Geology topics

David B. Bunnell

Publications and source records attributed to David B. Bunnell.

At least 19 recordsLinked to original sources

USGS2026

Key considerations for decision makers and stakeholders when identifying source populations for conservation translocations of fishes

Conservation translocations are undertaken to increase the viability of imperiled organisms and/or restore ecosystem functions or processes. A key step in the conservation translocation process is to decide which source or founder population is most likely to lead to translocation success. Existing guidance to inform this decision includes a variety of considerations, but few documents focus solely on this step. Furthermore, despite the importance of stakeholder engagement to long-term conservation success, guidance for selecting source populations rarely describes approaches for stakeholder inclusion. Herein, we undertook a literature review for fish conservation translocations and summarized key considerations (e.g., genetics, habitat, life history, effects on source or recipient populations and ecosystems, logistical) to be used when selecting candidate source populations. We describe the importance of including stakeholders and recommend that decision makers coproduce the source population decision with them. We propose a structured expert judgment approach to assess the probability that specific aspects of these considerations could be achieved for each candidate source population. Finally, we recommend synthesizing results of the expert judgement process to enable decision makers and, ideally, invited stakeholders to choose which source population(s) based on their previously identified fundamental objectives. Although we developed this approach for fishes, it could be used for other conservation translocation efforts where stakeholder involvement and synthesis of support for different source populations are deemed valuable in the planning process.

Global Ecology and Conservation↗

USGS2026

Two hundred years of historical spawning and nursery data for coregonine fishes in the Laurentian Great Lakes

Historical data can provide critical ecological information for species across the globe, many of which are facing unprecedented rates of ecosystem change. Yet, historical information related to freshwater species, especially fishes, remains scattered, often in original formats, and underutilized for informing conservation and restoration activities. Here, we present a Data Descriptor called Coregonine Spawning History (CORHIST), a database designed to house diverse data related to past spawning and nursery areas for fishes in the family Salmonidae, subfamily Coregoninae (ciscoes and whitefishes), in the Laurentian Great Lakes and their tributaries. Data for 11 species of coregonines historically occurring in the Great Lakes are included in CORHIST. Over 3,400 occurrence records at the coordinate scale have been entered, over 2,200 of which are for Cisco ( Coregonus artedi ) and Lake Whitefish ( C. clupeaformis )—two focal species for which there is either multinational conservation interest or restoration efforts underway in the Laurentian Great Lakes. CORHIST is already proving useful for several studies developing habitat suitability models and delineating spatial units for conservation or restoration planning.

Laurentian Great Lakes↗

USGS2026

Adaptive capacity of freshwater organisms in North America: Current understanding and future applications

Freshwater species are increasingly threatened by climate change, yet our ability to assess their vulnerability remains incomplete. Typically, climate change vulnerability assessments (CCVAs) evaluate three components: exposure, sensitivity, and adaptive capacity. Adaptive capacity, defined as the ability of a species to adjust to changing conditions, provides critical insight into how species may persist under future scenarios and can strengthen conservation planning by highlighting opportunities for resilience and targeted management strategies. Trait-based approaches offer a promising path for managers to operationalize adaptive capacity by identifying measurable biological and ecological traits that influence climate change response strategies. However, these insights are rarely integrated into broader vulnerability frameworks that support conservation decision making. We build on previous research to synthesize current understanding of adaptive capacity for three freshwater taxa in North America: fishes, mussels, and crayfishes. Our objectives were to: (1) assess the relevance of adaptive capacity factors for fishes, mussels, and crayfishes; (2) identify key opportunities and gaps in linking trait-based information into adaptive capacity assessments; and (3) illustrate how incorporating adaptive capacity can enhance management decisions for freshwater species under climate change. We used an expert workshop, literature review, and case studies to identify relevant adaptive capacity factors, assess available information, and evaluate inclusion in management contexts. We found that all three taxa had sufficient information to inform adaptive capacity assessments. In addition to existing adaptive capacity factors, we identified Morphology as an important yet underutilized cross-cutting diagnostic category when information was limited. By explicitly linking trait-based approaches with adaptive capacity frameworks, we offer practical guidance for improving climate adaptation strategies and prioritizing management actions for freshwater biodiversity under accelerating global change.

