Estimating growth from sex ratio-at-length data in species with sexual size dimorphism

Individual growth is one of the main processes which drive the population dynamic and stock productivity. Many fish have differential individual growth by sex. Growth is affected by sexual development, which is frequently reached at different sizes in males and females. Differences in growth per sex after maturity produce different patterns in sex proportions-at-length in the population. If these patterns are the consequence of changes in life history parameters, sex ratio-at-length data can be expected to contain significant information on the population life history. In this paper I first explore how post-maturity changes in life history may shape these patterns in sex ratio-at-length; secondly I explore how these data may be used to estimate growth parameters and finally I discuss how this information may be useful for stock assessment purposes. I use European hake data and life history parameters to model expected sex ratios. The results suggest that reproductive energy allocation leads to a lower growth rate in male hakes than in females. Moreover the sex ratio-at-length may provide useful information for estimating growth parameters in dimorphic species if additional information from other sources is available. Finally, these data can easily be factored into stock assessment models to help provide a better estimation of growth parameters and mortality rates. This valuable, accurate and cheap biological information (sex ratio-at-length) may play an important role in population dynamic models and stock assessment for species with sexual size dimorphism.Preprint

Oxygen and silicon abundances in Cygnus OB2: Chemical homogeneity in a sample of OB slow rotators

Cygnus OB2 is a rich OB association in the Galaxy which has experienced intense star formation in the last 20-25 Myr. Its stellar population shows a correlation between age and Galactic longitude. Exploring the chemical composition of its stellar content we will be able to check the degree of homogeneity of the natal molecular cloud and possible effects of self-enrichment processes. Our aim is to determine silicon and oxygen abundances for a sample of eight early-type slow rotators in Cygnus OB2 in order to check possible inhomogeneities across the whole association and whether there exists a correlation of chemical composition with Galactic longitude. We have performed a spectroscopic analysis of a sample of late O and early B stars with low rotational velocity, which have been chosen so as to cover the whole association area. We have carried out an analysis based on equivalent widths of metal lines, the wings of the H Balmer lines and FASTWIND stellar atmosphere models to determine their stellar fundamental parameters as well as the silicon and oxygen surface abundances. We derive a rather homogeneous distribution of silicon and oxygen abundances across the region, with average values of 12+log(Si/H)=7.53$\pm$0.08 dex and 12+log(O/H)=8.65$\pm$0.12 dex. We find a homogeneous chemical composition in Cygnus OB2 with no clear evidence for significant chemical self-enrichment, despite indications of strong stellar winds and possible supernovae during the history of the region. Comparison with different scenarios of chemical enrichment by stellar winds and supernovae point to star forming efficiencies not significantly above 10%. The degree of homogeneity that we find is consistent with the observed Milky Way oxygen gradient based on HII regions. We also find that the oxygen scatter within Cygnus OB2 is at least of the same order than among HII regions at similar Galactocentric distance.Comment: 15 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Using population synthesis of massive stars to study the interstellar medium near OB associations

We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the ejection of the two radioactive isotopes 26Al and 60Fe is followed, as well as the emission of hydrogen ionizing photons, and the kinetic energy of the stellar winds and supernova explosions. We investigate various alternative astrophysical inputs and the resulting output sensitivities, especially effects due to the inclusion of rotation in stellar models. As the aim of the code is the application to relatively small populations of massive stars, special care is taken to address their statistical properties. Our code incorporates both analytical statistical methods applicable to small populations, as well as extensive Monte Carlo simulations. We find that the inclusion of rotation in the stellar models has a large impact on the interactions between OB associations and their surrounding interstellar medium. The emission of 26Al in the stellar winds is strongly enhanced, compared to non-rotating models with the same mass-loss prescription. This compensates the recent reductions in the estimates of mass-loss rates of massive stars due to the effects of clumping. Despite the lower mass-loss rates, the power of the winds is actually enhanced for rotating stellar models. The supernova power (kinetic energy of their ejecta) is decreased due to longer lifetimes of rotating stars, and therefore the wind power dominates over supernova power for the first 6 Myr after a burst of star-formation. For populations typical of nearby star-forming regions, the statistical uncertainties are large and clearly non-Gaussian.Comment: Accepted by A&A, 12 page

La experiencia europea en recuperación de stocks sobreexplotados ¿Qué hemos aprendido del plan de recuperación de merluza?

