1996). Anglers were asked to identify the species of their harvested salmon and trout. Angler identifications were compared with identifications made by creel survey technicians. In total, 583 noncharter anglers and 92 charter boat captains identified 1,098 and 271 fish, respectively. Chinook salmon Oncorhynchus tshawytscha, rainbow trout O. mykiss, and lake trout Salvelinus namaycush dominated the observations. The greatest accuracy in identification by noncharter anglers was for lake trout (96%), followed by Chinook salmon (93%), rainbow trout (88%), brown trout Salmo trutta (85%), Atlantic salmon Salmo salar (67%), and coho salmon O. kisutch (60%). Identifications by charter captains were closer to identifications made by the creel survey technicians: accuracy for coho salmon and rainbow trout was 10...

Developing restoration targets for nearshore fish populations in two Areas of Concern in Lake Ontario

Restoration targets for nearshore fish populations in Hamilton Harbour and Toronto Harbour–Areas of Concern–were developed. Fish were captured in trap nets at Hamilton Harbour, Toronto Harbour, and nine unimpaired embayments of Lake Ontario. Embayments were sampled at least once and up to nine times during 2006–2013. Principal components analysis indicated the fish communities in unimpaired embayments clustered into two groups. One group had larger exposure distance (opening) to Lake Ontario and larger exposure index (surface area ÷ opening), and was termed “exposed.” The alternate group was “sheltered.” Fish communities in unimpaired embayments followed an aquatic macrophyte gradient of open-water species (e.g. White Bass, Gizzard Shad) at one end and species associated with vegetative cover (e.g. Bluegill, Pumpkinseed) at the other. A second fish community gradient was correlated with embayment opening and exposure index, and may be associated with habitat stability and exchanges with colder water from Lake Ontario. Hamilton Harbour is a sheltered embayment, but principal components analysis indicated the fish community was significantly different from all other embayments, consistent with its Area of Concern status. Northern Pike and Yellow Perch were the only target species in Hamilton Harbour close in abundance to unimpaired sheltered embayments. Common Carp, Brown Bullhead, Channel Catfish, and others were an order of magnitude higher than in unimpaired sheltered embayments. Toronto Harbour is an exposed embayment, and principal components analysis indicated the fish community was not significantly different from unimpaired embayments. Likewise, the abundance of most of the target species in Toronto Harbour was close to unimpaired embayments. Walleye, Smallmouth Bass, and Rock Bass were depressed and Gizzard Shad was elevated in Toronto Harbour, compared to unimpaired embayments.

Evaluation of the Remedial Action Plan goal for dissolved oxygen in Hamilton Harbour: A goal based on habitat requirements for Cisco

The Hamilton Harbour Remedial Action Plan has adopted a dissolved oxygen goal for restoring habitat in the pelagic portion of Hamilton Harbour based on the ecological needs of Cisco (Coregonus artedii), a fish formerly abundant in Hamilton Harbour. The goal for dissolved oxygen is based on retaining an adequate volume of optimum Cisco habitat characterized as temperature <20°C and dissolved oxygen >6 mg l−1 during the June to September period. The goal also specifies minimum habitat requirements for when optimum conditions are not achieved, that being a smaller volume of refuge habitat with temperature <20°C and dissolved oxygen >3 mg l−1 for no more than 2 weeks per year. Weekly temperature and dissolved oxygen profiles during May to October, 1987 to 2012 in the center of Hamilton Harbour were assessed to evaluate optimum and refuge Cisco habitat relative to the Remedial Action Plan goal for dissolved oxygen. This goal was met only in 2009. However, this was fortuitous, based on a combination of cooler water temperatures in May and June and exchanges of cool oxygenated water from Lake Ontario. From 1987 to 2002 optimum habitat was estimated to be absent at least one week and up to seven weeks during June to September. Cisco could not have survived in Hamilton Harbour during six of these years when refuge habitat was absent for one or two weeks. Since 2003, Cisco habitat in Hamilton Harbour improved markedly, as some refuge habitat was always present. As well, the number of weeks with inadequate refuge habitat, and with no optimum habitat has declined. These improvements in Cisco habitat since 2003 were related to higher dissolved oxygen in the mid-depths of Hamilton Harbour.