Cindy Chu

Linking fish population dynamics to habitat conditions: insights from the application of a process-oriented approach to several Great Lakes species

One of the major challenges facing fishery scientists and managers today is determining how fish populations are influenced by habitat conditions. Many approaches have been explored to address this challenge, all of which involve modeling at one level or another. In this paper, we explore a process-oriented model approach whereby the critical population processes of birth and death rates are explicitly linked to habitat conditions. Application of this approach to five species of Great Lakes fishes including: walleye (Sander vitreus), lake trout (Salvelinus namaycush), smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), and rainbow trout (Onchorynchus mykiss), yielded a number of insights into the modeling process. One of the foremost insights is that processes determining movement and transport of fish are critical components of such models since these processes largely determine the habitats fish occupy. Because of the importance of fish location, an individual-based model appears to be a nearly inescapable modeling requirement. There is, however, a paucity of field-based data directly relating birth, death, and movement rates to habitat conditions experienced by individual fish. There is also a paucity of habitat information at a fine temporal and spatial scale for many important habitat variables. Finally, the general occurrence of strong ontogenetic changes in the response of different life stages to habitat conditions emphasizes the need for a modeling approach that considers all life stages in an integrated fashion.

Evaluation of a Simple Method to Classify the Thermal Characteristics of Streams Using a Nomogram of Daily Maximum Air and Water Temperatures

Abstract This study assessed the applicability of an existing methodology to classify different stream sites into coldwater, coolwater, or warmwater areas based on their maximum air and water temperatures in summer. Using this methodology, single measurements of daily maximum air temperatures (≥24.5°C) and water temperatures at 1600 hours between July 1 and September 7 can be plotted on a nomogram to approximate the thermal classification of a site. Data from 122 sites throughout the Great Lakes basin, Ontario, indicated that the existing methodology should be revised to include sampling days from July 1 to August 31 instead of July 1 to September 7 and daily sampling periods between 1600 and 1800 hours as opposed to 1600 hours to capture the warmest temperatures at the sites. Data from 80 of the 122 sites consistently fell into the coldwater, coolwater, or warmwater categories. Data from 5 sites overlapped the coldwater and coolwater categories, whereas data from 37 sites overlapped the coolwater and war...

Potential spread of Great Lakes fishes given climate change and proposed dams: an approach using circuit theory to evaluate invasion risk

Abstract The Great Lakes currently harbour a number of non-native fishes that are thermally limited to the comparatively warm waters of Lake Erie and Lake Ontario. Climate change could facilitate the inland spread of many non-native species as the Great Lakes and their tributaries warm, putting thousands of inland lakes and streams at risk. We investigated how watershed network configurations, climate change and proposed hydro-power development could influence invasion risk in the Great Lakes Basin. Electric circuit theory was used to model hydrologic accessibility of aquatic ecological networks (i.e., lake, river, and impoundment chains) within tertiary watersheds. Risk of invasion was measured as the product of probability of non-native species spread (hydrologic accessibility) and amount of suitable thermal habitat under an ensemble of air temperature projections. Proposed hydro-power dam sites and their upstream catchments were used to evaluate changes in total risk of invasion given passable, semi-passable, and impassable dams. We show that projected climate change will lead to more coolwater stream and warmwater lake habitat. Overall invasion risk of cool- and warmwater species was highest in southern Ontario and surprisingly in northern watersheds draining into Lake Superior. This risk could be partially mediated by proposed dams if dams reduce connectivity and access to potentially suitable habitat. Our evaluation of mean invasion risk provides a broad-scale comparative tool for management of invasive species control options.

Estimating Fish Exploitation and Aquatic Habitat Loss across Diffuse Inland Recreational Fisheries

The current state of many freshwater fish stocks worldwide is largely unknown but suspected to be vulnerable to exploitation from recreational fisheries and habitat degradation. Both these factors, combined with complex ecological dynamics and the diffuse nature of inland fisheries could lead to an invisible collapse: the drastic decline in fish stocks without great public or management awareness. In this study we provide a method to address the pervasive knowledge gaps in regional rates of exploitation and habitat degradation, and demonstrate its use in one of North Americas largest and most diffuse recreational freshwater fisheries (Ontario, Canada). We estimated that (1) fish stocks were highly exploited and in apparent danger of collapse in management zones close to large population centres, and (2) fish habitat was under a low but constant threat of degradation at rates comparable to deforestation in Ontario and throughout Canada. These findings confirm some commonly held, but difficult to quantify, beliefs in inland fisheries management but also provide some further insights including (1) large anthropogenic projects greater than one hectare could contribute much more to fish habitat loss on an area basis than the cumulative effect of smaller projects within one year, (2) hooking mortality from catch-and-release fisheries is likely a greater source of mortality than the harvest itself, and (3) in most northern management zones over 50% of the fisheries resources are not yet accessible to anglers. While this model primarily provides a framework to prioritize management decisions and further targeted stock assessments, we note that our regional estimates of fisheries productivity and exploitation were similar to broadscale monitoring efforts by the Province of Ontario. We discuss the policy implications from our results and extending the model to other jurisdictions and countries.

