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Walleye (Sander vitreus) populations in Alberta, Canada, collapsed by the mid-1990s and were a case study in the paper Canada's Recreational Fisheries: The Invisible Collapse? Here we fit age-structured population dynamics models to data from a landscapescale monitoring program to assess walleye population status and reconstruct recruitment dynamics following the invisible collapse. Assessments indicated that populations featured low [F.sub.msy] values of approximately 0.2-0.3 under conservative assumptions for the stock-recruitment relationship but that many populations were lightly exploited during 2000-2018. Recruitment reconstructions showed that recovery from collapse in 33/55 lakes was driven in part by large positive recruitment anomalies that occurred during 1998-2002. Additionally, 15/55 lakes demonstrated cyclic recruitment dynamics. The documented recruitment anomalies and cyclic fluctuations could be due to environmental effect(s) or cannibalism, and experimentation is likely necessary to resolve this uncertainty. These findings contribute new information on the recovery dynamics of walleye following the invisible collapse and demonstrate the effectiveness of coupling traditional fisheries science models with broad-scale monitoring data to improve understanding of population dynamics and sustainability across landscapes. Au milieu des annees 1990, les populations de dore jaune (Sander vitreus) en Alberta (Canada) s'etaient effondrees, constituant une etude de cas dans l'article intitule Canada's Recreational Fisheries: The Invisible Collapse? Nous calons des modeles de dynamique de la population structures par age sur des donnees issues d'un programme de surveillance a l'echelle du paysage dans le but d'evaluer l'etat des populations de dore jaune et de reconstituer la dynamique du recrutement dans la foulee de l'effondrement invisible. Des evaluations indiquent que les populations presentent de faibles valeurs de [F.sub.msy] d'environ 0,2-0,3 pour des hypotheses prudentes concernant la relation de recrutement au stock, mais que de nombreuses populations ont ete legerement exploitees durant la periode de 2000 a 2018. Les reconstitutions du recrutement montrent que le retablissement suivant l'effondrement dans 33 lacs sur 55 etait partiellement mu par d'importantes anomalies positives du recrutement qui se sont produites durant la periode de 1998 a 2002. En outre, 15 lacs sur 55 presentaient une dynamique de recrutement cyclique. Les anomalies de recrutement et les fluctuations cycliques documentees pourraient etre dues a un ou des effets environnementaux ou au cannibalisme, et des experiences sont probablement necessaires pour lever cette incertitude. Ces constatations fournissent de nouveaux renseignements sur la dynamique du retablissement du dore jaune dans la foulee de l'effondrement invisible et demontrent l'efficacite du jumelage de modeles traditionnels issus des sciences halieutiques a des donnees de surveillance a grande echelle pour ameliorer la comprehension de la dynamique et de la perennite des populations a l'echelle du paysage. [Traduit par la Redaction], Introduction The invisible collapse of inland recreational fisheries is among the most influential papers published in fisheries science (hereinafter 'invisible collapse'; Post et al. 2002 in Sass and Allen 2014). [...]

Take a sequence of contactomorphisms of a contact three-manifold that C^0-converges to a homeomorphism. If the images of a Legendrian knot limit to a smooth knot under this sequence, we show that it is contactomorphic to the original knot. We prove this by establishing that, on one hand, non–Legendrian knots admit a type of contact-squashing (similar to squeezing) onto transverse knots while, on the other hand, Legendrian knots do not admit such a squashing. The non-trivial input from contact topology that is needed is (a local version of) the Thurston–Bennequin inequality. [ABSTRACT FROM AUTHOR]

Complexity of addressing cumulative effects that vary in space and time, especially for species occupying large ranges, makes conservation and recovery of populations difficult. In Alberta, declines of all three native stream trout species led to them being listed as species at risk. We developed a novel, semi‐quantitative cumulative effects modelling process to quantify threats using stressor‐response curves with a single common response scale, wherein inputs were determined for each population, and outputs were used to create population‐specific recovery action hypotheses to inform management. Using a case study of bull trout recovery in Rocky Creek, Alberta, we tested these hypotheses using a before–after control‐impacted design. Recovery actions positively affected bull trout, and the modelling approach provided insight into threats (sedimentation and angling effort) that most likely limited the population. [ABSTRACT FROM AUTHOR]

