|Zootecnia Tropical > Sumario de la Colección > Volumen 21|
Zootecnia Trop., 21(3):261-274. 2003
Management of tuna resources in Venezuela
Ana Cabello1*, Jesus Marcano1, Mirle Narváez2, Omelys Silva 2, Antonio Gómez 2, Bertha Figuera1, Osmicar Vallenilla1 y Hebel Salazar1
Instituto Nacional de Investigaciones Agrícolas (INIA).
Venezuela is considered an important tuna producer because its fleets operate in the Pacific and Atlantic Oceans and land about 80000 t/year. This landing is oriented 65% towards export, 20% to the canning industry, and 15% for direct consumption as fresh fish. The fleet captures five species of tuna, among other smaller scombrid species. All tuna species are highly migratory and shared among several countries. Tuna is one of the fish items with higher demand among consumers. Because of its importance, several aspects of its exploitation, like fishery, bromatological characteristics, and processing have been studied. Because is a species of high commercial importance with large nutritional value. This paper studies the relationship among catch, commercialization, and sanitary aspects, which are involved in the use of tuna as a food source and as an item for export. Currently, the fishery shows a decreasing trend in the landings of all tuna species. The bromatological evaluation confirmed a protein content of 23.65 to 24.78 % and low levels of heavy metals like Hg, Cd, Cu, and Zn. Since the current legislation in Venezuela regulating tuna byproducts only establishes critical levels for Hg, its revision is needed to incorporate other potentially hazardous heavy metals.
Key words: Tuna, management, bromatology, processing, nutritional value.
In Venezuela, tuna is one of the three most important commercial fish resources due to their annual landings, fleets with the Venezuelan flag operating in both, the Pacific and Atlantic oceans, their installed infrastructure for processing, the number of generated jobs, and the high incomes resulting from their commercialization. In addition, there is a wide acceptance of the different tuna species among the Venezuelan consumers, due to tuna good taste and its nutritional quality. In addition, there is a high demand in the international markets. Artisans and industrial methods perform tuna fisheries (Marcano, 2002). The industrial tuna fleet is the most relevant, and operates in the Atlantic and Pacific Oceans in front of the coasts of Ecuador and Colombia. This fleet landed more than 139,000 t in 2001, which is considered an extraordinary catch. Artisan fisheries operate inshore with vessels of little autonomy; their landings reach near 6,000 t per year and are sold as fresh fish or dry-salted.
Tuna is one of the resources that are processed by the Venezuelan canning industry. Seventy percent of the national landings (about 57,000 t) are processed this way, while 20% (about 20,000 t) is consumed in fresh, and 11% (about 8,250 t) is exported either completely or as loins (Cabello et al. 2002).
Venezuela is a member of the International Commission for the Conservation of Atlantic Tunas (ICCAT) and the Interamerican Tropical Tuna Commission (IATTC). These organizations evaluate the status of tuna and associated resources, and regulate their fishing in the Atlantic and Eastern Pacific Oceans, respectively. To accomplish these goals, they use information on annual catch and effort of all the fleets. The migratory nature of tuna and associated resources (sharks, billfish and marine mammals, incidentally captured along with tunas) makes them to be considered as international resources.
In 1988, Gaertner et al. set up a system for continuous collection of data on catch and effort using logbooks in industrial tuna vessels. On the same year, Pagavino et al. studied the evolution of the tuna surface fishery, while Eslava (1990) studied the Venezuelan long line tuna fishery in the Caribbean Sea. Marcano et al. (1994) described the biometric relations of yellowfin tuna landed by the Venezuelan long line fishery. All these studies have contributed to a better understanding of the tuna fishery in the country.
The objective of this study is to characterize the tuna fishery, considering the composition of the fleet, the type of fishing gear, operating zones, and the analysis of the catch and trends of the capture per unit of effort CPUE. The bromatological and toxicological characteristics of tuna meat were also evaluated, due to the importance of this raw material for the canning industry and for the diet of the Venezuelan people.
MATERIALS AND METHODS
The used information came from logbooks, landing checks, multispecific samplings in the harbors, historical databases on catch and effort maintained by INIA, and field samples that were analyzed in the Food Technology Laboratory of INA, Cumaná. The multispecific sampling was made at random and stratified in two levels; the primary units were the sets and the secondary the fish. The proportion and size structure of each species in the landings were evaluated. The total size of the sample was calculated using weight – length relationships for each species (Pagavino, 1990) and then extrapolated to the weight of the whole container of the vessels where the sample came from.
