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.
- 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.
- 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.
- Progress on a meta-analysis for comparing hook, bait and leader effects on target, bycatch and vulnerable fauna interactionsPublication . Casaca Santos, Catarina; Rosa, Daniela; Coelho, RuiThis paper describes the progress of an EU Project "Evaluation of the effects of hooks’ shape & size on the catchability, yields and mortality of target and by-catch species, in the Atlantic Ocean and adjacent seas surface longline fisheries". At this stage, a meta-analysis of 36 publications totaling 55 experiments was conducted to assess effects of hook, bait, and leader type on retention and at-haulback mortality rates of swordfish, blue shark, and loggerhead sea-turtle. Using circle hooks significantly lowers retention rates of loggerhead sea-turtles and swordfish. Fish bait significantly reduces the retention of loggerhead sea-turtles but does not significantly affect the retention of swordfish or blue shark. The effects of using wire leaders could not be assessed for the loggerhead turtle and significantly increased retention of blue sharks. As for at-haulback mortality, it was significantly reduced for swordfish when using circle hooks. Fish bait increased at-haulback mortality of blue shark and was not significant for the other taxa. The effects of using wire leaders on at-haulback mortality were only possible to calculate for blue shark and were not significant.