Browsing by Author "Rosa, Daniela"
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- Age and growth of shortfin mako in the South AtlanticPublication . Rosa, Daniela; Mas, Federico; Mathers, Alyssa; Natanson, Lisa J.; Carlson, John; Coelho, RuiThe shortfin mako, Isurus oxyrinchus (Lamnidae), is regularly caught as by-catch in pelagic longline fisheries and is among the most vulnerable sharks to this fishery. The age and growth of I. oxyrinchus was studied along a wide South Atlantic region. Data from 332 specimens ranging in size from 90 to 330 cm fork length (FL) for females and 81 to 250 cm FL for males were analysed. Growth models were fitted using the von Bertalanffy growth equation re-parameterised to calculate L0, instead of t0, and a modification of this equation using the known size at birth. The von Bertalanffy growth equation with fixed L0 (size at birth = 63 cm FL) with resulting growth parameters of Linf = 218.5 cm FL, k = 0.170 year-1 for males and Linf = 263.1 cm FL, k = 0.112 year-1 for females, seemed to underestimate maximum length for this species, while overestimating k. Given the poorly estimated parameters we cannot, to this point, recommend the use of the South Atlantic growth curves.
- Age and growth of the smooth hammerhead, Sphyrna zygaena, in the Atlantic Ocean: comparison with other hammerhead speciesPublication . Rosa, Daniela; Coelho, Rui; Fernandez-Carvalho, Joana; Santos, Miguel N.The smooth hammerhead Sphyrna zygaena (Sphyrnidae) is a pelagic shark occasionally caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Age and growth of S. zygaena was studied along a wide Atlantic region covering both the northern and southern hemispheres. Data from 304 specimens, caught between October 2009 and September 2014, ranging in size from 126 to 253 cm fork length (FL), were analysed. Growth models were fitted using the three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L0 (size at birth). Growth models were fitted to the sample data and data from several back-calculation models. The model fit to the quadratic modified Dahl-Lea back-calculated data seems to be the most appropriate to describe growth in this species, with resulting growth parameters of Linf = 285 cm FL, k = 0.09 year−1 for males and Linf = 293 cm FL, k = 0.09 year−1 for females. Compared with other species of the same genus, estimated growth coefficients for S. zygaena seem to fall in the low to middle range. Although further work is still needed, this study adds to knowledge of the vital life-history parameters of smooth hammerheads in the Atlantic Ocean, which can be used in the management and conservation of this species.
- Are shifts in species distribution triggered by climate change? A swordfish case studyPublication . Erauskin-Extramiana, Maite; Arrizabalaga, Haritz; Cabré, Anna; Coelho, Rui; Rosa, Daniela; Ibaibarriaga, Leire; Chust, GuillemSpecies shifts due to climate change are being recorded and reported worldwide. However, the accurate estimation and causal attribution of species shifts using spatial distribution indicators, such as the center of gravity, is challenging. This is particularly problematic for commercially exploited marine species with data from research surveys, commercial fisheries or other data collection methods that are not recorded homogeneously over time and space. Here, we propose a new framework to ascertain whether the changes in the spatial distribution of species are due to changes in habitat conditions, fishing activity or other factors. This approach is developed to help elucidate the main drivers of species shifts and it is based upon the comparison of historical trends in species distribution shifts among raw data and modeled: i) fishing effort, ii) population occurrence and abundance, iii) habitat, and iv) spatio-temporal reconstruction of the species distribution. We apply this new methodology to the case study of swordfish populations worldwide. On a global scale, 2 out of 6 stocks of swordfish shifted latitudinally during 1958–2004. Of those two, only the Mediterranean stock was associated with a linear trend change of its habitat. In two other stocks, the latitudinal center of gravity of populations occurrence varies following their habitats’ interannual variability; however, this shift is not linear. We further developed a worldwide habitat suitability model for swordfish and projected its distribution and abundance into the future under the RCP8.5 climate change scenario, the highest greenhouse gas concentration scenario, by the end of the century. Future projections estimate an overall swordfish decrease of 22% in CPUE (catch per unit of effort), with substantial decreases in most tropical areas, and a slight increase in its distribution range limits, both in the north and southern hemispheres.
