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71.
Increasing use of spatial management tools in fisheries requires an understanding of fleet response, and in particular to where displaced fishing effort is likely to move. We develop a state‐dependent decision‐making model to address the spatial allocation of effort in an Australian tuna longline fishery. We assume that fishers have an economic objective in deciding where to fish, but that decisions in any period are also influenced by the remaining quota held at the time of the decision. Key features of the model include endogenous price dynamics, a moving stock and a competitive pool of different vessel types operating from different port locations. We utilize this model to illustrate fleet responses to marine reserves and limits on fishing effort. The results illustrate that the model framework provides advantages over statistically based models in that decisions made in response to the imposition of a reserve are not consistent with a proportional reallocation of effort. Rather, the stochastic dynamic model yielded an overall profit level of ~4% higher relative to scenarios with no reserve. Incorporating the opportunity cost of a quota into the model resulted in an optimal utilization of effort, in which effort was concentrated in time periods and locations yielding maximized profit. Under a low level of effort relative to the season length, the model indicated an overall profit level 43% greater than the highest obtained when the same level of effort was applied solely within any given quarter of the season. 相似文献
72.
73.
为了研究氯硝柳胺在斑点叉尾(Ictalurus punctalus)组织中的残留消除规律,在静水条件下经安全性试验确定安全浓度后,直接对水族箱泼洒25%氯硝柳胺乙醇胺盐(NES)粉剂后采集斑点叉尾皮肤、肌肉和水样。采用高效液相色谱-质谱联用法(HPLC-ESI/MS/MS)测定样品中氯硝柳胺的浓度,结果表明,静水条件下25%氯硝柳胺乙醇胺对斑点叉尾的安全浓度为0.113 mg/kg;养殖水环境中氯硝柳胺能快速消解,实验第2天即低于1μg/L,并呈无规律性持续较长时间;用药24 h内,氯硝柳胺在鱼体肌肉和鱼皮中具有较强的蓄积能力,但48 h后,其在鱼皮和肌肉中呈现快速消除至较低浓度,但后期消除缓慢,并会持续一定时间;氯硝柳胺(NIC)在斑点叉尾肌肉和鱼皮中的消除半衰期T1/2分别为10.66和9.24 d,显著大于在水体中的消除半衷期。 相似文献
74.
三峡库区消落带适生植物固碳释氧能力研究 总被引:1,自引:0,他引:1
固碳释氧是植物的一项重要生态功能,三峡库区消落带分布范围广、面积大,对其适生植物的固碳释氧能力进行研究具有重要的意义。以重庆市三峡库区开州区至万州区消落带13种适生植物为研究对象,通过测定其净光合速率和叶面积指数,分析研究其固碳释氧能力。结果表明,13种适生植物的净光合速率日变化曲线主要呈单峰型或双峰型曲线,单峰型曲线植物有桑(Morus alba)、白芒(Miscanthus sinensis)和辣蓼(Polygonum hydropiper),其他10种植物中山杉(Taxodium‘Zhongshanshan’)、竹柳(Salix sp.)、柑橘(Citrus reticulata)、牡荆(Vitex negundo var.cannabifolia)、地桃花(Urena lobata)、苍耳(Xanthium sibiricum)、芦苇(Phragmites australis)、大狼杷草(Bidens frondosa)、鬼针草(Bidens pilosa)、合萌(Aeschynomene indica)的净光合速率日变化曲线均表现为双峰曲线,单位叶面积日净同化量为90.28~410.20 mmol/(m~2·d),固碳量为3.18~14.44 g/(m~2·d),释氧量为2.31~10.50 g/(m~2·d);单位土地面积日固碳量为6.15~65.47 g/(m~2·d),释氧量为4.48~47.62 g/(m~2·d)。单位叶面积固碳释氧能力聚类分析表明,乔木(3种)、灌木(3种)均分为两级,草本(7种)分为三级;单位土地面积固碳释氧能力分析表明,乔木(3种)、灌木(3种)和草本(7种)均分为两级;日固碳释氧能力较强的乔木为竹柳,灌木有地桃花和牡荆,草本有芦苇、辣蓼、鬼针草。本研究为三峡库区消落带生态修复工程中植被的选择应用提供了理论参考,为消落带修复工程示范区生态效益的评价提供了科学依据。 相似文献
75.
Trophic relationships and ecosystem characteristics in a newly-impounded man-made lake in Thailand 总被引:1,自引:0,他引:1
T. THAPANAND T. JUTAGATEE P. WONGRAT T. LEKCHOLAYUT C. MEKSUMPUN & S. JANEKITKARN A. RODLOI J. MOREAU & L. WONGRAT 《Fisheries Management and Ecology》2009,16(2):77-87
Abstract The trophic dynamics of a newly-impounded south east Asian reservoir, Pasak Jolasid, Thailand, monitored from its creation, were constructed using ecopath , a mass-balanced model. The trophic levels (TLs) of 36 ecological groups varied between 1.0 and 3.2. The majority of fish biomass was at the second TL, where the fishery is concentrated. Some food resources (benthic organisms and zooplankton) were not fully used, whereas phytoplankton and benthic algae were important components of the food web, which is based on phytoplankton and detritus. The implications of these findings are discussed in terms of ecological maturity of the ecosystem and possible fishery management of this multi-purpose reservoir. 相似文献
76.
