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Studies focusing on the visual cues sea turtles use to orient between the nesting site and the sea indicate that sea turtles use diffuse images for orientation and are highly myopic on land. The visual environment encountered by sea turtles, however, is very different in water than on land. In this study, operant conditioning techniques were used to explore the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in the marine environment. Turtles were trained, in a tank setting, to distinguish between a 45 mm striped panel and 50% gray panel by using squid as a food reward. Though the pace of training was limited by our guidelines for holding these animals in captivity and the amount of food we could give each animal in a week, all turtles were trained in under a month. Once training was achieved, the stripes were reduced in size (stripe width ranging from 45.0 – 0.035 mm) until the turtle chose the striped panel over the 50% gray panel based on chance; this level of choice was designated as threshold. Mean acuity threshold level for all turtles tested was found to be 0.078 (visual angle of 12.89 minutes of arc). These results are similar to those of other marine species and indicate that loggerhead sea turtles use distinct visual cues in the aquatic environment.

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--Using a bioenergetics model, we estimated daily ration and seasonal prey consumption rates for six age classes of juvenile sandbar sharks (Carcharhinus plumbeus) in the lower Chesapeake Bay summer nursery [...]

Abstract--Standard and routine metabolic rates (SMRs and RMRs, respectively) of juvenile sandbar sharks (Carcharhinus plumbeus) were measured over a range of body sizes (n=34) and temperatures normally associated with western [...]

Abstract--Age and growth estimates for salmon sharks (Latona ditropis) in the eastern North Pacific were derived from 182 vertebral centra collected from sharks ranging in length from 62.2 to 213.4 [...]