Linking the land and the lake: a fish habitat classification for the nearshore zone of Lake Ontario

Abstract: The nearshore zones of the Great Lakes provide essential habitat for biota and are perhaps the region of the lakes most susceptible to human impacts. The objective of our study was to develop a fish habitat classification for the nearshore zone of Lake Ontario based on physical characteristics of that zone, land cover in the surrounding watershed, and fish community patterns. Nearly 80% of the spatial variation in fish community data was described by 2 physical variables (average fetch and bathymetric slope of the nearshore zone) and 2 land-cover variables (urban/industrial development and mixed forest cover) in adjacent watersheds. These variables are likely to be surrogates for other conditions in the nearshore, such as wave action, circulation, vegetation, and water quality. A 12-group fish habitat classification was developed from those variables. Validation and significance tests identified similarities and differences among the fish communities in the classes and indicated that the number of classes should be collapsed to 3: exposed, sheltered, and developed/urbanized. In general, the western basin of the lake was developed, the central region was exposed, and the eastern region of the lake was a mix of exposed and sheltered classes. These results highlight that even in lakes as large as Lake Ontario, the nearshore fish community is influenced by watershed land cover, and emphasize that management or restoration of the nearshore ecosystem in lakes will require integration of aquatic, watershed, and land-cover management.

Do existing ecological classifications characterize the spatial variability of stream temperatures in the Great Lakes Basin, Ontario?

ABSTRACT Ecological classifications of stream ecosystems have been used to develop monitoring programs, identify reference and impacted systems, and focus conservation efforts. One of the most influential, but highly variable, components of stream ecosystems is water temperature but few geographically broad-scale and long-term programs exist to assess and monitor temperatures. This study evaluated if existing ecological classifications could be used to categorize the similarities and differences in stream temperatures across the Ontario portion of the Great Lakes Basin. Concordance between the spatial variability in temperatures and an existing ecological classification would support the use of that classification to define areas with similar temperatures, guide the development of a monitoring program, and inform management programs. The five classifications evaluated were the ecoregions and ecodistricts defined in the National Ecological Framework for Canada, the ecoregions and ecodistricts defined in the Ecological Land Classification of Ontario, and the aquatic ecosystem units defined in the Aquatic Ecosystem Classification (AEC) for the Ontario portion of the Great Lakes Basin. Hierarchical linear modelling and corrected Akaike Information Criterion indicated that the ecodistrict classifications characterized more of the spatial variability in temperatures than the ecoregion and AEC classification but temperatures were more variable among sites within classes than between classes. Therefore, none of the existing ecological classifications could be used to characterize thermal variability. Future research should examine if the inability of the existing classifications to capture the thermal variability translates into inaccurate classification of other ecosystem components such as water quality, and macroinvertebrate and fish assemblages.

The effectiveness of terrestrial protected areas for lake fish community conservation

Freshwater protected areas are rare even though freshwater ecosystems are among the most imperiled in the world. Conservation actions within terrestrial protected areas (TPAs) such as development or resource extraction regulations may spill over to benefit freshwater ecosystems within their boundaries. Using data from 175 lakes across Ontario, Canada, we compared common indicators of fish-assemblage status (i.e., species richness, Shannon diversity index, catch per unit effort, and normalized-length size spectrum slopes) to evaluate whether TPAs benefit lake fish assemblages. Nearest neighbor cluster analysis was used to generate pairs of lakes: inside versus outside, inside versus bordering, and bordering versus outside TPAs based on lake characteristics. The diversity and abundance indicators did not differ significantly across comparisons, but normalized-length size spectrum slopes (NLSS) were significantly steeper in lakes outside parks. The latter indicated assemblage differences (greater abundances of small-bodied species) and less-efficient energy transfer through the trophic levels of assemblages outside parks. Although not significantly different, pollution- and turbidity-tolerant species were more abundant outside parks, whereas 3 of the 4 pollution-intolerant species were more abundant within parks. Twenty-one percent of the difference in slopes was related to higher total dissolved solids concentrations and angling pressure. Our results support the hypothesis that TPAs benefit lake fish assemblages and suggest that NLSS slopes are informative indicators for aquatic protected area evaluations because they represent compositional and functional aspects of communities.