Browsing by Author "Isidro, Eduardo"
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- Age, growth and maturity in the chub mackerel (Scomber japonicus Houttuyn, 1782) from the Azores.Publication . Carvalho, Natacha; Perrotta, Ricardo G.; Isidro, EduardoSagittae from 349 specimens of chub mackerel collected between 1996 and 2002 were used in this study. Fork length ranged from 90 mm to 530 mm, corresponding to 9.6 mm and 56.57 mm TL ages ranged between 0 to 13 years. The von Bertalanffy growth equation was fitted to the length-at-age data and the estimated parameters were as follows: L∞ = 57.52 TL; k = 0.201 years-1; t0 = -1.093 years. Life span was estimated as being between 13 and 15.6 years and the instantaneous rate of natural mortality as 0.192. The spawning season in the Azores extends from March to August and length at 50% maturity was estimated as 27.78 cm TL (A50% = 2.23 years). Length-weight and length-length relationships were also determined: W = 0.0049FL3.2612; TL = 1.039 FL1.015; SL = 0.927FL 0.999.
- Estimates of biomass and potential yield for the deep-water red crab, Chaceon affinis and the toothed rock crab, Cancer bellianus (Decapoda: Brachyura) off the Azores (Mid-North Atlantic)Publication . Pinho, Mário Rui; Santos, Régis; Melo, Octávio; Isidro, Eduardo; Novoa-Pabon, Ana Maria; Leal, Wendell Medeiros; Gonçalves, João M.Available information on the deep-water red crab, Chaceon affinis and the toothed rock crab, Cancer bellianus, resulting from exploratory research surveys and commercial fishing experiments carried out in the Azorean Exclusive Economic Zone (EEZ), were summarized to estimate the biomass and potential yield (Maximum Sustainable Yield – MSY) for both fishery resources. The fishery potential was estimated through empirical methods usually applied when available information is scarce in line with the precautionary approach principle. Results suggest modest MSY values (considered as precautionary Total Allowable Catch – TAC), around 2,205 t for the deep-water red crab (2,159 t year-1 at seamounts and 46 t year-1 at coastal areas), and 471 t for the toothed rock crab (281 t year-1 at offshore seamounts and 189 t year-1 at coastal areas). Considering the limited available data and high uncertainty associated with these estimations, it is suggested that only a reduced number of vessels should be allowed to fish in the aggregated areas, namely coastal and seamount areas. The exploitation of these resources should be started in a very limited way followed by an ad hoc observer programme, aiming to collect reliable data that will allow, if it is the case, to raise in the future the exploitation level in a gradual and sustainable way.
- Estimating the impacts of eliminating fisheries subsidies on the small island economy of the Azores.Publication . Carvalho, Natacha; Rege, Sameer; Fortuna, Mário; Isidro, Eduardo; Edwards-Jones, GarethA major problem affecting world fisheries today is overcapacity of which overfishing is both a cause and a consequence. There is a general consensus that fisheries subsidies cause great harm to the resource by exacerbating the problems resulting from the common resource issues of fisheries leading to overexploitation of the resource through a new set of perverse incentives. Many now advocate that subsidies should gradually be terminated, and that capacity enhancing and fuel subsidies should be terminated immediately. On account of the global fisheries crises, highly subsidised fisheries and the anticipated reforms of the European Union's Common Fisheries Policy this study aimed to estimate the impact of eliminating fisheries subsidies on various macro and micro economic variables pertaining to the regional economy of the Azores using a dynamic computable general equilibrium model based on a social accounting matrix. The simulation results suggest that reduction, and in particular, elimination of fisheries subsidies would have a substantial effect on the region, however, the negative social and economic effects would be largely confined to the fishing sector. Conversely, the augmentation of fishery subsidies would benefit the fishing sector with an overall adverse effect on the rest of the economy..
