David Michael Warner

United States Geological Survey | USGS

Predators can shift their diets and even selectivity in response to changing environmental conditions. Since the early 2000s, Lake Huron experienced major food-web shifts that have caused changes in the prey availability and quality for consumers at multiple trophic levels. Previous studies have reported declining energetic condition for key plankt...

Mysis diluviana is one of the most abundant zooplankton by biomass in the Laurentian Great Lakes of North America, a predator of other zooplankton and an important prey for fishes. Studies of long-term trends in Lake Michigan have shown 2005–2016 densities to be 50–80% lower than 1990s densities, but these observations have been based on annual mon...

Pelagic-oriented alewife (Alosa pseudoharengus) and benthic-oriented round goby (Neogobius melanostomus) are two important prey fish in the Laurentian Great Lakes. In 2015, we evaluated their seasonal total energy (TE) across nine Lake Michigan transects. Round goby contained at least 48% more kilojoules of TE than alewife of equal length during sp...

Variability in abiotic and biotic factors during larval stages has profound impacts on fish recruitment. In Lake Michigan, where the composition of lower trophic levels has undergone considerable changes in the past decade, managers are concerned that fish recruitment could be negatively affected. We hypothesized that spatial variation in Lake Mich...

Accurate methods to track changes in lake productivity through time and space are critical to fisheries management. Chlorophyll a is the most widely studied proxy for ecosystem primary production and has been the topic of many studies. The main sources of chlorophyll a measurements are ship-based measures or multi-spectral satellite data. Autonomou...

The vertical distribution of zooplankton can have substantial influence on trophic structure in freshwater systems, particularly by determining spatial overlap for predator/prey dynamics and influencing energy transfer. The zooplankton community in some of the Laurentian Great Lakes has undergone changes in composition and declines in total biomass...

The USGS Great Lakes Science Center has conducted integrated acoustic and mid-water trawl surveys of Lake Huron during 1997 and annually from 2004-2015. The 2015 survey was conducted during September and included transects in Lake Huron's main basin, Georgian Bay, and North Channel. Mean lake-wide total pelagic fish density was 1,313 fish/ha and me...

Using various available time series for Lake Michigan, we examined changes in the Lake Michigan food web following the dreissenid mussel invasions and identified those changes most likely attributable to these invasions, thereby providing a synthesis. Expansion of the quagga mussel (Dreissena rostriformis bugensis) population into deeper waters, wh...

The ability of planktivorous fishes to exert top-down control on Bythotrephes potentially has far-reaching impacts on aquatic food-webs, given previously described effects of Bythotrephes on zooplankton communities. We estimated consumption of Bythotrephes by planktivorous and benthivorous fishes, using bioenergetics and daily ration models at near...

A new method was developed, evaluated, and applied to generate a global dataset of growing-season chlorophyll-a (chl) concentrations in 2011 for freshwater lakes. Chl observations from freshwater lakes are valuable for estimating lake productivity as well as assessing the role that these lakes play in carbon budgets. The standard 4 km NASA OceanCol...

1. Lakes Michigan and Huron, which are undergoing oligotrophication after reduction of phosphorus loading, invasion by dreissenid mussels and variation in climate, provide an opportunity to conduct large-scale evaluation of the relative importance of these changes for lake productivity. We used remote sensing, field data and an information-theoreti...

Fish stock-recruitment dynamics may be difficult to elucidate because of nonstationary relationships resulting from shifting environmental conditions and fluctuations in important vital rates such as individual growth or maturation. The Great Lakes have experienced environmental stressors that may have changed population demographics and stock-recr...

The USGS Great Lakes Science Center has conducted integrated acoustic and mid-water trawl surveys of Lake Huron during 1997 and annually from 2004-2015. The 2015 survey was conducted during September and included transects in Lake Huron's main basin, Georgian Bay, and North Channel. Mean lake-wide total pelagic fish density was 1,313 fish/ha and me...

Reductions in nutrient loads and impacts from invasive species may lower recruitment potential of Great Lakes fishes. Filtration by invasive quagga mussels has reduced phytoplankton biomass, shifted energy flow from pelagic to benthic pathways, and restricted phosphorus transport from nearshore to offshore. Biomass of large cladocerans and adult pl...

Hydroacoustic fisheries surveys have become standard for assessment of many fish species. Such data can be used for stock assessment models, fisheries ecology, forecasting, and setting harvest levels. Lakewide acoustic survey data from Lake Michigan will be used to highlight the potential of such surveys to go beyond "just monitoring". One difficul...

