Airborne spread of foot-and-mouth disease – Model intercomparison

Foot-and-mouth disease virus (FMDV) spreads by direct contact between animals, by animal products (milk, meat and semen), by mechanical transfer on people or fomites and by the airborne route, with the relative importance of each mechanism depending on the particular outbreak characteristics. Atmospheric dispersion models have been developed to assess airborne spread of FMDV in a number of countries, including the UK, Denmark, Australia, New Zealand, USA and Canada. These models were compared at a Workshop hosted by the Institute for Animal Health/Met Office in 2008. Each modeller was provided with data relating to the 1967 outbreak of FMD in Hampshire, UK, and asked to predict the spread of FMDV by the airborne route.A number of key issues emerged from the Workshop and subsequent modelling work: (1) in general all models predicted similar directions for livestock at risk, with much of the remaining differences strongly related to differences in the meteorological data used; (2) determination of an accurate sequence of events on the infected premises is highly important, especially if the meteorological conditions vary substantially during the virus emission period; (3) differences in assumptions made about virus release, environmental fate and susceptibility to airborne infection can substantially modify the size and location of the downwind risk area. All of the atmospheric dispersion models compared at the Workshop can be used to assess windborne spread of FMDV and provide scientific advice to those responsible for making control and eradication decisions in the event of an outbreak of disease.     

Effects of salinity on standard metabolic rate and critical oxygen tension in the giant freshwater prawn (Macrobrachium rosenbergii)

The extensively farmed giant freshwater shrimp, Macrobrachium rosenbergii, can survive salinities up to 26 g L^?1, but the commercially important grow‐out occurs exclusively in freshwater areas. Recent studies suggest the shrimp equally capable of growing in brackish as fresh water and a better understanding of how this species responds to changing salinity could significantly impact freshwater prawn farming in deltas and coastal areas. Here, the effect of salinity (0 and 15 g L^?1) on standard metabolic rate (SMR) and critical oxygen tension (P_crit) was measured in adult M. rosenbergii using intermittent closed respirometry. SMR was 79.8 ± 3.1 and 72.7 ± 2.9 μmol kg^?1 min^?1 in fresh and brackish water, respectively, with no significant difference between the two salinities (P = 0.122). During hypoxia M. rosenbergii maintained oxygen uptake down to a P_crit of 26.3 ± 1.4 mmHg in fresh and 27.2 ± 2.0 mmHg in brackish water (P = 0.682), showing that salinity had no overall effect on oxygen conductance in the animals. These findings are in agreement with recent growth studies and provide further evidence that grow‐out phase could be accomplished in brackish water areas. Thus, the predicted intrusions of brackish water in tropical deltas as a consequence of future global warming may not impact this important production.     

GREEN AND TECHNICAL EFFICIENT GROWTH IN DANISH FRESH WATER AQUACULTURE

Aquaculture is the fastest growing animal food processing sector in the world. Nevertheless, growth inside the Organization for Economic Co-operation and Development has been stagnating, with few exceptions. The main reason is strict environmental regulations. This study investigates if green growth can be achieved by introducing new environmentally friendly water purification systems in Danish fresh water aquaculture. Data Envelopment Analysis is used to investigate whether different water purification systems and farm size influence technical efficiency. The empirical results indicate that different water purification systems have no significant influence, although it increases with farm size. The policy implications are that green growth is possible by implementing the new water purification systems, but farmers have no incentive to adopt the new systems under the present regulation. If green growth should be achieved, the present regulation needs to be changed, providing the farmers with an incentive to adopt environmentally friendly production methods.     

