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Provedor de dados:  ArchiMer
País:  France
Título:  Otolith shape as a valuable tool to evaluate the stock structure of swordfish (Xiphias gladius) in the Indian Ocean
Autores:  Mahe, Kelig
Evano, Hugues
Mille, Tiphaine
Bourjea, Jerome
Data:  2014-09-29
Ano:  2014
Palavras-chave:  Xiphias gladius
Otolith shape
Fourier descriptors
Stock discrimination
Indian Ocean
Resumo:  Swordfish (Xiphias gladius) is an oceanic-pelagic species currently fully exploited by several fisheries in the Indian Ocean, with suspicion of overexploitation in the southwest, but without a clear understanding of the real stock structure within this Ocean. Population structure of the Indian stock was studied in the western Indian Ocean using 395 individual samples collected from 2009 to 2014. Sagittal otoliths of the fish have been removed and shape analysis performed on these calcified pieces. Otolith morphometrics data and normalized Elliptical Fourier Descriptors (EFDs) were then extracted automatically by the dedicated imageanalysis system TNPC. Preliminary, side effect was tested by Redundancy analysis (RDA) combined to permutation tests on 91 individual samples and showed no significant differences in the outline shape between the right and left otoliths. Consequently, 395 sagittal otoliths were used to identify stocks among several geographical areas (La Reunion, Mozambique channel, Rodrigues, South Africa, South Malagasy, Sri Lanka and Thailand) within the Indian Ocean. To investigate variations of otolith shape according to 4 explanatory variables, Principal Components Analysis (PCA) was applied to EFDs and a RDA with permutation tests was used on the first 7 PC selected by the broken-stick model. These tests demonstrated no significant effects, neither by sex (p=0.121), sampled year (p=0.725), or total length (p=0.464). Only, geographical area appeared to be significant (p<0.05). Regarding the relationship between the ratio otolith length/otolith width and the total length of fish, size effect was neither significant. Furthermore, Linear Discriminant Analysis (LDA) was performed and overall jackknifed classification success reached 30%. Finally, a clustering analysis has been realised using Ward's hierarchical algorithm, which discriminated 3 different groups; however each group was composed by some individual samples from all geographical areas. In conclusion, all these results did not show a clear geographicalseparation, which corroborate the recent genetic analysis at the Indian Ocean scale while identifying only a single swordfish stock component in this area.
Tipo:  Text
Idioma:  Inglês
Formato:  application/pdf
Direitos:  IOTC 2014


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