Culture-based fisheries in non-perennial reservoirs of Sri Lanka: influence of reservoir morphometry and stocking density on yield

Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [SD (fingerlings ha⁻¹)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002–2003. Basic limnological and morphometric parameters, including shoreline development (D_L) and shoreline area ratio (R_LA), were estimated for each of the 23 reservoirs. Bray–Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation (P < 0.05) between R_LA and total fish yield (Y). A multiple regression equation, Y = −693 + 4810 R_LA + 0.484 SD, was generated to estimate fish harvest in relation to SD.

Does adding wood to agricultural streams enhance biodiversity? An experimental approach

Riparian clearing and the removal of wood from channels have affected many streams in agricultural landscapes. As a result, these streams often have depauperate in-stream wood loads, and therefore decreased habitat complexity and lower levels of in-stream biodiversity. The introduction of wood was investigated as a possible rehabilitation technique for agricultural streams. Wood was re-introduced to eight streams in two separate high-rainfall, intensively grazed regions of Victoria, Australia and the effect on aquatic macroinvertebrate communities was measured. The addition of wood increased overall family richness and the richness of most functional feeding groups occupying edge and benthic habitats within the stream. Wood addition led to less overlap between benthic and edge macroinvertebrate communities, suggesting increased habitat heterogeneity within the stream ecosystem. Of all sampled habitats, wood supported the greatest density of families and was colonised by all functional feeding groups. Wood habitats also had the highest overall richness and supported the most taxa that were sensitive to disturbance. These findings suggest that re-introducing wood to agricultural streams is an appropriate rehabilitation technique where those streams are affected by reduced habitat complexity. Additional work is needed to confirm these findings over larger spatial and temporal scales.

Cement-Wood composites: effects of wood species, particle treatments and mix proportion

The aim of this research was to investigate the effects of wood species, particle treatments and mix proportion on the physical (density) and mechanical (compressive strength and dynamicmodulus of elasticity) properties of cement-wood composites. Different mix proportions were investigated, based on the cement: wood ratio of 0.3:0.7, in volume, with Pinus elliottii and Eucalyptus grandis sawdust percentages of 0-100, 25-75, 50-50, 75-25 or 100-0. Sawdust particles were pre-treated with either lime or cement coating to improve cement and wood compatibility. Results show that wood species, particle treatments and mix proportions may influence the physical and mechanical properties of cement-wood composites. In general, results confirm that Eucalyptus sawdust and cement are naturally compatible and do not require any previous particle treatment to avoid compatibility problems.