An ecosystem modelling approach to deriving viable harvest strategies for multispecies management of the Northern Gulf of California

• 1. An ecosystem analysis was developed focusing on resource exploitation and biodiversity conservation for the Northern Gulf of California. The main tools employed were a trophic ecosystem model and time dynamic simulations.
• 2. The ecosystem was represented by an Ecopath model that included 34 functional groups, from primary producers to top predators. It included relevant species in the area such as commercially important shrimp (e.g. Litopenaeus stylirostris) and highly endangered species (Phocoena sinus and Totoaba macdonaldi).
• 3. Temporal simulations of changing fishing effort allowed the evaluation of fishing impact on the ecosystem components and, particularly, on protected species. Formal optimization methods were applied with the purpose of searching viable temporal patterns of fishing effort that might minimize social, economic and conservationist conflicts in the area.
• 4. The results of those simulations showed the capability of the model to represent reference temporal series of relative biomass. The search for viable fishing strategies resulted in effort allocation consistent with those proposed by other studies; that is, a decrease in the industrial shrimp fleet (35–65%), a decrease in the gillnet fishing fleet (52–57%), and an increase of the artisanal shrimp fishery (63–222%).
• 5. The main conflicts in the Northern Gulf of California seem to take place between social and conservation interests, while the economic and ecological benefits seem to be relatively independent. The next steps towards conflict resolution and ecosystem management should consider the design and operation of MPAs already established in the region.

Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of growth,colour and other traits in F1 hybrid of Amphiprion percula (male) × A. ocellaris (female)

This study reported the traits values such as colour, feed conversion ratio (FCR), specific growth rate (SGR) and fluorescence capacity of F₁ hybrids of Amphiprion percula (male) and A. ocellaris (female). The hybrids exhibited significant variation in FCR (3.63 ± 0.56) and SGR (3.63% ± 0.44) compared with the pure breeds, A. percula (3.12 ± 0.42; 2.80% ± 0.42) and A. ocellaris (3.17 ± 0.43; 3.02% ± 0.19). An exponential relationship was found between FCR and SGR in both the breeds. Image analysis displayed a better colour performance of hybrid than the pure breeds. Individual body parts of the hybrid and pure breeds showed significant colour variation between each other. However, colour contrast of whole body of hybrid was found closer to A. ocellaris in hue cone and towards A. percula in saturation and brightness values. Hence, hybrid displays combination colour reflexion of both the parents. The total pigment content of hybrid (65.71 μg g^?1 ± 2.81) was found higher than A. ocellaris (62.01 μg g^?1 ± 2.29) and A. percula (56.71 μg g^?1 ± 2.56). Further, the spectroflurometric analysis revealed that the both hybrid and pure breeds having poor fluorescence on skin pigmentation. A direct positive heterosis was observed on the SGR, FCR, total pigment and spawning frequency, while negative effect was noted on total length of newly hatched larvae (TL), fertilization rate (FrR), hatching rate (HR), deformation rate (DFR) and survival rate (SR). Hence, multiple cross‐breeding programmes will help in developing high‐quality traits in successive generations.     

Root renewal of sugar beet as a mechanism of P uptake efficiency

Sugar beet (Beta vulgaris L.) was grown in two different long‐term P fertilization experiments on a sandy and a loamy soil. The P supply levels of the soils were ”︁low”, ”︁sufficient”, and ”︁high”, according to the German recommendation scheme. The low P level decreased shoot and storage root yield only on the loam soil, where the recovery of the P‐deficient plants after a drought period was slower than at a sufficient P supply. The size of the living root system, as determined by a conventional auger sampling method, peaked at early July and decreased until harvest on the sandy soil without any influence of the P level. On loam, the living root systems were more constant and larger at P shortage. Total root production, as determined by the ingrowth core method, was about 120 km m^—2 in the well P supplied loam treatments and 200 km m^—2 at P deficiency, which was 3—4 times and 5 times higher than the average size of the living root systems, respectively. Hence, a rapid root renewal took place. On sand, where no P deficiency occurred, total root production was not different between the P supply levels but higher than in the well‐supplied loam treatments. Modelling P uptake revealed that this root turnover and the concomitant better exploitation of the soil facilitates P uptake at a low P level in soil, but is of no advantage at a sufficient P supply. The increase of root production at P shortage increased calculated P uptake by 25% compared to a calculation with the ”︁usual” root production at a sufficient supply.     

