Tag Archives: Theis

Theis, S.*, Shirton, J.*, Barbeau, M.*, Ruppert, J. W. L.* and M.S. Poesch (2025) Growth and diet of Northern Pike (Esox lucius) in Boreal lakes: Implications for Ecosystem Management. Hydrobiologia 4(1): 1.

Abstract: 

An important top-down predator, the northern pike (Esox lucius), faces harsh environmental conditions in the northern boreal ecoregion. They are often managed for recreational fishing and, more recently, to create environmental offsets; strategies aimed at balancing ecological impacts by enhancing or restoring habitats. Our study examines northern pike populations in two remote boreal lakes in northern Alberta: Steepbank and Wappau. The lakes differ in size, vegetation cover, and trophic status, providing a natural experiment for investigating northern pike growth, condition, diet, and population density. Over three years (2018–2020), northern pike were sampled using gill nets. Population metrics, including growth, condition, and stomach contents, were compared between the lakes. Steepbank, a smaller, oligotrophic lake with low vegetation cover, showed lower prey fish densities compared to the larger, eutrophic Wappau, but it did not differ in northern pike catch per unit effort. Growth rates and body condition varied significantly between the lakes, with the northern pike in Wappau exhibiting faster growth and a better condition in the older age groups, while the younger northern pike in Steepbank had higher relative weights. A diet analysis revealed significant differences in prey consumption: Steepbank northern pike displayed higher rates of conspecific predation and invertebrate consumption, particularly in the younger age classes. These findings highlight how lake characteristics and prey availability shape northern pike population dynamics, offering valuable insights for lake management approaches in northern Alberta.

Citation: Theis S., Shirton J., Barbeau M., Ruppert J. W. L. and M.S. Poesch (2025) Growth and diet of Northern Pike (Esox lucius) in Boreal lakes: Implications for Ecosystem Management. Hydrobiologia 4(1): 1.

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Theis, S.*, Ruppert, J. L. W. and M. S. Poesch. (2023) Coarse woody habitat use by local fish species and structural integrity of enhancements over time in a shallow northern boreal lake assessed in a Bayesian modeling approach. Ecological Solutions and Evidence 4(2): e12200.

*Lab members: Sebastian Theis, Jonathan Ruppert (former member) and Mark Poesch. Check out opportunities in the lab!

Theis, S.*, Cartwright, L., Chreston, A., Coey, B., Graham, B., Little, D., Poesch, M. S., Portiss, R., Scott, R., Wallace, A., and J. L. W. Ruppert. (2025) Balancing sampling effort against costs for nearshore fish communities in Toronto waterfront, Lake Ontario. Fisheries Management and Ecology: 31(1): e12733.

Abstract: 

To enhance management of aquatic systems, long-term monitoring programs are crucial. However, managers often lack sufficient guidance in decision-making. In this study, we analyzed nearshore electrofishing data from Lake Ontario spanning 18 years and over 100,000 caught fish to assess sampling designs for various coastal habitats. Using simulation, we evaluated precision of Catch Per Unit Effort (CPUE) for all species, piscivores, and specialist species, at different levels of electrofishing sampling effort. For overall CPUE in any habitat type, increased precision declined with additional electrofishing runs, particularly after reaching 30–40 runs. Adjustments in sampling effort, such as adding 10 runs per year for open-coast sites, increased precision of overall CPUE by 10%. Adding 8 runs per year for wetlands increased precision of specialist-species CPUE by 10%. However, additional runs in embayments did not increase precision for all species, piscivores, or specialist species. Our findings underscore the importance of considering community composition and abundance when evaluating CPUE precision, and illustrates a flexible approach to optimize sampling effort in aquatic monitoring programs.

Citation: Theis, S., Cartwright, L., Chreston, A., Coey, B., Graham, B., Little, D., Poesch, M. S., Portiss, R., Scott, R., Wallace, A., and J. L. W. Ruppert. (2025) Balancing sampling effort against costs for nearshore fish communities in Toronto waterfront, Lake Ontario. Fisheries Management and Ecology: 31(1): e12733.

