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Santos M.N.,Instituto Nacional Dos Recursos Biologicos IP | Lino P.G.,Instituto Nacional Dos Recursos Biologicos IP
Journal of the Marine Biological Association of the United Kingdom | Year: 2010

The wedge sole (Dicologoglossa cuneata, Moreau 1881) is a commercially important species for the artisanal fleet operating off the south-western Iberian Peninsula. During 2004 and 2005 a study was undertaken aiming to provide a scientific basis for management. Data collection included information on aspects of the fishery, spawning season, size at first maturity, tangle and gill-net selectivity. Seven nominal mesh sizes were used (40, 45 and 50mm tangle nets and 40, 50, 60 and 70mm gill-nets). Spawning lasts from December to June, with peaks in March and May. Leóngth at first maturity for females was estimated at 18.5cm. Catch rates decreased sharply with increasing mesh size, with tangle nets providing the highest yields. The log-normal selectivity model provided the best fit for specimens that were wedged. The higher catch-per-unit-effort of the smaller mesh sizes and the modal length of the fitted selectivity curve being below the size-at-maturity for wedge sole, suggests that the 50mm nominal mesh size tangle net is the most appropriate for ensuring the fishery sustainability. Nevertheless, the minimum legal size should increase to at least 18cm and a time-area closure should be implemented off the Guadiana River mouth. Copyright © Marine Biological Association of the United Kingdom 2009. Source


Coelho R.,Instituto Nacional Dos Recursos Biologicos IP | Coelho R.,University of Algarve | Fernandez-Carvalho J.,Instituto Nacional Dos Recursos Biologicos IP | Amorim S.,Instituto Nacional Dos Recursos Biologicos IP | Santos M.N.,Instituto Nacional Dos Recursos Biologicos IP
Aquatic Living Resources | Year: 2011

The smooth hammerhead shark Sphyrna zygaena (Sphyrnidae) is regularly caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Recently, ICCAT (International Commission for the Conservation of Atlantic Tunas) issued recommendations underlining the need for more studies on the life history parameters of this and other pelagic shark species. To this end, the age and growth of S. zygaena were studied in the Eastern Equatorial Atlantic Ocean, in an area where growth parameters were not yet available for this species. Data from 139 specimens, caught between June and September 2009, ranging in size from 136 to 233 cm fork length (FL), were analysed. Preliminary trials were carried out to assess the most efficient growth band enhancement technique. These indicated that sectioning the vertebrae into 500 μm sections followed by staining with crystal violet produced the best results. Growth models were fitted using the traditional von Bertalanffy growth equation and a modification of this equation using a known size at birth. Growth models were compared using the Akaike information criterion (AIC). The von Bertalanffy growth equation seemed to be the most adequate model to describe growth in this species, with resulting growth parameters of L inf = 272 cm FL, k = 0.06 year for males and L inf = 285 cm FL, k = 0.07 year for females. In the first four years of life, S. zygaena grows 25 cm per year on average, but its growth slows down in later life. Future stock assessment models should incorporate these age and growth parameters for species management and conservation. © 2011 EDP Sciences, IFREMER, IRD. Source


Fernandez-Carvalho J.,Instituto Nacional Dos Recursos Biologicos IP | Coelho R.,Instituto Nacional Dos Recursos Biologicos IP | Coelho R.,University of Algarve | Erzini K.,University of Algarve | Neves Santos M.,Instituto Nacional Dos Recursos Biologicos IP
Aquatic Living Resources | Year: 2011

The bigeye thresher, Alopias supercilious, is commonly caught as bycatch in pelagic longline fisheries targeting swordfish. Little information is yet available on the biology of this species, however. As part of an ongoing study, observers sent aboard fishing vessels have been collecting set of information that includes samples of vertebrae, with the aim of investigating age and growth of A. supercilious. A total of 117 specimens were sampled between September 2008 and October 2009 in the tropical northeastern Atlantic, with specimens ranging from 101 to 242 cm fork length (FL) (176 to 407 cm total length). The A. supercilious vertebrae were generally difficult to read, mainly because they were poorly calcified, which is typical of Lamniformes sharks. Preliminary trials were carried out to determine the most efficient band enhancement technique for this species, in which crystal violet section staining was found to be the best methodology. Estimated ages in this sample ranged from 2 to 22 years for females and 1 to 17 years for males. A version of the von Bertalanffy growth model (VBGF) re-parameterised to estimate L 0, and a modified VBGF using a fixed L 0 were fitted to the data. The Akaike information criterion (AIC) was used to compare these models. The VBGF produced the best results, with the following parameters: L inf = 293 cm FL, k = 0.06 y -1 and L 0 = 111 cm FL for females L inf = 206 cm FL, k = 0.18 y -1 and L 0 = 93 cm FL for males. The estimated growth coefficients confirm that A. supercilious is a slow-growing species, highlighting its vulnerability to fishing pressure. It is therefore urgent to carry out more biological research to inform fishery managers more adequately and address conservation issues. © 2011 EDP Sciences, IFREMER, IRD. Source

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