Agency rivalry in a shared regulatory space and its impact on social welfare: The case of aquaculture regulation

This article is grounded in public choice theory and develops a framework to explain how non-benevolent behavior on the part of public regulators and the resulting lack of collaboration between different agencies have been affecting aquaculture growth. Although regulators are assumed to work for the best interest of the people, they can have their own rational agendas; such as career advancement, self-aggrandizement and loyalty for a particular political ideology. We show that when officials are non-benevolent and agencies have unequal relative decision-making power, it is likely that a more powerful agency dictates policies in favor of its own agenda, even when such policies may not necessarily lead to optimal social welfare. In the case of aquaculture, higher relative power of a pro-environment agency leads to underdevelopment of the sector, as is the case in developed countries, whereas larger relative power of a pro-industry agency leads to higher growth, as is the case in developing countries.     

Agglomeration externalities and technical efficiency: An empirical application to the pond aquaculture of Pangas and Tilapia in Bangladesh

This article analyzes the effects of agglomeration externalities on productivity and efficiency by applying a stochastic production frontier model with a technical inefficiency model to the aquaculture industry. Agglomeration externalities refer to the costs and benefits to firms from clustering. Agglomeration studies within aquaculture have focused on the intensive salmon industry, whereas this study focuses on low-technology, extensive pond aquaculture, representing most farmers in the developing world and using Bangladesh as an empirical case. The results show that there is a positive externality effect of regional industry size on the production possibility frontier and a negative effect on technical efficiency. Farm density enhances efficiency and the farm proximity to output markets decreases efficiency. Thus, policies aimed at increasing aquaculture pond production in developing countries should consider farm locations and their access to input and output markets, all of which affect farm productivity and efficiency.     

Establishing a benchmarking for fish farming – Profitability,productivity and energy efficiency of German,Danish and Turkish rainbow trout grow‐out systems

The promotion of Blue Growth in aquaculture requires an understanding of the economic drivers influencing the sector at farm level, but the collection of reliable and comparable data at this level is time‐consuming and expensive. This study suggests an alternative strategy for qualitative sampling of freshwater trout farms in Germany, Denmark and Turkey, using a combination of existing data, group discussions and interviews with trout farmers, consultants and researchers. Nine ‘typical’ trout farming models are described, focusing on profitability, productivity and energy efficiency and allowing in‐depth comparative economic analyses of different production systems at farm level, across regions. Our results show that the majority of the farms investigated have been profitable. Turkish farms benefit from competitive advantages due to low wages, low capital investment and favourable climate conditions. Large German farms profit from local market prices and advanced farm management. Danish farms using recirculating techniques remain competitive thanks to enhanced productivity and economy of scale. However, small traditional farms in Germany and Denmark may struggle to stay competitive in the long term. Organic farms in both countries face challenges of high feed costs and comparatively low productivity with mixed success. Using edible protein energy return on investment (epEROI) as an indicator of ecological sustainability, all surveyed farms compared very favourably with the terrestrial systems of animal meat production were investigated so far.     

The importance of live‐feed traps – farming marine fish species

This article analyses the challenges of different live‐feed regimes for the rearing of marine finfish larvae and discusses the potential alternative live feeds to avert a future live‐feed trap. Live feeds are indispensable for the successful rearing of larvae of most marine fish species. Brine shrimps (Artemia) and rotifers comprise the live feeds of choice in marine aquaculture today. However, their nutritional composition is deficient in especially essential fatty acids, and enrichment with fish oil is needed. Fish oil is considered a limited resource owing to its origin in fully exploited wild fish stocks. Moreover, fluctuations of the natural population of Artemia will, most likely, influence future availability and prices. This emphasizes the need for optimal exploitation of available live‐feed resources and development of new sustainable alternatives, such as copepods. An array of solutions to these problems are presented to avoid a future live‐feed trap and to reduce dependence on limited resources that influence future production possibilities, species diversification, price volatility and productivity in the aquaculture sector.     

