Susan E. Doka

A moving target—incorporating knowledge of the spatial ecology of fish into the assessment and management of freshwater fish populations

Freshwater fish move vertically and horizontally through the aquatic landscape for a variety of reasons, such as to find and exploit patchy resources or to locate essential habitats (e.g., for spawning). Inherent challenges exist with the assessment of fish populations because they are moving targets. We submit that quantifying and describing the spatial ecology of fish and their habitat is an important component of freshwater fishery assessment and management. With a growing number of tools available for studying the spatial ecology of fishes (e.g., telemetry, population genetics, hydroacoustics, otolith microchemistry, stable isotope analysis), new knowledge can now be generated and incorporated into biological assessment and fishery management. For example, knowing when, where, and how to deploy assessment gears is essential to inform, refine, or calibrate assessment protocols. Such information is also useful for quantifying or avoiding bycatch of imperiled species. Knowledge of habitat connectivity and usage can identify critically important migration corridors and habitats and can be used to improve our understanding of variables that influence spatial structuring of fish populations. Similarly, demographic processes are partly driven by the behavior of fish and mediated by environmental drivers. Information on these processes is critical to the development and application of realistic population dynamics models. Collectively, biological assessment, when informed by knowledge of spatial ecology, can provide managers with the ability to understand how and when fish and their habitats may be exposed to different threats. Naturally, this knowledge helps to better evaluate or develop strategies to protect the long-term viability of fishery production. Failure to understand the spatial ecology of fishes and to incorporate spatiotemporal data can bias population assessments and forecasts and potentially lead to ineffective or counterproductive management actions.

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.

Evidence of yellow perch, largemouth bass and pumpkinseed metapopulations in coastal embayments of Lake Ontario

Coastal embayments have been and will continue to be constructed along the northwest shoreline of Lake Ontario to restore and create warmwater fish habitat. However, very little is known about the biological connections among embayments. Using otolith microchemistry on pumpkinseed, largemouth bass and yellow perch collected from three constructed embayments in 2006–2009, we confirm that these three species of fish each exist in a metapopulation. We find that juvenile pumpkinseed, largemouth bass and yellow perch occupy embayments different from their natal habitat after their first winter, and for at least pumpkinseed, continue to move among embayments after their second winter. We hypothesize that these fishes move among embayments after haphazardly dispersing from their overwintering habitat to the littoral zone each spring. Habitat restoration and remediation efforts in coastal Great Lakes habitats should take a system-based management approach that considers the spatial proximity of embayments, and attempts to create or preserve connected networks.

Temporal trends and spatial patterns in the temperature and oxygen regimes in the Bay of Quinte, Lake Ontario, 1972-2008.

The temperature and oxygen regimes of the Bay of Quinte have been monitored, weekly or biweekly, in the open water season at a series of offshore index sites since 1972. Since 2001, temperature has been monitored in situ using loggers at both offshore and nearshore sites. This study was undertaken to assess the potential role of morphometry, climate, nutrient loading, and invasion by dreissenids in temporal trends and spatial patterns of temperature and oxygen regimes. The thermal regime was assessed using summer surface temperatures, Schmidts vertical stability values, and vertical stratification characteristics. When the Quinte studies began taking measurements in the hypolimnion, deeper stations were attaining low oxygen levels by the end of summer, raising concerns that the cumulative impacts of eutrophication might lead to anoxia. The bottom oxygen regime at sites that stratified was assessed using the hypolimnetic warming rates and the apparent oxygen depletion rates one meter off the bottom. Quintes maximum summer surface waters have warmed almost 1 o C from 1972 to 2008 in line with climate warming. Nearshore sites in the shallow upper Bay have similar temperatures to offshore index sites while those in the lower Bay are warmer. The warming of surface waters has increased the maximum Schmidts stability values at the deeper sites but thermocline depth or bottom temperatures have not changed. Hypolimnetic warming rates showed no temporal change but were inversely correlated with mean summer flow from the main river draining into the Bay. Oxygen depletion was variable but exhibited a downward trend in response to reduced phosphorus loading with neither climate warming nor the driessenid invasion having a detectable effect. Projected 21st C climate warming poses a threat to the Bay of Quinte ecosystem.

Environmental factors affecting growth of eastern sand darter (Ammocrypta pellucida)

Environmental factors affecting growth of the threatened eastern sand darter (Ammocrypta pellucida (Putnam, 1863)) were examined using specimens sampled from the northern edge of its range to determine the species’ critical habitat. Length-at-age increments were determined from scale samples as surrogates for growth rates based on back-calculated lengths using the Fraser–Lee method. During the first year of life, 82% of total length is attained, suggesting considerable energetic partitioning towards reproduction following age-0. Positive relationships between age-0 length increments and sand substrates and between age-0 length increments and mean annual channel discharge indicated greatest first-year growth within sand-dominated, high-discharge habitats. Environmental factors that occurred at coarse spatial and temporal levels (i.e., mean annual channel discharge) explained more of the growth variability among eastern sand darters than those occurring at fine levels (i.e., site-level substrate composition...

