Elasmobranch landings for the Portuguese commercial fishery from 1986 to 2001.
Fishing has been important to the livelihood of the Portuguese for centuries. Some coastal communities are almost totally dependent on fishing or related activities (DGPA, 1998). The nation's fishing grounds are delineated by an EEZ (Exclusive Economic Zone) of 1,700,000 [km.sup.2], encompassing both continental Portugal (with a coastline of 942 km) and two large insular regions surrounding the Azores and Madeira (DGPA, 1998).
Historically, fisheries have targeted elasmobranchs to supply the liver-oil or "squalene" market (Holts, 1988; Last and Stevens, 1994). Elasmobranchs have also been landed, and in many cases discarded, as the bycatch of other fisheries (Berkeley and Campos, 1988; Stevens, 1992). More recently, however, elasmobranchs have been targeted specifically to provide a source of protein in the form of meat and fins (Cailliet and Bedford, 1983; Holts, 1988).
The life history of elasmobranchs is characterized by slow growth rates, late maturity, long gestation periods, and the production of a small number of offspring (Holden, 1973; Pratt and Casey, 1990). These characteristics are customarily coupled with a distinctive predatory behavior (Gruber, 1982). Elasmobranchs therefore frequently represent an important "apex" role within their respective food web, and the depletion of their stocks could potentially cause a rapid and profound negative impact upon the ecosystem from which they are drawn (Gruber, 1982).
In addition, the nature of their life history frequently subjects elasmobranchs to a "high risk" of overfishing (Holden, 1973, 1974, 1977). Many publications highlight the inability of elasmobranchs to sustain strong fishing pressure for any extended period, as overfishing often translates into a rapid decline of population numbers (Pratt and Casey, 1990; Pepperell, 1992; Stevens, 1992; Musick et al., 1993; Sminkey and Musick, 1995). The delicate nature of elasmobranch populations emphasizes the need for effective conservation and management measures for this important taxonomic group.
In 1983, the Portuguese elasmobranch fishery expanded rapidly due to an increasing demand for shark by-products (i.e. oil, liver, etc.) and as the bycatch of an accelerated deep-sea teleost fishery (Nunes et al.(1)). In 1985, the demand for shark by-products peaked (oil prices reached US$4.00 - US$5.00 per liter) and then declined from 1987 to 1999 (oil prices decreasing to less than US$1.00 per liter) (Nunes et al.(1)). During the same period, the demand for elasmobranch flesh steadily increased, and at present, this represents the principal elasmobranch product marketed in Portugal. The flesh of these fishes is sold for human consumption either directly (in the case of many species of Rajidae and Squalidae) or indirectly (i.e. processed into other food products) (Nunes et al.(1)).
Portugal's elasmobranch fishery is not regulated, and thus there are no established size or catch quota limits. The "fishery" consists mainly of: 1) targeted deep-sea elasmobranch longlining; 2) targeted pelagic elasmobranch surface longlining; 3) bycatch of deep-sea elasmobranchs from black scabbardfish, Aphanopus carbo, longlining; 4) bycatch of pelagic elasmobranchs from teleost gill-netting, purse seining, and bottom trawling; and 5) bycatch of skates and rays from crustacean bottom trawling.
Despite their species' high-risk nature, elasmobranch fisheries have been little studied in this region. In Portugal, what little work has been published consists mainly of internal reports, most of which came from the Portuguese Marine Research Institute (Instituto de Investigacao das Pescas e do Mar, IPIMAR) (Silva (2,3,4), Silva and Pereira (5), and Figueiredo et al. (6)). This paper provides an introductory overview of the commercial Portuguese elasmobranch fishery and its evolution over the period between 1986 and 2001 and suggests possible avenues of future research.
The data for this study were obtained from the central commercial fishery authority for the Portuguese government (Direccao Geral das Pescas). Landed weights were totaled for each species, for all ports, for 1986-2001. Species whose landed weight exceeded 250 t are shown in Figure 1.