Global Change Biology Communications↗

USGS2026

Describing the seasonal abundance and growth rates of larval fishes across productivity gradients in Lake Huron in 2017

Several of the Laurentian Great Lakes, including Lake Huron, have undergone oligotrophication in the past decades and prey fish biomass has concomitantly declined. One potential mechanism to explain declines in prey fish is slower growth and lower survival at the larval stage. To determine whether reduced productivity affects the growth of larval fish, we sampled larval fishes and their environment approximately monthly from May through August 2017 at nine nearshore to offshore transects across Lake Huron that included North Channel, Georgian Bay, and the main basin. North Channel transects had the highest chlorophyll a concentrations and zooplankton densities. Rainbow smelt ( Osmerus mordax ), burbot ( Lota lota ), bloater ( Coregonus hoyi ), and shiners ( Notropis spp.) were the most abundant larval fish taxa, peaking in June and July. We aged rainbow smelt and bloater using otoliths, and estimates of growth rate revealed rainbow smelt always grew faster. For both species, we explained variation in total length by comparing 16 candidate linear mixed-effects models, with age, chlorophyll a , zooplankton, water temperature, larval fish density, and interactions with age as predictor variables. For rainbow smelt, the full model was best; zooplankton had the greatest effect, but it was negative and opposite from our hypothesis. For bloater, four candidate models were most parsimonious; water temperature had the greatest effect, and it was positive as predicted from our hypothesis. To more effectively evaluate whether zooplankton can limit larval fish growth and survival, we recommend that future designs conduct more frequently sampling within a year even at the expense of fewer transects.

Lake Huron↗

USGS2026

Decreased water transparency of nearshore Laurentian Great Lakes habitats is driven by increased dissolved organic carbon.

Little is understood of lake browning (due to increased dissolved organic carbon; DOC) in large lakes such as the Laurentian Great Lakes. Lake browning can alter whole lake ecosystems, including decreasing exposure to damaging ultraviolet radiation (UV-B) which is strongly and selectively attenuated by DOC more so than photosynthetically active radiation (PAR). We compared the changes in UV-B and PAR transparency to DOC data collected during the ice-free seasons from 62 nearshore sites in four of the five Great Lakes from 2002 to 2022 using linear mixed effects regression models based on backwards selected Bayesian information criteria. Regionally, DOC significantly increased from 2002 to 2022 by 0.5% per year on average. DOC strongly and inversely explained the variability of UV-B and PAR transparencies, as did seasons and offshore influence on these habitats. We provide regional evidence of lake browning within the nearshore habitats of the Great Lakes as a strong contrast to the well-documented increased offshore water transparency associated with the spread of invasive dreissenid mussels.

Great Lakes↗

USGS2025

Exposure to ultraviolet radiation induces escape hatching of Cisco (Coregonus artedi) embryos

Cisco (Otoonapii in Ojibwe; Coregonus artedi Lesueur, 1818), is a widely distributed stenothermic freshwater fish whose embryos typically incubate under ice and in the dark. We used Cisco as a model organism for testing the potential of UV-induced escape hatching behaviour. Owing to reduced ice cover and increased water transparency in north temperate lakes, these experiments provide insights into the resilience of coregonine embryos if exposed to ultraviolet radiation (UV-B; 280–320 nm). Eyed Cisco embryos were exposed to artificially sourced UV-B through a series of experiments that measured the hatching rate and fitness (heart rate and pigmentation pattern) 2 days after hatching and under cold [6.6°C] and warm [8.6°C] conditions. These experiments supported an extension of the escape hatching behaviour hypothesis, whereby UV-B exposure induced earlier (ca 30 days) and more punctuated hatching of Cisco embryos, independent of an increase in water temperature. UV-B exposure produced more larvae with irregular pigmentation patterns and reduced heart rates (by about 20%) – both of which could be indicative of reduced fitness. UV-induced escape hatching adusts the fundamental framework in which we characterise fish embryo resilience to increased UV-B exposure and the potential consequences of reduced ice cover. Earlier hatching from UV-B exposure could increase the recruitment bottleneck of these fish by reducing survivorship of the post-hatched larvae.

Minnesota↗

USGS2025

Are we heading towards a global decrease in coregonine catches?

