Perceptible changes on a global and regional scale are evident in earth's climate. In India, observed changes include an increase of air temperature, regional monsoon variation, frequent droughts and a regional increase in severe storm incidence in coastal states of India, along with indication of Himalayan glacier recession. The impact is being felt in the inland aquatic resources and their fisheries. Analysis of time series data of 30 years from published literature and from current investigations on the River Ganga and water bodies in its plains, indicate increased minimum water temperatures; 1.5°C in colder stretches of the Ganga and 0.2 to 1.6°C in the aquaculture farms of the State of West Bengal in the Gangetic plains. Rainfall has also increased in the post monsoon months of September–December. The impact is manifested in the breeding failure of the Indian Major Carps (IMC) and a consequent decline in fish spawn availability in river Ganga. Whereas, in fish farm hatcheries on the plains, a positive impact on breeding was observed in the advancement and extension of the breeding period of IMC by 45–60 days. A geographic shift of warm water fish species Glossogobius gurius and Xenentodon cancila to the colder stretch of the river Ganga was recorded. The predator prey ratio in the middle stretch in the river Ganga has also declined from 1:4.2 to 1:1.4 in the last three decades. Fish production has shown a distinct change in the last two decades in the middle stretch of river Ganga where the contribution of IMC has decreased from 41.4% to 8.3% and that of miscellaneous and catfish species increased. Climate change in India will put an additional stress on ecological and socio-economic systems that are already facing pressure. Thus the specific climate variables of importance to inland fisheries viz. enhanced water temperature, extreme events like flood and drought, storms and water stress require specific adaptation actions. An integrated water shed management strategy is essential going from the village level to the river basin level in a unified manner. Finally, it is suggested that assessments of inland fisheries vulnerability to climate change should also assess economic scenarios since adaptive capacity is closely linked to the financial capabilities.
The Ganges River is one of the largest river systems in the world and sustains a rich biodiversity of fish and fishers. In recent years, a decline in fish diversity and catch has become apparent due to various anthropogenic activities in the river basin. This study analyses the current fish diversity, distribution and community structure along the longitudinal gradient of the river and evaluates the ecological integrity of the riverine stretch applying a multimetric assessment approach. One hundred forty three fish species were recorded from the river and Cyprinidae was the dominant family. The middle stretch of the river exhibited dominance of small bodied erytopic, indigenous and exotic fish species with periodic and opportunistic life history strategies with significant decline of the large bodied prized Indian major carps. A tropic shift towards dominance of carnivore catfish species is evident. Non-metric multidimensional scaling revealed greater distribution and abundance of fish species with increasing river width and depth, higher sediment organic carbon, silt and clay along the river gradient. A significant change in the catches composition was evident from 1961 to 2010 in the middle stretch of the river at Allahabad. It reflected a progressive decline in proportion of Indian major carps (IMC) and the anadromous Shad Tenualosa ilisha and a significant increase in the proportion of exotic fish Cyprinus carpio and Oreochromis niloticus which represented 43–48% of the total catch. Assessment of biotic integrity showed that 28% of sample locations in the river supported fish assemblages under acceptable conditions.
The synthesis of bench-stable α,α-bis(trimethylsilyl)toluenes and tris(trimethylsilyl)methane is described and their use in stereoselective Peterson olefinations has been achieved with a wide substrate scope. Product stereoselectivity was poor with carbonyl electrophiles (E/Z ∼1:1 to 4:1) though this was significantly improved by employing the corresponding substituted N-benzylideneaniline (up to 99:1) as an alternative electrophile. The olefination byproduct was identified as N,N-bis(trimethylsilyl)aniline and could be easily separated from product by aqueous acid extraction. Evidence for an autocatalytic cycle has been obtained.
Highly stereoselective aza-Peterson olefinations from bench-stable α,α-bis(trimethylsilyl)toluene reagents and N-substituted imines have been achieved using TMSO(-)/Bu4N(+) as Lewis base activator in THF. Remarkably, and for the first time, N-t-butanesulfinyl imines were utilized for the synthesis of Z-stilbenes with excellent selectivities, while N-aryl imines generated E-stilbenes under identical reaction conditions. The protocol proved general for numerous examples with low molecular weight byproducts formed. The origin of the Z-selectivity is proposed to be a result of diastereoselective addition to N-t-butanesulfinyl imines followed by syn-elimination of an in situ formed hypervalent silicate.
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