Results 1 - 10 of 189
Results 1 - 10 of 189. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] Tuna are highly migratory pelagic species (HMPS) with great importance in commercial fishing. Several authors have highlighted the effect of climatic oscillations such as the NAO (North Atlantic Oscillation) on HMPS. This paper analyzes the effects of the NAO on two HMPS: albacore, Thunnus alalunga, and yellowfin tuna, Thunnus albacares. Fishing data from the Spanish fleet operating in the North Atlantic area were obtained from the International Commission for the Conservation of Atlantic Tunas (ICCAT) database. The results show a positive correlation between the NAO index and the Catch per Unit Effort (CPUE) for both albacore and yellowfin tuna, depicting a potential effect on their capturability. (Author)
[en] Migratory Fish travel downstream to reach larger body of water where the food is available. When they grows, migrate upstream to the place of their birth to spawn. In areas where fish have a commercial value and to keep alive these species as a part of environment, care must be done not to stop such migration specially by constructing the dams across the rivers. Diversion dams usually built across the river to divert some portion of the river flow for irrigation lands. In such dams, the engineers must provide a passage called 'FISHWAY'; for fish in order that fish can travel from down stream to the upstream of the dam. Of course, if such structure is not considered, the fish can not travel upstream to spawn, therefore in the long term these species will diminish. In this study a hydraulic model was conducted to investigate the hydraulic conditions of a vertical-slot type of fishway which has been considered for Ramhormoz diversion dam in the province of Khouzestan, Iran. The Froudian hydraulic model with the scale of 1:5 was constructed at the hydraulic laboratory of Shahid Chamran University. Tests were performed for the original design and two other alternatives slot-opening angles. Another fishway called Denil, also was tested. From the observation and data obtained from these tests, it was found that 90-degree slot opening provide suitable hydraulic conditions. Denil fishway also was found to satisfy the hydraulic criteria and due its simplicity and rapid construction was recommended to be used in this diversion dam. (author)
[en] Arca zebra, constitutes one of the fishing resources with the greatest economic impact in northeastern Venezuela, since it forms banks of commercial importance. During a period of nine months (May 2010-August 2011), the community structure of the organisms from the trawling fishery carried out by the fishermen of the area was identified, quantified and described. The biomass and abundance of the different groups were estimated to perform Abundance-Biomass Comparison Curves (ABC) with the objective of determining the degree of affectation by the trawling activity. A total of 3.249 organisms belonging to 130 species were grouped in five Phyla: Mollusca, Annelida, Arthropoda, Echinodermata and Chordata. The Sanders' diversity index was 122.9 with mollusks (70.87) and polychaetes (29.91) as the most diverse taxa. Mollusks had the highest abundance followed by polychaetes, crustaceans, echinoderms and ascidians. Mollusks and echinoderms made the largest contribution to total biomass. The most frequent species were: Mithraculus forceps, Phallucia nigra, Echinometra lucunter, Eunice rubra and Pinctada imbricata. The microgastropods Triphora melanura is recognized as a new record for the area and the polychaete Oenone fulgida, for Venezuela. The ABC curve showed that total abundance of organisms was above total biomass, suggesting that the fishery of Arca zebra has a negative effect on most groups of organisms, mainly on echinoderms, since many of them suffer strong physical damage at the time of extraction, therefore, there is a need to modify the trawl nets, increasing the mesh opening, but without endangering the economic viability of the fishery.
[en] This reports Herbei spirit oil spill incident and overcoming the accident, which includes congratulatory address and the reason of publishing, summary of the Herbei spirit oil spill incident, starting the oil spill, spreading oil and restoration, trouble of creature ecology and fishing industry, the worst pollution and effort to restore and to prevent, public sentiment and executive measurement, volunteer work for prevention, donation, hopeful wave in the east sea, new jump for the clean east sea, report of passion on oil spill incident and culture tour cluster of Chungnam east sea.