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Theis S.*, Chin, A. T.M., Wallace, A., Cartwright L., Fortin M.J., Poesch, M.S. and Ruppert, J.L.W. (2025) Complexity and spatial structuring of fish communities across urbanized watersheds and waterfronts. Urban Ecosystems 28: 1–18.

*Lab members: Sebastian Theis, Jonathan Ruppert (former member) and Mark Poesch. Check out opportunities in the lab!

Theis S.*, Chin, A. T.M., Wallace, A., Cartwright L., Fortin M.J., Poesch, M.S. and Ruppert, J.L.W. (2025) Complexity and spatial structuring of fish communities across urbanized watersheds and waterfronts. Urban Ecosystems 28: 1–18.

Abstract: 

Understanding the spatial structure and diversity of fish communities in urban environments is crucial for effective conservation and management. Our study investigates the complexity and spatial structuring of fish communities across urbanized watersheds and waterfronts in the Toronto region, identifying distinct groups based on sampling locations using modularity analysis and partial least square path modeling (PLS-PM). We evaluated the influence of environmental factors, including habitat, human impact, and species traits, on fish community composition. Our results reveal three distinct fish community groups. The first group, primarily located in major watersheds such as Humber and Rouge, is characterized by lower human impact and larger tracts of less developed land, where habitat variables like water quality play a significant role. These areas support species with intermediate tolerance levels. The second group includes diverse waterfront and nearshore habitats, where high species richness and variability are influenced by varied environmental conditions and riparian zones, with limited urban impact. The third group, encompassing some of the more urbanized areas, faces the constraints of urbanization and a high density of instream barriers, resulting in lower species diversity and a dominance of disturbance-tolerant species. Our findings highlight how different urban environments shape fish communities based on available habitat in interatom with species traits. This underscores the importance of tailored urban watershed management strategies based on urbanization levels and habitat constraints.

Citation: Theis S., Chin, A. T.M., Wallace, A., Cartwright L., Fortin M.J., Poesch, M.S. and Ruppert, J.L.W. (2025) Complexity and spatial structuring of fish communities across urbanized watersheds and waterfronts. Urban Ecosystems 28: 1–18.

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Theis S.*, Cartwright L., Chreston A., Coey B., Graham B., Little D., Poesch M.S., Portiss R., Wallace A. and J. L. W. Ruppert (2024). A multi-metric index for assessing two decades of community responses to broad scale shoreline enhancement and restoration along the Toronto waterfront. Aquatic Conservation: Marine and Freshwater Ecosystems 34: e24141.

*Lab members: Sebastian Theis, Jonathan Ruppert (former member) and Mark Poesch. Check out opportunities in the lab!

Theis S.*, Cartwright L., Chreston A., Coey B., Graham B., Little D., Poesch M.S., Portiss R., Wallace A. and J. L. W. Ruppert (2024). A multi-metric index for assessing two decades of community responses to broad scale shoreline enhancement and restoration along the Toronto waterfront. Aquatic Conservation: Marine and Freshwater Ecosystems 34: e24141.

Abstract:

The twin crises of climate change and biodiversity loss requires Notably, as one of the largest projects of its kind in the Great Lakes region (~500 hectares), extensive aquatic enhancement and restoration has been completed to support terrestrial and aquatic ecosystems with the intent of improving overall ecosystem health and biodiversity. Using twenty years of fish community data, we examined ecosystem responses in a spatio-temporal context across wetland and embayment ecotypes. Fish communities were assessed through a multi-metric index based on species life-history traits and habitat association. Generally, fish communities along the waterfront have transitioned from cool and coldwater pelagic species. Further, there are higher proportions of generalists and a higher proportion of native warmwater species, many of them piscivores, associated with cover and vegetation, that tend to meet community targets. Notably, these changes are more pronounced at Tommy Thompson Park compared to the rest of the waterfront, where communities approach natural reference levels. This result indicates the benefits and effectiveness of the decade long restoration efforts and subsequent monitoring of responses. This study provides important implications for large scale restoration and enhancement activities globally.

Citation: Theis S., Cartwright L., Chreston A., Coey B., Graham B., Little D., Poesch M.S., Portiss R., Wallace A. and J. L. W. Ruppert (2024). A multi-metric index for assessing two decades of community responses to broad scale shoreline enhancement and restoration along the Toronto waterfront. Aquatic Conservation: Marine and Freshwater Ecosystems 34: e24141.