Biological samples were collected from only two species of tuna, Thunnus albacares and Thunnus obesus, which are considered the most important by the canning industry. Between 6 and 12 samples were collected once a month for 9 months from commercial catches of two canning industries located at Cumaná, Sucre state, Venezuela. Each sample represented a pool of muscular tissue from different parts of the animal. Due to the high value of large size tunas, and since skin or muscle cuts decrease the value of animals aimed at the export market, tissue samples were obtained from middle size animals, in the range 65 to 1,200 cm fork length. Samples were taken to the Laboratory of Food Technology of INIA at Cumaná to be analyzed. The methods employed were those internationally recommended for the determination of proximal composition and heavy metals in food. The analyses of protein, humidity, ash, fat and salt contents followed A.O.A.C. (1994). Analyses of pH and total basic volatile nitrogen (TBVN) were performed according to the norm COVENIN 1315-79 (COVENIN 1979). Energetic value was estimated according to Deulofeu and Marenzi (1960). Mercury was analyzed according to Armstrong and Uthe (1971) and Cd, Cu and Zn were analyzed according to Leonard (1971).
Values of the physical-chemical evaluations were analyzed using a two way ANOVA procedure with replication (Sokal and Rohlf, 1995), in order to establish the significance of the variations between samples from the Atlantic and Pacific Oceans. A Duncan a posteriori test was used when required.
RESULTS AND DISCUSSION
Venezuela is considered an important tuna producer and has a fleet of 26 purseiners operating in the Eastern Pacific Ocean and 55 vessels, among purseiners, bate boats and long liners, operating in the Western Atlantic Ocean. The proportion of tuna landings from the Pacific Ocean accounts for 63% of the total catch, while the remaining 37% come from the Atlantic Ocean. During the last twenty years, catches from the Pacific Ocean have fluctuated from 9,000 t to 109,000 t, and catches from the Atlantic Ocean between 9,000 t and 41,000 t (Figure 1). In 2001, both fleets landed a record catch of 139000 t.
The fleet operating in the Pacific Ocean comprises only a purseiner, and has larger vessels (1,200 to 1,600 gross tonnages) with modern technology to search and catch schools of tuna. This fleet operates between the parallels 40 °N and 40 °S. In comparison, the fleet operating in the Atlantic Ocean
comprises 31 long line vessels, 14 bate boats, and 10 purseiners (600 GT). They operates between the parallels 3° and 20° N, and between meridians 50° and 75° W. Landings from the Pacific Ocean have a clear increasing trend, whereas those from the Atlantic Ocean by fishing gear, show stability since 1980 for bate boats and large variations for purseiners, with a decreasing trend, except for the year 2001 (Figure 2).
Fifteen species are landed, among tunas and tuna-like species, most being captured either with purseine net or hooked with live bate (Table 1). The yellowfin tuna, Thunnus albacares, represents 66.4% of the landings from the purseiners, 84.2% from the bate boats and 48.4% from the long liners. The latter and skipjack tuna, Katsuwonus pelamis, are the species with the greatest importance for the canning industry and for export, and were chosen as samples for bromatological and toxicological characterization.
The proximal composition of fish varies according to species and among them according to age, sex, physical condition or feeding (Kodaira, 1991). One of the supports for choosing a raw material for a technological process is the knowledge of nutritional parameters that helps taking decisions about proper conservation treatments that need to be applied. The proximal composition of the two species of tuna evaluated in this work showed a high protein content in meat (24.65% SKJ and 23.86% YFT; Table 2). There were no significant differences in the protein content between species, ocean of origin, or the interaction between these two variables (P>0.05). The variation of fat content showed similar results for species and ocean of origin (P>0.05), but the interaction between them was significant (P<0.05). The high protein content allowed its classification as lean meat, with a fat content lower than 5% for the evaluated samples. It is recommended that a 3 years period of sampling be performed in order to determine the variation of nutritional parameters, particularly the fat content, which is a parameter of great interest for commercialization and canning processes.
Ash content showed significant differences between species (P<0.05), but there were no significant differences between oceans or interaction (P>0.05). The high-recorded ash values (average 6.17%) could be associated to a high content of salt. This is due to the conservation methods of tuna on board, which use low temperature brine by mixing seawater, salt and ice, exposing the fish to a very high concentration of salt during the long period of the campaign, resulting in absorption of the salt by the tuna meat.
Water content, expressed as humidity, showed significant differences between species (P<0.05), but there were no significant differences between ocean of origin or interaction (P>0.05).
Quality parameters, like pH and total volatile basic nitrogen (TVBN), showed a wide range of variation. Fish under this condition can be classified into the Type II of commercial categories, since Type I would be fish of recent capture that has not been preserved on ice or frozen (López, 1985). This condition is due probably to the long periods tunas remain frozen on board and the lack of control of the freezing process. We recommend improvements in the methods and temperatures used for storing the tuna catch.
