Detection of food limitation in health of white sucker (Catostomus commersoni) 5 years after the closure of a bleached kraft pulp mill

Recovery of fish after implementing better management of effluent or following the closure of pulp mills is not well studied. Results from existing studies suggest the predominant responses observed during the operation of mills would predict a pathway of recovery, but this hypothesis has not been tested at mills with variable effects on fish. Multiple studies done at a mill in northern Ontario showed variable responses in white sucker (Catostomus commersoni), including effects on reproductive endpoints. Data from most years failed, however, to meet strict definitions of response patterns used in Environmental Effects Monitoring. After the permanent closure of the mill in 2006, white sucker were collected in 2011 to determine the status of fish. We predicted that no effects would be observed in white sucker after the mill's closure. Five years after the closure of the mill, however, female white sucker showed statistical food limitation. Males showed a similar trend, but fewer statistical differences. These changes, coupled with reduced catch rates, have not been previously observed downstream of this mill. Our results suggest that recovery of fish after the closure of mills may not be clearly associated with effects found during operation. The absence of recovery after closure may more broadly suggest relevance of effects of operational mills.