Estimating uncertainty in fish stock assessment and forecasting

A variety of tools are available to quantify uncertainty in age‐structured fish stock assessments and in management forecasts. These tools are based on particular choices for the underlying population dynamics model, the aspects of the assessment considered uncertain, and the approach for assessing uncertainty (Bayes, frequentist or likelihood). The current state of the art is advancing rapidly as a consequence of the availability of increased computational power, but there remains little consistency in the choices made for assessments and forecasts. This can be explained by several factors including the specifics of the species under consideration, the purpose for which the analysis is conducted and the institutional framework within which the methods are developed and used, including the availability and customary usage of software tools. Little testing of either the methods or their assumptions has yet been done. Thus, it is not possible to argue either that the methods perform well or perform poorly or that any particular conditioning choices are more appropriate in general terms than others. Despite much recent progress, fisheries science has yet to identify a means for identifying appropriate conditioning choices such that the probability distributions which are calculated for management purposes do adequately represent the probabilities of eventual real outcomes. Therefore, we conclude that increased focus should be placed on testing and carefully examining the choices made when conducting these analyses, and that more attention must be given to examining the sensitivity to alternative assumptions and model structures. Provision of advice concerning uncertainty in stock assessments should include consideration of such sensitivities, and should use model‐averaging methods, decision tables or management procedure simulations in cases where advice is strongly sensitive to model assumptions.     

The effect of trigger depth on self-feeder utilisation, growth and the vertical distribution of tank-held rainbow trout Oncorhynchus mykiss (Walbaum)

This study investigated the effect of placing a self-feeding trigger at either a) 1 cm below the water surface or b) mid-water (35 cm below the surface), on self-feeder usage, growth, feed wastage and fin damage of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). The vertical distribution of trout was also measured for the first 31 days of self-feeding. Group-held trout (n = 10 fish group^− 1, 5 groups treatment^− 1), weighing 51.06 g ± 8.09 g (mean ± SD) were held in 200 l cylindroconical tanks (depth = 75 cm) for 62 days. Trigger placement had no significant effect upon self-feeder conditioning, and upper trigger group (UTG) and lower trigger group (LTG) fish took an average of 16 ± 7.4 days and 14 ± 9.8 days to reach a stable level of self-feeding, respectively. Specific growth rate was significantly higher in UTG fish (1.83 ± 0.20 vs. 0.95 ± 0.21 for UTG vs. LTG fish, respectively) whilst condition factor and self-feeder utilisation (ration size, 1.21 ± 0.18 vs. 0.52 ± 0.15 kg tank^− 1 for UTG vs. LTG fish) were also significantly higher in UTG fish. Trigger depth had no significant effect on size heterogeneity, mortality, feed wastage, feed conversion ratio (FCR) or the incidence of caudal and dorsal fin splitting and fin erosion. Dorsal fin splitting decreased with time in UTG but not in LTG fish. Caudal fin erosion increased with time in UTG (upper lobe only) and LTG (both lobes). The vertical distribution of fish also differed between treatments and more LTG fish preferred the lower part of the tank. Placing a self-feeding trigger at a mid-water depth can significantly limit growth, condition factor and self-feeder utilisation in juvenile rainbow trout, in addition to hindering recovery from dorsal fin erosion.     

Genetic diversity,population structure,and historical demography of a highly vagile and human-impacted seabird in the Pacific Ocean: The red-tailed tropicbird,Phaethon rubricauda

