Suitability of small fish species for monitoring the effects of pulp mill effluent on fish populations

Abstract

Research was conducted to assess the suitability of small fish species as sentinel species for monitoring the effects of pulp mill effluent on fish populations. There has been recent concern that larger fish species may not be suitable monitors of local environments because they are mobile and capable of extensive movement beyond effluent exposure areas. Smaller, resident and non-migratory species (e.g., many minnows, sculpins, darters) were proposed as alternate sentinel species because they exhibit reduced mobility relative to larger species, tend to be more numerous, ad are not subject to commercial or sport fishing pressure. Evaluation of small species was based on their response to mill effluent, as well as the abundance and capture efficiency of each species. Responses were described by comparing whole organism (growth, reproduction, energy storage, age) and physiological (MFO induction, sex steroid levels) measurements in fish exposed to pulp mill effluent with comparable reference fish populations not exposed to effluent.

Research focused on spoonhead sculpin (Cottus ricei) and lake chub (Couesius plumbeus) of the Athabasca River, Alberta, to determine whether changes in whole-organism and physiological measurements could be detected in small fish species exposed to pulp mill effluent. Both species exhibited responses reflecting instream effluent conditiosn. Spoonhead sculpin exposed to kraft mill effluent showed an overall increase in body and organ size, reproductive commitment, MFO induction and steroid production relative to unexposed fish. As well, graded responses were observed in sculpin exposed to different concentrations of effluent, and persisted downstream for at least 50 km. In contrast, lake chub exposed to effluents from a thermomechanical and a chemithermomechanical mill exhibited few changes relative to reference chub. It was concluded that the response (i.e., little change) of lake chub reflected the low instream concentrations of non-kraft, totally chlorine free effluent in the area.

Research at the Moose River system, Ontario, investigated the consistency and relative sensitivity of responses between trout-perch (Percopsis omiscomaycus) and the larger white sucker (Catostomus commersoni) under similar conditions of pulp mill effluent exposure and mobility. At this site potential differences in mobility were minimized by the presence of upstream and downstream dams. Both species exposed to effluent from a thermomechanical mill exhibited differences in whole-organism and physiological measurements relative to reference fish. However, the response of trout-perch was not consistent with the response of white sucker. The inconsistency between responses made it difficult to determine how the opposing responses of each species were related, and which species was most sensitive to the instream conditions.

A more detailed examination of fish responses was necessary to facilitate the interpretation of responses, and the comparison between trout-perch and white sucker. An existing monitoring framework was revised and further developed to provide a synthesis of fish responses documented in the literature, and a greater understanding of the progression of fish responses to common mechanisms of stressors. By categorizing fish responses according to age structure, energy expenditure, and energy storage it was possible to simplify the responses, determine which part of the populations were being affected, and identify the probable mechanisms leading to the responses. From this information, it was evident that the responses of trout-perch and white sucker highlighted similar mechanisms of change despite the difference in response patterns, and that either species could be used as a sentinel species at this site. In addition, the framework also indicated that the response of spoonhead sculpin was consistent with information described in previous studies investigating water quality, algal growth and benthos communities.