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Forage fish form a critical trophic link in marine ecosystems, and yet, for many species, there is limited information available. As nations move from single species stock assessments to ecosystem approaches to fisheries management (EAFMs), more information on forage fish will be required. In this study, 50 years of scientific literature were systematically mapped for 11 forage fish species in Canada's Arctic, Atlantic, and Pacific oceans. The objectives were to identify (1) knowledge clusters and gaps and (2) the pressures studied in relation to forage fish outcomes. Of the 2897 articles mapped, the majority studied adults and the distribution, productivity, growth, and life history of commercially fished species. Knowledge gaps were identified for forage fish: (1) that were noncommercially exploited; (2) egg and larval life history stages of most species and juveniles of noncommercial species; (3) diets of most species; (4) migration and performance for all species and survival of noncommercial species; and (5) the effects of some pressures (e.g., large-scale climate pressures). Addressing these knowledge gaps would improve the application of EAFMs. Key words: forage fish, literature mapping, knowledge gaps, pressures, ecosystem role Si les poissons-fourrage forment un lien trophique cle dans les ecosystemes marins, peu d'information est disponible pour bon nombre d'especes. Alors que les nations delaissent les evaluations de stocks monospecifiques pour des approches ecosystemiques de gestion des peches (AEGP), plus d'information sur les poissons- fourrage sera necessaire. Nous avons cartographie systematiquement 50 annees de publications scientifiques sur 11 especes de poissons-fourrage dans les regions des oceans Arctique, Atlantique et Pacifique du Canada, les objectifs etant de cerner (1) les groupes de connaissances et les lacunes dans les connaissances et (2) les pressions etudiees par rapport a la situation de poissons-fourrage. Des 2 897 articles cartographies, la majorite s'interessent aux adultes, et a la repartition, la productivite, la croissance et le cycle biologique d'especes de poissons visees par la peche commerciale. Differentes lacunes dans les connaissances ont ete cernees concernant notamment (1) les poissons-fourrage non vises par la peche commerciale, (2) les etapes des oeufs et des larves du cycle biologique de la plupart des especes et les juveniles d'especes non visees par la peche commerciale, (3) le regime alimentaire de la plupart des especes, (4) la migration et la performance pour toutes les especes et la survie d'especes non commerciales et (5) les effets de certaines pressions (p. ex. pressions climatiques a grande echelle). Combler ces lacunes dans les connaissances permettrait d'ameliorer la mise en oeuvre d'AEGP. [Traduit par la Redaction] Mots-cles : poissons-fourrage, cartographie de la documentation, lacunes dans les connaissances, pressions, role ecosystemique, Introduction Small pelagic fish play a critical but often poorly understood role within trophic food webs and ecosystems (Boldt et al. 2019). They transfer energy from plankton to predators, such [...]

