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Thomas C. Pratt

Publications and source records attributed to Thomas C. Pratt.

14 recordsLinked to original sources
USGS2025

Lake sturgeon behavioral diversity in the Laurentian Great Lakes: Migratory patterns across populations and habitats

Background Characterizing the diversity of migration behaviors from the individual to the population level is essential for understanding how organisms respond to environmental variation and how these responses affect survival and habitat use. Lake sturgeon ( Acipenser fulvescens ) is a species of special concern in the Laurentian Great Lakes that are long-lived and generally classified as intermittent, adfluvial spawners. Observations of lake sturgeon movements at ecologically relevant spatiotemporal scales have shown that migration behavior often varies among individuals within the same population. However, studies on individual populations, particularly when focused only on a part of the life cycle (e.g., often spawning), provide just a partial understanding of the species’ full migratory scope and processes underlying expression of different migratory behaviors. To better understand lake sturgeon migratory diversity, we characterized and compared migratory behaviors of six lake sturgeon populations occupying environments that varied in habitat availability and connectivity in different Laurentian Great Lakes. Methods Sequence analysis combined with agglomerative hierarchical clustering and visual inspection of daily location data were used to identify distinct lake sturgeon migratory behaviors present in each population. Results Seven distinct migratory behaviors were identified based on differential patterns of lake and river use that encompass spawning and other seasonal periods. Behaviors were categorized as annual spring river, intermittent spring river, intermittent two-step, annual summer river, annual winter river, and annual interlake migrants along with river residents. The presence and frequency of migratory behaviors varied substantially among populations. Conclusions Our study demonstrated that migratory diversity is a general feature of lake sturgeon life history that may be partially shaped by habitat availability and connectivity. Given these results, we propose a conceptual model that links habitat availability and connectivity to migratory diversity and predict a positive association between them. This updated framework provides a cohesive basis for understanding lake sturgeon migratory behavior across variable ecological contexts in the Laurentian Great Lakes and will help promote future research to refute or refine the model.

Laurentian Great Lakes↗
USGS2025

Designing sortable guilds for multispecies selective fish passage

The importance of connectivity for freshwater organisms is widely recognised, yet in-stream barriers associated with population declines and increased risk of extinction remain globally ubiquitous. Despite their negative consequences, these barriers can protect aquatic communities by limiting the spread of invasive species, leading to conflicting management goals in some regions. Selective fish passage is a solution for the conflicting goals of passing native, desirable species while restricting the spread of invasives. Approaches that can target groups of species sharing similar attributes (i.e. guilds) are likely to be more efficient than those that target species individually, particularly in taxonomically diverse systems. We explored the guild structure of 220 Great Lakes freshwater fishes based on morphological, phenological, physiological and behavioural attributes associated with passage and movement. We identified five distinct guilds as well as the attributes most important for defining these groupings: maximum total length, trophic level, relative eye size, spawning temperature, spawning season, presence/absence of ampullary electroreceptors and the presence/absence of hearing specialisations. The approaches outlined in this work can be generalised to enhance selective fish passage in aquatic ecosystems worldwide.

Fish and Fisheries↗
USGS2025

Lake Superior fish community and fisheries, 2001–2022: An era of stability

Lake Superior is the least anthropogenically impacted of the Laurentian Great Lakes ecosystems, yet dramatic changes to the fish community are evident. Previous published works chronicled those changes and the efforts to rehabilitate the fish community through the year 2000. Here, we review through the year 2022, where post-rehabilitation stability was driven by lean lake trout ( Salvelinus namaycush namaycush) as the most abundant piscivore in nearshore waters, siscowet lake trout ( Salvelinus namaycush siscowet) as the most abundant piscivore in offshore waters, and a healthy, intact assemblage of native prey species, which created ecological redundancies and helped stabilize the food web. Stocking of non-native salmonines was reduced 74%, and populations of Chinook salmon ( Oncorhynchus tshawytscha) and coho salmon ( Oncorhynchus kisutch) were maintained through natural reproduction. Despite reduced stocking, yield from recreational fisheries was stable. Likewise, developments in population modeling led to evaluations and refinement of management strategies that helped create stability for lake trout, lake whitefish ( Coregonus clupeaformis ), and cisco ( Coregonus artedi ) fisheries. With lake trout rehabilitation achieved, focus shifted toward rehabilitation of native brook trout ( Salvelinus fontinalis ), lake sturgeon ( Acipenser fulvescens ), and walleye ( Sander vitreus ). Despite continued control efforts, sea lamprey ( Petromyzon marinus ) abundance increased considerably, and estimates of fish killed by lampreys averaged 2.65 million kg annually. Environmental changes have benefited sea lampreys and fostered thermal habitats more suitable to non-native organisms, posing new challenges for managers and researchers. Nevertheless, the post-rehabilitation stability in the contemporary fish community will help provide resilience to future perturbations in the ecosystem.