Also Read:

Theis S.*, Cartwright L., Chreston A., Wallace A., Graham B., Coey B., Little D., Poesch M.S., Portiss R., and J. Ruppert (In Press). Nearshore fish community changes along the Toronto Waterfront in accordance with management and restoration goals: Insights from two decades of monitoring. PLos One.

*Lab members: Sebastian Theis, Mark Poesch. Check out opportunities in the lab!

Theis S.*, Cartwright L., Chreston A., Wallace A., Graham B., Coey B., Little D., Poesch M.S., Portiss R., and J. Ruppert (2024). Nearshore fish community changes along the Toronto Waterfront in accordance with management and restoration goals: Insights from two decades of monitoring. PLos One: 19(2): e0298333.

Abstract:

Aquatic habitat in the Greater Toronto Area has been subject to anthropogenic stressors. The subsequent aquatic habitat degradation that followed led to the Toronto and Region waterfront being listed as an Area of Concern in 1987. Thus, extensive shoreline and riparian habitat restoration have been implemented as part of the Toronto and Region Remedial Action Plan in conjunction with local stakeholders, ministries, and NGOs in an overall effort to increase fish, bird, and wildlife habitat. A key aspect of current fish habitat restoration efforts, monitored by Toronto and Region Conservation Authority, is to account for long-term community changes within the target ecosystem to better understand overall changes at a larger spatial scale. Here we use electrofishing data from the past 20 years with over 100,000 records and across 72km of coastline to show how declines and fluctuations in fish biomass and catch along the waterfront are driven by a few individual species across three main ecotypes, such as coastal wetlands, embayments, and open coast sites, with the remaining species showing a high level of stability. Using community traits and composition for resident species we demonstrate native warmwater species have become more dominant along the waterfront in recent years, suggesting that restoration efforts are functioning as intended. Additionally, piscivore and specialist species have increased in their relative biomass contribution, approaching existing restoration targets. Altogether this waterfront-wide evaluation allows us to detect overall changes along the waterfront and can be beneficial to understand community changes at an ecosystem level when implementing and monitoring restoration projects.

Citation: Theis S., Cartwright L., Chreston A., Wallace A., Graham B., Coey B., Little D., Poesch M.S., Portiss R., and J. Ruppert (2024). Nearshore fish community changes along the Toronto Waterfront in accordance with management and restoration goals: Insights from two decades of monitoring. PLos One: 19(2): e0298333.

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Theis, S.*  Castellanos D.A., Hamann A. and M.S. Poesch. (2022) Exploring the potential role of habitat banks in preserving freshwater biodiversity and imperiled species in the United States. Biological Conservation 273: 109700.

*Lab members: Sebastian Theis, Mark Poesch. Check out opportunities in the lab!

Theis S.* and M. S. Poesch. (2024). What makes a bank a bank? Differences and commonalities in credit calculation, application, and risks in mitigation banks targeting freshwater fish species and associated ecosystems. Environmental Management: 73(1): 199-212.

Abstract:

Mitigation banking is part of the ever-expanding global environmental market framework that aims to balance negative approved anthropogenic impacts versus third-party provided ecosystem benefits, sold in the form of credits. Given the need to conserve freshwater biodiversity and habitat, banking has received great traction in freshwater systems. While extensive reviews and studies have been conducted on evaluating if equivalency between impacts and offset can be achieved, there is almost no research being done on the way credits are being generated. Synthesizing banking data through cluster analyses from 26 banks in the United States generating credits for freshwater species and systems, we show two dominant approaches: removing barriers and targeting whole communities. Both address crucial freshwater conservation needs but come with their risks and caveats. Using common characteristics and management practices within these two groups, we showcase and conclude that credit generation via barrier removal can be at risk of granting credit generation for too large of an area, leading to over-crediting. Banks targeting whole freshwater communities and accounting for landscape-level interactions and influences can potentially be detrimental for species on an individual level and large-scale credit availability as well as transfer can incentivize non-compliance with the mitigation hierarchy.

