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Dive into the research topics where Juan M. Hernández is active.

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Featured researches published by Juan M. Hernández.


Ecological Modelling | 2003

A growth model for gilthead seabream (Sparus aurata)

Juan M. Hernández; Eucario Gasca-Leyva; Carmelo J. León; J.M Vergara

This paper presents a growth model for gilthead seabream (Sparus aurata), which is one of the most culture species in the Mediterranean area. The model is designed by means of stochastic differential equations, and is based on previous research for other species [Modelisation de la Croissance des Poissons en Elevage, 1990]. Fish growth is assumed to be influenced by three fundamental factors: fish weight, water temperature, and ration size. The formulation incorporates fish physiology theory, requiring fewer specific parameters than other bionenergetic models. Empirical data were obtained from culture in the Canary Islands waters for a 30-month period. Some simulations were run to validate the model. Although the influence of water temperature on fish growth might need to be refined, satisfactory results are obtained. Two environmental scenarios are also examined, the “Atlantic” and “Mediterranean,” which vary in the annual cycles of water temperature. The results produce significant differences in the growth patterns between both areas, suggesting potential economic implications for the cultivation of larger commercial sizes.


European Journal of Operational Research | 2007

The role of the water temperature in the optimal management of marine aquaculture

Juan M. Hernández; Miguel León-Santana; Carmelo J. León

This paper analyses the influence of the water temperature over the optimal management of aquaculture farms. A fish growth model is presented and included in a general profit optimisation framework. Results reveal a positive influence of the average water temperature over the optimal harvesting time. The optimal ration size exhibits an uneven path with an upward phase in the warmer season followed by downward phase in winter time. An application for the seabream culture in the Mediterranean countries shows harvesting time and ration size very dependent on the water temperature and the stocking date. The risk involved with uncertainty of the environmental conditions is also estimated, which could explain the difference between the predicted optimal harvesting sizes and the real practice in commercial culture.


Aquaculture | 2002

Bioeconomic analysis of production location of sea bream (Sparus aurata) cultivation

Eucario Gasca-Leyva; Carmelo J. León; Juan M. Hernández; J.M Vergara

This paper develops a bioeconomic model to evaluate the production of gilthead sea bream in floating cages based on two locations, the Canary Islands and the Mediterranean. The model includes four sub-models: biologic, environment, production management, and economic. The biologic sub-model contains a growth model based on this species physiology. A wide range of farm scales were considered, deriving the production and input costs for each scale and scenario. The results for average costs showed increasing returns, with a rising internal rate of return (IRR). The efficient farm size was obtained for alternative management decisions and location scenarios. The results revealed that input costs, and therefore product costs, were higher in the Canary Islands than in the Mediterranean. However, environmental conditions in the Canary Islands are shown to be more favorable than in the Mediterranean, resulting in a more rapid growth, which leads to higher returns.


Journal of Environmental Management | 2015

Bioeconomic analysis of the environmental impact of a marine fish farm.

Miguel Rabassó; Juan M. Hernández

The evaluation of the environmental impact of aquaculture installations is nowadays a common social demand in many countries. The usual scientific approach to this question has been to assess the outcome from an ecological perspective, focussing on the effects produced on benthos or the water column and interactions with marine flora and fauna. In this paper, a bioeconomic model is developed to extend this traditional approach, to determine both the amount of total settled matter, its dispersion on the ocean floor and impacts on the marine ecosystem, while also taking into account other social considerations such as discounted net profits and investment returns. The model was applied to the case of off-shore gilthead seabream production in a coastal area of the Canary Isles archipelago, where the tidal current is predominant. Cage emissions and the degree of degradation of seagrass meadows on the seabed were taken as ecological impact indicators, while the net present value (NPV) for a specific time period was used as an economic indicator. By analysing the simulation results obtained by the bioeconomic model, we were able to determine the combination of production volume and harvest quantity which yields the greatest economic efficiency for different levels of degraded area.


Anatolia: An International Journal of Tourism and Hospitality Research | 2011

Spatial and environmental characteristics of rural tourism lodging units

Yolanda Santana-Jiménez; Rafael Suárez-Vega; Juan M. Hernández

The geographical characteristics of the site where a rural house is located determine its tourist affluence. By using a hedonic prices model, this paper estimates the influence of some spatial and environmental variables in the rental prices of rural houses in Gran Canaria, Spain. Geographic information systems (GIS) data are used to measure the geographical attributes associated with the house, such as the land use and the nearby population density. Other factors traditionally included in hedonic models are also analysed, such as the structural characteristics of the house and distance to some points of interest. The methodology allows us to obtain an estimation of the economic value of the location and environment surrounding a rural house. Spatial econometrics was applied to study the correlation of rental prices. Results indicate that environmental diversity and remoteness positively affect prices. Some recommendations are extracted from the results, which could help to orientate the tourist diversification policies applied to the island.


Tourism Economics | 2007

Economic welfare, the environment and the tourist product life cycle.