Lake Superior↗
USGS2025

Decision analysis of Integrated Pest Management: A case study on invasive sea lamprey in the Great Lakes Basin

Integrated Pest Management (IPM) provides a powerful framework for addressing threats to human well-being caused by nuisance species including invasives. We examined the hypothesis that adaptive management could erode barriers to IPM implementation by developing a decision-analytic adaptive management framework for invasive sea lamprey ( Petromyzon marinus ) IPM in the Laurentian Great Lakes of North America. The framework addressed objectives associated with coordinating multiple sea lamprey control actions at the regional scale and objectives associated with internal validity of control actions. We reduced the scope of possible management actions by orders of magnitude to the set of 6432 alternatives expected to be both socially acceptable and technically feasible. Using utility theory, we identified the management actions that optimized expected utility for all possible objective weighting schemes that considered tradeoffs between maximizing learning about control tactic efficacy and minimizing cost to the IPM program. Sensitivity analyses revealed that assumptions about the social acceptability of deploying electric weirs to control invasive sea lamprey influenced selection of the optimal control action, suggesting that resolving this source of uncertainty through iterative application of the framework may lead to improved sea lamprey control outcomes. Overall, we found that adaptive management enabled learning processes useful for overcoming barriers to IPM of invasive sea lamprey. It formalized learning about sea lamprey control tactic efficacy as an objective of the IPM institution, questioned previously held assumptions about what constitutes a viable control strategy, and enabled a management experiment with temporal and spatial replication.

Michigan, Ontario, Wisconsin↗
USGS2025

Archive of morphological data for the Coregonus artedi species complex of the Great Lakes, Lake Nipigon and Great Slave Lake

This publication is a user guide for an archive of morphological data recorded by various authors from North American ciscoes of the Coregonus artedi species complex (subfamily Coregoninae ). The archive is accessible from the Great Lakes Fishery Commission’s (GLFC) server, is open access, and contains data for the Laurentian Great Lakes; Lake Nipigon, Ontario; and Great Slave Lake, Northwest Territories. The archive comprises morphometrics and meristics (together metrics) for 6,700 individual Cisco of which 1,400 are accompanied by images. In addition, the archive contains metrics presented as arrays by W. N. Koelz, Coregonid fishes of the Great Lakes, Bulletin of the U.S. Bureau of Fisheries 43(2):297-643, which were based on 10,000 individuals. Spreadsheets in the Metrics folder of the archive are divided broadly into Contemporary and Historical subfolders and the Contemporary subfolder is further divided into Cisco Monograph and Extra Monograph subfolders to encourage statistical assessment of findings in GLFC Miscellaneous Publication 2023. The Images folder is organized into subfolders by lake. Tables in this user guide allow for quick determination of the availability of data by lake, subspecies, author, and year.

Laurentian↗
USGS2023

FishPass sortable attribute database: Phenological, morphological, physiological, and behavioural characteristics related to passage and movement of Laurentian Great Lakes fishes

