Summing It Up : How Do We Evaluate the Total Public Interest ?
publication quickly rose to the top of the " all-time best seller list " of Great Lakes Fishery Commission publications. It has been widely circulated and widely used as a guide to Great Lakes fishery values by the Great Lakes fishery management community, mainly because little other information has been available on this topic. Managers have been increasingly required over the last decade or two to evaluate fisheries programs and needs by courts, by legislatures and by their own administrations. The 1979 publication was intended as a handy reference to current research findings on Great Lakes fishery values, in response to this need. However, it soon became apparent that more was needed. Managers needed a better explanation of the reasoning behind these evaluations. When economists use market-based ideas to examine non-market situations, either new terminology must be invented, or old terminology must be stretched into a new environment. Things easily get lost in the translation. This publication, then, is more than just an update. It is also an attempt to explain the reasoning behind these estimates, including some of the subtle differences between closely related values. We realize that one small publication such as this is still insufficient. Managers and administrators must take additional steps if they are to use the full power of economics to their benefit. All members of the committee that worked on this publication look forward to working with members of the management community in an effort to more fully utilize economic information, both on an individual basis and in more formal efforts such as those conducted by the Great Lakes Fishery Commission. We also welcome feedback on the usefulness of this publication, so we can improve the next one. These estimates were developed by a workshop or " committee " of economists, listed below, who have actively worked on Great Lakes fisheries values and impacts over the last few years. After this publication was drafted, all members were asked to verify and update the information, as well as to comment in any other way. Thus, this publication represents a consensus of a diverse group of economics researchers and practitioners from the region. The author has benefited from comments on earlier versions by almost all members of the group, particularly those of Leroy J. Hushak, as well as from comments We were gratified to see, in putting these data together, that many new studies have been …
The use of alkalinity and conductivity measurements to estimate concentrations of 3-trifluormethyl-4-nitrophenol required for treating lamprey streams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lake Muzahi, Rwanda: limnological features and phytoplankton production
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NHinf4sup+-N can be high.Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m)In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.