No abstract

A relative weight approach was used to test the hypothesis that the condition of broad whitefish Coregonus nasus in the Prudhoe Bay region of Alaska increases during the summer feeding season in conjunction with their increasing lipid and protein contents and decreases during winter as fish consume these energy reserves. The conditions of individual fish collected across 12 summer dissection periods from 1988 to 1993 were indexed in terms of their residual values relative to a single whole‐population, least‐squares regression of loge(weight) against loge(length). Proximate body analyses of lipid and protein contents collected from individual fish across six dissection periods from 1991 to 1993 were also examined. Data pooled for individual year‐classes were used to test for increasing mean residual value, mean lipid content, and mean protein content during summer and for decreasing values of each during winter. Of the 68 cases examined (14 year‐classes over 6 years), mean residual value changed in the expected direction in 56 instances (P < 3.0 E–7). Of 24 cases in which seasonal changes in lipid and protein contents were available, lipid content changed in the expected direction in 23 instances (P < 3.0 E–6), and protein content changed in the expected direction in all 24 instances (P < 3.0 E–7). Mean residual value changed as expected in all 24 cases. The merits of relative condition‐relative weight in the study of fish ecology are discussed.

No abstract

Although the temperature preferences of fishes in air-saturated water have been studied intensively, very little is known of fishes' preferred temperatures in waters that are oxygendeficient. Plains minnows Hybognathus placitus acclimated near 21 C selected 30 C in a horizontal temperature gradient when dissolved oxygen was maintained between 5 and 9 mg.liter-L But when dissolved oxygen was lower, the acutely preferred temperature declined--from near 30 C at 4.8 mg.liter -• to 17 C at 2 mg.liter-L Subsequent experiments on routine metabolism of plains minnows at various constant temperatures between 16.5 and 29 C gave results consistent with the following hypothesis: in oxygen-deficient water, the plains minnow prefers the highest temperature (less than 30 C) at which it can operate within the zone of respiratory independence. In nature, a reduction of acutely preferred temperature would reduce oxygen demand and might lead the fish into more highly oxygenated water. Fishes must occupy dissolved-oxygen and temperature regimes that fall within physiologically tolerable limits. Reduction of dissolved oxygen lowers survival times of fishes at lethallyhigh temperatures (Alabaster and Welcomme 1962; Weatherly 1970); increased temperature within the zone of thermal tolerance causes incipient asphyxiation to occur at higher oxygen concentrations (Jones 1952; Downing and Merkins 1957). Furthermore, dissolved oxygen and temperature, as directive factors, can be important determinants of fish distribution (Dendy 1948; Bardach 1955; Brett 1956; Neill and Magnuson 1974). Thus, the behavior of fishes in a thermal gradient ought to be greatly influenced by the concentration of dissolved oxygen. But little is known of the preferred temperature of fishes in oxygen-deficient water.The original purpose of this study was to measure the effect of oxygen insufficiency on the 557

A one-dimensional advection model was used to simulate the movement of young (< 180 mm) anadromous least cisco (Coregonus sardinella) along the Beaufort Sea coast between the Colville River and Prudhoe Bay, Alaska. Two versions of the model simulated eastward movement during the month of July as the sum of wind-induced transport and constant dispersion. Model results were compared with fyke-net catch data collected from 1981 to 1992. Of the 12 years examined, the models correctly simulated no major arrival of fish in 1983, 1985, 1986, 1987, and 1992, simulated the exact day of arrival in 1981, 1989, and 1991, and were in error by 1 d in 1988. Approximately 71% of the error between simulated and observed arrival dates was associated with three specific years: 1982, 1984, and 1990. The model suggests that wind-governed circulation may reasonably account for the presence of young Colville River least cisco in the Prudhoe Bay area. Results are discussed in terms of their relevance for assessing the effects of Arctic oil development on regional fishery resources.