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Length-mass relationships, while often overlooked, form the basis of many fisheries science applications. Fisheriesindependent research surveys compile large databases of biological data that could hold a wealth of information regarding species' life history, which, for many, are data deficient and infrequently sampled. A flexible model using permutations of a broken stick and variance shift was applied to length-mass relationships to evaluate changes in the mean or variability of mass-at-length using data from deep-sea fishes and focusing on particularly poorly known deep-sea chondrichthyans. Changes in body shape and (or) in the scale of variability around mean mass-at-length were estimated for most species (94% of data sets examined). Such changes seemed likely to be correlated with biological factors, such as the onset of reproduction; 70% of length estimates for a variance shift correlated with the expected length-at-maturity. The model presented here could be applied to any fish where length and mass data are available, providing a way to estimate, validate, and investigate biological factors in species where macroscopic evaluations are unavailable or difficult to estimate. Les relations longueur-poids, bien que souvent negligees, forment la base de nombreuses applications en sciences halieutiques. Les releves de recherche independants des peches compilent d'imposantes bases de donnees biologiques qui pourraient contenir un tresor d'information concernant les cycles biologiques d'especes dont, pour bon nombre, les donnees sont insuffisantes et l'echantillonnage n'est pas frequent. Un modele souple reposant sur des permutations d'un baton rompu et d'un changement de variance a ete applique a des relations longueur-poids pour evaluer les variations de la moyenne ou de la variabilite du poids en fonction de la longueur en utilisant des donnees sur des poissons de grands fonds et en mettant l'accent sur des chondrichthyens de grands fonds particulierement meconnus. Les variations de la forme du corps ou de l'ampleur de la variabilite autour de la moyenne du poids en fonction de la longueur ont ete estimees pour la plupart des especes (94% des ensembles de donnees examines). Il semble probable que de telles variations soient correlees a des facteurs biologiques, comme le debut de la reproduction; 70% des estimations de la longueur pour un changement de variance etaient correlees a la longueur a la maturite attendue. Le modele presente pourrait etre applique a n'importe quel poisson pour lequel des donnees de longueur et de poids sont disponibles, offrant ainsi un moyen d'estimer, de valider et d'etudier des facteurs biologiques chez des especes pour lesquelles des evaluations macroscopiques sont indisponibles ou difficiles a estimer. [Traduit par la Redaction], Introduction The relationship between length and mass, while often overlooked, is an important component of fisheries population models (Froese 2006). The relationship between length (L) and mass (W) is conventionally [...]

Ecosystem and multi-species models are used to understand ecosystem-wide effects of fishing, such as population expansion due to predation release, and further cascading effects. Many are based on fisheries models that focus on a single, depleted population, and may not always behave as expected in a multi-species context. The spawning stock recruitment (SSR) relationship, a curve linking the number of juvenile fish to the existing adult biomass, can produce dynamics that are counter-intuitive and change scenario outcomes. We analysed the Beverton–Holt SSR curve and found a population with low resilience when depleted becomes very productive under persistent predation release. To avoid implausible increases in biomass, we propose limiting recruitment to its unfished level. This allows for specification of resilience when a population is depleted, without sudden and excessive increase when the population expands. We demonstrate this dynamic and solution within an end-to-end ecosystem model, focusing on myctophids under fishing-induced predation release. We present one possible solution, but the specification of stock-recruitment models should continue to be a topic of discussion amongst multi-species and ecosystem modellers and empiricists going forward. [ABSTRACT FROM AUTHOR]

The Chatham Rise is a highly productive deep-sea ecosystem that supports numerous substantial commercial fisheries, and is a likely candidate for an ecosystem based approach to fisheries management in New Zealand. We present the first end-to-end ecosystem model of the Chatham Rise, which is also to the best of our knowledge, the first end-to-end ecosystem model of any deep-sea ecosystem. We describe the process of data compilation through to model validation and analyse the importance of knowledge gaps with respect to model dynamics and results. The model produces very similar results to fisheries stock assessment models for key fisheries species, and the population dynamics and system interactions are realistic. Confidence intervals based on bootstrapping oceanographic variables are produced. The model components that have knowledge gaps and are most likely to influence model results were oceanographic variables, and the aggregate species groups 'seabird' and 'cetacean other'. We recommend applications of the model, such as forecasting biomasses under various fishing regimes, include alternatives that vary these components. [ABSTRACT FROM AUTHOR]