Above parr: Lowland river habitat characteristics associated with higher juvenile Atlantic salmon (Salmo salar) and brown trout (S. trutta) densities

Understanding juvenile salmonid habitat requirements is critical for their effective management, but little is known about these requirements in lowland rivers, which include important but unique salmonid habitats. We compared the relative influence of in-stream Ranunculus cover, water depth, prey abundance, distance upstream and two previously unexplored factors (water velocity heterogeneity and site colonisation potential) on summer densities of juvenile Atlantic salmon and brown trout. We applied electrofishing, habitat surveys and macroinvertebrate kick sampling, and calculated the site colonisation potential from salmon redd surveys across 18–22 sites in a lowland river in 2015–2017. Due to a recruitment crash in 2016, models including and excluding this unusual year were explored. Excluding 2016 data, juvenile salmon densities showed a positive association with Ranunculus cover and numbers of nearby upstream redds, and a negative association with distance upstream from the tidal limit. Trout densities were positively associated with velocity heterogeneity, indicating a potential indirect influence of Ranunculus mediated by water velocity. When including 2016, year had the largest effect on densities of both species, highlighting the impact of the recruitment failure. These findings uncover interspecific differences in the habitat requirements of juvenile salmonids in lowland rivers. Velocity heterogeneity and site colonisation potential had high explanatory power, highlighting that they should be considered in future studies of habitat use. These findings demonstrate that temporal replication and recruitment dynamics are important considerations when exploring species–habitat associations. We discuss potential management implications and argue that Ranunculus cover could be an important management tool in conservation of lowland salmonids.     

Browsing of sallow (Salix caprea L.) and rowan (Sorbus aucuparia L.) in the context of life history strategies: a literature review

Sallow (Salix caprea L.) and rowan (Sorbus aucuparia L.) constitute small proportions of the deciduous tree volume in Scandinavia, but are highly preferred winter forage for moose and red deer, which occur at historically high densities. Thus, a possible decline of these tree species has been indicated. Against this background, we have reviewed the life histories of relevance for browsing, as well as the basic biology and genetics of sallow and rowan. The species show similarities with respect to short lifespan, small size and sympodial growth pattern, which are risk factors in a browsing context. They also have high juvenile growth rate, important for growing quickly out of reach of browsers. Sallow depends strongly on disturbance for establishment and is more demanding with respect to soil and light conditions than rowan, possibly important for the substantially lower abundance of sallow on the Norwegian Forest Inventory plots. Similarly, the relative recruitment of small size classes of sallow is less than for rowan. Although recruitment is reported to be hampered in wintering areas with high moose or red deer densities, the inventory data, however, dating only back to 1994, do not suggest a general decrease in any of the species. Sallow and rowan saplings show low mortality in moose and deer dominated areas and the species can be characterised as rather resilient to browsing. Of more concern is that browsing can constrain the development of mature rowan and sallow trees locally, with possible consequences for associated epiphytic biodiversity.     

Temporal development of ash dieback symptoms and spatial distribution of collar rots in a provenance trial of Fraxinus excelsior

European ash (Fraxinus excelsior) is threatened by Hymenoscyphus pseudoalbidus, the agent of ash dieback disease. Beside ordinary ash dieback symptoms, collar rots have been reported on declining ashes as an additional problem of increasing severity. Since 2009, ash dieback has been surveyed annually in a provenance trial on four different sites in southwest Germany (Metzler et al. in Ger J For Res 183:168–180, 2012). The trial was established in 2005. Data of tree growth, ash dieback symptoms and collar rot prevalence were collected by surveying the trial in summer 2012 and compared with previously published data of the trial. Evaluations revealed a continuous and considerable increase in dieback severity since 2009. The results suggest that the infection process has not come to a standstill yet. Up to 2012, 6 % of the trees remained symptomless, whereas mortality added up to 9 %. There were significant differences in ash dieback severity between the investigated provenances. Collar rot prevalence ranged from 19 to 59 % between study sites. Moreover, high spatial dependency of collar rot prevalence could be detected within sites. Collar rots were more abundant on trees of severe ash dieback intensity, but could also be detected on 15 % of otherwise healthy trees. Mycelium from collar rots could be identified by means of RFLP analyses and sequencing of the ITS region as most likely belonging to Armillaria gallica. The possible roles of Armillaria spp. and H. pseudoalbidus in collar rot formation are discussed.