Ecosystems undergo dynamic changes owing to species invasions, fisheries management decisions, landscape modifications, and nutrient inputs. At Lake Michigan, new invaders (e.g., dreissenid mussels (Dreissena spp.), spiny water flea (Bythotrephes longimanus), round goby (Neogobius melanostomus)) have proliferated and altered energy transfer pathway...

Aquatic food webs that incorporate multiple energy channels (e.g., nearshore benthic and pelagic) with varying productivity and turnover rates convey stability to biological communities by providing independent energy sources. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and potentia...

Using a Bayesian modeling approach, we developed a multispecies statistical age-structured model to assess trade-offs between predatory demands and prey productivities, with the aim to inform management of top predators. Focusing on the Lake Michigan fish community, we assessed these trade-offs in terms of predation mortalities and productivities o...

The USGS Great Lakes Science Center (GLSC) conducted acoustic and midwater trawl surveys of Lake Huron during 1997 and annually during 2004-2013. The 2013 survey was conducted during September and October and included transects in Lake Huron’s main basin, Georgian Bay, and North Channel. Pelagic fish density was 1,033 fish/ha in 2013 and increased...

Understanding the relative importance of top-down and bottom-up regulation of ecosystem structure is a fundamental ecological question, with implications for fisheries and water-quality management. For the Laurentian Great Lakes, where, since the early 1970s, nutrient inputs have been reduced, whereas top-predator biomass has increased, we describe...

Standardized methods of data collection and analysis ensure quality and facilitate comparisons among systems. We evaluated the importance of three recommendations from the Standard Operating Procedure for hydroacoustics in the Laurentian Great Lakes (GLSOP) on density estimates of target species: noise subtraction; setting volume backscattering str...

Pelagic fish assessments often combine large amounts of acoustic-based fish density data and limited midwater trawl information to estimate species-specific biomass density. We compared the accuracy of five apportionment methods for estimating pelagic fish biomass density using simulated communities with known fish numbers that mimic Lakes Superior...

Rainbow smelt Osmerus mordax represent an important prey for several recreationally valuable piscivores in the Great Lakes and support locally important fisheries throughout the region. However, rainbow smelt populations have suffered steep declines in abundance over the past two decades, which may be associated with prolonged poor recruitment succ...

Understanding trophic dynamics is essential in any ecological system. In systems with numerous invasive species this necessity is increased due to the possible deleterious effects they induce. Lakes Michigan and Superior offer not only such features with zooplankton, but also dichotomous communities of native and non-native fishes. Even though many...

Since Pacific salmon stocking began in Lake Michigan, managers have attempted to maintain salmon abundance at high levels within what can be sustained by available prey fishes, primarily Alewife Alosa pseudoharengus. Chinook Salmon Oncorhynchus tshawytscha are the primary apex predators in pelagic Lake Michigan and patterns in their prey selection...

The opossum shrimp (Mysis diluviana) is a vital component of Great Lakes food webs. Baseline data on the nutritional condition of Mysis populations are necessary to evaluate potential impacts of recent, dramatic changes in the lower food webs of lakes Michigan and Huron. Information on lipid and fatty acid content can reveal patterns of health and...

Standardization of acoustic (AC) data processing has advanced the field, but standard methods for incorporating mid-water trawl (MT) data when estimating species density are lacking. We developed a pelagic fish simulator that populated an artificial lake to mimic communities present in 3 Great Lakes. Virtual surveys mimicked data a real vessel coul...

Hydroacoustic estimates of fish density are an important aspect of fisheries monitoring and research. A Standard Operating Procedure for collection and analysis of hydroacoustic data in the Laurentian Great Lakes (GLSOP) was published in 2009 to facilitate comparisons across lakes. Here we evaluate the importance of three particular recommendations...

Fisheries acoustic assessments in the Laurentian Great Lakes have typically been conducted with single-frequency systems operating at 120 kHz. The use of a single frequency tends to limit the ability to distinguish species using scattering characteristics. Recent efforts have revealed the utility of using a combination of frequencies to distinguish...

Because it is not possible to identify species with echosounders alone, trawling is widely used as a method for collecting species and size composition data for allocating acoustic fish density estimates to species or size groups. In the Laurentian Great Lakes, data from midwater trawls are commonly used for such allocations. However, there are no...