Coregonines have specific ecological needs, making them potentially very vulnerable to changes in lake conditions. A contemporary concern is that many lakes worldwide are experiencing environmental changes due to anthropogenic pressure and climate warming. Here, we compiled long-term data of coregonine catches from 27 lakes from three continents in the northern hemisphere. Declines in catch were observed in 67% of the lakes during the first two decades of the 21 st century, with a significant trend (p-value<0.05) in 44% of the cases. An analysis to determine whether trends are globally linked to environmental conditions and specific lake attributes was carried out on 26 lakes for the period 2000–2019. Several local declines in catches had already been documented in the literature and are likely to be due to local forcing such as nutrients, species invasions and changes in fishing practices. Nevertheless, on a global scale, our results indicate that lakes, which exhibited a significant decrease in catch were larger and more nutrient-poor than other lakes. The rate of change in catches appeared to be related to the trophic state of the lake. The specific effect of warming is difficult to determine during the studied period. When warming occurred outside the period of egg incubation, decreasing trends were more frequently observed in nutrient-poor than in mesotrophic lakes. In conclusion, our findings suggest that achieving oligo- or ultraoligotrophic conditions, as required in developed countries to control phytoplankton blooms and enhance water quality, could pose significant challenges for future management of coregonine fisheries.

International Journal of Limnology↗

USGS2025

Stable C and N isotope analyses redefine cisco as pelagic piscivores in Lake Michigan

Lake Michigan’s cisco ( Coregonus artedi ) population is in the midst of an expansion (2011-present) recovering from near extirpation levels observed in the 1970 s. Strong evidence of piscivory derived from observed diet analyses suggests the population may occupy a unique trophic position relative to typical expectations for the species. To verify these observations, cisco and their prey were collected from 2017 to 2020 for stable C and N isotope analyses. Leveraging existing stable isotope datasets for Lake Michigan, the trophic position of cisco was assessed by quantifying the isotopic niche space occupied relative to common salmonine piscivores and prey fish species. Diet mixing models were constructed to estimate the relative importance of potential prey sources to cisco diets. Results suggested that cisco occupied an isotopic niche similar to Pacific salmonines ( Oncorhynchus spp.) and brown trout ( Salmo trutta ) that are mainly piscivorous. Conversely, there was low isotopic niche overlap with prey fish species that are mainly planktivorous. Mixing models suggest greater reliance on pelagic prey sources (including alewife Alosa pseudoharengus and Bythotrephes longimanus ) in cisco diets when compared with observations of stomach contents. Under the present ecological conditions in Lake Michigan, it appears that adult cisco in this population occupy the trophic role of a pelagic piscivore.

Lake Michigan↗

USGS2025

Evaluating how changing climate and water clarity can affect restoration of native coregonine fishes in midwestern lakes

In the upper midwestern United States, coregonine fishes (e.g., ciscoes and whitefishes) have provided a key food source for Indigenous peoples since time immemorial. In the last century, however, several anthropogenic stressors including overfishing, declining quality of key habitat (e.g., dams, algal blooms), and negative interactions with invasive species have led to declines in the fisheries that coregonines support. Hence, fishery managers have undertaken steps to conserve existing diversity or re-introduce species that have been locally extirpated. This study assessed the extent to which changes in water clarity and climate pose challenges for conservation of coregonines and sought to provide information to inform management decisions about which populations would be best for reintroduction. Through experiments, we found that a Cisco ( Coregonus artedi ) population at the southern edge of its range had no marked advantages in respiration or thermal tolerance, relative to a northern Great Lake population. This result indicates that the latter population would be a reasonable candidate for reintroduction in Lake Erie, where warming water could be a potential impediment. Other laboratory experiments revealed that Cisco could be vulnerable to increasing ultraviolet radiation (UV; 280 – 320 nm) penetration in lakes due to reduced ice cover and increased water clarity owing to water quality improvements and/or invasive mussel filtration. Our experiments found that UV exposure causes earlier hatching, more irregular pigmentation near the head and yolk-sac region, and reduced heart rate. Therefore, UV could be a heretofore unrealized threat to Cisco populations. Through the completion of additional final products from this project and additional research connecting laboratory and field data together, the extent to which the eggs and larvae of coregonine species could be vulnerable to increased UV associated with increasing water clarity or reduced ice cover will help inform restoration or conservation planning for these fish.

