Browsing by Author "Roel, B A"

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    The assessment of Iberian sardine: A Bayesian State-Space model incorporating migration and Spatially-Disaggregated data
    (2006) Cunningham, Carryn L; Roel, B A
    One of the assessment models for Iberian sardine (Sardina pilchardus) to be considered as part of work package 7 of the EU-project Sardine Dynamics and Stock Structure in the North-East Atlantic (SARDYN), is that of a Bayesian state-space model. This model, based on the one developed for the North East Atlantic mackerel population (Cunningham 2002), explicitly models the migration of the sardine between different areas during the year and incorporates, where possible, new data resulting from other SARDYN work packages. This model is used to evaluate an initial set of alternative hypotheses of stock-structure and migration.
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    Birthdate distribution of juvenile anchovy, Engraulis capensis caught in the Southern Benguela ecosystem
    (Elsevier, 1992) Waldron, M E; Armstrong, M J; Roel, B A
    Birthdate distributions of anchovy recruits caught during research surveys in June 1985 and June 1989 were compiled from weighted length frequency distributions, aged samples and length frequencies from commercial catches. Birthdates ranged from July to March with a peak in October for both year-classes. However, birthdate distribution for the 1989 year-class showed comparatively few fish spawning after October 1988. Also, the growth rate of recruits was slower in 1989 than in 1985. It is proposed that the very weak 1989 year-class of anchovy and the low spawning biomass subsequently observed were a result of poorer-than-average egg production and survival of prerecruits spawned after October 1988, and the slow rate of growth of juvenile anchovy recruited till June 1989.