[FIGURE 1 OMITTED]
Landed weights were compiled by port for all species during the period. Ports with landings of >1,000 t are shown in Figure 2. Ports or regions with landings for a specific species >25% of the total landings of that species for all of Portugal, are shown in Figure 3. Annual species landings trends were further examined using a linear regression analysis (Table 1, Fig. 4-13).
[FIGURES 2-13 OMITTED]
Mean yearly price per kilogram (PPK) was calculated per species to examine changes in "demand" and the results of linear regression analysis are given in Table 2. Mean yearly PPK for all species was also calculated (Fig. 14). (7)
[FIGURE 14 OMITTED]
Changes in fishing "effort" during the study period were examined. The number of vessels registered to fish in Portuguese waters was totaled for each year between 1992 and 2000 and trends were examined. (No data were available for 1986-1991.)
Yearly weight landings and mean yearly PPK's were compared to examine the current "status" of the 14 most heavily landed elasmobranch, i.e. the slopes of the regression analyses of yearly landings and mean yearly PPK's, for each species, were reviewed (Table 2), and those species exhibiting significant trends are shown in Figures 4-13.
Catch and Effort History
During the 16-year study period, the total landed weight of elasmobranchs was 82,704 t, averaging 5,169 t ([+ or -] 795 t) per year. These landings represented 18 families, 29 genera, and 34 species of shark and ray (Table 1). The ten groups most often landed were Raja spp., Centroscymnus coelolepis, Scyliorhinus spp., Centrophorus granulosus, Centrophorus squamosus, Prionace glauca, Mustelus spp., Torpedo spp., Isurus oxyrinchus, and Dalatias licha (Fig. 1), and they accounted for 91.2% of the total weight landed (75,433 t).
Care should be taken when examining these results, as the fishermen often identified elasmobranchs by their common name. Experience has demonstrated that the fishermen and fishery officials were accurate at identifying individual elasmobranch species. However, two taxa were notable for the way in which they were inappropriately recorded. First, 1.9% (or 1,564 t) of the total landings were attributed to the group "pleurotremata," a taxonomic term adopted for those shark species that fishermen could not identify accurately. Hence, the group "pleurotremata" was excluded from Figure 1. Second, 1.3% (or 1,036 t) of the total landings were attributed to Oxynotus centrina. The Portuguese common name for this species, "peixe porco," is also the common name for a local teleost, Balistes carolinensis. Hence, the data for Oxynotus centrina was considered unreliable and was also excluded from Figure 1. Finally, 290 t of elasmobranch liver and 2,101 t of elasmobranch oil were also landed during the period between 1986 and 2001. These totals are still included in the grand total of 82,704 t.
The ten ports with the highest landings were Sesimbra, Peniche, Viana do Castelo, Nazare, Lisboa, Matosinhos, Figueira da Foz, Olhao, Povoa do Varzim, and Sines (Fig. 2). These ports accounted for 82.6% of the landings, or 68,295 t. The remaining 17.4% of the total weight landed was drawn from an additional 59 ports scattered throughout continental Portugal.
Some elasmobranch species were landed along much of the coast of Portugal. These included Raja spp., Scyliorhinus spp., Torpedo spp., Isurus oxyrinchus, Galeus melastomus, Dasyatidae, Hexanchus griseus, Lamna nasus, Cetorhinus maximus, Echinorhinus brucus, and Etmopterus spp. (Fig. 3). Other elasmobranch species were often caught in specific regions. Total annual landings have been decreasing since 1990 and remained below 5,000 t after 1993 (Fig. 14).
Yearly landings for Centroscymnus coelolepis demonstrated a significant increase over the test period (Fig. 5, Table 2). Significant increases in yearly landings were also observed for Scyliorhinus spp., and Galeus melastomus (Fig. 6, 12, and Table 2). Significant decreases in yearly landings were observed for Raja spp., Centrophorus granulosus, Mustelus spp., Torpedo spp., and Squatinidae (Fig. 4, 7, 10, 11, 13, and Table 2).
