Browsing by Author "Santos, Miguel"
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- Characterization and standardization of Atlantic sailfish (Istiophorus albicans) catch rates in the east Atlantic from the Portuguese pelagic longline fisheryPublication . Coelho, Rui; Lino, Pedro; Santos, MiguelThis document analyzes the catch, effort and standardized CPUE trends for the eastern Atlantic stock of Atlantic sailfish (Istiophorus albicans) captured by the Portuguese pelagic longline fleet from 1999-2015. Nominal annual CPUE were calculated as kg/1000 hooks and were standardized with Generalized Linear Models (GLM) with Tweedie distribution and using year, quarter, area and targeting effects (ratios) as explanatory variables. Model goodness-of-fit was determined with AIC and the pseudo coefficient of determination, and model validation was analyzed with residual analysis. The final standardized CPUE series shows a general decrease in the initial years, between 1999 and 2010, followed by a general increase in the more recent years, until 2015, with some inter-annual oscillations. This paper presents the first index of abundance for Atlantic sailfish estimated from captures from the Portuguese pelagic longline fleet in the east Atlantic and can be used for future stock assessments of the species
- Effects of leader material on catches of shallow pelagic longline fisheries in the southwest Indian OceanPublication . Santos, Miguel; Lino, Pedro; Coelho, RuiCatches from a commercial longline fishery targeting swordfish (Xiphias gladius) on monofilament nylon leaders were compared with catches on wire leaders in the Indian Ocean. More taxa were caught on wire leaders, which also showed higher catch rates (13% and 56%, in number and weight, respectively) of blue shark (Prionace glauca). In contrast, catch rates of swordfish were not significantly affected by leader material. Nylon leaders showed lower at-haulback mortality for most bony fishes, except swordfish. Higher bite-off rates were observed on nylon monofilament, likely owing to the escape of species with sharp teeth, such as sharks. Both leader types caught most species within similar size ranges, but larger mean sizes of blue shark were recorded on wire leaders. The value per unit of effort (VPUE) of the retained catch did not differ between leader materials; however, VPUEs are highly dependent on market fluctuations. Banning wire leaders could be an effective way of reducing shark catches, particularly blue shark catches, in the southwest Indian Ocean.
- Modeling species composition and mortality rates of sea turtles in the Portuguese pelagic longline fishery targeting swordfish in the Atlantic Ocean: preliminary results using statistical modelsPublication . Coelho, Rui; Rosa, Daniela; Lino, Pedro; Santos, Miguel
- New observations on the bluefin tuna trap fishery off southern Portugal (NE Atlantic) between 1998-2014: trends on potential catches, catch-at-size and sex ratiosPublication . Santos, Miguel; Rosa, Daniela; Coelho, Rui; Lino, PedroThis paper updates information previously presented on the bluefin tuna catches from a tuna trap fishery operating off the southern coast of Portugal (Algarve). Trends of intra- and interannual catches were analysed and relationships between the potential catches and ICCAT management regulations for the Mediterranean Sea explored. The catch rates of bluefin tuna in the tuna trap off the Algarve remained relatively low between 1998 and 2008, but were followed by increasingly high catches thereafter, with an observed peak during the 2011 season. Significant negative correlations were observed between the catches and the number of allowable fishing months for purse-seines, longlines and bait boats in the Mediterranean Sea, meaning that the catch increased as the number of allowable fishing months for those fishing gears decreased. On the other hand, a positive relationship was observed between the catches and the minimum landing size (MLS), meaning that the catch rates in the tuna trap increased as the MLS for bluefin tuna also increased. These results seem to corroborate other fisheries indicators regarding the recovery of the Eastern Atlantic and Mediterranean Sea stock.
- Shark research and data collection program : progress on the age and growth of the shortfin mako in the Atlantic OceanPublication . Coelho, Rui; Carlson, John; Natanson, Lisa; Rosa, Daniela; Mas, Federico; Mathers, Alyssa; Domingo, Andrés; Santos, MiguelThis paper presents an update of the age and growth study within the ICCAT Shark Research and Data Collection Program (SRDCP), including the current development status and plans for the 2nd phase of the project. There are currently 469 vertebrae samples (205 females, 257 males and 7 specimens with unidentified sex) collected and processed from both the North and Southern hemispheres. The sample distribution is much more complete in the north, while in the south at this stage there are only samples from the equatorial region. The size range of the samples varies from 52 cm to 366 cm FL. The next steps of this projects is proposing a workshop on age reading and growth in order to prepare a reference set of vertebrae that can be used as a guideline for the readings of the remaining sample, and also discuss aspects of age validation and band deposition periodicity. The final results will be presented to the SCRS sharks working group in 2017, in order to contribute to the 2017 shortfin mako stock assessment.
- Standardized CPUE of blue shark in the Portuguese pelagic longline fleet operating in the north AtlanticPublication . Coelho, Rui; Santos, Miguel; Lino, PedroThis working document analyzes the catch, effort and standardized CPUE trends for the north Atlantic blue shark captured by the Portuguese pelagic longline fleet. Nominal annual CPUE were calculated as kg/1000 hooks and were standardized with Generalized Linear Models (GLM) and Generalized Linear Mixed Models (GLMM) using year, quarter, area, gear type, targeting effects and area:quarter interactions as fixed factors, and year:area as random effects. Sensitivity analyzes were carried out for the model type (lognormal, tweedie, gamma or delta lognormal), the definition of targeting effects (based on ratios or cluster analysis), and definition of areas. Model goodness-of-fit and comparison was carried out with AIC and the pseudo coefficient of determination (R2 ), and model validation with a residual analysis. The final standardized CPUE trend shows a general increase over the studied period, between 1997 and 2014, with some inter-annual oscillations. This paper presents the first index of abundance for the blue shark estimated from captures from the Portuguese pelagic longline fleet in the North Atlantic, and can be used in future stock assessments models.