James A. Hoyle

Alternative Ecological Pathways in the Eastern Lake Ontario Food Web—Round Goby in the Diet of Lake Trout

ABSTRACT Round goby (Neogobius melanostomus) range expansion and their possible inclusion in the diet of lake trout (Salvelinus namaycush) were investigated. Fish community index bottom trawls in eastern Lake Ontario (Kingston basin) during summer 2003 and 2004 indicated the presence of the round goby at relatively low densities (3.72 × 10−2 ± 5.24 × 10−3 fish/m2) in depths up to 30 m. Lake trout (mean fork length = 585 ± 78 mm and mean weight = 2,770 ± 1,134 g) stomach contents showed round goby to be the second most abundant diet item at almost 20% by number (36% by mass). Round goby ingested by lake trout ranged in total length from 50 to 110 mm. The most important prey species in terms of abundance (68%) and mass (56%) was alewife (Alosa pseudoharengus). Alewives were the most important diet item for all sizes of lake trout sampled, except those in the 550 - 650 mm size class, which ingested more round goby by mass than alewife. Round goby range expansion to deep water and prominence in the diet of lake trout signal significant change in the eastern Lake Ontario food web.

Comparison of Lake Whitefish (Coregonus clupeaformis) Growth, Condition, and Energy Density between Lakes Erie and Ontario

ABSTRACT Patterns in abundance, growth, and condition of lake whitefish (Coregonus clupeaformis) from Lake Erie were compared with those from Lake Ontario. Discontinuous assessment data were available from 1972 to 2003 for each lake to describe abundance, growth, and condition, while a seasonally intensive field program was undertaken in 2003 to describe diet, energy density, and gonadosomatic index (GSI). Through time, abundance declined more in Lake Ontario than in Lake Erie. Length-at-age (growth) and condition both declined significantly in Lake Ontario but did not change in Lake Erie. Diet analysis revealed chironomids, dreissenid mussels and sphaeriids made up the bulk of lake whitefish diet in Lake Erie. Diet in Lake Ontario exhibited more seasonal variability with amphipods and gastropods comprising the bulk of the spring and fall diets, and dreissenid mussels dominating summer diets. Lake whitefish energy density (J/g wet mass) was significantly higher in Lake Erie than in Lake Ontario, increasing with body mass and strongly correlated with water content. Female gonadosomatic index was also significantly greater in Lake Erie than in Lake Ontario. Biological attributes of lake whitefish from Lake Erie did not change greatly from the late 1980s to 2003 while fish from Lake Ontario exhibited decreased size-at-age and condition likely due to decreased energy content of diets compared to pre-dreissenid mussel conditions, and possibly lower availability of benthic prey compared to Lake Erie.

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.

Fish community indices of ecosystem health: How does the Bay of Quinte compare to other coastal sites in Lake Ontario?

The Index of Biotic Integrity (Minns et al., 1994) was used to evaluate ecosystem health in the Bay of Quinte, Lake Ontario. Despite being classified an Area of Concern (AOC) in 1985, Index of Biotic Integrity (IBI) values at Bay of Quinte fell within the range or exceeded values from reference locations elsewhere in Lakes Ontario and Erie. Fish survey data collected from 1988–2009 in the Bay of Quinte and elsewhere indicated that (1) the Bay of Quinte has relatively healthy fish habitat despite the AOC designation, (2) Bay of Quinte IBI scores increased significantly between 1990 and 1999 due to changes in relative species richness and (3) differences in fish communities were correlated with physical habitat attributes at survey locations. Data from both nearshore electrofishing and trap net surveys confirmed that the Bay of Quinte supports a highly productive and diverse fish community.

Reappearance of Deepwater Sculpin in Lake Ontario: Resurgence or Last Gasp of a Doomed Population?

ABSTRACT Deepwater sculpin (Myoxocephalus thompsonii) were abundant in Lake Ontario in the 1920s and at least common into the 1940s. By the 1960s they were rare and, thereafter, some considered the population extirpated even though a synoptic survey of the lake in 1972 produced three, relatively large (148–165 mm total length, TL), and presumably old, specimens from the northern half of the lake. Deepwater sculpin were absent from annual survey catches in the 1980s and did not reappear until 1996, when three were caught in northern Lake Ontario. Isolated collections of deepwater sculpin continued during 1998–2004. Catches during 1996–2004 included five smaller individuals, 89–118 mm TL. In 2005, catches increased sharply, with 18 deepwater sculpin collected from southern waters and one from northern waters. Moreover, young, small sculpin were dominant in 2005—16 of the 19 sculpins averaged 68 ± 12 mm total length (± 1 s.d.). The young fish observed since 1996 could have originated from reproduction by the small in-lake population, from downstream drift of planktonic larvae from Lake Huron, or both. The presence of juveniles is a clear sign that conditions for survival of young deepwater sculpin are becoming more favorable, perhaps because of reduced abundance of alewife (Alosa pseudoharengus), a pelagic planktivore linked to depression of deepwater sculpin in Lake Michigan, and also low abundances of burbot (Lota lota) and lake trout (Salvelinus namaycush), benthic piscivores.

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.

Larval Lake Whitefish abundance, diet and growth and their zooplankton prey abundance during a period of ecosystem change on the Bay of Quinte, Lake Ontario

Studies to examine larval Lake Whitefish (Coregonus clupeaformis) abundance, diet composition and growth, and the abundance of their zooplankton prey were conducted during eight years (1991–1993, 1995–1996 and 2003–2005) over the course of two decades that spanned a period of major ecosystem change—primarily dreissenid mussel related impacts—on the Bay of Quinte, northeastern Lake Ontario. Larval fish were captured in shallow, nearshore waters (0.2–2.0 m) from early April to mid-May each year. Larval Lake Whitefish fed primarily on cyclopoid copepods and small-bodied cladocerans. The key finding of our studies was that prey abundance declined by 89% from the earlier (1991–1993, 1995–1996) to the later (2003–2005) sampling years. Larval fish growth during spring was significantly correlated with prey availability. Recruitment to the juvenile stage in August was correlated with spring prey availability and larval fish growth. The observed decline in larval Lake Whitefish prey in the Bay of Quinte may be contributing to poor stock performance during and following a period of significant ecosystem change.

The Bay of Quinte: a model for large lake ecosystem management

Ecosystemmanagementoranecosystemapproachtomanage-ment has received a lot of attention in the fisheries literatureover the past decade; however, the ecosystem approach hasbeenappliedintheGreatLakesformuchlonger(Christieetal.1986).Theecosystemapproachwasarticulatedinthe1978revisiontotheGreatLakesWaterQualityAgreementandhasbeenadrivingconceptinthemanagementoftheGreatLakes.Eventhoughtheecosystemapproachhasbeenprominentinthescienceandmanagement oftheGreatLakesformorethan30years, much of the recent literature on the approach has beenaimedatapplyingtheecosystemapproachtofisheriesmanage-ment. Here we briefly identify some of the main componentsofanecosystemapproachtomanagement(whetheritisman-agementoffisheries,habitat,orlargelakes),identifyhowsci-ence contributes to this process, and then present the Bay ofQuinte as a model of the benefits of taking an ecosystemapproach to research in support of management.

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.