Modelling the application of chemicals in box potato stores

Chemicals are applied in crop stores for the control of diseases and, in the case of potatoes, sprouting. Non‐uniform deposition of chemicals on crop surfaces can lead to excessive chemical residues in parts of the store and impaired efficacy in those parts of the store where deposition is low. With the aim of improving the efficiency of chemical applications, this paper presents a transient three‐dimensional model consisting of the mass, momentum and energy equations which were solved to predict the air flows, temperature and moisture changes of the air and crops and the movements and deposits of small airborne particles of chemical in box potato stores. The crop was treated as a porous medium and the interaction between the air flow and crop was described by the Ergun equation. The movements of three sizes of chemical particles were predicted and the results validated against measurements of deposits of CIPC (a common potato sprout suppressant) in a 3‐tonne experimental store. The predictions showed good agreement with the measured trends in the spatial variation of deposits. Measured deposits varied between 16.3 and 176.0 mg CIPC per kg of potatoes while predicted values varied between 13.1 and 140.3 mg CIPC per kg of potatoes. The largest difference between measured and predicted deposit was 37.2%. © 2000 Society of Chemical Industry     

A theoretical study of discriminating parameters in metabolic resistance to insecticides

In the case where resistance to an insecticide is associated with increased metabolism of the insecticide, it should not be concluded that the resistance is due only to the increased metabolism (i.e. metabolic hypothesis). Here, we study theoretically the pharmacokinetic consequences of a resistance mechanism due to increased metabolism. We consider two cases: treatment with the initial dose D₀ applied to the susceptible strain and the treatment with the initial dose αD₀, with α>1, applied to the resistant strain. We show the conditions for which the metabolism hypothesis is conceivable. The time τ, from which the mortality of the susceptible strain is significantly higher than that of the resistant strain, is an important parameter in determining the validity of the metabolic hypothesis. The more τ increases, the more the conditions are favourable to this hypothesis. Our work suggests an approach to test the metabolic hypothesis from experimental results. © 1998 SCI     

Simulating the effects of tax exemptions on fertiliser use in Benin by linking biophysical and economic models

The sluggish increase in the area productivity of staple crops is a major factor causing increased dependence of African countries on food imports. The increased use of mineral fertiliser may dramatically improve the food balance of many countries and result in lower food prices, higher food supply and consumption, and improved food security and nutritional status. In Benin, West Africa, political measures to improve farmers’ access to fertiliser are biased in favour of cotton production. This article simulates the impact of universal tax exemptions for fertiliser use on crop yields, food balances, and the use of land resources for the most important staple crops in Benin using a crop growth model and an agricultural sector model. The simulation results indicate that tax exemptions on fertiliser use could have positive effects on physical productivity and would increase food security until 2025 as compared to a baseline scenario. At the same time, the pressure on land resources would not be aggravated, so that better access to fertiliser may help to curb excessive cropland expansion in Benin.     

Intensification of New Zealand beef farming systems

This study used whole-farm management, nutrient budgeting/greenhouse gas (GHG) emissions and feed formulation computer tools to determine the production, environmental and financial implications of intensifying the beef production of typical New Zealand (NZ) sheep and beef farming systems. Two methods of intensification, feeding maize silage (MS) or applying nitrogen (N) fertiliser, were implemented on two farm types differing in the proportions of cultivatable land to hill land (25% vs. 75% hill). In addition, the consequences of intensification by incorporating a beef feedlot (FL) into each of the farm types were also examined.Feeding MS or applying N fertiliser substantially increased the amount of beef produced per ha. Intensifying production was also associated with increased total N leaching and GHG emissions although there were differences between the methods of intensification. Feeding MS resulted in lower environmental impacts than applying N even after taking into account the land to grow the maize for silage. Based on 2007/08 prices, typical NZ sheep and beef farms were making a financial loss and neither method of intensification increased profitability with the exception of small annual applications of N, especially to the 75% hill farm. These small annual additions of N fertiliser (<50 kg N/ha/yr applied in autumn and late winter) resulted in only small increases in annual N leaching (from 11 to 14 kg N/ha) and GHG emissions (from 3280 to 4000 kg CO₂ equivalents/ha). Limited N applications were particularly beneficial to 75% hill farms because small increases in winter carrying capacity resulted in relatively large increases in the utilisation of pasture growth during spring and summer than the 25% hill farms. Intensification by incorporating a beef feedlot reduced environmental emissions per kg of beef produced but considerably decreased profitability due to higher capital, depreciation and labour costs. The lower land-use capability farm type (75% hill) was able to intensify beef production to a proportionally greater extent than the higher land-use capability farm (25% hill) because of greater potential to increase pasture utilisation associated with a lower initial farming intensity and inherent constraints in the pattern of pasture supply.     

