Modelling the impacts of environmental variation on habitat suitability for Pacific saury in the Northwestern Pacific Ocean

We developed habitat suitability index (HSI) models for two size classes of Pacific saury Cololabis saira in the Northwestern Pacific Ocean. Environmental data, including sea surface temperature, sea surface height, salinity, and net primary production, and catch and effort data from Taiwanese distant‐water stick‐held dip net fisheries during the main fishing season (August–October) during 2002–2015 were used. Habitat preferences and suitable habitat area differed between size classes. The suitable habitat was located between 40–47.5°N and 145–165°E for large‐sized Pacific saury but encompassed a greater area (35–47°N and 140–165°E) for medium‐sized Pacific saury. Both size classes were affected by substantial interannual variation in the environmental variables, which in turn can be important in determining the potential fishing grounds. We found a significant negative relationship between the suitable habitat area and the Niño3.4 indices with a time‐lag of 6 months for the large‐sized (r = ?0.68) and medium‐sized (r = ?0.42) Pacific saury, respectively, as well as the total landings of Pacific saury by all fishing fleets (r = ?0.46). As remotely‐sensed environmental data become increasingly available, HSI models may prove useful for evaluation of possible changes in habitat suitability resulting from climate change or other environmental phenomena and in formulating scientific advice for management.     

Fish movement and habitat use depends on water body size and shape

Abstract –  Home ranges are central to understanding habitat diversity, effects of fragmentation and conservation. The distance that an organism moves yields information on life history, genetics and interactions with other organisms. Present theory suggests that home range is set by body size of individuals. Here, we analyse estimates of home ranges in lakes and rivers to show that body size of fish and water body size and shape influence home range size. Using 71 studies including 66 fish species on five continents, we show that home range estimates increased with increasing water body size across water body shapes. This contrasts with past studies concluding that body size sets home range. We show that water body size was a consistently significant predictor of home range. In conjunction, body size and water body size can provide improved estimates of home range than just body size alone. As habitat patches are decreasing in size worldwide, our findings have implications for ecology, conservation and genetics of populations in fragmented ecosystems.     

Linking small pelagic fish and cetacean distribution to model suitable habitat for coastal dolphin species,Delphinus delphis and Tursiops truncatus,in the Greek Seas (Eastern Mediterranean)

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Exposure assessment of professional pesticide users during treatment of potato fields

In this study four different mixing/loading and application practices in potato fields were monitored for exposure of operators to pesticides. Each operation – mixing, loading, and application – was measured individually in order to assess its relative contribution to the total exposure value. Inhalation exposure was measured by trapping the pesticides with a sorbent tube while sampling the air around the operator's face. Dermal deposition, which was measured by means of cotton gloves on the hands and by attaching patches to the operator's clothing, was the main contributor to the total exposure. Dermal deposition on the hands during mixing and loading exceeded all other dermal values. The experimental results are compared with the results obtained by the exposure assessment model PHED V1.1. This model gives an underestimation of the levels of operator exposure during mixing, loading and application. © 1999 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     

Genetic parameters for resistance against Flavobacterium columnare in Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

Columnaris disease is a major cause of mortality in tilapia hatcheries and commonly occurs during the summer season in Thailand. One way of reducing the problem is by selective breeding for increased disease resistance. The objective of this study was to estimate quantitative genetic parameters for resistance against columnaris in the Chitralada 4 strain of Nile tilapia. Data from 43 full‐sib families (2,580 records) of fry (age = 32 ± 4 days post‐hatch) were used in the analyses. Initially, fry were subjected to bath challenge with Flavobacterium columnare (LD₅₀ concentration = 1.2 × 10⁶ CFU/ml) for 14 days. Disease resistance was defined as the number of days from challenge until death (DD) or as a binary trait (dead/alive) on day 14. Linear animal and sire‐dam models were used for DD, while threshold animal, threshold sire‐dam, binary linear animal and binary linear sire‐dam models were used for binary outcomes. Covariate effect of age, fixed effect of challenge day and random effects of the individual animals or sires and dams were included in the models. Mean survival was 32.4 ± 11.6%, and survival rates of the best and poorest families were 70% and 8%, respectively. The highest estimate of heritability (0.30 ± 0.025) was obtained under the threshold sire‐dam model. Heritability estimates for DD (0.16 ± 0.034 and 0.17 ± 0.046) were comparable to those obtained from the threshold animal (0.15 ± 0.031) and the binary linear (0.14 ± 0.045 and 0.15 ± 0.044) models. The linear animal and sire‐dam models for DD and the threshold sire‐dam models performed equally with similar values of r_EBV (0.629, 0.628 and 0.627) and accuracy of selection (0.793, 0.793 and 0.791). This study reveals the potential of selective breeding to increase disease resistance to F. columnare in the studied population of Nile tilapia.     