Cooperator Report↗

USGS2024

Reconstructing half a century of coregonine recruitment reveals species-specific dynamics and synchrony across the Laurentian Great Lakes

Understanding how multiple species and populations vary in their recruitment dynamics can elucidate the processes driving recruitment across space and time. Lake Whitefish ( Coregonus clupeaformis ) and Cisco ( C. artedi ) are socioecologically important fishes across their range; however, many Laurentian Great Lakes populations have experienced declining, poor, or sporadic recruitment in recent decades. We integrated catch and age data from 38 long-term surveys across each of the Great Lakes and Lake Simcoe, resulting in a combined time series spanning 1960–2019. We estimated Lake Whitefish and Cisco year-class strength (YCS) in each lake using longitudinal mixed-effects regressions of relative cohort abundance. We subsequently quantified interspecific, spatial, and temporal synchrony in YCS using correlation and dynamic factor analyses. Lake Whitefish YCS was positively spatially synchronous on average, and YCS in all six lakes was elevated during the 1980s–1990s. In contrast, Cisco YCS was sporadic, not spatially synchronous, and highly variable around long-term, lake-specific means. YCS was not synchronous between species in any lake. Collectively, our analyses demonstrate that these species exhibit differential recruitment dynamics that may be regulated by species-specific factors. Results from this study can be leveraged in future research on the causes and consequences of cross-species, cross-basin recruitment variability.

Laurentian Great Lakes↗

USGS2024

Synthesizing professional opinion of Lake Whitefish and Cisco recruitment drivers across the Great Lakes

Disentangling the suite of ecological drivers that explain recruitment variability for Lake Whitefish Coregonus clupeaformis and Cisco C. artedi is of critical importance for their conservation, management, and stewardship in the Laurentian Great Lakes. However, recruitment is inherently variable and can be regulated by many interacting processes, the relative importance of which can vary spatially, temporally, and ontogenetically. Given this complexity, comparisons across lakes and species that identify overarching hypotheses could efficiently guide future research. Using facilitated deliberations among fishery professionals (n = 57) with expertise in Great Lakes Coregonus spp., we synthesized current knowledge regarding (1) which biophysical processes are most important for driving contemporary recruitment between species, among lakes, and across life stages and (2) mechanisms by which those drivers regulate recruitment at key life stages. Participants affirmed the hypothesis that many drivers interact in complex ways to regulate Lake Whitefish and Cisco recruitment. Large-scale climatic processes affecting early life-stage growth and survival were consistently considered important. Other drivers were only deemed influential in certain lakes, highlighting perceived context-dependent recruitment dynamics. Notably, recruitment in Lakes Superior, Michigan, and Huron was considered limited during larval and early juvenile life stages by low productivity, whereas spawning-habitat degradation and reduced metapopulation diversity were hypothesized to limit recruitment during embryonic and larval stages in Lakes Erie and Ontario. Several drivers were hypothesized to similarly impact Lake Whitefish and Cisco during early life stages, while drivers acting on post-larval life stages were typically distinct between species. The hypotheses synthesized herein can guide future research on Lake Whitefish and Cisco recruitment dynamics in the Great Lakes.

Great Lakes↗

USGS2024

Testing food web theory in a large lake: The role of body size in habitat coupling in Lake Michigan

The landscape theory of food web architecture (LTFWA) describes relationships among body size, trophic position, mobility, and energy channels that serve to couple heterogenous habitats, which in turn promotes long-term system stability. However, empirical tests of the LTFWA are rare and support differs among terrestrial, freshwater, and marine systems. Further, it is unclear whether the theory applies in highly altered ecosystems dominated by introduced species such as the Laurentian Great Lakes. Here, we provide an empirical test of the LTFWA by relating body size, trophic position, and the coupling of different energy channels using stable isotope data from species throughout the Lake Michigan food web. We found that body size was positively related to trophic position, but for a given trophic position, organisms predominately supported by pelagic energy had smaller body sizes than organisms predominately supported by nearshore benthic energy. We also found a hump-shaped trophic relationship in the food web where there is a gradual increase in the coupling of pelagic and nearshore energy channels with larger body sizes as well as higher trophic positions. This highlights the important role of body size and connectivity among habitats in structuring food webs. However, important deviations from expectations are suggestive of how species introductions and other anthropogenic impacts can affect food web structure in large lakes. First, native top predators appear to be flexible couplers that may provide food web resilience, whereas introduced top predators may confer less stability when they specialize on a single energy pathway. Second, some smaller bodied prey fish and invertebrates, in addition to mobile predators, coupled energy from pelagic and nearshore energy channels, which suggests that some prey species may also be important integrators of energy pathways in the system. We conclude that patterns predicted by the LTFWA are present in the face of species introductions and other anthropogenic stressors to a degree, but time-series evaluations are needed to fully understand the mechanisms that promote stability.

