L'écologie Spatiale des Relations Prédateur-Proie dans les Lacs

The pelagic zone of lakes is defined as the water column over the area of the lake benthos that does not receive enough light from the sun to allow macrophytes to grow. The four chapters of this thesis explore the spatial ecology of predator-prey interactions between schooling fish and their fish predators in this featureless environment. We first developed novel hydroacoustics methods to study fish and fish school swimming behaviour in the pelagic zone (Chapter 1 and 2). Then we characterized our in-situ school formation and prey movement observations using an ideal gas model to better understand the mechanisms that lead to fish and school densities during the daytime (Chapter 2 and 3). With this model we estimated the functional relationship between the schooling prey densities and predator encounter rates, and verified with empirical data a counterintuitive relationship that encounter rates decreased as overall prey densities increased (Chapter 3). The encounter rates suggested that predation within the pelagic zone might be greatly influenced by external forces if they provide spatial structure which encourages greater degrees of prey aggregation in predictable locations. In this regard we examined the predator-prey dynamics under wind and found large redistributions of prey and predators under windy conditions leading to greater aggregations in downwind locations. Further, we found that our study fish were larger in lakes that were oriented into the wind, perhaps demonstrating a benefit to fish growth under windy conditions (Chapter 4).Ph

Acoustically derived fish size-spectra within a lake and the statistical power to detect environmental change.

Fisheries acoustic surveys are increasingly being used to monitor the abundance of fish stocks yet their adoption as a tool to monitor changes in community size-spectra have not been well explored. In this study we use a series of historical acoustic surveys of the pelagic zones of three arms of Lake Opeongo to determine if acoustically derived size-spectra indicators (slope and height) can be effectively measured and used as a monitoring tool. Acoustic size spectra indicators were successfully measured for every survey, and resembled the same indicators found in netting surveys. From 2005 to 2009 the slope of the size-spectra became shallower, likely due to a decrease in abundance in schooling prey fish. Estimates of sources of survey variation including fish size estimates and inter-basin differences were low (The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The length of environmental review in Canada under the Fisheries Act

There is a common misconception among government officials that environmental regulations are bad for economic growth. Citing economic reasons, the Canadian federal government passed legislation in 2012 restricting the length of environmental reviews of new developments, even though review times were not empirically known. Using annual reports to Parliament from 2001 to 2010, we estimated using time-series analyses that review times under the Fisheries Act conformed to the new government mandated review times prior to major legislative changes to federal environmental oversight. The majority of submissions were processed within 1 year for mitigated impacts and within 2 years for authorized impacts. While it is possible that a minority of projects take longer, there is no evidence of large backlogs in the review process, and Canadian review times appear quicker than those in the United States. We highlight the need for empirical estimates of the costs of environmental regulations before governments enact substantial legislative changes that reduce environmental oversight and offer alternate recommendations for expediting environmental review times. </jats:p

Fish life history dynamics: Shifts in prey size structure evoke shifts in predator maturation traits

A bioenergetics framework is developed to predict optimal life history responses to environmentally driven changes in the rate of energy production by a predator. This framework is used to predict the responses of age at maturation, size at maturation and asymptotic size to changes in the predator/prey size ratio. Predators feeding on relatively smaller prey (i.e., having larger predator/prey size ratios) have lower growth efficiency and are predicted as a consequence to mature earlier, at smaller sizes and reach smaller asymptotic sizes. This prediction was tested using a 78 year time series (1936-2013) of data from a natural population of Lake Trout (Salvelinus namaycush) in Lake Opeongo, Algonquin Park, Ontario, Canada. A large decrease in the predator/prey size ratio for this population occurred over the period 1950-65 when a preferred prey (Cisco: Coregonus artedii) was introduced to the lake. This decrease was followed by ~ 20 years of constancy in the size ratio and then 25 years of progressive increase. Lake trout life history responded plastically during both periods and consistently with our predictions. Extensive analysis of available data provided little empirical support for alternative explanations for the observed changes in Lake Trout size and maturity (e.g. changes in Cisco and/or Lake Trout density and harvest rates). The framework developed here derives plastic life history changes from fixed developmental thresholds that are based on the scaling of net production with body size, and can be used to predict the shape of maturation reaction norms for the major shifts in community structure that are compactly summarized by changes in size spectrum parameters.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

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

<div><p>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 America’s 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.</p></div

The spatial distribution of the road coverage (grey lines) and distribution of projects (black dots) approved under the <i>Fisheries Act (1985)</i> delineated by Ontario’s Fisheries Management Zones.

<p>The spatial distribution of the road coverage (grey lines) and distribution of projects (black dots) approved under the <i>Fisheries Act (1985)</i> delineated by Ontario’s Fisheries Management Zones.</p

The spatial distribution of the yields of accessible fisheries in 2005 delineated by Ontario’s Fisheries Management Zones.

<p>The spatial distribution of the yields of accessible fisheries in 2005 delineated by Ontario’s Fisheries Management Zones.</p

The spatial distribution of the area of fish habitat protected using the average of the lower and upper bounds of our estimates in 2005 delineated by Ontario’s Fisheries Management Zones.

<p>The spatial distribution of the area of fish habitat protected using the average of the lower and upper bounds of our estimates in 2005 delineated by Ontario’s Fisheries Management Zones.</p

The spatial distribution of the surplus yield remaining following a fishing season in 2005 delineated by Ontario’s Fisheries Management Zones.

<p>The spatial distribution of the surplus yield remaining following a fishing season in 2005 delineated by Ontario’s Fisheries Management Zones.</p

The proportion of individual project sizes in numbers (left column) and in their cumulative sum of potential impact area to fish habitat (right column) from all the permits under the <i>Fisheries Act (1985)</i> granted in Ontario in 2005 to developers.

<p>We present two scenarios that represent a lower and upper bound to our estimates of fish habitat protected for each permit: Scenario 1) Letters of Advice represent generally small projects, and Scenario 2) Letters of Advice represent projects that without the <i>Fisheries Act (1985)</i> would have impacted standard project-specific areas of fish habitat (i.e. HADDs).</p