- Experimental harvesting of juvenile common octopus Octopus vulgaris, for commercial ongrowing in the AzoresPublication . Pham, Christopher K.; Isidro, EduardoOctopus aquaculture is currently restricted to ongrowing of sub-adult to commercial size because culture of paralarvae remains a bottleneck. In most countries, commercial ongrowing rely upon existing pot fisheries for octopuses for obtaining their specimens. In the Azores, such fishery does not exist and effective methods of harvest are required if farming is to be implemented. In this study, we investigated the potential of obtaining subadult octopuses on the coast of Faial Island, Azores. Two sets of traps (n=30) consisting of 3 PVC tubes within cement blocks were set-up on two different substrates; soft sediment (Pedro Miguel) and rocky-sand (Pasteleiro) at depth varying between 10 and 30 metres. From June to August 2006, 11 hauls per site were performed. A total of 191 octopuses (from 1.1 to 989 g; average = 135.3 g) were captured. Catches in the soft sediment site were significantly higher than in the other location (CPUE: mean ± SD: 0.33 ± 0.17 vs. 0.15 ± 0.17 octopus trap-1 hour-1*100). The catch was initially dominated by octopus of 300-400 g but as fishing continued, this size classes disappeared and was replaced by smaller individuals. As a result, half of the catch at both sites (51.8%) was composed of specimens with a weight equal or inferior to 50 grams. The occurrence of summer recruitment event combined with a natural displacement of larger individuals into deeper waters is most probably responsible for this pattern. Our results showed that in shallow water and during this period of the year, individuals inferior to 50 grams are far more abundant than larger octopuses and should be the target size class for ongrowing activities.
- Fish larvae and zooplankton biomass around Faial Island (Azores archipelago). A preliminary study of species occurrence and relative abundance.Publication . Sobrinho-Gonçalves, Luis; Isidro, EduardoPlankton hauls were conducted off Faial island (Azores archipelago, NE Atlantic), to a depth of 100 m, between February and June 1998, covering the spawning period of a number of commercially important fish species. Seventy-three fish larvae taxa were identified, of which 51 were quantified, one of them a new record for the region, Glossanodon leioglossus (Valenciennes, 1848). The fish larvae community was dominated by mesopelagic and bathypelagic elements (namely Myctophidae and Gonostomatidae), a typical oceanic island environment composition. Total zooplankton showed a biomass peak in May that could correspond to the Spring “bloom”. However, the fish larvae showed an abundance minimum in May and a maximum in June, presenting a general negative relationship with zooplankton biomass and indicating a temporal asynchrony between their annual cycles of production. The comparison of fish larvae abundance with those of other NE Atlantic regions suggests that the zooplankton production in the Azores may be similar to the one found in the Iberian Peninsula continental shelf. Significant spatial density gradients (for fish larvae and zooplankton) were not found with either bathymetry or distance from shore.
- Recruitment and growth of Megabalanus azoricus (Pilsbry, 1916) on artificial substrates: first steps towards commercial culture in the AzoresPublication . Pham, Christopher K.; Girolamo, Mirko De; Isidro, EduardoThis paper reports the results of preliminary research evaluating the potential of farming Megabalanus azoricus. From March 2006 to September 2006, artificial substrates were immersed bi-monthly in a shallow water bank located in the channel separating the islands of Faial and Pico, Azores. They were monitored monthly for a period of 12 months by scuba-diving. M. azoricus rapidly colonised the immersed substrates, establishing itself as the dominant organism. Even though recruitment was observed year round, there was a peak in recruitment between June and October. The substrate immersed for the longest period (15 months) presented final densities of 1109 ind. m-2, from which 20.2% were of edible size. Growth was monitored for 18 isolated barnacles for 8 months. Growth rate proved to be high (base diameter; 0.08 ± 0.02 mm day-1; mean ± SD), with individuals reaching diameters of 21.35 ± 6.2 mm after 8 months. Considering this growth rate, it was estimated that after a further 9 months, over 80% of the total densities (on the oldest substrate ) would be harvestable, thus suggesting a production cycle of 17 to 24 months. Although much further research is needed, the species presents all characteristics of a potential candidate to initiate the aquaculture industry in the Azores.