In-stream barriers pose threats to fishes, including habitat loss, constraints on migration, and reduced connectivity between populations. Despite many negative consequences, barriers can serve to protect native species by limiting the spread of invasive species. For example, in the Laurentian Great Lakes, physical barriers have long been used to control invasive sea lamprey ( Petromyzon marinus ) populations by limiting access to potential upstream spawning and rearing habitat. Selective fish passage systems could solve this management trade-off, termed the “connectivity conundrum”, but must efficiently pass multiple native or desirable species while blocking invasive species. Designing such fish passage systems requires an understanding of the attribute dimensions of the fish community, specifically, the phenology, morphology, physiology, and behaviour of each species. Here, we describe the first comprehensive collection of sortable attributes associated with fish passage. The integrated database consists of 21 biological attributes that influence the movement and passage of 220 species in the Great Lakes, including native species, established non-native species, and unestablished but potentially invasive fishes. Data coverage varies with species, taxonomic orders, and attribute dimensions. Behavioural attributes were typically underrepresented in the literature, and the ecology of potential invaders was not well understood. The synthesis described herein is a critical step towards a holistic approach to fish passage design and may help to inform management actions related to population connectivity. The database is openly accessible online and is expected to be updated periodically.

Laurentian Great Lakes↗
USGS2019

Stream characteristics associated with feeding type in silver( Ichthyomyzon unicuspis ) and northern brook ( I. fossor ) lampreys and tests for phenotypic plasticity

In most lamprey genera, “paired” species exist in which the larvae are morphologically indistinguishable but adult feeding type differs. The lack of diagnostic genetic differences in many pairs has led to suggestions that they constitute a single gene pool with environmentally influenced feeding types. To investigate whether stream characteristics are correlated with feeding type in the parasitic silver lamprey Ichthyomyzon unicuspis and nonparasitic northern brook lamprey I. fossor, eight variables (pH, alkalinity, conductivity, discharge, total dissolved solids, and density of larval sea lamprey Petromyzon marinus, Ichthyomyzon spp., and total larval density) were compared among eight streams with only silver lamprey, 10 with only northern brook lamprey, and 13 with both species, using classification tree analysis. The most parsimonious model had a 24% misclassification rate, with silver lamprey tending to inhabit streams with higher sea lamprey larval density and northern brook lamprey tending to inhabit streams with higher Ichthyomyzon larval density. We then conducted a pilot study investigating phenotypic plasticity in a lab-based common garden experiment and an in situ transplant experiment. These studies encountered myriad difficulties and were unable to demonstrate plasticity, but did identify challenges associated with culturing Ichthyomyzon larvae. Development of effective rearing procedures for Ichthyomyzon lampreys is essential for any future similar studies.

Great Lakes, Lake Champlain basin↗
USGS2017

In situ assessment of lampricide toxicity to age-0 lake sturgeon

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2′, 5-dichloro-4′-nitrosalicylanilide (niclosamide) are used to control sea lamprey ( Petromyzon marinus ), an invasive species in the Great Lakes. Age-0 lake sturgeon ( Acipenser fulvescens ), a species of conservationconcern, share similar stream habitats with larval sea lampreys and these streams can be targeted for lampricide applications on a 3- to 5-year cycle. Previous laboratory researchfound that lake sturgeon smaller than 100 mm could be susceptible to lampricide treatments. We conducted stream-side toxicity (bioassay) and in situ studies in conjunction with 10 lampricide applications in nine Great Lakes tributaries to determine whether sea lamprey treatments could result in in situ age-0 lake sturgeon mortality, and developed a logistic model to help predict lake sturgeon survival during future treatments. In the bioassays the observed concentrations where no lake sturgeon mortality occurred (no observable effect concentration, NOEC) were at or greater than the observed sea lamprey minimum lethal concentration (MLC or LC99) in 7 of 10 tests. We found that the mean in situ survival of age-0 lake sturgeon during 10 lampricide applications was 80%, with a range of 45–100% survival within streams. Modeling indicated that in age-0 lake sturgeon survival was negatively correlated with absolute TFM concentration and stream alkalinity, and positively correlated with stream pH and temperature. Overall survival was higher than expected based on previous research, and we expect that these data will help managers with decisions on the trade-offs between sea lamprey control and the effect on stream-specific populations of age-0 lake sturgeon.