Lake Michigan↗

USGS2024

Climate-influenced phenology of larval fish transport in a large lake

Elucidating physical transport phenologies in large lakes can aid understanding of larval recruitment dynamics. Here, we integrate a series of climate, hydrodynamic, biogeochemical, and Lagrangian particle dispersion models to: (1) simulate hatch and transport of fish larvae throughout an illustrative large lake, (2) evaluate patterns of historic and potential future climate-induced larval transport, and (3) consider consequences for overlap with suitable temperatures and prey. Simulations demonstrate that relative offshore transport increases seasonally, with shifts toward offshore transport occurring earlier during relatively warm historic and future simulations. Intra- and inter-annual trends in transport were robust to assumed pelagic larval duration and precise location and timing of hatching. Larvae retained nearshore generally encountered more favorable temperatures and zooplankton densities compared to larvae transported offshore. Larval exploitation of nearshore resources under climate change may depend on a concomitant shift to earlier spawning and hatch times in advance of earlier offshore transport.

Lake Michigan↗

USGS2024

Improving how science informs policy within the Ecosystem Approach

Science is fundamental to sound policies, particularly when it comes to implementing an Ecosystem Approach. Science can and should inform nearly all facets of an Ecosystem Approach, yet challenges remain to realizing this goal. To help identify and better understand these challenges we used a qualitative comparative case study approach to identify and characterize the challenges and successes of implementing a science-driven Ecosystem Approach in the Laurentian Great Lakes. These case studies include delisting of Areas of Concern, improving coastal resilience, and addressing declining offshore lake productivity. These case studies were selected because they provide a set of very different, yet complementary, cases for assessing implementation, as well as the factors influencing the science-policy exchange. Through this comparative study, we identified a diverse set of challenges and successes, that were both systemic and case specific. Emerging from this comparative assessment were principles and enabling conditions (e.g. scale, governance, shared goals) we believe are critical to consider when establishing or improving a science-driven Ecosystem Approach.

Aquatic Ecosystem Health & Management↗

USGS2024

How diverse is the toolbox? A review of management actions to conserve or restore coregonines

Over the past centuries, coregonines have been exposed to a range of stressors that have led to extinctions, extirpations, and speciation reversals. Given that some populations remain at risk and fishery managers have begun restoring coregonines where they have been extirpated, we reviewed the primary and gray literature to describe the diversity of coregonine restoration or conservation actions that have been previously used. Although stocking of hatchery-reared fish has been commonly used for supplementing existing coregonine fisheries, we considered stocking efforts only with specifically conservation or restoration goals. Likewise, conservation-driven efforts of translocation were not widespread, except in the United Kingdom for the creation of refuge populations to supplement the distribution of declining stocks. Habitat restoration efforts have occurred more broadly and have included improving spawning habitat, connectivity, or nutrient concentrations. Although harvest regulations are commonly used to regulate coregonine fisheries, we found fewer examples of the creation of protected areas or outright closures. Finally, interactions with invasive species can be a considerable stressor, yet we found relatively few examples of invasive species control undertaken for the direct benefit of coregonines. In conclusion, our review of the literature and prior Coregonid symposia revealed relatively limited direct emphasis on coregonine conservation or restoration relative to more traditional fishery approaches ( e.g. , supplementation of fisheries, stock assessment) or studying life history and genetics. Ideally, by providing this broad review of conservation and restoration strategies, future management efforts will benefit from learning about a greater diversity of potential actions that could be locally applied.