[en] The paper presents the results of a feasibility-study carrie out by ENEA with the technical support of ICRAP. Owing to its conclusions, the authors can locate some areas of possible application of fish-radurization both for the inner and for the foreign market. The former may offer in particular the opportunity of the on-board radurization, because of its peculiar characteristics. The latter may be particularly receptive in the case of those countries where refrigerating line is lacking and where the distribution of fresh fish-products seems rather difficult
[en] Shrimp trawl fishing is a relevant activity that contributes significantly to the generation of economic resources for Ecuador through the creation of jobs and the commercialization of the shrimps. Unfortunately the high variability of the marine ecosystem signals are complex making forecasting a difficult task. This paper evaluates the use of singular spectrum analysis (SSA) for improving forecasting by conventional methods. SSA is implemented in four steps, embedding, decomposition, grouping, and diagonal averaging. The effective length of the embedding window is selected by means of the information provided by the differential energy of the eigenvalues. The SSA decomposition is used to extract two types of components, one of low frequency which represents the inter-annual component, and the other of high frequency which represents the annual component. Once the components have been obtained, three models based on SSA are implemented, the first is based on the autoregressive model (SSA-AR), the second is an artificial neural network (ANN) based on the Levenberg-Marquardt algorithm (SSA-ANN-LM), and the third is another ANN based on the Cuckoo Search algorithm (SSA-ANN-CS). The historical data that was used to evaluate the models are the shrimp monthly catches in the Gulf of Guayaquil from 2000 to 2012. The empirical results show the superiority of the proposed models with respect to the conventional models. The best approximation was achieved with the enhanced model SSA-AR, with a MAPE of 1.0%, a R2 of 99% and a RMSE of 1.5%.
[es]La pesca por arrastre de camarón es una actividad relevante que contribuye de manera significativa con la generación de recursos económicos para Ecuador a través de la empleabilidad y la comercialización. Por desgracia, la alta variabilidad de las señales de los ecosistemas marinos presenta complejidad, tornando el pronóstico de stock en una tarea difícil. En este trabajo se evalúa Análisis de Espectro Singular (SSA) para mejorar la predicción de los métodos convencionales. SSA se implementa en cuatro etapas, embebido, descomposición, agrupación y promedio de las diagonales. La longitud efectiva de la ventana de embebido se selecciona por medio de la información proporcionada por la energía diferencial de los valores propios. La descomposición SSA se utiliza para extraer dos tipos de componentes, una de baja frecuencia que representa la componente interanual, y otra de alta frecuencia que representa la componente anual. Una vez obtenidas las componentes se implementan tres modelos de pronóstico. El primer modelo es lineal autorregresivo (SSA-AR), el segundo es una Red Neuronal Artificial (ANN) basada en Levenberg-Marquardt (SSA-ANN-LM) y el tercero es otra ANN basada en Cuckoo Search (SSA-ANN-CS). Los datos históricos utilizados para evaluar los modelos son las capturas mensuales de camarón en el Golfo de Guayaquil desde el año 2000 hasta el 2012. Los resultados empíricos muestran la superioridad de los modelos propuestos con respecto a los modelos convencionales. La mejor aproximación se logra con el modelo SSA-AR, con un MAPE de 1.0%, un R2 de 99.9% y un RMSE de 1.5%.
[en] In the present paper, the author considers the problem of dynamic optimization of the exploitation policy connected with the combined harvesting of two competing fish species, each of which obeys the logistic growth law. The singular extremal trajectory in the phase plane is derived by taking the harvesting effort as a dynamic variable. Biological or bioeconomic interpretations of the constraints required for this singular extremal are also given. (author)
[en] The sardine Sardinella aurita, fished since 1927, is Venezuela's most significant fishery resource. The national catch reached a record high of 200,000 tons in 2004 but diminished nationally by 50% in 2005 and by 90% on Margarita Island, marking the beginning of a crisis in sardine fishing. Based on indicators of overexploitation, the fishing authority increased the minimum size required for capture and prohibited fishing for three months in 2013. The validity of these measures is studied here. A reduction in size may indicate intensive exploitation, and thus, the records of 28,217 sardines measured between 2002 and 2016 in the southeast region of Margarita Island were examined. Prior to the crisis, in 2003 and 2004, the average size was 195.48 and 196.95 mm in total length (TL), respectively. With the onset of the crisis (2005), the size was 201.95 mm, surpassing the measurements obtained in the other years of the period studied (181.27 to 191.89 mm). The conclusion was drawn that no great change was identifiable in the annual average size, providing no support for the supposed overexploitation. The 20 cm TL value reported by certain studies for the average length at maturity (Lm50%) is discussed in relation to the increase in the minimum size of capture to 19 cm and considered to be flawed by biased sampling. Moreover, the sardine stock would already have been exhausted were the Lm50% value of 20 cm accurate because for decades, the average size of capture had been < 20 cm. The true Lm50% of S. aurita is ≤ 17 cm, as in the eastern Atlantic Ocean (African waters and the Mediterranean Sea). Furthermore, the prohibition of fishing from January-March is not warranted because the ban occurs during months when sardine eggs show relatively low abundance in the plankton. Fishing gear and statistics are also discussed. This study leads to the recommendations that management measures be reconsidered and that the consequences of fishing with equipment known as the machine be investigated.