Browsing by Author "Monteiro, C. C."
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- An experimental study of gill net and trammel net 'ghost fishing' off the Algarve (southern Portugal)Publication . Erzini, Karim; Monteiro, C. C.; Ribeiro, J.; Santos, M. N.; Gaspar, M.; Monteiro, P.; Borges, T. C.Four 100 m lengths of both monofilament gill nets and trammel nets were deployed at depths between 15 and 18 m off the coast of the Algarve (south of Portugal) between April 1995 and June 1996. The nets were set on a natural rocky bottom with one end cut loose to simulate lost nets. Changes in net structure (net height, effective fishing area, movement, colonisation, wear and tear) and their catches (species, sizes, numbers, and biomass) were monitored by divers. Similar patterns were observed in all the nets, with a sharp decrease in net height and effective fishing area, and an increase in visibility within the first few weeks. Net movement was negligible except in the case of interference from other fishing gears. Catch rates were initially comparable to normally fished gill nets and trammel nets in this area, but decreased steadily over time. No sea birds, reptiles or mammals were caught in any of the 8 nets. Catches were dominated by fish (89 % by number, at least 27 species), in particular by sea breams (Sparidae) and wrasses (Labridae). Under the conditions experienced throughout the study the fishing Lifetime of a 'lost' net is between 15 and 20 wk. Based on an exponential model, we estimated that 100 m lengths of gill net and trammel net will catch 314 and 221 fish respectively over a 17 wk period. However, we consider this to be an underestimate due to high rates of predation and scavenging by octopuses, cuttlefish, moray eels, conger eels, and other fish such as the wrasse Coris julis. When the nets were surveyed in the following spring, 8 to 11 mo after being deployed, they were found to be completely destroyed or heavily colonised by algae and had become incorporated into the reef.
- A comparison of direct macrofaunal mortality using three types of clam dredgesPublication . Gaspar, Miguel; Miguel de Sousa Leitão, Francisco; Santos, M. N.; Chícharo, Luís; Dias, M. D.; Chícharo, Alexandra; Monteiro, C. C.The white clam Spisula solida is harvested along the entire coast of Portugal using mechanical dredges. In this study, the total direct mortality of the macrobenthic community caused by three types of clam dredges (north dredge—ND, traditional dredge—TD, and the metallic grid dredge—GD) used in the S. solida fishery was determined and compared. The relationship between mortality and catching efficiency for each type of dredge was also assessed. Our results showed significant differences for total direct mortality between the ND and both the GD and TD dredges. This difference was largely attributed to the mortality of animals that died in the dredge track as a direct result of the physical damage inflicted by the dredge passing. It was also found that the damage to uncaught individuals is directly related to gear efficiency. The lower catching efficiency of the ND (64%) led to a higher proportion of damaged individuals being left in the dredge path, when compared with the more efficient GD (98%) and TD (90%) dredges. Short and long-term implications of the impact of dredging on the composition of benthic communities are discussed. From fisheries management and ecological points of view, there are obvious advantages to introduce into the bivalve dredge fisheries more efficient and selective dredges in order to reduce the number of damaged individuals and by-catch, and consequently decreasing the impact on the macrobenthic communities.
- A comparison of monofilament gillnet and small hook longline selectivity in a multispecies artisanal fishery in the Algarve, Southern PortugalPublication . Erzini, Karim; Santos, M. N.; Monteiro, C. C.; Gonçalves, J. M. S.; Bentes, L.; Lino, Pedro G.As part of ongoing studies concerned with the small-scale fisheries of the South of Portugal, experimental fishing was carried out with monofilament gillnets and small hook longlines within the same area. Sixty-two species were caught, of which 20 were common to both gears. Pronounced differences in terms of the relative importance of different species in the catches were observed. Size selection patterns also differed, with highly overlapped hook catch distributions and few species showing evidence for size selectivity. In contrast, strong selectivity was characteristic of species which tend to be "wedged" in gillnets. Whereas smaller stretched mesh sizes (particularly 40 and 50 mm) caught significant numbers of illegal sized fish, this was minimal in the longlines. Some implications for management are discussed.
