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POPULATION DYNAMICS OF FRESHWATER INDIAN CARPS IN THE LOWER REACH OF THE BRAHMAPUTRA RIVER, ASSAM. M. Choudhury end M. Karthikeyen", Central Inland Capture Fisheries Research Institute, Guwahati, Assam, India. "Central Inland Capture Fisheries Research Institute, Reservoir Division, Bangalore- 560010, India. Freshwater Indian major carps fishery is the commercially most important fishery in the lower reach of the river Brahmaputra. Certain aspects of population dynamics of these species of the river have been dealt in this study. Based on length frequency distributions, the age of Indian major carps viz. Catla cotta, Labeo rohita, Cirrhinus mrigala and Labeo calbasu has been determined. Length-weight relationship of these species has been established. The parameters Lam, K and to of the von Bertalanffy growth equation have been estimated. The total mortality rates (Z) have been estimated using Beverton and Holt (1956) model and natural mortality rates (M) by the equation of Pauly (1980), Sekharan (1975) and Alagaraja (1984). The average annual stock and the average standing stock were estimated for each species alongwith annual rate of exploitation (Beverton and Holt, 1957; Ricker, 1975). Both the estimated average annual stock and average standing stock of Iridian major carps have been found to be higher than that of the average annual catch indicating that an increased yield cou-d be achieved by increasing the fishing effort without the stock being affected. Fishways and migrations of grayling (Thymalfus thymallus L.) aad landlocked brown trout (Salmo buffo L.) in river Glomma, Eastern Norway. Arne Linl0kken Environmental administration, Fylkcshuset, N-2301 Hamar, NORWAY. 3034 grayling and 2888 brown trout were captured and floy-tagged in 6 fishways in the Glomma river system in Hedmark county, Norway, during 1985 - 1988. The fishways arc constructed in connection W dams built for production of electrical power. Two of them are situated at the outlet of regulated lakes, while the rest are situated in the river. The purpose of the registration was to evaluate the efficiency of the fishways and the effect of the dams and fishways on the migration of grayling and brown trout. The migrations start in May or Junc, when the water temperature cxcceds 5 - 6 °C. During summer, there was a tendency that moderate or low discharge through the dam increased the number of fish entering the Fshways. Very few fish enters the fishways if no water goes through the dam or iC there is a flood. The reduced migration at flood conditions is probably caused by difficulties for the fish to fmd into the fishways, which has a discharge of less than I m3/s. Spawning migration of grayling occures in May. During this period more than 200 grayling may enter one of the fishways whithin one week. In the other fishways grayling occttre only sporadiglly before late Junc or early July, when the grayling migrates upstream to feed. This activity has been observed by fishermen and has been known to local inhabitant since the old days. The migration of grayling decreases from sumtncr to autumn. Migration of brown trout takes place during late spring, summer and autumn. Most important to the stock is the spawning migration which lasts more or less during the whole summer and autumn until spawning in September/October. The brown trout in Glomma usually mature from ca. 30 cm and spawners of 50 - GO cm length arc common. Immature brown trout also passes the fishways, and a peak in this migration was registrated in October in three of the fishway. This migration is probably an ascending emigration from the recruitrncnt areas located downstream dtese fishways. Longest migration of grayling registrated was 50 km upstream, whereas the longest migration o[ brown trout was 122 km. The fastest upstream movement oC grayling and brown trout registrated was 2.5 and 4.0 km/day, respectively. Recapture of tagged fish by anglers indicate that most of the grayling and brown trout stock live within river stretches oC20 - 30 km length. This is shorter than the migrations the fishermen claim to have observed in earlier days, which was also supported by small scale tagging experiments done at the time when the dams were built. Fish tagged in the upper fishway seemed to have longer migrations, 40 - 50 km, than fish tagged in the lower fishways. In the lower stretch the power plants and fishways are placed along Glomma and the tributary South Rena in shore distances, 12 - 30 km, from each other. Grayling and brown wut may have shortened their migrations and become more stationary.