Citation: Theis S. and M. S. Poesch. (2024). What makes a bank a bank? Differences and commonalities in credit calculation, application, and risks in mitigation banks targeting freshwater fish species and associated ecosystems. Environmental Management: 73(1): 199-212.

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Theis S.*, and M.S. Poesch (2022) Assessing conservation and mitigation banking practices and associated gains and losses in the United States. Sustainability 14: 6652.

*Lab members: Sebastian Theis, Mark Poesch. Check out opportunities in the lab!

Theis, S.* and M. S. Poesch. (2024).  Mitigation bank applications for freshwater systems: Control mechanisms, project complexity, and caveats. PLOS One 19(2): e-292702.

Abstract:

Biodiversity and mitigation banking has become a popular alternative offsetting mechanism, especially for freshwater species and systems. Central to this increase in popularity is the need for sound control mechanisms to ensure offset functionality. Two commonly used mechanisms are monitoring requirements and staggered release of bank credits over time. We used data from 47 banks in the United States, targeting freshwater systems and species. Based on the 47 banks meeting our criteria we showed that control mechanisms generally scale with increased project complexity and that banks release most of their total credit amount within the first 3 years. We further showed that advance credits are common and can increase the potential for credit release without providing tangible ecological benefits. Physical and biological assessment criteria commonly used by banks let us identify three main bank types focusing on connectivity, physical aspects, and habitat and species and their application possibilities and caveats to provide different ecosystem benefits for freshwater species and systems affected by anthropogenic development.

Citation: Theis, S. and M. S. Poesch. (2024).  Mitigation bank applications for freshwater systems: Control mechanisms, project complexity, and caveats. PLOS One 19(2): e-292702.

Also Read:

Theis S.*, and M.S. Poesch (2022) Assessing conservation and mitigation banking practices and associated gains and losses in the United States. Sustainability 14: 6652.

*Lab members: Sebastian Theis, Mark Poesch. Check out opportunities in the lab!

Theis, S.*, Ruppert, J. L. W. and M. S. Poesch. (2023) Coarse woody habitat use by local fish species and structural integrity of enhancements over time in a shallow northern boreal lake assessed in a Bayesian modeling approach. Ecological Solutions and Evidence 4(2): e12200.

Abstract:

  1. The introduction of coarse woody habitat has been a widely adopted management practice for restoring and enhancing freshwater aquatic ecosystems. Although responses of aquatic fish and invertebrate communities have largely been documented for lotic systems, benefits for lentic ecosystems have been mostly unevaluated.
  2. We tested the responses of fish populations to coarse woody habitat structures through a Bayesian modeling approach in a northern boreal lake in Alberta, Canada by enhancing a stretch of littoral zone with low structural complexity through introduction of coarse wood bundles and whole tree structures. The study site was split into three treatments, a Spaced treatment (structures 30 m apart), a Clustered treatment (structures 15 m apart), and an unaltered area (Control).
  3. Catch per unit effort and Catch per unit area data were collected over 2 years and posterior model predictions showed an increase in habitat use of the enhanced areas by spottail shiner – Notropis hudsonius; northern pike – Esox lucius; white sucker – Catostomus commersonii; brook stickleback – Culaea inconstans. No probable effect on overall fish condition, measured in Relative Weight, was linked to the enhancements.
  4. Across the two-year study, wood bundles degraded faster compared to the whole tree drops, coinciding with leveling off catch per unit effort and catch per unit area predictions near wood bundles, although catch predictions increased near the whole tree structures. Structural degradation set in as early as 1 week post construction for wood bundles and was mostly related to anchoring aspects.
  5. Results from our study provide evidence for the benefits provided by coarse woody habitat within northern boreal lake systems.  They furthermore highlight the short-lived nature of wood bundles built with biodegradable substances.  Methodologically our results offer evidence on the feasibility and utility of predictive modeling frameworks in addressing pseudoreplication and providing informative value for ecological studies.

Citation: Theis, S., Ruppert, J. L. W. and M. S. Poesch. (2023) Coarse woody habitat use by local fish species and structural integrity of enhancements over time in a shallow northern boreal lake assessed in a Bayesian modeling approach. Ecological Solutions and Evidence 4(2): e12200.

