Calcite covering of sediment as a possible way of curbing blue-green algae

Natural calcite precipitation in lakes is a well-known control mechanism of eutrophication. In hard-water lakes, calcite deposits on the flat bottoms of shallow lakes and near the shores of deeper lakes resulted from biogenic decalcification during the millenia after the last glacial period. The objective of a new restoration technology is to intensify the natural process of precipitation by utilizing the different qualities of calcareous mud layers. In a pilot experiment in Lake Rudower See, East Germany, phosphorus-poor deeper layers of the sediments were flushed out and spread over the phosphorus-rich uppermost sediments, to promote the co- precipitation of calcite with phosphorus from the water-column.

Changes of water quality and sediment phosphorus of a small productive lake following decreased phosphorus loading

Esthwaite Water is the most productive or eutrophic lake in the English Lake District. Since 1945 its water quality has been determined from weekly or biweekly measurements of temperature, oxygen, plant nutrients and phytoplankton abundance. The lake receives phosphorus from its largely lowland-pasture catchment, sewage effluent from the villages of Hawkshead and Near Sawrey, and from a cage-culture fish farm. From 1986 phosphorus has been removed from the sewage effluent of Hawkshead which was considered to contribute between 47% and 67% of the total phosphorus loading to the lake. At the commencement of phosphorus removal regular measurements of phosphorus in the superficial 0-4 cm layer of lake sediment were made from cores collected at random sites. Since 1986 the mean annual concentration of alkali-extractable sediment phosphorus has decreased by 23%. This change is not significant at the 5% level but nearly so. There has been no marked change in water quality over this period. Summer dominance of blue-green algae which arose in the early 1980s after decline of the previous summer forms, Ceratium spp., has been maintained. Improvement in water quality is unlikely to be achieved at the present phosphorus loading.

Reference area as a factor affecting potential yield estimates of coral reef fishes

A compilation of 48 estimates of Caribbean and Pacific coral reef fish catches, ranging from 0.1 to 23.7 t km super(-2) year super(-1), obtained from coral reef areas ranging from 0.1 to nearly 4-10 super(5) km super(2), are used to show that observed catches, and hence potential yield estimates, depend strongly on the reference area. The implications for coral reef fisheries assessments are discussed.

Estimating the maximum sustainable yield of bonito (Sarda chiliensis, Scombridae) of northern Chile from monthly catch data

Monthly catch data of bonito Sarda chiliensis from northern Chile, from 1976 to 1989, were used to obtain a series of estimates of the Z-G parameter (i.e., total mortality minus the growth coefficient in weight). This series was then used to estimate a maximum sustainable yield of 4,500 t/year through a modified version of the surplus production model of J. Csirke and J. Caddy. The status of the fishery is discussed.

Estimation of deepwater snapper yield from Tongan seamounts

The data from two years' monitoring of the Tongan seamount fishery were analyzed the two main export species are Pristipomoides filamentosus and Etelis coruscans. K.R. Allen's model was used to obtain estimates of catchability and recruitment and of a surplus production of 737 kg per nautical mile (nm) of 200 m contour. This compared reasonably well to total landings. Using this estimate, the annual surplus production for Tonga's 294 nm of 200 m contour is 217 t. The level of fishing mortality was found to be 0.3/year.

Growth, mortality and yield-per-recruit of the poor cod, Trisopterus minutus capelanus, from the Strait of Sicily

Length-based methods (LBMs) were used to study the growth of Trisopterus minutus capelanus in the Strait of Sicily (Messina Strait). A total of 16,304 'merluzzetto' or poor cod collected by experimental trawling off the southern coast of Sicily during spring, summer, autumn 1986 and winter 1987 were measured in order to estimate the length structure of the population. Length-frequency distribution were analyzed and normal components were discriminated. Von Bertalanffy growth parameters were derived from the mean length of the normal components. The growth parameters obtained by weighted non-linear regression were: K=0.462 (yr super(1)), L sub( infinity )=222.3 (TL,mm) and t sub(o)=-0.679 yr. The resulting growth performance index ( Phi ') was 4.36, a value slightly lower than those derived for Western Mediterranean (mean Phi '=4.45) and Adriatic ( Phi '=4.58) populations and slightly higher than that derived for Hellenic waters ( Phi '=4.27). On the basis of the von Bertalanffy parameters estimated, an array of age-specific instantaneous natural mortality rate (M sub(t)=0.5-1.1) and an average value of total natural mortality rate (Z=2.1 yr super(1)) were estimated and used in the Thompson and Bell yield per recruit (Y/R) analysis in order to evaluate the status of the fishery and forecast the effects of changes in the fishing pattern. Results indicate that this resource is overexploited and that Y/R could be increased by postponing the age at first capture from 0.5 to 1.0 yr. Even a slight reduction in fishing mortality could improve the performance of the fishery. At the present level of exploitation, and assuming a constant recruitment, the spawning stock biomass per recruit (SPR) is well below the conservative threshold of 30% of the pristine or unexploited SPR.

Coping with the Lionfish Invasion: can targeted removals yield beneficial effects?

Invasive species generate significant environmental and economic costs, with maintenance management constituting a major expenditure. Such costs are generated by invasive Indo-Pacific lionfish (Pterois spp.) that further threaten already stressed coral reefs in the western Atlantic Ocean and Caribbean Sea. This brief review documents rapid range expansion and potential impacts of lionfish. In addition, preliminary experimental data from targeted removals contribute to debates about maintenance management. Removals at sites off Little Cayman Island shifted the size frequency distribution of remaining lionfish toward smaller individuals whose stomachs contained less prey and fewer fish. Fewer lionfish and decreased predation on threatened grouper, herbivores and other economically and ecologically important fishes represent key steps toward protecting reefs. However, complete evaluation of success requires long-term data detailing immigration and recruitment by lionfish, compensatory growth and reproduction of lionfish, reduced direct effects on prey assemblages, and reduced indirect effects mediated by competition for food. Preventing introductions is the best way to avoid impacts from invasive species and early detection linked to rapid response ranks second. Nevertheless, results from this case study suggest that targeted removals represent a viable option for shifting direct impacts of invasive lionfish away from highly vulnerable components of ecosystems.

Linking climate change, rice yield, and migration: the Philippine experience

This study tests the hypothesis that climate change, through its rice productivity impacts, induces out-migration in the Philippines. Results show that climate change effects such as increasing night time temperature and extreme rainfall pattern, by way of reduction in rice yield and farm revenues, significantly increases the number of Overseas Filipino Workers. Findings also show that overseas migration of female workers is more sensitive to climate and rice productivity changes compared to male overseas migration. However, unlike overseas migration, the reduction in yield and farm revenues act as a constraint to domestic migration.