Carmelo J. León; Juan M. Hernández; Matías González

The tourist product life cycle model predicts different stages of the evolution of the industry in a particular region, focusing on the number of tourists visiting over a period of time. In this paper, we consider the role of environmental degradation and the decline in natural capital as determinants of the tourist product life cycle and the implications for economic welfare. It is shown that the optimal trajectory of tourist consumption increases when the stock of natural capital is high and environmental attributes are preserved, and tend to decline when the tourist product has reached a low level of natural capital, which is defined as the stock of natural resources giving value to the tourist product. The main implication is that the evolution of demand as represented by the number of tourists does not need to match economic welfare. In addition, the evolution of the tourist product life cycle converges to a stationary solution characterized by positive levels of tourist consumption and natural capital. The results have implications for the optimal management of the number of tourists and the environmental attributes of tourist destinations. Optimal taxation can play a role in financing the maintenance of the optimal level of natural capital in the stationary state.


Aquaculture Economics & Management | 2001

Cost minimization and input substitution in the production of gilthead seabream

Carmelo J. León; Juan M. Hernández; Eucario Gasca-Leyva

Abstract This paper studies cost minimization decisions by utilizing a simple bioeconomic model for gilthead seabream (Sparus aurata). This model is based on a biological growth model which accounts for the effects of temperature and ration size. Although the implicit production function derived from the growth model is shown to be quasiconcave, it is not homothetic nor quasilinear. Further, technology shows increasing returns with respect to ration size and harvesting time. Optimization decisions are analyzed in two different contexts, a restricted biological setting and an expanded economic problem. It is shown that the optimal ration size increases for the latter context, reaching values commonly accepted in current industrial practice. Even though the elasticity of substitution to the shadow input prices is positive at the optimal ration size, the latter is rather robust to changes in input prices. However, optimal costs show larger sensitivity to the labor price than to the feeding and managerial costs.


Applied Economics | 2006

The effects of water temperature in aquaculture management

Carmelo J. León; Juan M. Hernández; Miguel León-Santana

This study examines the impact of water temperature on the optimal management of the ration size and fish weight in off-shore farm aquaculture. A model for the expected returns of the farm is developed which includes a fish growth function influenced by fish weight, the ration size and water temperature. The output transportation cost has an ambiguous effect on the harvesting size, but the impact of water temperature is positive. These results explain empirical evidence in the Canary Islands that unfavourable economic conditions could be overcome by environmental advantageous conditions raising productivity.


Journal of Travel Research | 2015

The Influence of Remoteness and Isolation in the Rural Accommodation Rental Price among Eastern and Western Destinations

Yolanda Santana-Jiménez; Ya Yen Sun; Juan M. Hernández; Rafael Suárez-Vega

Experiencing the context of a rural environment is the fundamental aspect of rural travel. In order to estimate quantitative influences of the rural environment, this paper proposes to proxy rurality through two indicators: isolation and remoteness. The estimation of a hedonic pricing model with the use of both Geographic Information Systems and spatial econometrics allows obtaining the specific influence of these factors on rural lodging room prices. The methodology is applied to two tourist destinations with similar characteristics from Eastern (Taiwan) and Western (Spain) cultures. Results show that visitors’ preferences for isolation are significant but differ between these two regions. The main reasons that explain this divergence are population density differences between origin and destination, domination of international versus domestic visitors, and the intrinsic destination characteristics and perceived image. Managerial recommendations on how to emphasize the factors in the promotion of accommodation services are derived from the present study.


Aquaculture Economics & Management | 2011

EFFECT OF RATION AND SIZE HETEROGENEITY ON HARVEST TIME: TILAPIA CULTURE IN YUCATAN, MEXICO

Roger Domínguez-May; Juan M. Hernández; Eucario Gasca-Leyva; Gaspar R. Poot-López

Size heterogeneity is a common phenomenon in aquaculture systems and influences final production and economic yield. Among other factors, this variability is determined by ration. These variables directly affect potential returns and therefore influence the recommendations made for optimum aquaculture system management. As part of the search for more profitable culture strategies, a bioeconomic model was developed to analyze the effect of size heterogeneity and ration on optimum harvest time and size, thus creating a new methodological tool. Size dispersion was included using a continuous, size-structured population model incorporating the effect of ration on growth. Theoretical results were applied in a case study of tilapia culture in Yucatan State, Mexico, in which optimum ration levels and harvest times clearly differed between size heterogeneity and homogeneity models. Case study results indicated the use of different recommended ration and harvest management strategies depending on real and/or potential target market.

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Dive into the Juan M. Hernández's collaboration.

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Carmelo J. León

University of Las Palmas de Gran Canaria

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Rafael Suárez-Vega

University of Las Palmas de Gran Canaria

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Yolanda Santana-Jiménez

University of Las Palmas de Gran Canaria

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Miguel León-Santana

University of Las Palmas de Gran Canaria

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Gaspar R. Poot-López

Universidad Autónoma de Yucatán

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Marcelo E. Araneda

Instituto Politécnico Nacional

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Tatiana David-Negre

University of Las Palmas de Gran Canaria

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J.M Vergara

University of Las Palmas de Gran Canaria

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