We compared Bythotrephes population demographics and dynamics to predator (planktivorous fish) and prey (small-bodied crustacean zooplankton) densities at a site sampled through the growing season in Lakes Michigan, Huron, and Erie. Although seasonal average densities of Bythotrephes were similar across lakes (222/m2 Erie, 247/m2 Huron, 162/m2 Mich...

Since Pacific salmon stocking began in Lake Michigan, managers have attempted to maintain salmon abundance at levels near the maximum that can be sustained by available orage fishes, primarily alewife (Alosa pseudoharengus). The trophic link between Chinook salmon (Oncorhynchus tshawytscha) and alewife is among the strongest and most exclusive of s...

Mysis relicta is an important food web intermediary between phytoplankton, zooplankton, and fish and is likely a conduit for energy and nutrients between benthic and pelagic habitats. With the decline of Diporeia sp. in the Great Lakes, Mysis is now the only large, high-lipid prey item available for many fish species. A number of native and non-nat...

1. Oligotrophic lakes are generally dominated by calanoid copepods because of their competitive advantage over cladocerans at low prey densities. Planktivory also can alter zooplankton community structure. We sought to understand the role of planktivory in driving recent changes to the zooplankton community of Lake Huron, a large oligotrophic lake...

Mysis diluviana is an important part of the food web in all of the Laurentian Great Lakes except Lake Erie. While it has historically been an important food item for fish, recent declines in Diporeia spp. may have resulted in greater predation pressure on M. diluviana. The literature on recent abundance and production of M. diluviana in Lake Huron...

Between 2003 and 2007, several trophic level indicators in Lake Huron underwent declines, including chlorophyll, Diporeia, cladoceran and cyclopoid zooplankton, planktivorous fishes, and piscivores. Using a 2007 monthly field sampling and bioenergetics modeling approach, we focused on the planktivore/zooplankton trophic interaction, seeking to dete...

The USGS Great Lakes Science Center conducted acoustic/midwater trawl surveys of Lake Huron during 1997 and annually during 2004-2009. The 2009 survey was conducted during September and October, and included transects in Lake Huron's Main Basin, Georgian Bay, and North Channel. Main Basin estimates of pelagic fish density and biomass were higher in...

Spatial patterns in the biomass of pelagic fish in Lake Huron have persisted over 10 years even though biomass decreased 86% and the fish community shifted from dominance by non-native species (rainbow smelt, Osmerus mordax) to dominance by native species (bloater, Coregonus hoyi). Based on multivariate analyses of acoustic biomass data and abiotic...

Rudstam, L. G., Parker-Stetter, S. L., Sullivan, P. J., and Warner, D. M. 2009. Towards a standard operating procedure for fishery acoustic surveys in the Laurentian Great Lakes, North America. – ICES Journal of Marine Science, 66: 1391–1397. Acoustic surveys are conducted annually in all five of the Laurentian Great Lakes and Lake Champlain to ass...

To predict effects of modifying the daily bag limit (DBL) on management of Chinook salmon Oncorhynchus tshawytscha and alewives Alosa pseudoharengus, we analyzed harvest and effort data collected from both charter and noncharter anglers during 1997–2005 in Michigan waters of Lake Michigan. Overall, the percent of anglers who caught the DBL of three...

Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes have had widespread success in Lake Superior; but in other Great Lakes, populations of lake trout are maintained by stocking. Recruitment bottlenecks may be present at a number of stages of the reproduction process. To study eggs and fry,...

Mysis relicta can be observed on echograms as a sound scattering layer when they migrate into the water column at night to feed on zooplankton. However, quantitative measures of mysid abundance with hydroacoustics requires knowledge of mysid target strength (TS), a method of removing fish echoes and contribution from noise, and an understanding of...

We used growth and diet data from a fishery-independent survey of Chinook salmon Oncorhynchus tshawytscha, acoustic estimates of prey density and biomass, and statistical catch-at-age modeling to study the influence of the year-class strength of alewife Alosa pseudoharengus on the prey selection and abundance of age-1 Chinook salmon in Lake Michiga...

Emerald shiners Notropis atherinoides were formerly common in Lakes Huron and Michigan, but declined during the 1960s as the exotic alewife Alosa pseudoharengus proliferated. The Lake Huron emerald shiner population was chronically depressed through 2004; however, we detected resurgence in emerald shiner density and biomass in Lake Huron during aco...

The alewife Alosa pseudoharengus, an invader to the Laurentian Great Lakes from the Atlantic Ocean, has been blamed for causing major disruptions of Great Lakes fish communities during the past 50 years. We reviewed the literature and examined long-term data on fish abundances in the Great Lakes to develop a new synthesis on the negative effects of...

