Exposure of fish to biologically treated bleached‐kraft mill effluent. 3. Fish habitat and population assessment

Abstract

AbstractPopulations of mountain whitefish (Prosopium williamsoni) and longnose sucker (Catostomus catostomus) exposed to bleached‐kraft mill effluent (BKME) in the Wapiti/Smoky river system in northwestern Alberta were compared to similar populations in a reference river system (the upper North Saskatchewan River). Fish species distribution and relative abundance patterns were linked to natural events such as floods and low flows, and to habitat quality. There was no evidence that fish were avoiding the effluent plume area; relative abundance was often highest near the effluent discharge due to use of this area for overwintering and rearing. Radiotelemetry and recapture studies indicated that fish movements could be both rapid and extensive, occurring during spawning periods and at other times of the year. Thus, exposure could not be assumed to be related to capture location alone; separate exposure measures were necessary. Populations of exposed mountain whitefish and longnose sucker were growing and reproducing successfully. Higher condition factors in exposed longnose suckers and greater mesenteric fat stores in exposed individuals of both species were not accompanied by any apparent disruption in allocation of energy to reproduction or growth. The age structure of the populations showed that there had been no losses of age classes through reproductive or recruitment failures, and growth curves were indistinguishable from reference curves. There were no correlations between indicators of exposure and population‐level effects. Important natural phenomena, including a one‐hundred‐year flood and natural upstream/downstream habitat gradients, affected species distribution and were correlated with some population parameters such as condition factors and relative gonad size.