There is debate among ecologists about whether total habitat area or patch arrangement contributes most to population and/or
community responses to fragmented or patchy landscapes. We tested the relative effects of patch area and isolation for predicting
bird occurrence in a naturally patchy landscape in the Bear River Mountains of Northern Utah, USA. We selected focal patches
(mountain meadows) ranging in elevation from 1,920 to 2,860 m and in size from 0.6 to 182 ha. Breeding birds were sampled
in each focal meadow during the summers of 2003 and 2004 using variable-distance point transects. Logistic regression and
likelihood-based model selection were used to determine the relationship between likelihood of occurrence of three bird species
(Brewer’s sparrow, vesper sparrow, and white-crowned sparrow) and area, isolation, and proximity metrics. We used model weights
and model-averaged confidence intervals to assess the importance of each predictor variable. Plots of area versus isolation
were used to evaluate complex relationships between the variables. We found that meadow area was the most important variable
for explaining occurrence for two species, and that isolation was the most important for the other. We also found that the
absolute distance was more appropriate for evaluating isolation responses than was the species-specific proximity metric.
Our findings add clarity to the debate between ecologists regarding the relative importance of area and isolation in species
responses to patchy landscapes. 相似文献
77.
78.
- 1. This paper reports on the dynamics of the coral community structure at A Ma Wan (AMW) and A Ye Wan (AYW) in Tung Ping Chau, Hong Kong, focusing on data collected before and after the summer typhoon seasons in 1997 to 1999. This period (1999) experienced the highest frequency of severe tropical cyclones to hit Hong Kong with one cyclone being the strongest to hit in the last 23 years (1984 to 2006).
- 2. This is part of a long‐term monitoring programme of subtropical coral communities that has been set up in AMW since May 1997 and AYW since May 1998 with nine fixed position 40 m long transects and 0.5 m × 0.5 m permanent quadrats laid at 5 m intervals along each transect. A total of 45 scleractinian coral species from 21 genera (12 families) was recorded, with 40 species in AMW and 32 species in AYW recorded at the beginning of the study.
- 3. Multidimensional scaling ordinations showed distinct spatial variations in the coral communities within and between sites. These variations were probably a result of the differential effects of the repeated cyclone impacts on the communities. Cyphastrea serailia, Goniopora lobata, Montipora peltiformis and Pavona decussata were the dominant species most strongly affected by cyclone impacts at AMW, experiencing a 6.2–16.2% loss of mean area cover during the study period. Some dominant species (e.g. P. decussata) in AYW also experienced a 6.5–14.3% loss of mean area cover within the same period.
- 4. Overall, these coral community structures appeared relatively stable and resistant to repeated physical disturbances. However, they may have low resilience towards more severe disturbances in the future. Preserving the resilience of coral communities/species in Tung Ping Chau should be one of the main goals of coral conservation strategies for the island.
79.
Relationship between stable carbon isotope discrimination and water use efficiency under regulated deficit irrigation of pear-jujube tree 总被引:2,自引:0,他引:2
Ningbo Cui Taisheng Du Shaozhong Kang Fusheng Li Xiaotao Hu Mixia Wang Zhijun Li 《Agricultural Water Management》2009,96(11):1615-1622
To investigate the relationship between stable carbon isotope discrimination (Δ) of different organs and water use efficiency (WUE) under different water deficit levels, severe, moderate and low water deficit levels were treated at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of field grown pear-jujube tree, and leaf stable carbon isotope discrimination (ΔL) at different growth stages and fruit stable carbon isotope discrimination (ΔF) at fruit maturation stage were measured. The results indicated that water deficit had significant effect on ΔL at different growth stages and ΔF at fruit maturation stage. As compared with full irrigation, the average ΔL at different growth stages and ΔF at fruit maturation stage were decreased by 1.23% and 2.67% for different water deficit levels, respectively. ΔL and ΔF among different water deficit treatments had significant difference at the same growth stage (P < 0.05). Under different water deficit conditions, significant relationships between the ΔL and WUEi (photosynthesis rate/transpiration rate, Pn/Tr), WUEn (photosynthesis rate/stomatal conductance of CO2, Pn/gs), WUEy (yield/crop water consumption, Y/ETc) and yield, or between the ΔF and WUEy and yield were found, respectively. There were significantly negative correlations of ΔL with WUEi, WUEn, WUEy and yield (P < 0.01) at the fruit maturation stage, or ΔL with WUEi and WUEn (P < 0.01) over whole growth stage, respectively. ΔF was negatively correlated with WUEy, WUEn and yield (P < 0.05), but positively correlated with ETc (P < 0.01) over the whole growth stage. Thus ΔL or ΔF can compare WUEn and WUEy, so the stable carbon isotope discrimination method can be applied to evaluate the water use efficiency of pear-jujube tree under the regulated deficit irrigation. 相似文献
80.