The USGS Great Lakes Science Center conducted acoustic and midwater trawl surveys of Lake Huron in 1997, 2004, 2005, and 2006. The 2006 survey was conducted during August and was comprised of Lake Huron's main basin. Main basin estimates of pelagic fish density were higher in 2006, primarily due to increased age-0 rainbow smelt Osmerus mordax abund...

The USGS Great Lakes Science Center conducted annual acoustic/midwater trawl surveys of Lake Huron from 2004-2007. The 2007 survey was conducted during September and October, and included transects in Lake Huron's main basin, Georgian Bay, and North Channel. Main basin estimates of pelagic fish density were similar during all four years. Biomass es...

Cercopagis pengoi, a zooplanktivore first discovered in Lake Ontario in 1998, may reduce availability of prey for planktivorous fish. Cercoapgis pengoi is most abundant in late summer and fall. Therefore, we hypothesized that abundance of small zooplankton (bosminids and cyclopoids) species would decrease at that time. To determine if the establish...

The USGS Great Lakes Science Center conducted acoustic/midwater trawl surveys of Lake Huron in 1997, 2004, and 2005. The 2005 survey was conducted during September- October, and included transects in Lake Huron's main basin, Georgian Bay, and the North Channel. Estimates of pelagic fish density were higher in 2005 than 2004, primarily due to increa...

Alewives Alosa pseudoharengus contain thiaminase activity that has been implicated in the development of a thiamine deficiency and associated effects in salmonines of the Great Lakes basin. Little is known about the factors that regulate thiaminase activity in alewives. We sampled alewives of uniform size (60–120 mm) during the summer of 1998 from...

Freshwater alewives have been shown to be quite sensitive to cold water, and evidence exists to suggest that entire year classes have died in severe winters. Although a number of factors influence alewife survival rates, it is likely that overwinter mortality is substantial in most years. In spite of the apparent importance of overwinter mortality,...

Moe Pond, Otsego County, New York, is an artificial impoundment created by the damming of a natural wetland in 1939. It was dominated by blue-green algal blooms between at least 1970–1998. During that time a few scattered clones of sedges (Cyperaceae) along the shoreline were the only vascular plants present. The zooplankton community was dominated...

Diets of alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) were examined before (1997) and after (1998 and 1999) the establishment of the predatory cladoceran Cercopagis pengoi in Lake Ontario. Cercopagis pengoi was absent in both fish stomachs and zooplankton samples in 1997, but by August 1998, its distribution was lake-wide and s...

Acoustic abundance of fish depends directly on the target strength (TS) of the fish surveyed. We analyzed 70 and 120 kHz acoustic data from two lakes with abundant rainbow-smelt (Osmerus mordax) populations. Using repeated surveys through the summer growing season, we derived a relationship between TS (dB) and fish length L (cm) at 120 kHz (TS = 19...

Changes at several trophic levels in Otsego Lake from the 1930s to present are described relative to changes in the planktivorous fish community. Prior to the late 1980s, cisco (Coregonus artedi) was the dominant planktivore. The alewife (Alosa pseudoharengus) appeared in 1986 and subsequently became dominant. Two patterns emerged when we contraste...

The predatory impacts of Cercopagis pengoi, a planktivorous cladoceran first observed in Lake Ontario in 1998, were assessed by examining patterns in the distribution and population dynamics of macrozooplankton. Specifically, we determined the vertical distribution of C. pengoi in Lake Ontario with respect to other zooplankton species and possible...

Acoustic estimation of absolute fish abundance depends on knowledge of the relationship between target strength (TS) and size for the species of interest. We have derived a relationship between in situ TS and both length (L, cm) and mass (W, g) for alewives Alosa pseudoharengus in Lake Ontario and eight inland lakes in New York to provide equations...

Alewife abundance in Otsego Lake has been monitored in 11 of the last 14 years using littoral trap netting efforts. Hydroacoustic surveys of alewife (Alosa pseudoharengus) density have been conducted in Otsego Lake since 1996 (except for 1998). Alewife density during this period ranged from a low of 968 fish/ha in May 2002 to a high of 14,797 fish/...

Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2009 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates....

Acoustic surveys were conducted in the fall during the years 1992-1996 and 2001-2005 to estimate prey fish biomass in Lake Michigan. Midwater trawling during the surveys provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2005 survey includ...