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Natural mortality rates (M) are poorly quantified and commonly identified as a key source of uncertainty in fish stock assessments. Increasingly, stock assessments account for size- and age-dependence in M instead of using a constant M for all sizes and ages, as has traditionally been the default assumption. Empirical studies show that M is approximately inversely proportional to body length in fish populations, and this generalization has been used together with a von Bertalanffy growth curve to derive an age-dependent M. Here we extend this approach to the three commonly used growth functions of the Richards family (i.e., Logistic, von Bertalanffy, and Gompertz growth models). These models allow flexible production of various growth curves with a sigmoid shape and an upper asymptote, making them useful for displaying diverse growth curves for various long-lived fishes. The influences of growth parameters on predicted M were investigated, and the outcomes were compared among the three growth models. Age-dependent M for blue sharks (Prionace glauca) were estimated as an example. Key words: allocation methods, age-dependent natural mortality, theoretical model, long-lived fish, Richards model family, blue shark, 1. Introduction Reliable information about the natural mortality rates (M)--the aggregate of several processes including predation, starvation, and senescence (Hampton 2000)--can contribute to greater accuracy in fish stock assessments and [...]

We have developed a population dynamics model that considers the spatial segregation by sex and ontogenetic stages of pelagic sharks. The model was used to evaluate the performance of harvest strategies based on ecological characteristics. We proposed five harvest strategies for longline fisheries based on the ecological characteristics of blue shark (Prionace glauca) in the North Pacific. Management objectives for depleted populations are to increase yield to the level that provides maximum sustainable yield through increases in biomass without collapsing the fishery. Deterministic and stochastic analyses were undertaken. We determined that the harvest of male sharks was robust to uncertainty of environmental changes, reducing the likelihood of fishery collapse and stabilizing yield and mean biomass. The harvest of male sharks was also robust to the uncertainties of biological parameters such as natural mortality and steepness. These results suggested that if there was no sperm limitation or impact on the mating behavior of the species, the harvest of males would be the most appropriate harvest strategy for blue shark in the North Pacific. Nous avons developpe un modele de dynamique des populations qui integre la segregation spatiale selon le sexe et les stades ontogeniques des requins pelagiques. Ce modele a ete utilise pour evaluer la performance de strategies de peche basees sur des caracteristiques ecologiques. Nous avons propose cinq strategies de peche pour les peches a la palangre basees sur les caracteristiques ecologiques du requin bleu (Prionace glauca) dans le Pacifique Nord. Les objectifs de gestion pour les populations affaiblies consistent a accroitre le rendement jusqu'au niveau qui fournit le rendement equilibre maximum en augmentant la biomasse sans que la peche s'effondre. Des analyses deterministes et stochastiques ont ete effectuees. Nous avons determine que la strategie de peche visant les requins males est robuste au vu de l'incertitude associee aux changements environnementaux, reduisant la probabilite d'effondrement de la peche et stabilisant le rendement et la biomasse moyenne. La prise de requins males est egalement robuste au vu des incertitudes associees a des parametres biologiques comme la mortalite naturelle et le taux de variation. Ces resultats donnent a penser que, si du sperme est present en quantite suffisante et qu'il n'y a pas d'incidence sur le comportement d'accouplement de l'espece, la prise de males constituerait la meilleure strategie de peche pour le requin bleu du Pacifique Nord. [Traduit par la Redaction], Introduction Over the past few decades, many pelagic sharks have faced widespread declines in numbers due to fisheries expansion into the open ocean (Baum et al. 2003; Myers et al. [...]

We designed and synthesized molecular tweezers consisting of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C 60 or C 70 in solution. Titration studies by optical and 1 H NMR analyses revealed a 1:1 composition of the resulting complexes. X-ray diffraction analysis elucidated their solid-state structures, in which two azabuckybowl units surround one fullerene molecule. The large association constants stabilize the complexes toward redox reactions and the purification process on silica-gel column chromatography. The linker enabled tuning of the cavity size for binding of fullerenes, achieving complementary fullerene hosts for C 60 and C 70 : the carbazole-bridged dimer preferentially associates with C 70 over C 60 , while the phenanthrene-bridged dimer interacts with C 60 more strongly than C 70 . Electrochemical analysis in combination with density functional theory calculations indicated the existence of intermolecular charge-transfer interactions between the buckybowl units and the fullerenes. Nonlinear optical measurements showed that the two-photon absorption cross sections of the molecular tweezers are enhanced upon association with fullerenes.

A directly connected azabuckybowl dimer was synthesized via a palladium-catalysed C-H/C-Br coupling. The electron-donating nature of the pyrrolic nitrogen atoms of the azabuckybowl enabled a strong complexation with pristine C 60 . In the presence of two equivalents of C 60 , the azabuckybowl dimer formed crystals with a 1 : 2 stoichiometry. Conversely, in diluted solution, complexes with a 1 : 1 stoichiometry of the dimer and C 60 were detected predominantly, and these precipitated upon increasing the concentration of C 60 . Scanning electron microscopy images of the precipitate showed fibre-like aggregates, indicating the formation of supramolecular assemblies with 1D chain structures. A variable-temperature 1 H NMR analysis revealed that the precipitate consists of the dimer and C 60 in a 1 : 1 ratio.