- Assessing the effects of hook, bait and leader type as potential mitigation measures to reduce bycatch and mortality rates of shortfin mako: a meta-analysis with comparisons for target, bycatch and vulnerable fauna interactionsPublication . Rosa, Daniela; Casaca Santos, Catarina; Coelho, RuiA meta-analysis of 24 publications was conducted to assess effects of hook, bait and leader type on retention rates of target, bycatch and vulnerable species of the pelagic longline fishery. Retention rate and at-haulback mortality rate analyses considered hook type, bait type, the combination of both variables and leader type. Turtles and swordfish had a lower retention rate with circle hooks. In contrast, retention rates of 3 sharks and 2 tuna species were greater with circle hooks. Bait type alone did not seem to significantly influence the retention rates of most of the species examined. Results were mixed when considering the combined effects of hook and bait type. Wire leader led to a decrease in retention rates of bony fishes and a mix for elasmobranchs. For at-haulback mortality, hook type was the most influential, while bait type only influenced blue shark at-haulback mortality. Leader type did not have a significant effect. The results presented here should be considered preliminary. Future work will consider information on at-haulback mortality rates for bony fishes and sea turtle and expanded information on fishery characteristics.
- Fishery indicators for the shortfin mako (Isurus oxyrinchus) caught by the portuguese pelagic longline fishery in the Atlantic: nominal CPUEs, catch-at-size and at-haulback mortalityPublication . Coelho, Rui; Rosa, Daniela; Lino, PedroThis paper provides an overview of fishery indicators for the shortfin mako shark captured by the Portuguese pelagic longline fishery in the Atlantic, in terms of catch-at-size, nominal CPUEs and at-haulback mortality. The analysis is based on data from fishery observers, port sampling and skippers logbooks (self sampling), from 1997-2015. In general, there was a large variability in the nominal CPUE trends for the north Atlantic, with a slight increase during the period. For the catch-at-size there were no major trends in the time series, but the sizes tended to be larger in the South Atlantic and with a larger variability. The at-haulback mortality was similar between sexes, with a trend for decreasing mortality rates with increasing specimen size. The data presented in this working document should be considered preliminary and is presented in preparation for the 2017 shortfin mako stock assessment in the Atlantic Ocean.
- Hook, bait and leader type effects on surface pelagic longline retention and mortality rates: a meta-analysis with comparisons for target, bycatch and vulnerable fauna interactionsPublication . Casaca Santos, Catarina; Rosa, Daniela; Coelho, RuiA meta-analysis of 24 publications was conducted to assess effects of hook, bait and leader type on retention and at-haulback mortality rates of target, bycatch and vulnerable species of the pelagic longline fishery. Turtles and swordfish had lower retention rates with circle hooks. In contrast, retention rates of 3 sharks and 2 tuna species were greater with circle hooks. Bait type did not seem to significantly influence the retention rates of most of the species examined. Wire leader lead to a decrease in retention rates of bony fishes and a mix for elasmobranchs. For athaulback mortality, hook type was the most influential, with 5 elasmobranch species and 6 bony fishes having a significantly lower at-haulback mortality rates when using circle hooks. Bait type and leader type did not have a significant effect on at-haulback mortality rates for most species. The results presented here should be considered preliminary. Future work will consider expanded information on fishery characteristics.