La sobrepesca es uno de los principales problemas que tienen que abordar los organismos gestores de las pesquerías si pretenden obtener de éstas el máximo rendimiento sostenible. Cuando la sobrepesca se mantiene en el tiempo, la respuesta esperable por parte de las poblaciones explotadas es una reducción de su capacidad reproductiva de tal manera que su recuperación se hace difícil y se alarga en el tiempo con importantes consecuencias económicas y sociales. Es entonces cuando los planes de recuperación son necesarios. Los planes de recuperación surgen en Europa como un caso especial de los planes de gestión plurianuales, donde el principal objetivo es recuperar la capacidad reproductiva de stocks sobreexplotados. Estos instrumentos han sido inicialmente promovidos por la ONU a través de distintos acuerdos y han sido trasladados por los organismos gestores a sus normas legales. En Europa la principal norma es la Política Pesquera Común (PPC). La PPC pretende garantizar que la actividad pesquera sea sostenible desde el punto de vista medioambiental, económico y social. Para ello ha desarrollado diferentes ámbitos, uno de los cuales son los planes plurianuales. En este trabajo se pretende dar a conocer a la comunidad científica de la CTMFM la manera como la Unión Europea ha gestionado la recuperación de stocks sobreexplotados mediante sus planes plurianuales. La merluza fue uno de los primeros stocks identificados como sobreexplotados que se gestionó mediante un plan de recuperación. En 2004 se empezó a trabajar en ese plan que fue finalmente implementado en 2006. Ya han pasado 8 años lo que lo convierten en un buen ejemplo donde revisar los procesos del plan: la elaboración, el seguimiento y sus resultados. Como en todas las acciones de gestión donde la incertidumbre es un elemento ineludible ha habido aciertos y errores. Aprender de ambos es la mejor lección podemos sacar de esta experiencia.CTMFMVersión del editor0,000

A preliminary gadget model to assess the Spanish Red seabream fishery of the Strait of Gibraltar

This work shows the first implementation of gadget (an age-length based model) to the Spanish Red seabream fishery data from the Strait of Gibraltar: gadget is a toolbox developed to implement marine ecosystem models considering the fishing effect. Our goal is to launch a new approach for the Red seabream fishery assessment following Icelandic deepwater stocks example. Sooner or later, we would like to change the current category of this deep water fishery: from data poor to stocks with quantitative assessments. These trials should be attempted before planning a future Benchmark Grou

An Applied Framework for Incorporating Multiple Sources of Uncertainty in Fisheries Stock Assessments

Estimating fish stock status is very challenging given the many sources and high levels of uncertainty surrounding the biological processes (e.g. natural variability in the demographic rates), model selection (e.g. choosing growth or stock assessment models) and parameter estimation. Incorporating multiple sources of uncertainty in a stock assessment allows advice to better account for the risks associated with proposed management options, pro- moting decisions that are more robust to such uncertainty. However, a typical assessment only reports the model fit and variance of estimated parameters, thereby underreporting the overall uncertainty. Additionally, although multiple candidate models may be considered, only one is selected as the ‘best’ result, effectively rejecting the plausible assumptions behind the other models. We present an applied framework to integrate multiple sources of uncertainty in the stock assessment process. The first step is the generation and condition- ing of a suite of stock assessment models that contain different assumptions about the stock and the fishery. The second step is the estimation of parameters, including fitting of the stock assessment models. The final step integrates across all of the results to reconcile the multi-model outcome. The framework is flexible enough to be tailored to particular stocks and fisheries and can draw on information from multiple sources to implement a broad variety of assumptions, making it applicable to stocks with varying levels of data avail- ability The Iberian hake stock in International Council for the Exploration of the Sea (ICES) Divisions VIIIc and IXa is used to demonstrate the framework, starting from length-based stock and indices data. Process and model uncertainty are considered through the growth, natural mortality, fishing mortality, survey catchability and stock-recruitment relationship. Estimation uncertainty is included as part of the fitting process. Simple model averaging is used to integrate across the results and produce a single assessment that considers the multiple sources of uncertainty.Versión del edito

Effect of contact lens surface properties on comfort, tear stability and ocular physiology