1. Many seabird breeding colonies have recovered from heavy anthropogenic disturbance after conservation actions. The widely distributed red-tailed tropicbird, Phaethon rubricauda, was used as a model species to assess potential anthropogenic impacts on the genetic diversity of breeding colonies in the Pacific Ocean.
2. Cytochrome c oxidase subunit I and control region sequences analyses were conducted across the range of the species in the Pacific Ocean. The study sites were at islands without human-related disturbance (non-impacted islands) and with human-related disturbance (impacted islands). We hypothesized that (i) breeding colonies of the red-tailed tropicbird on impacted islands have lower genetic diversity compared with colonies on non-impacted islands, and (ii) breeding colonies of the red-tailed tropicbird show significant fine and broad-scale genetic structure across the Pacific Ocean. Bayesian skyline analyses were conducted to infer past changes in population sizes.
3. Genetic diversity was similar between impacted and non-impacted islands. There was significant broad-scale genetic structure among colonies separated by over 6,000 km, but a lack of significant fine-scale genetic structure within Australasia and Hawai'i, although a significant level of differentiation was found within Chile with Φ_ST analyses. Skyline analyses showed that effective population sizes remained relatively constant through time, but experienced either a slight decrease or the end of an expansion event through the last 1,000 years. These changes may be related to the arrival of humans on Pacific islands.
4. Impacted islands may have received immigrants from other relatively close islands, buffering the loss of genetic diversity. However, it is also possible that colonies have retained ancestral variation or that a large effective population size coupled with a long generation time (13 years) has prevented the loss of genetic diversity in human-impacted islands. Future research using higher-resolution markers is needed to resolve the population genetic structure of the red-tailed tropicbird in an ecological time-scale.

     

芽胞杆菌益生菌在水产业的应用

芽孢杆菌被认为兼有改善水生动物消化道和改良水环境的双重功效而受重视。文中阐述了益生菌在水产养殖中应用的最新理论、技术和趋势,包括运用分子生物学方法进行菌株的分型鉴定和安全性检测,对病原菌和病原性病毒的拮抗试验,以及一系列的大田养殖试验,以验证芽胞杆菌益生菌产品在水产上尤其是在大型养虾场应用的功效。     

Inheritance of molecular markers and sex in the Australian freshwater crayfish, Cherax destructor Clark

Inheritance of three kinds of molecular genetic markers (mtDNA, random‐amplified polymorphic DNAs (RAPDs) and allozymes) and sex were investigated in crossbreeding experiments between three populations of the Australian freshwater crayfish Cherax destructor. Crossbreeding did not disrupt the ively maternally inherited, and allozyme and RAPD markers were transmitted following expected Mendelian principles for co‐dominant and dominant traits respectively. Unlike these three markers, sex ratios were found to be distorted by crossbreeding in some families. Two crossbred families produced only females. The implications of these findings for freshwater crayfish population genetics, taxonomy and aquaculture are discussed.     

Muscle ammonia stores are not determined by pH gradients

The theory of non-ionic diffusion predicts that ammonia will distribute between intracellular and extracellular tissue compartments according to transmembrane pH gradients. The distribution of ammonia and¹⁴C-DMO were compared in white muscle and plasma of rainbow trout (Salmo gairdneri) at rest, and following exhaustive exercise. Under both experimental conditions, intracellular ammonia levels far exceeded those predicted by transmembrane pH gradients. Calculated equilibrium potentials for ) were very close to published resting values of membrane potential E_m in fish white muscle. We conclude that NH ₄ ⁺ is permeable across cell membranes and that intracellular ammonia stores are not determined by pH gradients.The term ammonia or T_amm will be used to indicate the total ammonia concentration, while NH ₄ ⁺ and NH₃ will refer to ammonium ion and nonionic ammonia, respectively.     

合并是大势所趋——访荷兰花荷拍卖市场执行总裁蒂姆

荷兰花荷拍卖市场(FloraHolland)是世界上最大的花卉交易公司,每年有价值1.8亿欧元的花卉和绿色植物在这里交易,交易额占到荷兰花卉交易额的54%。主要出口国家集中在欧洲,如德国、英国、法国、意大利、比利时。主要的进口国有肯尼亚、津巴布韦、以色列等。2006年10月26日,世界上最大的两个花卉拍卖市场,即荷兰阿斯米尔拍卖市场(Aalsmeer)和荷兰花荷拍卖市场在荷兰海牙签署合并意向书,一个拥有40亿欧元产值的强大的拍卖市场即将成立。合并后的市场将沿用花荷的名称,并使用阿斯米尔的红色郁金香标识,总部将设在阿斯米尔。