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Abstract--Commercial fishermen have argued that localized concentrations of spiny dogfish (Squalus acanthias) in the northeast U.S. shelf large marine ecosystem (NES LME) have impeded their fishing operations when monitoring surveys [...]

Increased commercial importance of spiny dogfish (Squalus acanthias) combined with an often debated, and controversial, ecological impact has warranted an investigation of the relationship among distribution, environment, and prey to better understand the species ecology and inform management. To elucidate mechanisms behind distributional changes, we modeled seasonal occurrence and abundance of neonate, immature, and mature spiny dogfish as functions of abiotic and biotic factors using generalized additive models and Northeast Fisheries Science Center bottom trawl survey data. Significant nonlinear relationships were widespread throughout dogfish stages and seasons. Seasonal occurrence was tightly linked to depth and bottom temperature, with year and Julian day influential for some stages. While these factors also influenced abundance, ecological factors (e.g., squid abundances) significantly contributed to trends for many stages. Potential impacts of climate change were evaluated by forecasting distributions under different temperature scenarios, which revealed higher regional probabilities of occurrence for most stages during a warmer than average year. Our results can be used to better understand the relationship between sampling periods and movement drivers to survey catchability of the population in the Northeast (US) shelf large marine ecosystem. L'importance commerciale croissante de l'aiguillat commun (Squalus acanthias), combinee a un impact ecologique controversy faisant l'objet d'un debat soutenu, a motive l'etude du lien entre repartition, milieu et proies dans le but de mieux comprendre l'ecologie de cette espece et d'en eclairer la gestion. Afin de faire la lumiere sur les mecanismes qui sous-tendent les variations de la repartition, nous avons modelise la presence et l'abondance saisonnieres d'aiguillats communs nouveau-nes, immatures et matures en fonction de facteurs abiotiques et biotiques, a l'aide de modeles additifs generalises et de donnees de leves au chalut de fond du Northeast Fisheries Science Center. Des relations non lineaires significatives etaient repandues pour tous les stades de vie de l'aiguillat et toutes les saisons. La presence saisonniere etait etroitement reliee a la profondeur et la temperature au fond, l'annee et le jour julien exerqant une influence pour certains stades. Si ces facteurs influenqaient egalement l'abondance, des facteurs ecologiques (p. ex. l'abondance de calmars) avaient une incidence significative sur les tendances pour de nombreux stades. Les impacts potentiels des changements climatiques ont ete evalues en predisant les repartitions pour differents scenarios de temperature, ce qui a revele des probabilites regionales accrues de presence pour la plupart des stades durant des annees plus chaudes que la normale. Nos resultats peuvent servir a une meilleure comprehension du lien entre les periodes d'echantillonnage et les facteurs influenqant les deplacements dans revaluation de la capturabilite de la population dans le grand ecosysteme marin de la plate-forme du Nord-Est etats-unien., Introduction The Magnuson-Stevens Fishery Conservation and Management Act of the United States emphasizes the integration of ecosystem considerations into assessment methods (Link et al. 2011) consistent with a move towards [...]

Declines in abundance of commercially valuable groundfish have highlighted the ecological and commercial importance of previously underutilized elasmobranchs in the Northeast (US) shelf large marine ecosystem (NES LME). Seasonal distributions and ontogenetic habitats of one such species, spiny dogfish (Squalus acanthias), were investigated using Northeast Fisheries Science Center (NEFSC) bottom trawl survey data (1963-2009). Neonate, immature, and mature dogfish all selected warmer, more saline, and more southerly locations during spring compared with available locations. During autumn, larger dogfish occupied relatively warmer, shallower, and less saline waters while neonates selected higher salinities. There were strong ontogenetic patterns in habitats occupied. Contrary to expectation, geographic range contracted as abundance increased during autumn. This suggests that niche constraints override density-dependent effects, although detection of relationships within stages was limited by low statistical power. The proportion of mature female survey catch within the Mid-Atlantic Bight was significantly related to temperature, suggesting that environmental conditions surveyed may impact population trends. Collectively, these results highlight critical habitats, suggest mechanisms behind ontogenetic habitat selection, and provide insight into how changing environmental conditions may impact stock assessment. Les baisses d'abondance de poissons de fond a valeur commerciale soulignent l'importance ecologique et commerciale d'elasmobranches auparavant sous-utilises dans le grand ecosysteme marin de la plateforme continentale du nord-est des Etats-Unis (NES LME). Les repartitions saisonnieres et les habitats ontogeniques d'une de ces especes, l'aiguillat commun (Squalus acanthias), ont ete examines a la lumiere de donnees de releves au chalut de fond (1963-2009) du Northeast Fisheries Science Center (NEFSC). Parmi les sites disponibles, les aiguillats nouveau-nes, immatures et matures choisissaient tous des emplacements relativement chauds, salins et meridionaux au printemps. A l'automne, les aiguillats plus grands occupaient des eaux relativement chaudes, moins profondes et moins salines, alors que les nouveau-nes choisissaient des eaux de plus forte salinite. L'occupation des habitats definissait des motifs ontogeniques marques. Contrairement aux attentes, l'aire de repartition geographique diminuait parallelement a l'augmentation de l'abondance a l'automne, ce qui donne a penser que les contraintes touchant a la niche l'emportent sur les effets dependants de la densite, bien que la faible efficacite statistique limite la detection de relations pour des stades donnes. La proportion de femelles matures capturees dans le cadre des releves dans le golfe Medio-atlantique etait significativement reliee a la temperature, donnant a penser que les conditions ambiantes pourraient avoir une incidence sur les tendances des populations. Collectivement, ces resultats font ressortir des habitats essentiels et des mecanismes possibles de selection d'habitats ontogeniques et jettent un eclairage sur l'incidence de l'evolution des conditions ambiantes sur l'evaluation des stocks. [Traduit par la Redaction], Introduction Understanding the habitat preferences of marine fishes is important when describing their spatial distribution and ecology (Perry and Smith 1994; Smith and Page 1996; Shepherd et al. 2002) and [...]

Abstract: Depletion experiments are conducted to estimate efficiency of sampling gear and density of organisms. Traditional models for analyzing these experiments make restrictive assumptions that are often violated. We present [...]

Describes ecosystem tradeoffs in managing fisheries in New England. Lack of coherence between federal laws governing uses of marine resources; Implications of ecosystem tradeoffs in sea scallop, groundfish and pelagic fisheries; Impediments and benefits of implementing ecosystem-based management of fisheries.

Numerous surveys have shown that fish species richness (number of species) is positively correlated with lake pH. However, species richness of fish communities is also correlated with lake size, and low-pH lakes are often small. Thus, conclusions drawn from examination of fish community structure relative to spatial (among-lake) variation in pH have been limited by uncertainties regarding the confounded effects of lake area. We used two statistical methods, analysis of covariance and a nonparametric blocked comparison test, to remove effects of lake area and compare fish species richness in low-pH and high-pH lakes. Data from six previous surveys of water chemistry and fish communities in lakes of Ontario and northern Wisconsin were examined. Lakes with low pH (≤6.0) contained significantly fewer fish species than lakes with high pH (>6.0) when the effect of lake area was considered. A simple probabilistic model showed that the ability to detect differences in species richness is low when lake areas and the pool of potential colonizing species are small. We recommend the blocked comparison test for separating the effects of lake area and pH on species richness and urge critical examination of inferences based on analyses of fish communities in small lakes. [ABSTRACT FROM AUTHOR]