- Leader material and bait effects on target and bycatch species caught in an Atlantic Ocean pelagic longline fisheryPublication . Casaca Santos, Catarina; Santos, Miguel N.; Rosa, Daniela; Coelho, RuiThe influence of bait type and leader material on target and bycatch species was assessed through fishing experiments in the Portuguese shallow pelagic longline fishery in the Atlantic Ocean. Wire leaders were found to decrease catch rates of commercially valuable species such as bigeye tuna and yellowfin tuna, while increasing catch rates of elasmobranchs, including the blue shark and shortfin mako. The odds ratios of capture swordfish and tunas also decrease when using wire leaders, while elasmobranchs have higher odds ratios of capture and athaulback mortality when using wire leaders. Squid bait led to higher catches of targeted tuna species, however it also resulted in higher catches of marine turtles. For most of the taxa caught at-haulback mortality risk was found to be higher on squid bait, which may be related with increased deep-hooking events. While bait type and leader material did not significantly affect size selectivity for most species, wire leaders were found to retain larger blue sharks and fish bait attracted smaller-sized swordfish. This study showed that banning wire leaders on pelagic longline fisheries is an effective measure for reducing the retention of pelagic shark species, particularly of large size blue sharks.
- Local indicators for global species: Pelagic sharks in the tropical northeast Atlantic, Cabo Verde islands regionPublication . Coelho, Rui; Macías, David; Ortiz de Urbina, Josetxu; Martins, Albertino; Monteiro, Carlos; Lino, Pedro G.; Rosa, Daniela; Casaca Santos, Catarina; Bach, Pascal; Murua, Hilario; Abaunza, Pablo; Santos, Miguel N.Pelagic sharks are an important bycatch in pelagic fisheries, especially for drifting longlines targeting swordfish. In the Cabo Verde Archipelago (tropical NE Atlantic), pelagic shark catches can reach a significant proportion of the total catches. Due to the increased concern on the status of pelagic shark species, this study was developed to enhance the current knowledge of those sharks in the Cabo Verde region in comparison to the adjacent areas, especially associated with European Union (EU) pelagic longline fishing activity. Stock status indicators for the two main species, blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus), were developed, based on fisheries data from logbooks and onboard scientific observers, including analysis of size frequency distributions and standardized catch-per-unit-of-effort (CPUE) indexes over time. The standardized CPUEs have been stable or increasing for both species in the past 10 years, indicating no signs of local depletion. In terms of sizes, the blue shark catch is composed mainly of adults, which can be a sign of a stable population. On the contrary, the catch of shortfin mako is composed mainly of juveniles, which in conjunction of a decrease of mean size might be a cause of concern, highlighting possible overfishing on the species in the region. Thirty satellite tags, 25 archival miniPATs and 5 SPOT GPS, were deployed in the Cabo Verde Exclusive Economic Zone (EEZ), showing that those species are highly mobile. The biomass and size distributions were modeled with spatial and seasonal models (GAMs) identifying locations where juveniles are predominantly concentrated and that should be prioritized for conservation. This work presents new information on the status of pelagic sharks in the Cabo Verde region in the context of those highly migratory species, and can now be used to promote more sustainable fisheries in the region.
- Management strategy evaluation operating model conditioning: a swordfish case studyPublication . Mosqueira, Iago; Fu, Dan; Coelho, Rui; Rosa, DanielaEvaluation of fish stock status is a key step for fisheries management. Tuna Regional Fisheries Management Organizations (t-RFMOs) are moving towards management strategy evaluation (MSE), a process that combines science and policy and depends on technical aspects, developed by scientists, designed to meet management objectives established by managers and other stakeholders. In the Indian Ocean, the current management advice for swordfish (Xiphias gladius) is based on an ensemble of 24 models considering four areas of uncertainty about the stock dynamics. There is an ongoing MSE process for swordfish, and this paper describes the methodology being applied for the conditioning of the operating model (OM), including model selection and validation. In the MSE, nine sources of uncertainty were considered, each being characterized by 2-3 levels. A partial factorial design was employed to reduce the number of models from a full factorial design to those needed to encompass the overall uncertainty. A selection and validation process was carried out, filtering models that converged, showed good predictive skills, and provided plausible estimates. Overall, the estimated spawning stock biomass (SSB) relative to SSB at maximum sustainable yield (MSY), and fishing mortality (F) relative to F-MSY encompasses the estimates of the stock assessment ensemble at the most optimist area of the distribution. The MSE for swordfish is an ongoing process that is expected to provide more robust management advice in the future. Further developments to the OM can still occur, but the methods presented herein can be applied to this, or other species, MSE processes.
- 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
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