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Analysis of tagging data from North Atlantic Albacore (Thunnus Alalunga): Attrition Rate Estimates ArchiMer
Ortiz De Zarate, Victoria; Bertignac, Michel.
In this study, an attempt is made to estimate natural mortality rate for North Atlantic albacore. We implement a spatially aggregated tag-attrition model to analyse the results of an albacore tagging experiment conducted in the Bay of Biscay from 1988 to 1991. The model predicts probabilities of the possible fates of tagged fish and the tags that they carry. The model includes several parameters consisting of catchabilities by fleets involved in recaptures and a combination of natural mortality plus emigration from the study area. Model fitting is carried out by finding the maximum of a multinomial likelihood function. Effect of reporting rate values on the estimations are evaluated and several hypothesis on the pre-mixing period of the tagged fish...
Tipo: Text Palavras-chave: Bay of Biscay; Attrition rate; Model; Natural mortality estimation; Albacore.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/2001/publication-977.pdf
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Can we detect the effects of environmental variations on fish populations through VPA outputs? the North Atlantic albacore case ArchiMer
Kell, Laurence T; Fromentin, Jean-marc; Ortiz De Zarate, Victoria; Arrizabalaga, Haritz.
Past studies have indicated that numbers-at-age 1 of albacore may be correlated with the winter NAO index in the previous year. Two main hypotheses have been stressed to explain such observation, i.e. an impact of the NAO on the recruitment or on migration patterns and consequently in the availability and catchability of specific age classes to the surface fishery. The objective of the present paper is to test whether such processes can be distinguished using VPA outputs. We first computed simple cross-correlations between the NAO at various lags, catches-at-age, Numbers-atage and F-at-age estimated in the last assessment. Since results were inconclusive, simulations were undertaken. The results showed that the probability of detecting spurious...
Tipo: Text Palavras-chave: Thunnus alalunga; North Atlantic Oscillation; Simulation model; Virtual population analysis; Correlation coefficient; NAO.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/00194/30503/28913.pdf
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