International Journal of Limnology↗

USGS2024

Larval coregonine density and diet composition along beaches of northern Lake Michigan

Recent oligotrophication in Lake Michigan has contributed to reduced biomass of spring zooplankton and a shift in the zooplankton assemblage toward more calanoid copepods. These changes have likely altered prey availability for first feeding native fish species that hatch in early spring, including coregonines. While spring zooplankton density and community composition are routinely monitored in offshore areas of Lake Michigan, descriptions of zooplankton in nearshore areas such as shallow beach environments and associated diet characteristics among larval coregonine species are limited. In this study, we describe the nearshore (<1 m depth, beach environment) zooplankton community in northeastern Lake Michigan during early spring 2015-2019 and compare the diets and diet selectivity of larval Lake Whitefish ( Coregonus clupeaformis ) and Cisco ( C. artedi ). Zooplankton density and composition varied among years, but calanoid copepods and copepod nauplii consistently dominated the zooplankton assemblage. Cisco and Lake Whitefish larvae were captured regularly, with Elk Rapids containing the highest proportion of Ciscoes each year. Calanoid and cyclopoid copepods were common in diets and estimated to have a positive selection. Although previous research has indicated high consumption of cyclopoid copepods by larval coregonines in Lake Michigan, our results provide new evidence that larval Lake Whitefish and Cisco of northeastern Lake Michigan will also consume and positively select for calanoid copepods when they are abundant. As such, should calanoid zooplankton continue to dominate the copepod community in Lake Michigan, larval coregonines appear capable of exploiting this abundant prey to improve their likelihood of survival to later life stages.

Michigan↗

USGS2024

Comparison of cisco (Coregonus artedi) aerobic scope and thermal tolerance between two latitudinally-separated populations

The cisco Coregonus artedi is a coldwater fish that is distributed throughout much of Canada and the northern United States, including the Laurentian Great Lakes. Cisco historically supported large commercial fisheries in the Great Lakes during the late 1800s and early 1900s, but many populations declined and never recovered. Restoration efforts focusing on re-establishing cisco in the Great Lakes are underway, but increasing water temperatures may hinder these efforts. Therefore, we examined aerobic scope and thermal tolerance of allopatric cisco populations from different latitudes and habitats to determine if a southern latitude population (Crooked Lake, Indiana, USA) near the southern edge of cisco distribution was better adapted to withstand warmer water temperatures than a northern latitude population (Les Cheneaux Islands, Michigan, USA; Lake Huron). As expected, both stocks demonstrated increases in metabolic rates and absolute aerobic scope with increased temperature. Northern cisco had significantly lower aerobic scope compared to southern cisco at both treatment temperatures of 10 and 13 °C. Both cisco stocks had high thermal tolerances when challenged by temperatures increased to 20 and 23 °C but low tolerances at 26 °C. Cisco thermal tolerances increased with acclimation temperature, but we did not detect a difference in thermal tolerances between northern and southern cisco. Although southern cisco had higher capacity for aerobic metabolism, both stock sources had high thermal tolerances at the upper end of their thermal limits. Therefore, either population would be likely suitable for reintroduction into Great Lakes habitats, even with expected warming in the future.

Indiana, Michigan↗

USGS2024

Synchrony of alewife, Alosa pseudoharengus, year-class strength in the Great Lakes region

Fish recruitment is interannually variable and challenging to predict. Annual recruitment is often regionally synchronized among populations and identifying drivers of such synchrony may help shed light on recruitment dynamics. We investigated interannual variation of alewife Alosa pseudoharengus recruitment by estimating year-class strength for populations from three of the Laurentian Great Lakes (lakes Huron, Michigan, and Ontario) using annual assessment survey data from 1968 to 2022. We first determined the age when year-class strength was set for each dataset. We then used a mixed-modeling approach incorporating age, year-class, and sampling year to estimate year-class strength for each study lake. Thereafter, we evaluated regional synchrony in year-class strength across the three lakes and evaluated potential climatic drivers of synchrony. Our results suggest that alewife year-class strength is set by age-1. Our model-derived indices of alewife year-class strength were synchronized among the three lakes, and we identified spring-summer degree-days as a potential regional driver of synchrony. This analysis highlights the potential for strong influence of climatic conditions on fish recruitment in large freshwater systems.

Canadian Journal of Fisheries and Aquatic Sciences↗