The range of pH values for skipjack from the Pacific Ocean was 5.82 to 6.71 and 5.57 to 6.76 for the fish from the Atlantic Ocean. The range of pH for yellowfin tuna was 5.92 to 6.78 (Pacific Ocean) and 5.36 to 6.79 (Atlantic Ocean). The use of salt as solute to speed up the freezing process has an effect upon pH variation. Premoli (1986) reported a pH value of 6.4 for very fresh fish, while Gómez and Cabello (1994) reported a pH value of 5.4 for frozen tuna delivered to cannery. These authors indicated that the transportation means between harbors and the storage facilities or cannery severely affected the freshness of the raw material. In occasions, frozen tuna are transported in trucks without cover, exposing the fish to direct sun light and high temperature. Nowadays the use of covers in the trucks is common as well as the use of refrigerated trucks for transportation of frozen tuna.
The values for TVBN were below the maximum allowed for human consumption (125 μg/100 g dry weight), indicating that the raw material was in good condition to be used in the canning process. However, TVBN values were variable in both species from either ocean, and were considered high for fresh raw material. This condition is associated with the long campaigns leading to storage periods longer than three months. Gómez (1994) reported that environmental temperature plays an important role in the increases of non-protein-nitrogen compounds in conserved fish meat.
The energetic value of the two species of tuna was 113.16 cal/g for T. albacares and 109.70 cal/g for K. pelamis. These values associate tuna meat to low calorie diets, because of the low fat content. The condition of migratory species forces them to spend large amounts of energy into motion, thus lowering the fat stored in the meat.
The toxicological evaluation was made due to the growing concern on increasing pollution of marine coasts and oceans, which affect the life of fish living in them and could threat the safe commercialization and consumption of tuna meat. Moreno (1998) commented on the growing interest in the study of heavy metals effect on marine organisms and the fact that trace quantities of them (approximately 50 μg/kg) are essential for a large number of organisms, including plants. COVENIN (1981), in its norm 1766-81 (in revision), refers as maximum limits for content of Hg, Cd, and Cu values of 0.5, 0.1, and 10 μg/kg, respectively. Zinc has not been included as contaminant yet. Tunas, in their continuous migration among coastal waters and oceans, are particularly susceptible to accumulate heavy metals and other pollutants. For tunas from the Pacific and Atlantic Oceans, the detected concentration of Hg, Cu, and Zn were below the permissible limits in Venezuela for human consumption (Table 3). Only the concentration of Cd in two sampling periods was above the permissible limits for human consumption. This situation represents an alert, so effort must be increased to reduce discharges of industrial wastes into the oceans.
The authors appreciate the assistance of J. Alió in the technical revision and translation of this document. We also thank the help received from the companies FIPACA and Alimentos Margarita C.A., for providing the tuna samples and companies spaces for their processing.
Manejo del recurso atunero en Venezuela
Venezuela es considerada como un importante productor de atún porque su flota faena en los Océanos Pacífico y Atlántico y aporta 80.000 t/año. Esta producción se distribuye en 65% para exportación, 20% a la industria conservera nacional y 15% al consumo fresco. Todas las especies de atún son altamente migratorias y compartidas con otros países. El atún es uno de los peces con más demanda por parte de los consumidores. Debido a su importancia, varios aspectos de su explotación, como la pesquería, las características bromatológicas y procesamiento, se ha estudiado. Siendo estas especies de alta importancia comercial, con gran valor nutricional, se estudia la relación entre captura, comercialización y aspectos sanitarios que están involucrados en el uso de atún como fuente de alimento y como un insumo para la exportación. Para lograr estos objetivos se realizaron muestreos en puerto y se recolectaron muestras que fueron analizadas en el Laboratorio de Tecnología de Alimentos utilizando métodos físico-químicos y bioquímicos como la cromatografía de absorción atómica para la determinación de metales pesados. Actualmente, la pesquería muestra una tendencia decreciente en los desembarcos de todas las especies de atún. La evaluación bromatológica confirmó un contenido de proteína entre 23,65 y 24,78% con bajos niveles de metales pesados como Hg, Cd, Cu y Zn. En la legislación actual en Venezuela la regulación de atún por productos sólo establecen los niveles críticos para Hg, su revisión es necesaria para incorporar otros metales pesados potencialmente peligrosos.
Palabras clave: Atún, manejo, bromatología, procesamiento, valor nutricional.
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|Zootecnia Tropical > Sumario de la Colección > Volumen 21|