A global benchmark map of water productivity for rainfed and irrigated wheat

The growing pressure on fresh water resources demands that agriculture becomes more productive with its current water use. Increasing water productivity is an often cited solution, though the current levels of water productivity are not systematically mapped. A global map of water productivity helps to identify where water resources are productively used, and identifies places where improvements are possible. The WATPRO water productivity model for wheat, using remote sensing data products as input, was applied at a global scale with global data sets of the NDVI and surface albedo to benchmark water productivity of wheat for the beginning of this millennium. Time profiles of the NDVI were used to determine the time frame from crop establishment to harvest on a pixel basis, which was considered the modelling period. It was found that water productivity varies from approximately 0.2 to 1.8 kg of harvestable wheat per cubic metre of water consumed. From the 10 largest producers of wheat, France and Germany score the highest country average water productivity of 1.42 and 1.35 kg m⁻³, respectively. The results were compared with modelling information by Liu et al. (2007) who applied the GEPIC model at a global scale to map water productivity, and by Chapagain and Hoekstra (2004) who used FAO statistics to determine water productivity per country. A comparison with Liu et al. showed a good correlation for most countries, but the correlation with the results by Chapagain and Hoekstra was less obvious. The global patterns of the water productivity map were compared with global data sets of precipitation and reference evapotranspiration to determine the impact of climate and of water availability reflected by precipitation. It appears that the highest levels of water productivity are to be expected in temperate climates with high precipitation. Due to its non-linear relationship with precipitation, it is expected that large gains in water productivity can be made with in situ rain water harvesting or supplemental irrigation in dry areas with low seasonal precipitation. A full understanding of the spatial patterns by country or river basin will support decisions on where to invest and what measures to take to make agriculture more water productive.     

渤海中国对虾生态容量变化研究

基于1982年和2014~2015年渤海渔业资源与环境调查数据,采用Ecopath模型,分析了渤海生态系统的营养关系、结构及功能参数,评估了中国对虾(Fenneropenaeus chinensis)在渤海的生态容量变化。结果显示,渤海生态系统中底栖甲壳类、软体动物等功能群处于重要的营养位置,但中国对虾不是渤海生态系统的关键种,其生物量的增加对口虾蛄(Oratosquilla oratoria)、三疣梭子蟹(Portunus trituberculatus)、多毛类、底栖甲壳类有负影响,花鲈(Lateolabrax japonicus)、虾虎鱼类等生物量的增加将对中国对虾产生负影响。渤海生态系统2个时期均处于发育的不稳定期,仍有较高的剩余生产量有待利用,2014~2015年渤海生态系统成熟度和稳定性较1982年有所降低,系统出现一定程度的退化。中国对虾1982年和2014~2015年在渤海的生态容量为0.810和0.702 t/km~2;与当年依据调查数据评估的生物量相比较,中国对虾有较大的增殖潜力,当生物量增长至71.68倍和585倍时,仍不会超过生态容量。     

Modelling growth and body composition in fish nutrition: where have we been and where are we going?

Mathematical models in fish nutrition have proven indispensable in estimating growth and feed requirements. Nowadays, reducing the environmental footprint and improving product quality of fish culture operations are of increasing interest. This review starts by examining simple models applied to describe/predict fish growth profiles and progresses towards more comprehensive concepts based on bioenergetics and nutrient metabolism. Simple growth models often lack biological interpretation and overlook fundamental properties of fish (e.g. ectothermy, indeterminate growth). In addition, these models disregard possible variations in growth trajectory across life stages. Bioenergetic models have served to predict not only fish growth but also feed requirements and waste outputs from fish culture operations. However, bioenergetics is a concept based on energy-yielding equivalence of chemicals and has significant limitations. Nutrient-based models have been introduced into the fish nutrition literature over the last two decades and stand as a more biologically sound alternative to bioenergetic models. More mechanistic models are required to expand current understanding about growth targets and nutrient utilization for biomass gain. Finally, existing models need to be adapted further to address effectively concerns regarding sustainability, product quality and body traits.