Browsing by Author "Gutierrez-Estrada, Juan Carlos"
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- Deep water longline selectivity for black spot seabream (Pagellus bogaraveo) in the Strait of GibraltarPublication . Czerwinski, Ivone Alejandra; Gutierrez-Estrada, Juan Carlos; Erzini, Karim; Hernando, José AntonioSpecies and size selectivity of the deep water longline traditionally used in commercial fishing of the black spot seabream (Pagellus bogaraveo) were studied in the Strait of Gibraltar with four sizes of hooks. Black spot seabream contributed up to 88% of the catch by number. Catch and by-catch rates differed for the different hooks and fishing trials. Significant differences in average fish length between all hooks, except in one case, were found. The comparison of two experimental fishing trials within 4 years indicates a displacement towards smaller sizes in the size frequency distributions. The results of this study show that the fishing gear can be size selective depending on hook size. The fitted selectivity models for each experiments were very different despite having two hooks in common. This is probably due to the very different catch size distributions in the two periods, which suggests that the population size structure changed significantly between 2000/2001 and 2004/2005.
- Effects of environmental conditions and fishing operations on the performance of a bottom trawlPublication . Queirolo, Dante; Hurtado, Carlos F.; Gaete, Erick; Soriguer, Milagrosa C.; Erzini, Karim; Gutierrez-Estrada, Juan CarlosTrawl performance was studied based on net spread and variability in the contact of the footrope with the seabed and their relationship with vessel operations, catch weight, and environmental conditions. Artificial neural networks (ANNs) and generalized additive models (GAMs) were used to model the response of each variable. For the variables net spread and variability in footrope contact (VFC), the ANN models were more accurate than the GAMs, with greater generalization capacity in the validation phase. In the best ANN model for net spread, all variables were significant. The relationship between tow direction and wind direction (tactic) was most important in the sensitivity analysis. Net spread increased with increasing towing speed and windspeed, and decreased with increasing wave height. In the ANN model for VFC, there were differences among vessels, and both scope ratio and catch size were not significant. VFC increased with increasing depth and decreased with increasing towing speed and windspeed. The results demonstrate that both operational variables and environmental conditions affect trawl performance, and suggest that survey protocols designed based on this information might help to improve the precision of biomass estimates.