We develop a mechanistically motivated von Bertalanffy growth model to estimate growth rate and its predictors from spatial-temporal data and compare this model's performance with a suite of commonly used mixed-effects growth models. We test these models with simulated data and then apply them to test whether concerns that high density is causing growth suppression of walleye (Sander vitreus) in Alberta, Canada, are supported using data collected during 2000-2017. Simulation experiments demonstrated that models that failed to account for complex dependency structures often resulted in growth rate estimates that were less accurate and biased low as judged by median absolute relative error and median relative error, respectively. The magnitude of this bias depended on the parameter values used for simulation. For the case study, a spatial-temporal model was more parsimonious and had higher predictive performance relative to simpler models and did not support the slow-growing walleye hypothesis in Alberta. These findings demonstrate the importance of considering spatial-temporal correlation in analyses that rely on surveillance-style monitoring datasets, particularly when examining relationships between life-history traits and environmental characteristics. Nous developpons un modele de croissance de von Bertalanffy a relations mecanistes pour estimer le taux de croissance et ses variables predictives a partir de donnees spatiotemporelles et comparons la performance de ce modele a une serie de modeles de croissance a effets mixtes couramment utilises. Nous mettons ces modeles a l'essai en utilisant des donnees simulees et les appliquons ensuite pour verifier si des donnees recueillies de 2000 a 2017 appuient l'interpretation proposee qu'une forte densite causerait une suppression de la croissance de dores jaunes (Sander vitreus) en Alberta (Canada). Des experiences de simulation demontrent que les modeles qui ne tiennent pas compte de structures de dependance complexes produisent souvent des estimations des taux de croissance moins exactes et biaisees vers le bas, comme indique par l'erreur relative mediane absolue et l'erreur relative mediane, respectivement. La magnitude de ce biais depend des valeurs des parametres utilisees pour la simulation. Pour l'etude de cas, un modele spatiotemporel s'avere plus parcimonieux et presente une meilleure performance predictive que les modeles plus simples et n'appuie pas l'hypothese des dores a croissance lente en Alberta. Ces resultats demontrent l'importance de tenir compte des correlations spatiotemporelles dans les analyses qui reposent sur des ensembles de donnees de type surveillance, en particulier pour l'examen des relations entre des caracteres du cycle biologique et des caracteristiques du milieu ambiant. [Traduit par la Redaction], Introduction Inland recreational fisheries are embedded in complex social-ecological systems (see Carruthers et al. 2019), generate ~US$51 billion * [year.sup.-1] in North America (Funge-Smith 2018), and support important ecosystem services [...]

We contrast catchability of walleye (Sander vitreus) and northern pike (Esox lucius) populations with angling fisheries across regions that differ twofold in growing-degree-days and productivity and sixfold in fish diversity. Populations of both species in Alberta, Wisconsin, Minnesota, and Oneida Lake, New York, had density-dependent catchability with approximately tenfold higher catchability in Alberta than in the other regions when density was controlled for. There is no evidence that the higher catchability estimates for Alberta walleye and northern pike are due to differential spatial distributions, enhanced hook avoidance due to catch and release or to differential size structure of the populations, or to differences in harvest regulations. We argue that the most likely explanation for the tenfold higher catchability is increased hunger resulting in enhanced foraging activity in the region with a substantially shorter growing season, lower prey productivity, and lower prey community diversity. Regardless of the proximate causes, higher catchability of fish harvested in recreational fisheries in Alberta substantially increases their vulnerability to overharvest and collapse if angling effort is unabated. Nous comparons la capturabilite de populations de dore jaune (Sander vitreus) et de grand brochet (Esox lucius) dans la peche sportive dans diverses regions presentant des differences du simple au double du nombre de degres-jour de croissance et de la productivite, et du simple au sextuple en ce qui concerne la diversite des poissons. Des populations des deux especes en Alberta, au Wisconsin, au Minnesota et dans le lac Oneida (New York) presentaient des capturabilites dependantes de la densite, celle de l'Alberta etant environ dix fois superieure a celles des autres regions quand la densite etait prise en consideration. Aucune observation ne porte a croire que les estimations de capturabilite plus elevees pour les dores jaunes et les grands brochets en Alberta decoulent de repartitions differentielles, d'un plus grand evitement des hamecons en raison de la peche avec remise a l'eau, de differences sur le plan de la structure de tailles des populations ou de differences touchant a la reglementation des prises. Nous postulons que l'explication la plus vraisemblable pour la capturabilite dix fois plus elevee en Alberta est la faim plus intense se traduisant par une activite de quete de nourriture accrue dans cette region caracterisee par une periode de croissance sensiblement moins longue, la productivite plus faible des proies et la plus faible diversite des communautes de proies. Quelles qu'en soient les causes immediates, a defaut d'une reduction de l'effort de peche sportive, la plus grande capturabilite des poissons vises par cette peche en Alberta accroit considerablement leur vulnerabilite a la surexploitation et a l'effondrement. [Traduit par la Redaction], Introduction Sustainable management of harvested populations requires understanding of population-level responses to exploitation, knowledge that is often lacking (Mace and Reynolds 2001). Generalizations can be hard to draw since susceptibility [...]

We prove that the number of Reeb chords between a Legendrian submanifold and its contact Hamiltonian push-off is at least the sum of the ℤ 2 -Betti numbers of the submanifold, provided that the contact isotopy is sufficiently small when compared to the smallest Reeb chord on the Legendrian. Moreover, the established invariance enables us to use two different contact forms: one for the count of Reeb chords and another for the measure of the smallest length, under the assumption that there is a suitable symplectic cobordism from the latter to the former. The size of the contact isotopy is measured in terms of the oscillation of the contact Hamiltonian, together with the maximal factor by which the contact form is shrunk during the isotopy. The main tool used is a Mayer–Vietoris sequence for Lagrangian Floer homology, obtained by "neck-stretching" and "splashing". [ABSTRACT FROM AUTHOR]

An obituary for Joseph Schieser Nelson, an ichthyologist is presented.