As would be expected, mean yearly PPK values increased over the test period for all species, reflecting a price increase associated with inflation (Table 2). However, some species demonstrated marked average annual increases of over 10% per annum. Annual average PPK increases were 10% for Raja spp., 8% for Centroscymnus coelolepis, 8% for Scyliorhinus spp., 12% for Centrophorus granulosus, 9% for Centrophorus squamosus, 17% for Prionace glauca, 10% for Mustelus spp., 12% for Torpedo spp., 9% for Isurus oxyrinchus, 22% for Dalatias licha, 16% for Galeus melastomus, 14% for Alopias vulpinus, 8% for Myliobatidae, and 20% for Squatinidae. These PPK increases exceeded the official annual average inflation rate in Portugal during the same period of 4.64% [+ or -] 0.92% (Pereira (8)).
Mean yearly PPK for all elasmobranch landings increased from 0.64 in 1986 to 1.83 in 2001; a mean yearly increase of 7.88% [+ or -] 12% (Fig. 14). Interestingly, mean yearly PPK briefly peaked in 1991. During the previous year, total landings reached a maximum peak at 6,768 t and then dropped by 19.5% to 5,451 t (Fig. 14). The increased mean yearly PPK in 1991 could therefore possibly reflect an increased demand for elasmobranch fishes during that year (Fig. 14) which was not echoed by sufficient landings.
The total number of registered fishing vessels decreased from 6,864 in 1992 to 5,013 in 2000, a decrease of 27% or a mean yearly decrease of 3.84% [+ or -] 1.85%. During the same period, landings of Scyliorhinus spp. increased (from 556 to 725 t, an increase of 30%) (Fig. 6). This was repeated for Centrophorus squamosus (from 422 to 478 t, an increase of 13%) (Fig. 8), Galeus melastomus (from 17 to 41 t, an increase of 137%) (Fig. 12), and Alopias vulpinus (from 13 to 15 t, an increase of 12%).
During the same period (i.e. 1992-2000), landings of Centrophorus granulosus decreased at a much greater rate than the total vessels registered (from 958 to 54 t, a decrease of 94%) (Fig. 7). Similar observations were made for Prionace glauca (from 374 to 316 t, a decrease of 16%) (Fig. 9), Mustelus spp. (237 to 41 t, a decrease of 83%) (Fig. 10), Torpedo spp. (from 96 t to 34 t, a decrease of 65%) (Fig. 11), Dalatias licha (from 25 t to 5 t, a decrease of 80%), Myliobatidae (from 15 t to 9 t, a decrease of 43%), and Squatinidae (from 8 t to 1 t, a decrease of 92%) (Fig. 13).
Landings and mean yearly PPK for Centroscymnus coelolepis both increased significantly over the period of study (Fig. 5 and Table 2). This observation was repeated for Scyliorhinus spp., and Galeus melastomus (Fig. 6, 12, and Table 2).
Landings for Raja spp. decreased significantly, while mean yearly PPK increased significantly over the period of study (Fig. 4 and Table 2). This observation was repeated for Centrophrous granulosus, Mustelus spp., Torpedo spp., and Squatinidae (Fig. 7, 10, 11, and 13 and Table 2).
Between 1986 and 1996, the Portuguese commercial fishing fleet landed 2,437,700 t of fishes and invertebrates, a mean of 221,609 [+ or -] 4,827 t per annum (DGPA, 1998). During the same period, 62,333 t of elasmobranchs were landed, constituting 2.56% of the total catch. During the period of this study (1986-2001), mean annual elasmobranch landings were 5,169 [+ or -] 795 t. By comparison, Indonesia recorded mean annual landings of 70,000 t between 1987 and 1991. Mexico, the United States, and the Philippines reported mean annual landings of 34,000, 25,000, and 18,000 t, respectively (Bonfil, 1994). By comparison, other European nations such as Spain, Italy, and Norway reported mean annual landings of 18,000, 10,000, and 8,000 t between 1987 and 1991, respectively (Bonfil, 1994).