Journal of Great Lakes Research↗
USGS2017

Spatial mismatch between sea lamprey behaviour and trap location explains low success at trapping for control

Crucial to the management of invasive species is understanding space use and the environmental features affecting space use. Improved understanding of space use by invasive sea lamprey ( Petromyzon marinus ) could help researchers discern why trap success in large rivers is lower than needed for effective control. We tested whether manipulating discharge nightly could increase trap success at a hydroelectric generating station on the St. Marys River. We quantified numbers of acoustically tagged sea lampreys migrating up to, and their space use at, the hydroelectric generating station. In 2011 and 2012, 78% and 68%, respectively, of tagged sea lampreys reached the generating station. Sea lampreys were active along the face, but more likely to occur at the bottom and away from the traps near the surface, especially when discharge was high. Our findings suggest that a low probability of encountering traps was due to spatial (vertical) mismatch between space use by sea lamprey and trap locations and that increasing discharge did not alter space use in ways that increased trap encounter. Understanding space use by invasive species can help managers assess the efficacy of trapping and ways of improving trapping success.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2016

Ciscoes ( Coregonus , subgenus Leucichthys ) of the Laurentian Great Lakes and Lake Nipigon

This study of the ciscoes ( Coregonus , subgenus Leucichthys ) of the Great Lakes and Lake Nipigon represents a furtherance through 2015 of field research initiated by Walter Koelz in 1917 and continued by Stanford Smith in the mid-1900s—a period spanning nearly a century. Like Koelz’s study, this work contains information on taxonomy, geographical distribution, ecology, and status of species (here considered forms). Of the seven currently recognized forms ( C. artedi , C. hoyi , C. johannae , C. kiyi , C. nigripinnis , C. reighardi , and C. zenithicus ) described by Koelz as major in his 1929 monograph, two ( C. johannae and C. reighardi ) are extinct. In addition, C. alpenae , described by Koelz but subsequently synonymized with C. zenithicus , although extinct, is recognized as valid making a total of eight major forms. Six of these forms, all but C. artedi and C. hoyi , have been lost from Lake Michigan, and seven have been lost from Lake Huron, leaving in Lake Huron only C. artedi and an introgressed deepwater form that we term a hybrid swarm. C. artedi appears, like its sister form C. alpenae , to have been lost from Lake Erie. Only C. artedi remains extant in Lake Ontario, its three sister forms ( C. hoyi , C. kiyi , and C. reighardi ) having disappeared long ago. Lakes Superior and Nipigon have retained their original species flocks consisting of four forms each: C. artedi , C. hoyi , and C. zenithicus in both lakes; C. kiyi in Lake Superior; and C. nigripinnis in Lake Nipigon. Morphological deviations from the morphotypes described by Koelz have been modest in contemporary samples. Overall, C. kiyi and C. artedi were the most morphologically stable forms while C. hoyi , C. nigripinnis , and C. zenithicus were the least stable. Although contemporary populations of C. artedi from Lakes Michigan and Huron are highly diverged from the morphotypes described by Koelz, the contemporary samples were of undescribed deep-bodied forms unlikely to have been sampled by Koelz because of their association with bays. Of the two intact species flocks, Lake Nipigon’s was much less stable morphologically than Lake Superior’s even though Lake Nipigon is far less disturbed. Two priorities for research are determining the role of developmental plasticity in morphological divergence, especially within C. zenithicus of Lake Superior, and the basis for morphological divergence in C. artedi .

Lake Nipigon, Laurentian Great Lakes↗
USGS2013

Morphometric variation among spawning cisco aggregations in the Laurentian Great Lakes: are historic forms still present?

Cisco (Coregonus artedi Leseur, formerly lake herring Leucichthys artedi Leseur) populations in each of the Laurentian Great Lakes collapsed between the late 1920s and early 1960s following a multitude of stressors, and never recovered in Lakes Michigan, Erie and Ontario. Prior to their collapse, Koelz (1929) studied Leucichthys spp. in the Great Lakes basin and provided a description of their diversity. Three cisco morphotypes were described; a ‘slim terete’morphotype (L. artedi artedi), a ‘deep compressed’ morphotype (L. artedi albus), and a deep-bodied form resembling tullibee in western Canadian lakes (L. artedi manitoulinus). Based on body measurements of 159 individuals (Koelz 1929), we used discriminant function analysis (DFA) to discriminate historic morphotypes. Shapes of historic morphotypes were found to vary significantly (Pillai’s trace = 1.16, P < 0.0001). The final DFA model used nine body measurements and correctly classified 90% of the historic cisco. Important discriminating measurements included body depth, eye diameter, and dorsal fin base and height. Between October-November of 2007-2011, we sampled cisco from 16 Great Lakes sites collecting digital photographs of over 1, 700 individuals. We applied the DFA model to their body measurements and classified each individual to a morphotype. Contemporary cisco from Lakes Superior, Ontario and Michigan were predominantly classified as artedi, while the most common classifications from northern Lake Huron were albus and manitoulinus. Finding historic morphotypes is encouraging because it suggests that the morphological variation present prior to their collapse still exists. We conclude that contemporary cisco having shapes matching the missing historic morphotypes in the lower lakes warrant special consideration as potential donor populations in reestablishment efforts.