Aim: Retrospective analysis of different contact lens wearing groups suggests lens surface lubricity is the main factor influencing contact lens comfort. However, the examined commercially available contact lenses differ in material and design as well as surface properties. Hence this study isolates the contribution of lens surface properties using an ultra-thin coating technology. Methods: Nineteen habitual contact lens wearers (21.6. ±. 1.7years) wore formofilcon B soft monthly disposable contact lenses with and without coating technology modified surface properties for a month each in a randomised double-masked cross-over study. Objective non-invasive: breakup time (NIKBUT), NIKBUT average and ocular redness (Jenvis grading scale) were evaluated (Keratograph 5M) after 1 week and 1 month of wear. Symptoms were assessed using the Contact Lens Dry Eye Questionnaire (CLDEQ-8); perceived vision quality and subjective lens comfort at insertion, mid-day and end of the day were rated with four Visual Analog Scales. Results: Perceived visual quality (F = 5.049,p = 0.037), contact lens dry eye symptoms (F = 14.408,p = 0.001) and subjective lens comfort (F = 28.447,p. . 0.05). Lens surface wettability and ocular redness were not correlated to changes in symptoms (p. >. 0.05). Conclusion: As previously hypothesised, enhancing the physical surface properties of a soft contact lens improves subjectively rated wearer comfort, which, in turn, should result in reduced contact lens discontinuation

TENTH WORKSHOP ON THE DEVELOPMENT OF QUANTITATIVE ASSESSMENT METHODOLOGIES BASED ON LIFE-HISTORY TRAITS, EXPLOITATION CHARACTERISTICS, AND OTHER RELEVANT PARAMETERS FOR DATA-LIMITED STOCKS (WKLIFE X)

The Workshop on the Development of Quantitative Assessment Methodologies based on Life history traits, exploitation characteristics, and other relevant parameters for data-limited stocks (WKLIFE X), chaired by Carl O'Brien (UK) and Manuela Azevedo (Portugal) met virtually 5–9 October 2020, to further develop methods for stock assessment and catch advice for stocks in Categories 3 and 4, focusing on the provision of sound advice rules that are within the ICES MSY framework. This tenth workshop was convened to further address the challenges to the evidence base for the provision of ICES advice with specific reference to data-limited stocks. There is an increasing number of fish stocks in Categories 3 and 4 for which assessment of status relative to MSY proxy reference points is available but for which short-term forecasts and MSY-based ad vice are not available. For assessments using the stochastic surplus production model in contin uous time (SPiCT), WKLIFE X developed and evaluated ‘fractile rules’ that account for uncer tainty and allow to consider any percentile and demonstrated that ‘fractile rules’ are more effec tive and precautionary than the median rule (50th percentile) and the ‘2-over-3’ rule. Additional work on advice rules for stocks in Category 3 based on life-history traits (k), tested through sim ulation and management strategy evaluation (MSE), showed that the addition of specific multi pliers based on the stock’s life-history characteristics decreases the risk of the control rule´s per formance. Annex 3 to this report contains the revised technical guidance on methods and advice rules for stocks in Category 3. The revision of the accumulated decade of ICES documentation on methods and advice for data-limited stocks into a stand-alone technical guidance document requires significant effort and dedicated work beyond the time available at the WKLIFE X meet ing. It is proposed that a dedicated workshop be established to undertake and complete the up dating and revision into a single reference documentICES, U

The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS

The apparent lack of massive O-type stars near the zero-age main sequence (at ages < 2 Myr) is a topic widely discussed. Different explanations for this elusive detection have been proposed, but no firm conclusions have been reached yet. We reassess this empirical result benefiting from the high-quality spectroscopic observations of >400 Galactic O-type stars gathered by the IACOB and OWN surveys. We used temperatures and gravities from a iacob-gbat/fastwind spectroscopic analysis to locate our sample in the Kiel and spectroscopic HR diagrams. We evaluated the completeness of our sample of stars, observational biases using information from the Galactic O star catalog (GOSC), systematics of our methodology, and compare with other recent studies using smaller samples of Galactic O-type stars. We base our discussion on the spectroscopic HR diagram to avoid the use of uncertain distances. We performed a detailed study of the young cluster Trumpler-14 as an example of how Gaia cluster distances can help to construct the associated classical HR diagram. The apparent lack of massive O-type stars near the ZAMS with masses between 30 and 70 Msol persist even when spectroscopic results from a large, non-biased sample of stars are used. We do not find correlation between the dearth of stars and observational biases, limitations of our methodology, or the use of spectroscopic HR diagram instead of the classical one. Investigating the efficiency of mass accretion during the formation process we conclude that an adjustment of the accretion rate towards lower values could reconcile the hotter boundary of detected O-type stars and the theoretical birthline. Last, we discuss that the presence of a small sample of O2-O3.5 stars found closer to the ZAMS might be explained taking into account non-standard star evolution (e.g. binary interaction, mergers, or homogeneous evolution).Comment: 20 pages, 15 figures, accepted for publication in Astronomy & Astrophysic