Riparian restoration offsets predicted population consequences of climate warming in a threatened headwater fish

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Performance of a photo‐heterotrophic,hypersaline system for intensive cultivation of white leg shrimp (Litopenaeus vannamei) with minimal water replacement in lined ponds using a stochastic approach

The aim of the study was to evaluate the performance of Litopenaeus vannamei in an intensive photo‐heterotrophic hypersaline system with minimal seawater replacement, and establish relationships between parameters of a stochastic production model and relevant water quality variables. Six experimental 1000 m² lined ponds were stocked at a density of 120 shrimp m^?2 for a 105‐day trial. Salinity increased from 37 to 45 ± 2 g/L, and the water level was maintained with the weekly addition of filtered seawater, equivalent to 1.6% per day. The stochastic model predicted that, at harvest, there is 95% confidence that the system produces between 12.1 and 14.7 t/ha with a mean final individual weight of 13.1 g and a mean survival of 84.2%. Sensitivity analyses showed that dissolved oxygen and individual final weight of shrimp were the main variables influencing yield variance. Nitrogenous compounds were maintained between optimal cultivation levels (NH₃–NH₄⁺ = 0.73 ± 0.43 mg/L, N–NO₂^? = 0.09 ± 0.05 mg/L, N–NO₃^? = 3.22 ± 0.11 mg/L). Heterotrophic bacteria (6.6 ± 3.4 × 10⁵ CFU/ml) and chlorophyll‐α concentration (108.5 ± 80.2 μg/L) showed a similar development pattern, indicating a strong relationship between bacteria and microalgae during cultivation. Vibrio spp. concentrations were low (1.24 ± 1.42 × 10³ CFU/ml). It was shown that the photo‐heterotrophic system could be used in hypersaline conditions, typical of semi‐arid regions, to consistently produce between 12.1 and 14.7 t/ha in 15 weeks.     

You cannot fight fire with fire: a demographic model suggests alternative approaches to manage multiple herbicide‐resistant Avena fatua

Multiple herbicide‐resistant (MHR ) weed populations pose significant agronomic and economic threats and demand the development and implementation of ecologically based tactics for sustainable management. We investigated the influence of nitrogen fertiliser rate (56, 112, 168, or 224 kg N ha^?1) and spring wheat seeding density (67.3 kg ha^?1 or 101 kg ha^?1) on the demography of one herbicide susceptible and two MHR Avena fatua populations under two cropping systems (continuous cropping and crop‐fallow rotation). To represent a wide range of environmental conditions, data were obtained in field conditions over 3 years (2013–2015). A stochastic density‐dependent population dynamics model was constructed using the demographic data to project A. fatua populations. Elasticity analysis was used to identify demographic processes with negative impacts on population growth. In both cropping systems, MHR seedbank densities were negatively impacted by increasing nitrogen fertilisation rate and wheat density. Overall, MHR seedbank densities were larger in the wheat‐ fallow compared with the continuous wheat cropping system and seedbank densities stabilised near zero in the high nitrogen and high spring wheat seeding rate treatment. In both cropping systems, density‐dependent seed production was the most influential parameter impacting population growth rate. This study demonstrated that while the short‐term impact of weed management tactics can be investigated by field experiments, evaluation of long‐term consequences requires the use of population dynamics models. Demographic models, such as the one constructed here, will aid in selecting ecologically based weed management tactics, such as appropriate resource availability and modification to crop competitive ability to reduce the impact of MHR .