- Depth segregation phenomenon in Donax trunculus (Bivalvia : Donacidae) populations of the Algarve coast (southern Portugal)Publication . Gaspar, Miguel; Chicharo, Luis; Vasconcelos, P.; Garcia, A; Santos, A. R.; Monteiro, C. C.A study was undertaken to evaluate the existence of depth segregation between size classes of Donax trunculus populations that occur along the Algarve coast (southern Portugal). Five collecting areas were sampled in the Ria Formosa barrier islands, namely in the Culatra, Barreta and Armona Islands, between March and June 1998. The study was based on size frequency distribution analysis and shell biometric relationships, The size frequency distribution showed the predominance of smaller individuals (<25 mm) in the renewal area (0.5-1.0 m depth) and the prevalence of larger individuals (greater than or equal to25 mm) at greater depths (4.0-6.0 in depth). The biometric study revealed the existence of significant differences in the type of growth between size classes in relation to depth distribution and burrowing activity. On the basis of these results, some specific management measures were proposed for this important bivalve fishery, taking into account the distinct fishing strategies and operations (manual and boat-operated dredging) performed at different depths.
- Diplodus spp. assemblages on artificial reefs: importance for near shore fisheriesPublication . Azevedo Leitão, F. Marina; Santos, M. N.; Erzini, Karim; Monteiro, C. C.Artificial reefs have been deployed along the southern coast of Portugal (Algarve) since 1990 to enhance artisanal fisheries. The objectives of this study were to: (1) describe the colonisation process; (2) assess the role of the artificial reefs in terms of juvenile recruitment and growth and as mating/spawning areas and (3) evaluate the potential of artificial reefs as near shore artisanal fishing grounds for three economically important fish species, Diplodus bellottii (Steindachner), Diplodus sargus (L.) and Diplodus vulgaris (Geoffroy Saint-Hilaire). The fish assemblages were monitored after the deployment of a large artificial reef (Faro/Ancao) in 2002. Colonisation rates for the three species were fast. Artificial reefs play a multiple role for Diplodus spp., acting as recruitment, growth and nursery areas for juveniles, and spawning/mating areas for adults, and can thus be considered essential fish habitat. Three months after deployment of the artificial reefs, exploitable biomass was 16, 29 and 8 kg per reef group, respectively, for D. bellotti, D. sargus and D. vulgaris. These results indicate that artificial reefs quickly become good fishing grounds, where suitable financial yields may be obtained by fisher. Moreover, the artificial reefs became new and alternative fishing grounds, allowing reduction of fishing effort over traditional rocky areas that are scarce along the Algarve coast. Management measures for artificial reefs, in terms of fishing strategies, are discussed.
- Effect of tooth spacing and mesh size on the catch of the Portuguese clam and razor clam dredgePublication . Gaspar, Miguel; Castro, Margarida; Monteiro, C. C.Experiments on the selectivity of the clam and razor clam dredges were carried out during July 1995, on the south coast of Portugal. The effects of mesh size and tooth spacing were investigated for both the clam and razor clam dredges. Four different mesh sizes (25, 35, 40, and 50 mm) and three different tooth spacings (15, 20, and 25 mm for the clams Spisula solida and Venus striatula, and 10, 15, and 20 mm for the razor clam Ensis siliqua) were used. The results indicated that the tooth spacing did not have an effect on the selectivity. The best mesh sizes were 40 mm for the clam fishery (S. solida and V. striatula) and 66 for the razor clam (E. siliqua). These mesh sizes will result in considerable reduction in the numbers of small- and medium-sized individuals in the catch. (C) 1999 International Council for the Exploration of the Sea.