Opportunities for Improving Aquatic Restoration Science and Monitoring through the Use of Animal Electronic-Tagging Technology

The ecological effectiveness of widespread and costly aquatic restoration efforts is often unknown. We reviewed studies incorporating electronic-tagging techniques (including radio, acoustic, satellite, biologging, and passive integrated transponder tags) into restoration-monitoring programs and discuss novel uses of these technologies and experimental design considerations. We found 25 studies, mostly published after 2005. Most were focused on salmonids or monitored the residency of species at artificial reefs. Few studies used site-level replication or data collected prior to restoration or at control sites, which limits the usefulness of their results for evaluating restoration effectiveness. The use of electronic tags and related sensors (e.g., temperature, depth) can reveal how habitats are used and their associated bioenergetic costs or benefits. These technologies are focused on individual- and population-level responses and complement traditional methods of assessing abundance, richness, and community composition but must be deployed in conjunction with well-designed experiments to truly better inform evaluations of restoration effectiveness.

Effects of water levels and water level regulation on the supply of suitable spawning habitat for eight fish guilds in the Bay of Quinte, Lake Ontario

Lake Ontario water levels are regulated under the International Joint Commissions Order of Approval. We assessed the availability of spawning habitat for eight fish guilds (grouped by vegetation and spawning temperature preferences) that use nearshore habitat in the Bay of Quinte, Lake Ontario, under regulated and pre-project water level scenarios. Our model used habitat characteristics of depth, substrate, vegetation cover and temperature across 14,876 habitat units and guild-based habitat suitabilities to assess the weighted suitable area (WSA) available for spawning. During the modelled 1951–2000 period, regulated water levels were on average 0.25 m lower than pre-project levels and varied about half as much. Overall, the large and shallow upper bay within the Bay of Quinte benefited from pre-project flows whereas the smaller and deeper lower bay benefited from regulated flows. Higher variance in water levels increased highly suitable wetland area and higher mean water levels increased the availability of shallow flooded area in the upper and middle bays, where the bathymetry is gradually sloping. The number of days over which WSA was available was generally greater for high temperature guilds, and appeared to decrease when temperature mismatches occurred in a season. Results emphasize the complexity of the relationship between fish habitat supply and water level regime.

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.

Water circulation in Toronto Harbour

We present an overview of physical processes that drive water circulation within the extended system of coastal embayments in the Toronto Harbour. The different water circulation patterns occur at various spatial and temporal scales, and our article provides context for the various efforts to improve water quality by the Toronto and Region Remedial Action Plan. Velocity profiles and water level measurements showed that the harbour’s Helmholtz pumping mode drives a 1-h period oscillation, which can influence flushing of the shallow embayments. This process likely persists year-round and would lead to flushing time-scales of between 1–11 days for these shallow embayments. If this ubiquitous pumping is combined with solar heat fluxes, it partially explains the persistent temperature gradients amongst the shallow embayments. In the larger and deeper (∼10 m) Inner Harbour, the prevailing westerly winds drive most of the mean circulation, with a current entering through the Western Gap and leaving through the Eastern Gap. This wind driven circulation leads to a residence time of water in the Inner Harbour between 7–14 days. In addition, periodic strong and sustained westerly winds can induce frequent upwelling events in Lake Ontario (between 4 to 10 times during the stratified season) that mildly increase the exchange flow and help maintain good water quality by exchange nearshore waters with cleaner hypolimentic waters. The intrusion of cold water into the harbour can also lead to highly variable temperature regimes with sudden drops in temperature that could have negative effects on aquatic organisms.

Telemetry-Determined Habitat Use Informs Multi-Species Habitat Management in an Urban Harbour

Widespread human development has led to impairment of freshwater coastal wetlands and embayments, which provide critical and unique habitat for many freshwater fish species. This is particularly evident in the Laurentian Great Lakes, where such habitats have been severely altered over the last century as a result of industrial activities, urbanization, dredging and infilling. In Toronto Harbour, extensive restoration efforts have been directed towards improving the amount and quality of aquatic habitat, especially for fishes. To evaluate the effectiveness of this restoration work, use of the restored area by both target species and the fish community as a whole must be assessed. Individuals from four species (Common Carp, Largemouth Bass, Northern Pike and Yellow Perch) were tagged and tracked continuously for 1 year using an acoustic telemetry array in Toronto Harbour area of Lake Ontario. Daily site fidelity was estimated using a mixed-effects logistic regression model. Daily site fidelity was influenced by habitat restoration and its interactions with species and body size, as well as season and its interactions with species and body size. Daily site fidelity was higher in restored sites compared to non-restored sites for Yellow Perch and Northern Pike, but lower for Largemouth Bass and Common Carp. For all species, daily site fidelity estimates were highest during the summer and lowest during autumn. The approach used here has merit for evaluating restoration success and informing future habitat management activities. Creating diverse habitats that serve multiple functions and species are more desirable than single-function-oriented or single-species-oriented designs.