Hydrographic conditions on Flemish cap in July 2000 and comparison with those observed in 1999

10 páginas, 5 figuras, 1 tabla.-- Scientific Council MeetingHydrographic conditions on Flemish Cap in July 2000 are described after a survey with 94 CTD stations. Current conditions over Flemish Cap are described and compared with those observed in 1999. Since the middle-1990s temperatures have been increasing until 1999. In 2000 salinities and temperatures keep the above normal values of the last recent years with slightly lower values than those observed in 1999. This occurs in the water column up to 200 m depth. A well-developed layer with temperatures higher than 4ºC was observed all around the Cap below 200 m depth. This relative warming in water that spreads around the Cap at an unusual depth is probably due to a combination of two processes: firstly by a mixture with North Atlantic waters and secondly by a high permanence time in the anticyclonic gyre.This paper was supported by the European Commission (DG XIV, Study 98-048) and CSIC.Peer reviewe

New Local-scale hydrographic observation on the Flemish Cap in July 1996

8 pages, 7 figures.The research cruise "FC96" was made on the Flemish Cap area on board the RV Cornide de Saavedra from 28 June to 14 July 1996. The survey consisted of a series of 121 random bottom trawls over Flemish Cap inside the boundaries of the 732 m isobath. A CTD station was established either at the beginning or at the end of each trawl for a total of 116 stations. Three different water masses were detected. Two of them are already known: (a) Labrador Current waters, spreading around the Bank; (b) Central Cap seawater, the solar heated Labrador waters retained over the Cap. These waters made an anti-cyclonic gyre of 4–12 cm per sec. Both water masses tended to become stable at 200 m depth, with temperatures about 3.5°C and salinities about 34.85 psu. A third water mass which had not been previously described on Flemish Cap was the Slope Water, found in the southwest area of the Cap between 200–300 m, where it occupied two separate areas with temperatures higher than 4.5°C and salinities higher than 34.90 psu. These intrusions of Slope Water on the Flemish Cap seemed to affect the distribution of some fish species. In particular, they coincided with the breaking of continuity in the geographic distribution of some demersal species, like the redfish Sebastes marinus and S. fasciatusThis paper is a contribution to the UE project "Analysis of exploited fish stocks on Flemish Cap" ref. AIR1-CT92-0558.Peer reviewe

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

A Survey-based Assessment of Cod in Division 3M

13 páginas, 8 tablas, 4 figuras.-- Scientific Council MeetingThe cod stock in NAFO division 3M is in fishing moratorium since 1999. Commercial catches have been very low since then, although they were noticeable in 2006. During the last few years a survey-based assessment method has been used to evaluate the stock status in a stochastic way. The method takes into account uncertainties in survey results as well as in catchability estimates. The present document updates the results of the assessment conducted in 2006 (details in Murua et al. 2006) incorporating the survey data from 2006. The results indicate a strong age 1 abundance value in 2006 and an increasing trend in spawning stock biomass (SSB) after its lowest value attained in 2003. Nevertheless, the probability that SSB is presently below Blim is still very high. The abundances at age 1 estimated for 2005 and 2006 are the highest since 1993. As a consequence, there is some expectation that the increasing SSB trend may continue during the next few years.Peer reviewe

Identification of Female Cod (Gadus morhua) from Flemish Cap (Northwest Atlantic) at the Beginning of Ripening

18 páginas, 3 figuras, 6 tablas.-- Scientific Council MeetingOvaries of cod from Flemish Cap were sampled at three different times during the reproductive cycle. We study the use of the oocytes in the circumnuclear ring, cortical alveoli and vitellogenesis stages, the postovulatory follicles and gonosomatic index for the identification of females at the beginning of the ripening. The results obtained indicate that there is a period of less than two months between the end of spawning and the beginning of the development of the cortical alveoli stage, and more than three months to the beginning of vitellogenesis in all mature females. It is necessary to wait for these periods to use these structures to identify all the females at the beginning of ripening. Postovulatory follicles last a long time in the ovary, and their identification is possible seven months after spawning; the reconstruction of the last maturation ogive can be made three months after spawning. The mean gonosomatic index of mature and immature females showed significant differences three months after spawning, but the overlap between the maximum and minimum values impedes the use of this index to identify all females at the beginning of ripening.Peer reviewe

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

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

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

Reference Points Based on Dynamic Optimisation: A Versatil Algorithm for Mixed Fishery Management with Bio-economic Agestructured Models

Single-species management objectives may not be consistent within mixed fisheries. They may lead species to unsafe situations, promote discarding of over-quota and/or misreporting of catches. We provide an algorithm for characterising bio-economic reference points for a mixed fishery as the steady-state solution of a dynamic optimal management problem. The optimisation problem takes into account: i) that species are fishing simultaneously in unselective fishing operations and ii)intertemporal discounting and fleet costs to relate reference points to discounted economic profits along optimal trajectories. We illustrate how the algorithm can be implemented by applying it to the European Northern Stock of Hake (Merluccius merluccius), where fleets also capture Northern megrim (Lepidorhombus whiffiagonis) and Northern anglerfish (Lophius piscatorius and Lophius budegassa). We find that optimal mixed management leads to a target reference point that is quite similar to the 2/3 of the Fmsy single-species (hake) target. Mixed management is superior to singlespecies management because it leads the fishery to higher discounted profits with higher long-term SSB for all species. We calculate that the losses due to the use of the Fmsy single-species (hake) target in this mixed fishery account for 11.4% of total discounted profits