Also Read:

Theis, S.*, Ruppert, J.*, Shirton, J.* and M.S. Poesch (2022) Measuring beta diversity components and beneficial effects of coarse woody habitat introduction on invertebrate and macrophyte communities in a shallow northern boreal lake: implications for offsetting. Aquatic Ecology 56: 793-814.

*Lab members: Sebastian Theis, Jonathan Ruppert and Mark Poesch. Check out opportunities in the lab!

Theis, S.*  Castellanos D.A., Hamann A. and M.S. Poesch. (2023) Small-bodied fish species from western United States will be under severe water stress by 2040. Conservation Science and Practice: e12856.

Abstract:

Human need to appropriate freshwater in combination with climate change has intensified the rapid decline in freshwater biodiversity. Based onUsing census data, threat assessments, life history traits, as well as projections for anticipated water stress, we carried out a risk assessment for 216 currently imperiled freshwater species in the United States. , the The results suggest that Southwestern, and the Rocky Mountains, regions willwere predicted to experience the highest increase in future water stress for 2040 in 41 minor watersheds. Resident-small species in the Southwest, found in single locations (21.6%) or on local level highly localized (62.2%), were listed as endangered (n = 37) and are predicted to experience severe water stress increases by Endangered species in the Rocky Mountains (n = 9), were found on a single basins or local level had localized distributions (33.3%), and had exhibiting predominantly potamodromous  behaviour (66.7%). Furthermore, many endangered species in key regions lack life-history data (41%). Our results highlight predict patterns of imperilment associated with life history traits and distributions, but that were unrelated to overall fish biodiversity or biodiversity hotspots. that assessing species using The research therefore highlights that biodiversity as an indicators may not be useful to prioritize conservation efforts for identifying future impacts to imperiled species, since many regions undergoing high water stress did not coincide with biodiversity hotspots. Keywords: Climate Change; Water Stress; Biodiversity; Preservation.

Citation: Theis S., Castellanos-Acuna D., Hamman A. and M. S. Poesch. (2023) Small-bodied fish species from western United States will be under severe water stress by 2040. Conservation Science and Practice: e12856.

Also Read:

Miller, M., Stevens, C. and M. S. Poesch. (In Press). Effectiveness of Spawning Substrate Enhancement for Adfluvial Fish in a Regulated Sub-Arctic River. River Research and Applications.

*Lab members: Sebastian Theis and Mark Poesch. Check out opportunities in the lab!

Theis, S.*  Castellanos D.A., Hamann A. and M.S. Poesch. (2022) Exploring the potential role of habitat banks in preserving freshwater biodiversity and imperiled species in the United States. Biological Conservation 273: 109700.

Abstract:

Habitat banking, a conservation approach to offset habitat loss, has been widely accepted and implemented in the United States, especially for the protection of freshwater ecosystems. The potential adequacy of the habitat banking approach has, however, not yet been formally quantified in the context of its underlying framework and policies. Using a gap analysis approach, we test the current adequacy and future potential of habitat banking for 2313 approved and 552 pending banks in the United States. In the analysis, we consider water stress due to projected climate change, freshwater diversity, imperiled species, and human population growth, among other factors. The results show that the highest conservation urgency was assigned to states in the Southwest with high levels of species imperilment and large increases in anticipated water stress. The banking network covers most of the freshwater biodiversity hotspots in the East and Southeast. Land ownership is a potential driver for the low bank density in western states, with large proportions of land being owned and managed through federal agencies and only 58 banks situated on federal land. While the banking network in the United States is one of the most developed on a global level, gaps and priority areas can be clearly identified to strengthen the current network and its role in preserving freshwater habitat and diversity. Keywords: Offsetting; Conservation policy; Biodiversity market; Preservation.

Citation: Theis, S.  Castellanos D.A., Hamann A. and M.S. Poesch. (2022) Exploring the potential role of habitat banks in preserving freshwater biodiversity and imperiled species in the United States. Biological Conservation 273: 10970.

Also Read:

Theis, S.* and M. S. Poesch. (In Press).  Mitigation bank applications for freshwater systems: Control mechanisms, project complexity, and caveats PLOS One.

 

*Lab members: Sebastian Theis and Mark Poesch. Check out opportunities in the lab!