Lake Michigan;Lake Erie;Lake Ontario;Lake Huron;La↗
USGS2012

Unintended consequences and trade-offs of fish passage

We synthesized evidence for unintended consequences and trade-offs associated with the passage of fishes. Provisioning of fish passageways at dams and dam removals are being carried out increasingly as resource managers seek ways to reduce fragmentation of migratory fish populations and restore biodiversity and nature-like ecosystem services in tributaries altered by dams. The benefits of provisioning upstream passage are highlighted widely. Possible unwanted consequences and trade-offs of upstream passage are coming to light, but remain poorly examined and underappreciated. Unintended consequences arise when passage of native and desirable introduced fishes is delayed, undone (fallback), results in patterns of movement and habitat use that reduce Darwinian fitness (e.g. ecological traps), or is highly selective taxonomically and numerically. Trade-offs arise when passage decisions intended to benefit native species interfere with management decisions intended to control the unwanted spread of non-native fishes and aquatic invertebrates, or genes, diseases and contaminants carried by hatchery and wild fishes. These consequences and trade-offs will vary in importance from system to system and can result in large economic and environmental costs. For some river systems, decisions about how to manage fish passage involve substantial risks and could benefit from use of a formal, structured process that allows transparent, objective and, where possible, quantitative evaluation of these risks. Such a process can also facilitate the design of an adaptive framework that provides valuable insights into future decisions.

Fish and Fisheries↗
USGS2011

Balancing aquatic habitat fragmentation and control of invasive species: Enhancing selective fish passage at sea lamprey control barriers

Barriers to prevent spawning migrations of sea lampreys Petromyzon marinus remain an important component of an integrated sea lamprey management program in the Laurentian Great Lakes. Concerns about effects on nontarget fishes have led to the construction of specially designed vertical-slot trap-and-sort fishways to mitigate potential barrier effects. To improve passage at these fishways, we used passive integrated transponder technology to assess the performance of two fishways located on low-head sea lamprey barriers. Fishways on the Big Carp River (which flows into Lake Superior) and Cobourg Brook (which flows into Lake Ontario) were assessed for attraction efficiency, trap attraction and retention, and passage efficiency. Based on the results of these assessments, fishways were modified by increasing the trap volume and altering the funnel characteristics to reduce escapement from the trap and then reassessed. Attraction efficiency for all tagged fish was high (≥80%) at both sites in all years. Fishway modifications improved passage from 35% in 2003 to 88% and 64% in 2004 and 2005, respectively, at the Big Carp River. As expected, white suckers Catostomus commersonii , an obligate migrant, had higher attraction and passage efficiency, fewer passage attempts, and shorter migration delay than did rock bass Ambloplites rupestris , a facultative migrant. No improvements were seen at Cobourg Brook, where passage efficiency remained low (7% in 2003, 10% in 2005), probably because of the loss of attraction flow. At both fishways, individual fish averaged 3-10 attempts to pass through the fishways and had their migrations delayed 1-2 weeks. The observed improvements to the Big Carp River fishway, which resulted in high fishway attraction and passage rates for white suckers, suggest that vertical-slot fishways can help mitigate the effects of low-head barriers for some species. Our study provides a rigorous quantifiable approach to assessing fishway performance that can be employed widely and successfully to assess initial fishway design and subsequent modifications.

Big Carp River, Cobourg Brook↗