- Gill net selectivity for European hake Merluccius merluccius from southern Portugal: implications for fishery managementPublication . dos Santos, M. N.; Gaspar, M.; Monteiro, C. C.; Erzini, KarimA study of European hake Merluccius merluccius gill net selectivity was undertaken off the Algarve (Southern Portugal), between 1999 and 2001. Four nominal mesh sizes (70, 80, 90 and 100 mm) were used in fishing trials and the 'share each length class catch total' (SELECT) method was used to fit gill net selectivity curves. Hake were caught in the same size range by all mesh sizes, between 17 and 65 cm total length. While most fishes were wedged, significant and similar proportions were entangled in all mesh sizes, contributing to the wide size range, and in some cases, bimodal shape of catch size frequency distributions. Insignificant numbers of undersized hake were caught, with most catches consisting of mature female fish. Catch rates decreased sharply with increasing mesh size. The bimodal model gave the best fit for hake that were wedged, with estimated modal lengths of 40.1, 46.7 and 51.0 cm for the 70, 80 and 90 mm nominal mesh sizes, respectively. The high catch per unit effort of the smallest mesh size, with most fish caught being female, together with the fact that the modal length of the fitted selectivity curve is well below the size at maturity for hake in Portuguese waters, suggests that the 80 mm nominal mesh size is more appropriate for ensuring resource sustainability.
- Influence of mesh size and tooth spacing on the proportion of damaged organisms in the catches of the Portuguese clam dredge fisheryPublication . Gaspar, Miguel; Miguel de Sousa Leitão, Francisco; Santos, M. N.; Sobral, M.; Chícharo, Luís; Chicharo, Maria Alexandra Teodosio; Monteiro, C. C.Experiments to assess the effect of mesh size and tooth spacing on the catch of Spisula solida were undertaken with the aim of determining an optimal combination of these two characteristics to minimize the dredging impact on by-catch species. However, our data showed that tooth spacing, mesh size and the interactions between these two factors did not affect the number of damaged macrofaunal individual’s caught. This may be because infauna entered the dredge without passing through the space between the teeth and the mesh of the net bag closed as it was stretched by the weight of the contents, preventing the escape of the caught individuals. Thus, independently of mesh size, when the dredge is towed over the sediment, the retained individuals were injured due to abrasion between animals and/or between animals and debris. The severity of injuries inflicted by dredging on different macrobenthic species is related to their morphology and fragility.
- Influence of tow duration and tooth length on the number of damaged razor clams Ensis siliquaPublication . Gaspar, Miguel; Castro, Margarida; Monteiro, C. C.The incidence of shell damage due to dredging was studied in the bivalve Ensis siliqua off Lagos, on the south coast of Portugal. Three tow durations (1, 3 and 5 min) and 2 tooth lengths (30 and 40 cm) were investigated. Both factors affected the proportion of damaged individuals. The increase of tooth length results in lower proportions of damaged razor clams. An increase in tow duration increased total numbers caught but also increased the proportion of damaged clams. It is suggested that dredges with 40 cm teeth and tows of 1 min duration should be used in this fishery, although experiments should be undertaken in order to evaluate the environmental and ecological impact of dredges.
- Long-term changes in fish communities of the Ria Formosa coastal lagoon (southern Portugal) based on two studies made 20 years apartPublication . Ribeiro, J.; Monteiro, C. C.; Monteiro, P.; Bentes, L.; Coelho, R.; Gonçalves, J. M. S.; Lino, P. G.; Erzini, KarimFish communities of the Ria Formosa coastal lagoon (south Portugal) were sampled on a monthly basis with a beach seine at 4 sites, during two different time periods: 1980-1986 and 2001-2002. Community indices, species ranking and multivariate analysis were used in order to identify changes in the fish community between the two time periods. A total of 153,511 fish representing 57 taxa were recorded. Although species composition was very similar for both sampling periods, multivariate analysis performed on annual species abundance in number and weight revealed differences in fish community structure between the two periods. Structural changes in fish community were related mostly to a sharp decrease in the abundance of Mugilidae from 1980-1986 to 2001-2002. These changes were probably associated to a decrease in organic matter contents and nutrients concentrations due to improvements in sewage treatment and better water circulation inside the lagoon. The changes in fish community structure are more evident in the inner areas of the lagoon than near the inlet. The association between changes in sewage patterns and changes in the ichthyofaunal community structure reinforces the importance of fish communities as a biological indicator of human induced changes in marine systems. (c) 2007 Elsevier Ltd. All rights reserved.