Edward L. Mills

Exotic Species in the Great Lakes: A History of Biotic Crises and Anthropogenic Introductions

Through literature review, we documented introductions of non-indigenous aquatic flora and fauna into the Great Lakes basin since the early 1800s. We focused on the origin, probable mechanism(s) of introduction, and the date and locality of first discovery of Great Lakes exotic species. The Laurentian Great Lakes have been subject to invasion by exotic species since settlement of the region by Europeans. Since the 1800s, 139 non-indigenous aquatic organisms have become established in the Great Lakes. The bulk of these organisms has been represented by plants (59), fishes (25), algae (24), and mollusks (14). Most species are native to Eurasia (55%) and the Atlantic Coast (13%). As human activity has increased in the Great Lakes watershed, the rate of introduction of exotic species has increased. Almost one-third of the organisms have been introduced in the past 30 years, a surge coinciding with the opening of the St. Lawrence Seaway in 1959. Five categories of entry mechanisms were identified: unintentional releases, ship-related introductions, deliberate releases, entry through or along canals, and movement along railroads and highways. Entry mechanisms were dominated by unintentional releases (29%) and ships (29%). Unintentional releases included escapees from cultivation and aquaculture, bait, aquarium, and other accidental releases. Ship-related introductions included ballast water (63%), solid ballast (31%), and fouling. Introductions via canals represent a small percentage of entries into the Great Lakes. We have identified 13 non-indigenous species (9%) that have substantially influenced the Great Lakes ecosystem, both economically and ecologically. The apparent lack of effects of 91 % of the exotic species in the Great Lakes does not mean that they have had little or no ecological impact. Alterations in community structure may predate modern investigations by decades or centuries, and the effects of many species have simply not been studied. As long as human activities provide the means through which future species can be transported into the Great Lakes basin, the largest freshwater resource in the world will continue to be at risk from the invasion of exotic organisms.

Bridging Troubled Waters: Biological Invasions, Transoceanic Shipping, and the Laurentian Great Lakes

Abstract Release of contaminated ballast water by transoceanic ships has been implicated in more than 70% of faunal nonindigenous species (NIS) introductions to the Great Lakes since the opening of the St. Lawrence Seaway in 1959. Contrary to expectation, the apparent invasion rate increased after the initiation of voluntary guidelines in 1989 and mandatory regulations in 1993 for open-ocean ballast water exchange by ships declaring ballast on board (BOB). However, more than 90% of vessels that entered during the 1990s declared no ballast on board (NOBOB) and were not required to exchange ballast, although their tanks contained residual sediments and water that would be discharged in the Great Lakes. Lake Superior receives a disproportionate number of discharges by both BOB and NOBOB ships, yet it has sustained surprisingly few initial invasions. Conversely, the waters connecting lakes Huron and Erie are an invasion hotspot despite receiving disproportionately few ballast discharges. Other vectors, including canals and accidental release, have contributed NIS to the Great Lakes and may increase in relative importance in the future. Based on our knowledge of NIS previously established in the basin, we have developed a vector assignment protocol to systematically ascertain vectors by which invaders enter the Great Lakes.

Exotic Species and the Integrity of the Great Lakes.

Edward L. Mills is a senior research associate in the Department of Natural Resources, Cornell University Biological Field Station, Bridgeport, NY 13030. Joseph H. Leach is a senior scientist at the Ontario Ministry of Natural Resources, Lake Erie Fisheries Station, Wheatly, Ontario, Canada NOP 2PO. James T. Carlton is a professor of marine sciences and the director of the Maritime Studies Program, Williams College-Mystic Seaport, Mystic, CT 06355, and Carol L. Secor is a graduate student in the Department of Biological Sciences, University of South Carolina, Columbia, SC 29208. Both Mills and Leach have served on a special task force on exotics for the Great Lakes Fishery Commission. Carltons research examines the global movement of exotic species resulting from ship ballast introductions. ?1994 American Institute of Biological Sciences. Cumulative effects of

Changes in the Dreissenid Community in the Lower Great Lakes with Emphasis on Southern Lake Ontario

Abstract A field study was conducted in the lower Great Lakes to assess changes in spatial distribution and population structure of dreissenid mussel populations. More specifically, the westward range expansion of quagga mussel into western Lake Erie and toward Lake Huron was investigated and the shell size, density, and biomass of zebra and quagga mussel with depth in southern Lake Ontario in 1992 and 1995 were compared. In Lake Erie, quagga mussel dominated the dreissenid community in the eastern basin and zebra mussel dominated in the western basin. In southern Lake Ontario, an east to west gradient was observed with the quagga mussel dominant at western sites and zebra mussel dominant at eastern locations. Mean shell size of quagga mussel was generally larger than that of zebra mussel except in western Lake Erie and one site in eastern Lake Erie. Although mean shell size and our index of numbers and biomass of both dreissenid species increased sharply in southern Lake Ontario between 1992 and 1995, the increase in density and biomass was much greater for quagga mussels over the 3-year period. In 1995, zebra mussels were most abundant at 15 to 25 m whereas the highest numbers and biomass of quagga mussel were at 35 to 45 m. The quagga mussel is now the most abundant dreissenid in areas of southern Lake Ontario where the zebra mussel was once the most abundant dreisenid; this trend parallels that observed for dreissenid populations in the Dneiper River basin in the Ukraine.