Euphausiids are a keystone species in marine food webs of the Northeast Pacific Ocean, important for forage fish, commercial fish species and marine predators such as seabirds and whales. Ecosystem-based fisheries management relies on realistic lower-trophic-level information for forecasting under future changing climate scenarios. We synthesised information from quantitative modelling studies analysing the relationship between euphausiids and their environment for two species of euphausiids that dominate assemblages in this region--Euphausia pacifica and Thysanoessa spinifera. Studies analysed suggest that variables reflecting the physical and biological environment in situ, features reflecting the geomorphic marine landscape, and large-scale climate indices all significantly affect euphausiid biomass and distribution. Temperature was the most tested predictor variable in the euphausiid models reviewed; however, it was significant in fewer models than other variables tested. We review and compare model structures, predictor variable selection and temporal lag phases to develop recommendations for species distribution modelling of euphausiids in the Northeast Pacific Ocean. We believe the results from this review will be applicable globally across regions with similar climates where euphausiids are numerous and can be adapted for different species and environments. Les euphausiaces sont des especes cles dans les reseaux trophiques marins du nord-est de l'ocean Pacifique, d'importance pour des poissons-fourrages, des especes commerciales de poissons et des predateurs marins, dont des oiseaux marins et des baleines. La gestion ecosystemique des peches requiert de l'information sur les niveaux trophiques inferieurs pour etablir des previsions associees a des scenarios de changements climatiques futurs. Nous presentons une synthese de l'information issue d'etudes de modelisation quantitatives de la relation entre les euphausiaces et leur milieu dans le nord-est du Pacifique pour deux especes d'euphausiaces dominants dans les assemblages--Euphausia pacifica et Thysanoessa spinifera. Les etudes analysees indiqueraient que des variables qui refletent le milieu physique et biologique en place, des caracteristiques du paysage geomorphologique marin et des indices climatiques a grande echelle ont tous une incidence significative sur la biomasse et la repartition des euphausiaces. Si la temperature est la variable predictive la plus souvent analysee dans les modeles d'euphausiaces examines, elle s'avere toutefois significative dans un moins grand nombre de modeles que d'autres variables analysees. Nous passons en revue et comparons les structures de modeles, la selection de variables predictives et les phases de decalage temporel afin de formuler des recommandations pour la modelisation de la repartition d'especes d'euphausiaces dans le nord-est de l'ocean Pacifique. Nous croyons que les resultats de la presente synthese pourront etre appliques dans differentes regions du monde aux climats semblables ou les euphausiaces sont nombreux et qu'ils peuvent etre adaptes aux conditions oceanographiques propres a differentes especes. [Traduit par la Redaction], 1. Introduction Coastal seas are regions of rich biomass and high biodiversity. Active management of marine resources is often concentrated around the coast where anthropogenic and economic needs most often [...]

The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4-6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success. Si le declin des epaulards residents du Sud (Orcinus orca) pourrait etre cause par une penurie de proies, il existe peu de donnees permettant de valider cette hypothese. Nous comparons la disponibilite de proies (saumons chinooks, Oncorhynchus tshawytscha) recherchees par les epaulards residents du Sud dans le detroit de Juan de Fuca durant l'ete a l'abondance et la repartition des saumons chinooks disponibles pour la population beaucoup plus grande et croissante d'epaulards residents du Nord qui s'alimentent dans le detroit de Johnstone. Nous employons des echosondeurs multifrequences embarques pour cerner d'eventuelles differences entre les champs de proies qui pourraient expliquer la dynamique de ces deux populations d'epaulards. Contrairement aux attentes, nous constatons que les deux habitats des epaulards presentent des repartitions parcellaires de proies qui ne presentent pas de differences sur le plan de la frequence de presences de proies ou de la composition des tailles de poissons. La densite de poissons dans chaque parcelle est cependant de quatre a six fois plus grande dans l'habitat des epaulards residents du Sud. Ces constatations n'appuient pas l'hypothese voulant que les epaulards residents du Sud soient aux prises avec une penurie de proies dans la mer des Salish durant l'ete et indiqueraient qu'une combinaison d'autres facteurs influe sur le succes global de la quete de nourriture. [Traduit par la Redaction], Introduction The southern residents are a seasonally migrating population of killer whales (Orcinus orca) that specialize in consuming salmon. They have declined in numbers since 2011, and are listed as [...]