Information about the distribution of elasmobranch species throughout Portuguese waters has not been previously available except for limited data provided by IPIMAR research surveys (Figueiredo, (9,10). Figure 3 indicates that some elasmobranch species were landed relatively heavily at specific ports, suggesting some relationship between species distribution and geographic location. This possibility is supported by the fact that fishing vessels rarely strayed far from their home port during normal operation (i.e. <20 km except in exceptional circumstances). In addition, modern fishing ports in Portugal have grown up around traditional fishing villages, and there is little evidence to suggest that local demand or infrastructure resulted in heavier landings of specific elasmobranch species in a given region.
One possible reason for the regional difference in elasmobranch landings is an interplay between the distribution of these species throughout Portuguese waters as dictated by their ecology, local bathymetry, and the specificity of different fishing techniques.
The possible effect of bathymetry and fishing techniques on the capture of specific species may be evidenced by the higher landings of Raja spp. and Gymnura altavela from the port of Olhao. In this region of Portugal, the 1,000 m isobath is approximately 58.8 km from the coastline (Viriato et al., 1996). The shallower conditions in this area favor crustacean bottom trawlers, one of the principal sources of these benthic elasmobranch species.
Similarly, the largest bottom longline fleet in Portugal operates from the port of Sesimbra, located very close to the edge of the continental shelf. Here, the 1,000 m isobath is only 13.7 km from the coastline (Viriato et al., 1996). Vessels from Sesimbra are large and able to operate down to 3,000 m, while vessels from other ports are generally smaller and are seldom able to operate below 1,000 m. During a survey of deep-sea fishes by the Portuguese Marine Research Institute (IPIMAR), one of the authors (Correia (11)) observed that Centroscymnus coelolepis was very rarely caught at depths shallower than 800 m. Depth of fishing operation could therefore account for the heavier landings of the deep-sea sharks Centroscymnus coelolepis and Centrophorus squamosus in this region. Finally, the port of Peniche operated a large surface long line fleet, possibly accounting for the relatively higher landings of Prionace glauca and Isurus oxyrinchus, and the lower landings of deep-sea sharks.
These examples appear to support the conjecture that the use of specific fishing techniques and operation depths could have been species selective and account for the composition of landings at specific geographic locations. Unfortunately, there is insufficient information available to draw solid conclusions about habitat preferences (Capape, 1985). In addition, there is a relative lack of literature on the topography of Portuguese waters below 400 m (Viriato et al., 1996). In an effort to better understand the Portuguese EEZ and improve the management of marine resources, the IPIMAR is currently conducting topography surveys along the Portuguese coastline, with the ultimate objective of mapping the sea floor down to a depth of 1,000 m.
The increase in landings demonstrated between 1992 and 1995 (Fig. 14) could be the result of increasing demand. One possible scenario is that an interest in marketing elasmobranchs was rekindled when deep-sea sharks were caught in large numbers as bycatch of the "booming" Aphanopus carbo fishery. When the value of the flesh was recognized and demand grew, elasmobranchs may have then been increasingly targeted during the late 1980's and early 1990's.
There have been no CPUE (catch per unit effort) studies for the Portuguese commercial elasmobranch fishery. In the absence of CPUE data, another approach was used to try and get some indication of fishery trends. Changes in the annual landings of each species were compared with changes in a "demand" indicator--mean annual price per kilogram. This allowed some cautious inferences about the "status" of each elasmobranch species. Every species was ranked according to three distinct categories: category I, where significant changes were not discernible for landings and/or price and therefore the status of the species was undetermined; category II, where significantly increasing landings and significantly increasing price were interpreted as a species subjected to possible commercial exploitation; and category III, where significantly decreasing landings and significantly increasing price were interpreted as a species subjected to possible risk of over-fishing (Table 2). This theoretical approach was supported by the observation that mean yearly price per kilogram briefly peaked in 1991 while landings slumped, potentially reflecting an increased demand by the consumers of elasmobranch fishes during that year.
In general, annual elasmobranch landings decreased over the period between 1986 and 2001. During the same period of time, teleost and invertebrate landings also decreased suggesting that there had not been an obvious shift in target taxa (DGPA, 1998). One reason for this decline was probably as a response to a directive from the European Union to reduce the size of fishing fleets throughout Europe (DGPA, 1998). Between 1992 and 1999 the fishing fleet decreased by 23.1%. This was paralleled by a 23.5% decline in total landings for all species of fishes and invertebrates. However, during the same period elasmobranch landings decreased by 32.7% suggesting that a reduction in the size of the fishing fleet alone did not account for the decline in elasmobranch landings.
Mean price per kilogram increased over the period of study for all of the 14 species examined. This result probably reflects, in part, a natural price increase due to inflation. However, all displayed rates increased well in excess of the official rate of inflation. This suggests that an increased consumer demand was driving the price of elasmobranch meat and by-products higher.
Centroscymnus coelolepis and Scyliorhinus spp. demonstrated significantly increased landings and a significantly increased price over the period of study (category II, Table 2). As these species may be subjected to commercial exploitation, their stocks should be monitored closely, allowing the formulation of adequate management strategies.
The rate at which the fishing fleet decreased in size was greatly exceeded by the rate at which landings decreased for all category III species (i.e. Raja spp., Centrophorus granulosus, Mustelus spp., Torpedo spp., and Squatinidae). As such, it is possible to suggest that decreasing "effort" alone, did not account for the decreased landings observed. This conjecture is supported by the fact that some species demonstrated increased landings over the same period of study (e.g. Centroscymnus coelolepis, Scyliorhinus spp., Prionace glauca, and Galeus melastomus). One could therefore very cautiously suggest that the category III species are at risk of being over-exploited and are in need of immediate management.
Interestingly, the five category III species diverge somewhat phylogenetically. It could be expected that species showing signs of over-exploitation would share common life-history traits, such as low fecundity and long gestation periods (Natanson and Cailliet, 1986). However, Mustelus spp. is often associated with higher rates of reproduction (Yudin and Cailliet, 1990). The fact that this species was associated with other category III animals is a motive for concern. It either casts doubt on the interpretation of landings and price trends, or alternatively, it could indicate very strong fishing pressures, or even the removal of the sexually mature size class, as the cause of decline in this species.
In conclusion, it appears as if Centroscymnus coelolepis, Scyliorhinus spp., Prionace glauca, and Galeus melastomus are currently being heavily targeted, while Raja spp., Centrophorus granulosus, Mustelus spp., Torpedo spp., and Squatinidae may be at risk of over-fishing, either within localized fishing grounds, or throughout the EEZ. These species certainly merit the focus of future research.
The limitations of price per kilogram and registered fishing vessels as indicators of "demand" and "effort" should be carefully considered when examining the conclusions of this article. Clearly, CPUE studies are required for the development of robust management plans. However, in the absence of CPUE data, perhaps the relationship between PPK and landings in historical data sets can be used as a useful early warning indicator of species at possible risk of over-exploitation.
Table 1.--Species of elasmobranchs recorded in Portuguese waters, indicating: species with confirmed landings (*) and unconfirmed landings (?) by the commercial fishery (after Sanches, 1986). Order Species Lamniformes ? Alopias superciliosus * Alopias vulpinus Carcharodon carcharias * Cetorhinus maximus * Isurus oxyrinchus * Lamna nasus ? Mitsukurina owstoni Odontaspis ferox Odontaspis noronhai Carchariniformes Apristurus laurussonii ? Carcharhinus falciformis ? Carcharhinus limbatus ? Carcharhinus longimanus ? Carcharhinus obscurus ? Carcharhinus plumbeus * Galeorhinus galeus * Galeus melastomus * Mustelus asterias * Mustelus mustelus * Prionace glauca Pseudotriakis microdon Rhizopdonodon acutus * Scyliorhinus canicula ? Scyliorhinus stellaris * Sphyrna zygaena Squaliformes * Centrophorus granulosus * Centrophorus squamosus * Centroscymnus coelolepis Centroscymnus crepidater Centroscymnus cryptacanthus * Dalatias licha * Deania calcea * Echinorhinus brucus * Etmopterus pusillus * Etmopterus spinax * Oxynotus centrina Scymnodon obscurus Scymnodon ringens * Somniosus microcephalus Somniosus rostratus Squaliolus laticaudus * Squalus acanthias ? Squalus blainvillei Hexanchiformes Chalmydoselachus anguineus Heptranchias perlo * Hexanchus griseus Pristiformes Pristis pristis Squatiniformes * Squatina squatina Torpediniformes ? Torpedo marmorata ? Torpedo nobiliana ? Torpedo torpedo Rajiformes Amblyraja radiata ? Dasyatis centroura ? Dasyatis pastinaca Dipturus batis Dipturus linteus Dipturus oxyrinchus * Gymnura altavela * Leucoraja circularis Leucoraja fullonica Leucoraja naevus Manta birostris Mobula mobular * Myliobatis aquila Pteromylaeus bovinus ? Raja asterias ? Raja brachyura * Raja clavata ? Raja maderensis ? Raja microocellata ? Raja miraletus ? Raja montagui * Raja undulata Rhinobatos rhinobatos Rostroraja alba Table 2.--Slopes of species landings and price per kilogram (PPK) as estimated using a linear regression analysis for each of the 16 most heavily landed elasmobranchs reported in the Portuguese commercial fishery between 1986 and 1999. Species with significance of F value < 0.05 (marked with *) displayed a significant change over time for the parameter analyzed. This change was an increase if the corresponding slope was positive and a decrease if the corresponding slope was negative. Landings (kg/year) Species Slope [r.sup.2] Sig. F Rem. Raja spp. -47.413 0,41 0,01 * Centroscymnus coelolepis 24.983 0,42 0,01 * Scyhorhinus spp. 16.400 0,87 0,00 * Centrophorus granulosus -72.067 0,75 0,00 * Centrophorus squamosus -6.461 0,15 0,14 Prionace glauca 10.733 0,23 0,06 Mustelus spp. -28.265 0,88 0,00 * Torpedo spp. -6.731 0,85 0,00 * Isurus oxyrinchus -238 0,00 0,80 Dalatias licha -9.716 0,44 0,00 * Galeus melastomus 1,434 0,58 0,00 * Alopias vulpinus -755 0,02 0,57 Myliobatidae -164 0,02 0,64 Squatinidae -3.434 0,42 0,01 * PPK (US$/year) Species Slope [r.sup.2] Sig. F Rem. Raja spp. 0,13 0,960 0,00 * Centroscymnus coelolepis 0,06 0,893 0,00 * Scyhorhinus spp. 0,02 0,944 0,00 * Centrophorus granulosus 0,16 0,946 0,00 * Centrophorus squamosus 0,10 0,941 0,00 * Prionace glauca 0,05 0,744 0,00 * Mustelus spp. 0,11 0,909 0,00 * Torpedo spp. 0,12 0,970 0,00 * Isurus oxyrinchus 0,12 0,635 0,00 * Dalatias licha 0,06 0,701 0,00 * Galeus melastomus 0,03 0,508 0,00 * Alopias vulpinus 0,07 0,816 0,00 * Myliobatidae 0,05 0,830 0,00 * Squatinidae 0,09 0,643 0,00 * Species n Category (1) Raja spp. 16 III Centroscymnus coelolepis 16 II Scyhorhinus spp. 16 II Centrophorus granulosus 16 III Centrophorus squamosus 16 I Prionace glauca 16 I Mustelus spp. 16 III Torpedo spp. 16 III Isurus oxyrinchus 16 I Dalatias licha 16 III Galeus melastomus 16 II Alopias vulpinus 16 I Myliobatidae 16 I Squatinidae 16,00 III (1) Category I: significant changes were not discernible for landings and / or price and therefore the status of the species was undetermined; Category II: significantly increasing landings and significantly increasing price were interpreted as a species subjected to possible commercial exploitation; Category III: significantly decreasing landings and significantly increasing price were interpreted as a species subjected to possible risk of over-fishing.
We are indebted to Fernanda Guia and Teresa Cunha (Direccao Geral das Pescas) who provided the time and effort to extract the data used in this report from the National fishery database. We would also like to thank John Stevens (CSIRO) and several anonymous reviewers for their valuable comments.
(1) Nunes, M. L., I. Baptista, R. M. Campos. and A Viegas. 1989. Aproveitamento e valorizcao de algumas especies de tubarao. Relat. Tec. Cient. INIP, Lisboa, 7, 38 p.
(2) Silva, H. M. 1983. Preliminary studies of the exploited stock of kitefin shark Scymnorhinus licha (Bonnaterre, 1788) in the Azores. ICES/ CM 1983/G:18, 13 p.
(3) Silva, H. M. 1987. An assessment of the Azorean stock of kitefin shark Dalatias licha (Bonnaterre, 1788). ICES/CM 1987/G:66, 10 p.
(4) Silva, H. M. 1988. Growth and reproduction of kitefin shark Dalatias licha (Bonnaterre, 1788) in Azorean waters. ICES/CM 1988/G:21, 15 p.
(5) Silva, A. A., and J. J. Pereira. 1999. Catch rates for pelagic sharks taken by the Portuguese swordfish fishery in the waters around the Azores, 1993-1997. ICCAT SCRS/98, 12 p.
(6) Figueiredo, I., M. J. Figueiredo, and O. Moura. 1995. Distribution, abundance and size composition of blackmouth catshark (Galeus melastomus) and small-spotted dogfish (Scyliorhinus canicula) on the slope of the Portuguese South and Southern West coasts. ICES/CM 1995/G:9, 38 p.
(7) PPK was converted from PTE (Portuguese Escudos) to US$ (United Stales dollars) using the mean conversion rate for 1999 of 195 to 1.
(8) Pereira, A. E. 2000. A inflacao e o indice de precos no consumidor. Dossiers didacticos, Instituto Nacional de Estatistica. Lisboa. 21 p.
(9) Figueiredo, I., M. J. Figueiredo, and O. Moura. 1995. Distribution, abundance and size composition of blackmouth catshark (Galeus melastomus) and small spotted dogfish (Scyliorhinus canicula) on the slope of the Portuguese south and southern west coasts. Int. Council Explor. Sea, Demersal Fish Committee, CM 1995 (G:9), 38 p.
(10) Figueiredo, M. J., I. Figueiredo, and J. Correia. 1996. Caracterizacao geral dos recursos de profundidade em estudo no IPIMAR. Relat. Cient. Tec. Inst. Port. Invest. Marit. 21, 50 p.
(11) Correia, J. 2003. Oceanario de Lisboa, Doca dos Olivais 1990-005 Lisboa, Portugal.
Berkeley, S. A., and W. L. Campos. 1988. Relative abundance and fishery potential of pelagic sharks along Florida's east coast. Mar. Fish. Rev. 50(1):9-16.
Bonfil, R. 1994. Overview of world elasmobranch fisheries. FAO Fish. Tech. Pap. 341, 119 p.
Cailliet, G. M., and D. W. Bedford. 1983. The biology of three pelagic sharks from California waters and their emerging fisheries: a review. CalCOFI Rep. 24:57-69.
Capape, C. 1985. Nouvelle description de Centrophorus granulosus (Schneider, 1801) (Pisces, Squalidae). Donnees sur la biologie de la reproduction et le regime alimentaire des specimens des cotes tunisiennes. Bull. Inst. Natl. Sci. Tech. Oceanogr. Peche Salambo. 12:97-141.
DGPA. 1998. Pescas em Portugal 1986-1996. Inst. Nac. Estatistica, Direccao-Geral Pescas Aquicult. (DGPA), Lisboa, 279 p.
Gruber, S. H. 1982. Role of the lemon shark, Negaprion brevirostris (Poey) as a predator in the tropical marine environment: a multidisciplinary study. Fla. Sci. 45:46-75.
Holden, M. J. 1973. Are long-term sustainable fisheries for elasmobranchs possible? Rapp. P.-V. Reun. Cons. Int. Explor. Mer. 164:360-367.
--. 1974. Problems in the rational exploitation of elasmobranch populations and some suggested solutions. In F. R. Jones (Editor), Sea fisheries research, p. 117-137. J. Wiley & Sons, N.Y.
--. 1977. Elasmobranchs. In J. A. Gulland (Editor), Fish population dynamics. p. 187-215. J. Wiley & Sons, N.Y.
Holts, D. B. 1988. Review of U.S. west coast commercial shark fisheries. Mar. Fish. Rev. 50(1):1-8.
Last, P. R., and J. D. Stevens. 1994. Sharks and rays of Australia. CSIRO, Sydney, 513 p.
Musick, J. A., S. Branstetter. and J. A. Colvo-coresses. 1993. Trends in shark abundance from 1974 to 1991 for the Chesapeake bight region of the U.S. mid Atlantic coast. U.S. Dep. Commer., NOAA Tech. Rep. NMFS 115:1-18.
Natanson, L. J., and G. M. Cailliet. 1986. Reproduction and development of the Pacific angel shark, Squatina californica, off Santa Barbara, California. Copeia 1986(4):987-994.
Pratt, H. L. Jr., and J. G. Casey. 1990. Shark reproductive strategies as a limiting factor in directed fisheries, with a view of Holden's method of estimating growth parameters. U.S. Dep. Commer., NOAA Tech. Rep. NMFS. 90:97-109.
Pepperell, J. G. 1992. Trends in the distribution, species composition and size of sharks caught by gamefish anglers off south-eastern Australia, 1961-90. Aust. J. Mar. Freshwater Res. 43:213-225.
Sanches, J. G. 1986. Nomenclatura e diagnose dos principals peixes marinhos de Portugal (ciclostomos, selaceos e holocefalos). Lisboa, INIP (Pub. Avulsas. 9), 184 p.
Sminkey, T. R., and J. A. Musick. 1995. Age and growth of the sandbar shark, Carcharhinus plumbeus, before and after population depletion. Copeia 1995 (4):871-883.
Stevens, J. D. 1992. Blue and mako shark by-catch in the Japanese long-line fishery off south-eastern Australia. Aust. J. Mar. Freshwater Res. 43:227-236.
Viriato, A., M. J. Figueiredo, I. Figueiredo, and J. CorreiaJ. 1996. Atlas de apoio a pesca de arrasto na vertente continental portuguesa. Inst. Invest. Pescas Mar. IPIMAR, Lisboa, 51 p.
Yudin, K. G., and G. M. Cailliet. 1990. Age and growth of the gray smoothhound, Mustelus californicus, and the brown smoothhound, M. henlei, sharks from central California. Copeia 1990(1): 191-204.
The authors are with the Oceanario de Lisboa, Doca dos Olivais, 1990-005, Lisboa, Portugal [e-mail: firstname.lastname@example.org].
|Printer friendly Cite/link Email Feedback|
|Author:||Correia, Joao P.S.; Smith, Mark F.L.|
|Publication:||Marine Fisheries Review|
|Date:||Jan 1, 2003|
|Previous Article:||The Marine life fishery in Florida, 1990-98.|
|Next Article:||Tenets, principles, and criteria for management: the basis for systemic management.|