Predation by Alewives on Lake Trout Fry in Lake Ontario: Role of an Exotic Species in Preventing Restoration of a Native Species

Lake trout (Salvelinus namaycush) restoration efforts in Lake Ontario have resulted in an abundance of spawning fish of hatchery-origin but virtually no detectable natural recruitment. One explanation has been predation by non-native alewives (Alosa pseudoharengus) on lake trout fry. The purpose of this study was to determine if alewives could be important predators on lake trout fry. In the laboratory, fry behavior was examined to ascertain when fry would be present in the water column during a 24-hour period and to determine the acceptability of fry as food for alewives. In aquaria exposed to ambient light regimes, sac fry activity in the water column was much greater at night than during day-light hours (P < 0.001). In laboratory tanks, lake trout fry (15-34 mm) were aggressively eaten by alewives (118-175 mm). Field studies were conducted at Stony Island Reef, Lake Ontario in 1989-1993 to determine whether alewives and fry were present at the same time on the reef, if alewives fed when on the reef, and if alewives fed upon naturally-produced lake trout fry. Lake trout fry captured in traps indicated that sac and emergent fry were available as prey from the middle of April through the third week of May. The first capture of alewives in gillnets set adjacent to the fry traps was typically in early May and corresponded to the peak capture of sac fry in traps. Food was present in 86% of the 1,239 alewives captured after sunset over the 5-year period. Ten lake trout fry were found in 6 of the 62 alewives captured after sunset on 20 May 1993 at Stony Island Reef; no fry were found in alewife stomachs caught on other dates. Predation by alewives might have caused substantial mortality of lake trout fry from spawning areas in Lake Ontario where alewives were abundant and could also be an important source of mortality in similar areas of Lakes Michigan and Huron. Increased stocking of predatory salmonids to suppress the alewife could enhance survival of fry and speed restoration in Lake Ontario, but suppression seems unlikely under current strategies to manage the alewife as forage for non-native salmonids. In this context, lakewide goals should be re-focused on restoration in localized areas where alewives do not congregate during the spring and predation on lake trout fry would be minimal—such as at offshore shoals.

Impact on Daphnia pulex of Predation by Young Yellow Perch in Oneida Lake, New York

Abstract The response of a Daphnia pulex population to fluctuations in abundance of young (age-0) yellow perch Perca flavescens was examined in Oneida Lake, New York, 1975–1979. Comparison of yellow perch biomass and Daphnia pulex abundance suggested daphnid populations could tolerate predation by 10 kg of young fish˙hectare-1 but reproduction could not compensate for predation when biomass of young exceeded 20–40 kg˙hectare-1. Consumption by young yellow perch exceeded Daphnia pulex production in 1975 and 1977, when daphnids disappeared, but maximum daily consumption was less than 27% of production in 1976 when daphnids were abundant through late summer. Since 1968, D. pulex populations have persisted through late summer in years when young yellow perch were scarce and disappeared when young were abundant. The decisive role of young yellow perch in the regulation of Daphnia pulex abundance is of importance to the broader fish community in Oneida Lake.

INDIVIDUAL‐BASED MODEL OF YELLOW PERCH AND WALLEYE POPULATIONS IN ONEIDA LAKE

Predator–prey dynamics and density dependence are fundamental issues in ecology. We use a detailed, individual-based model of walleye and yellow perch to investigate the effects of alternative prey and compensatory responses on predator and prey population dynamics. Our analyses focus on the numerical and developmental responses of the predator, rather than the traditional emphasis on functional responses. The extensive database for Oneida Lake, New York, USA was used to configure the model and ensure its realism. The model follows the daily growth, mortality, and spawning of individuals of each species through their lifetime. Three ecologically distinct periods in the history of Oneida Lake were simulated: baseline, high mayfly densities, and high forage fish densities. Mayflies and forage fish act as alternative prey for walleye. For model corroboration, the three periods were simulated sequentially as they occurred in Oneida Lake. Model predictions of abundances, size at age, and growth and survival ra...

Trophic Dynamics and Development of Freshwater Pelagic Food Webs

The open water or pelagic zones of lakes are characterized by complex interactions that sometimes include edge effects from nearshore and near-bottom areas (Hutchinson 1957). The freshwater pelagia occur in water bodies ranging from small lakes to the world’s great lakes and communities inhabiting this zone are affected by small- to large-scale physical, chemical, and biological processes. Community interactions in pelagic food webs are trophically dynamic and are governed by nutrient limitation, competition, predation, and other ecological forces. Rate processes in pelagic food webs are generally faster than those in terrestrial systems (Paine 1980) and consequently producer controlled and consumer controlled trophic level interactions are more readily observed. Freshwater pelagic food webs have been studied intensively in this century and there is growing awareness of their complexity and uniqueness in aquatic ecology (Persson et al. this volume).

Energetics, Food Consumption, and Growth of Young Yellow Perch in Oneida Lake, New York

Abstract A study to determine the energy content of young (age-0) yellow perch Perca flavescens and their prey, measure metabolism, and relate energy supply and intake to fish growth was conducted in Oneida Lake, New York during the summers of 1975–1977. Growth rates in these years were similar in early summer when young yellow perch were 20 to 50 mm total length and fed almost exclusively on Daphnia pulex but varied widely in late summer when the diet was more diverse. In early summer, food intake averaged 23% of body energy content, young yellow perch assimilated about 68% of the daily ration, and gross efficiency averaged 27%. Comparison of observed growth and energy available for growth calculated from an energy budget indicated estimates of food intake and respiration were reasonable. In years when the D. pulex population collapsed in late summer, young yellow perch shifted to alternate prey and growth declined. Variation in first-year growth, mediated by D. pulex abundance, may determine the contrib...

Evidence for Remote Effects of Dreissenid Mussels on the Amphipod Diporeia: Analysis of Lake Ontario Benthic Surveys, 1972–2003

ABSTRACT The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m2 at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m2 to 63/m2 between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces.