JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. INSTAAR, University of Colorado andThe Regents of the University of Colorado, a body corporate, contracting on behalf of the University of Colorado at Boulder for the benefit of INSTAAR are collaborating with JSTOR to digitize, preserve and extend access to Arctic and Alpine Research.ABSTRACT Arctic streams in Beaufort Sea drainages from Prudhoe Bay, Alaska, to the Mackenzie River delta are described and classified. Mountain Streams originate in the Arctic Mountain Province and are the largest streams in the study area. These are cold waters (usually less than 100C) which flow about five months of the year. Arctic char is the common fish species in these streams, and the density of benthic invertebrates is typically low (100 organisms/m2). Spring Streams are small spring-fed tributaries of Mountain Streams. Most are fresh water with temperatures of 3 to 7?C although thermal and mineral springs do occur. The springs are inhabited by Arctic char and high densities of benthic invertebrates (10,000 organisms/m2). Tundra Streams originate in the Foothills and Coastal Plain Provinces and flow for 3.5 to 4.5 months of the year. Their waters are stained brown and have a lower pH, conductance and lower concentrations of calcium than found in Mountain or Spring Streams. Summer water temperatures may exceed 16?C. These streams are used as spawning and rearing areas by grayling. Densities of benthic invertebrates are between the other stream types.

A normal (205– to 340-mm fork length at maturity) and a dwarf (85– to 135-mm fork length at maturity) form of least cisco (Coregonus sardinella) exist sympatrically in Trout Lake, Yukon Territory. Dwarf ciscoes have significantly fewer gill rakers, lateral lines scales, and pyloric caeca and significantly more vertebrae, on the average, than normal ciscoes. Dwarf cisco mature earlier than normals (age 3 vs. age 6); however, normals are longer lived (maximum age 23 vs. age 14) and may produce nearly 30 times the annual complement of eggs produced by dwarf cisco. Spawning of dwarf cisco may precede that of the normals, and there is some evidence of both spatial segregation of the two forms by selective schooling and of differences in food habits.Key words: least cisco, Coregonus sardinella; dwarfing, Yukon, North Slope, life history

In the Upper and Lower Babine rivers the fry of sockeye salrnon (Oncorhynchus nerka) emerge and move downstream, predominately at night, before reaching low-velocity areas along the stream margins. After a period of days or weeks these fry migrate upstream, close inshore, during the day. The diel pattern of upstream movement appears to be bimodal. The seasonal periodicities of both downstream and upstream movement are related to water temperatures.Upstream migrants were larger than downstream migrants in the Upper Babine River but not in the Lower Babine River. Upper River upstream migrants were similar in length to Lower River upstream migrants during 1964 but not in 1965. In both years Upper River fry weighed proportionately more than Lower River fry, and in both rivers 1964 fry weighed proportionately less than 1965 fry. Some possible explanations of these observations are discussed.Early in the season, fry tend to disperse alongshore after entering the lake. Later they leave these inshore areas and become entirely pelagic.The principal foods of fry both in the river and in the Iake were copepod and cladoceran plankters.Both fish and birds were found to be preying on sockeye salmon fry. Fry appear to be more vulnerable to predation in the river than in the lake.The upstream movement of fry in the Babine River does not appear to differ appreciably from upstream movements in other areas. A comparison of fry movements in the Babine River and the Fulton River, where fry move only downstream, suggests that the differences in behaviour are genetically rather than environmentally induced.It is suggested that, because of high mortalities in the prepelagic period, upstream-migrant populations will only develop where the environment of both the river and the rearing lake are especially favourable.

A comparison is made of the growth, morphometry, age at maturity, food, and depth distribution of pygmy whitefish (Prosopium coulteri) in four British Columbia lakes. In Tacheeda and Cluculz Lakes where the species is of the usual dwarfed variety, the fish exists sympatrically with two other whitefishes, the mountain whitefish (Prosopium williamsoni) and the lake whitefish (Coregonus clupeaformis). These slow-growing pygmy whitefish differ markedly in morphometry and depth distribution from the "giant" pygmy whitefish of McLeese and Maclure Lakes which live in the absence of other whitefishes. The possibility that differences in the populations might be due to interspecific competition is discussed.

An examination of Arctic grayling (Thymallus arcticus) collected on either side of the continental divide (Brooks Range) in Alaska revealed that lateral line scale counts were significantly higher on the North Slope than in the Yukon Basin to the south. An examination of geographic variation in this character within the North American range of the species suggested a division into three geographic areas: an area of uniformly low mean counts in the Bering Sea–North Slope of Alaska; an area of uniformly high counts in the remainder of Alaska and parts of the Yukon Territory and British Columbia; an area of variable mean counts in the Northwest Territories. Only two glacial refugia need be postulated to explain this pattern if it is assumed that populations in the first and last of these areas have a similar Mississippian origin and the high count populations a Beringian origin.