The choice of spatial scale and modelling technique used to capture species--habitat relationships needs to be considered when ascertaining environmental determinants of habitat quality for species and communities. Fish densities and environmental data were collected at three Laurentian lakes using underwater surveys by four snorkelers collecting fine spatial data acquired through geographic positioning systems. At both fine (20 m) and broad (100 m) spatial scales, tree-based approaches, which incorporated both linear and nonlinear relationships, explained more variation than their linear counterparts. At the finest spatial scale considered (20 m), local environmental conditions, such as habitat structure and heterogeneity, were important determinants of fish habitat selection. At the broadest spatial scale considered (100 m), fish tended to select habitat based on both local environmental features and riparian development. Moran's eigenvector maps further revealed that fish-habitat associations were operating at broader spatial scales than the predefined analytical units, which can be partially attributed to the spatial structure of environmental conditions acting at spatial scales greater than 100 m. This study highlights the importance of evaluating statistical approaches at different spatial scales to identify key determinants of habitat quality for species, ultimately to assess the effects of perturbations on ecosystems. Le choix de l'echelle spatiale et de la technique de modelisation utilisees pour cerner les relations espece--habitat doit etre pris en consideration dans l'evaluation des determinants environnementaux de la qualite de l'habitat pour les especes et les communautes. Des densites de poissons et des donnees environnementales ont ete mesurees pour trois lacs laurentiens dans le cadre de leves sous-marins par quatre plongeurs en apnee qui ont recueilli des donnees de haute resolution spatiale a l'aide de systemes de positionnement global (GPS). Aux echelles spatiales tant fine (20 m) que plus grossiere (100 m), les approches arborescentes, qui integrent des relations lineaires et non lineaires, expliquaient une plus grande partie de la variation que leurs pendants lineaires. A l'echelle spatiale etudiee la plus fine (20 m), les conditions environnementales locales, comme la structure et l'heterogeneite de l'habitat, etaient des determinants importants de la selection de l'habitat par le poisson. A l'echelle la plus grossiere (100 m), les poissons avaient tendance a choisir leur habitat en fonction de caracteristiques environnementales locales et de l'amenagement des rives. Les cartes de vecteurs propres de Moran (MEM) ont en outre revele que les associations poisson--habitat s'exprimaient a des echelles spatiales plus larges que les unites analytiques predefinies, ce qui peut etre partiellement attribuable a la structure spatiale des conditions environnementales operant a des echelles spatiales superieures a 100 m. L'etude met en relief l'importance d'evaluer les approches statistiques a differentes echelles spatiales pour cerner les determinants cles de la qualite de l'habitat pour les especes afin, ultimement, d'evaluer les effets de perturbations sur les ecosystemes. [Traduit par la Redaction], Introduction Habitats can be altered by anthropogenic means, such as resource exploitation and habitat destruction, and can have wide-ranging ecological repercussions, including alterations in habitat availability. Numerous studies have shown [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jpubeco.2005.10.004 Byline: Pascal Belan (a)(b), Stephane Gauthier (c)(d) Keywords: Indirect taxation; Commodity grouping; Exemptions Abstract: This paper analyzes the optimal structure of indirect taxation when the number of available tax rates is smaller than the number of taxable commodities. Such a constraint requires to choose the levels of tax rates and the groups of commodities that will be taxed at equal rates (or exempted). In a partial equilibrium framework, with a single agent and a low amount of tax collection, it is shown that the process of allocation of commodities to groups depends on both price elasticities and consumption spendings. Still, the optimal tax structure displays a weak form of the inverse elasticity rule; consumption spendings influence the size of the fiscal base, and may lead to many tax exemptions. Author Affiliation: (a) LEN (Universite de Nantes), France (b) EUREQua (Universite de Paris 1), France (c) CREM (Universite de Caen), France (d) CREST-LMA, 15 bd Gabriel Peri, 92245 Malakoff Cedex, France Article History: Received 9 August 2004; Revised 21 October 2005; Accepted 23 October 2005 Article Note: (footnote) [star] We thank Guy Laroque, Vincent Merlin, an anonymous referee and the editor of this Journal, Soren Blomquist, for many helpful suggestions. The usual disclaimers apply.

The relevance of rational expectations solutions to the class of linear univariate models is analyzed. The determinacy criterion is applied to the sets of coefficients of the linear difference equations.

The relationship between the local determinacy of a stationary equilibrium in the perfect foresight dynamics, and its local stability in the dynamics arising from econometric learning procedures is studied. Attention is focused on linear scalar economies, where agents forecast only one period ahead with a fixed number of predetermined variables.