Setting Ecological Targets for Laurel Creek

Bruce Kilgour
Department of Biology,
University of Waterloo,
Waterloo, ON

Prior to implementation of a remedial action plan for an urbanized aquatic system, it is important for managers to clearly specify tangible ecosystem goals. This paper outlines a framework for defining tangible ecological goals for aquatic systems. In this paper I make the assumption that one objective of remediation would be to maintain or improve the condition of natural assemblages which include fish, benthos, macrophytes, etc. Since the focus of this workshop was the Laurel Creek watershed, I discuss such methods with respect to application of the framework to Laurel Creek.

Setting ecosystem goals requires that managers first specify the trophic group(s) that are hoped will be maintained or protected. Second, managers must obtain information that will allow them to determine acceptable conditions for the selected trophic group.

Understand what we are protecting or hoping to improve

Selection of one or two trophic groups for protection/remediation can be a very philosophical issue. However, there are several ways to rationalize the use of fish for setting ecosystem targets. Being the top consumer and long lived, fish integrate all of the various impacts that may be influencing the lower trophic levels, but generally respond only to long-term factors. Knowing that fish populations require remediation, provides some certainty that other trophic levels also require remediation. In addition, one of the major pieces of legislation in Canada, the Canadian federal Fisheries Act, has a guiding principal of maintaining the productive potential of fish and fish habitat. The underlying theme in this act is the maintenance of fish populations.

If we are interested in protecting fish, we should be setting limits based on fish. We should also be measuring an appropriate aspect of fish. For example, we could measure or monitor the abundances of a single game species (e.g., brook trout) in the system, or monitor variations in species composition. Kilgour (1997) demonstrated that monitoring species composition would more likely result in our ability to detect effects on fish, even if we were only interested in a single games species like brook trout. The improved ability to detect problems using whole community surveys is a result of whole community endpoints being less variable than abundances of single species.

Setting Targets for Fish Populations/Communities

Understanding when a fish population or fish community is under stress and requires rehabilitation, depends upon knowledge of the types of assemblages that we would normally expect in a stream uninfluenced by urbanization. In Laurel Creek, we would be interested in knowing what the fish community would normally have been like had there been no urban system. By sampling streams that have similar physical and chemical characteristics, but that differ from Laurel Creek in having no urbanization in the surrounding areas, we can begin to understand the degree to which the fish fauna of Laurel Creek have changed as a result of urbanization. This is the general approach taken by Fitzgerald (1996) and Kilgour (1997) in their assessments of the fish fauna of Laurel and Canagagigue Creeks.

Ecological criteria are the numeric values that denote acceptable and unacceptable conditions for our ecological endpoint. Ecological criteria can only be specified after we have accumulated data describing normal or background conditions. Figure 1 illustrates the usual distribution of observations of an ecological endpoint from a survey of unaltered locations. Regardless of what we are measuring, the normal range of variation usually follows a normal (bell) curve. We can use this normal curve to denote what are acceptable and unacceptable conditions in a fishery such as Laurel Creek. The normal range of variation is often denoted as the numeric values under the normal curve that include 95% of the observations from the reference locations (Kilgour, 1997). Observations outside of this range can be considered indicative of unacceptable ecological conditions because it would be unusual for a natural (unimpacted) community to have a larger or smaller value. Use of such an approach for setting ecological criteria has been common in the United States (Davis and Simon, 1995), and is now part of federal legislation in Canada (Environment Canada, 1997). The use of such criteria does, however, require novel statistical approaches as described by Kilgour (1997).

Use of Surrogate Ecosystem Responses to Predict Changes in Fish

Because fish can take a long time to respond to improvements in physical and chemical habitat, Kilgour (1997) proposed the use of benthic invertebrates as a surrogate response for fish communities. Benthic invertebrates take on the order of 1-2 years to respond to significant improvements in physical and chemical habitat. In contrast, fish could be predicted to take up to 5-10 years because they are much longer lived than invertebrates (i.e., stream fish live 5-10 years, whereas benthic invertebrates usually live less than 2 years). Kilgour (1997) demonstrated that the composition of benthic invertebrates was a consistent predictor of the composition (and thus health) of a fish community. He also derived critical values for benthos that coincided with acceptable conditions for fish. Critical values tended to vary according to the methods used and habitat from which benthos were collected. As a consequence, the potential use of benthos as a tool for predicting changes in fish requires some preliminary calibration of the joint fish-benthos response to urbanization. Construction of a joint fish-benthos response to urbanization has already been done for Laurel Creek (Kilgour, 1997).


Improving ecological conditions is a commendable goal. Cost-effective and defendable rehabilitation does, however, require clear definitions of what it is we are hoping to improve or protect. In stream systems, the federal Fisheries Act argues for the protection of fish. Based on the Fisheries Act, and recent revisions to other federal legislation (i.e., Environment Canada, 1997), we can now set tangible and objective ecological criteria for systems such as Laurel Creek. Based on protection of the fish community in Laurel Creek, one could set out to describe the normal variation in creeks such as Laurel, or use historical data to construct a range of expectation for the creek in order to set numerical limits.

The use of benthos as a surrogate ecosystem endpoint also has potential. If rehabilitative measures are taken in Laurel Creek, benthos would be able to provide an earlier indication of success. Benthos would respond to true improvements within the first one to two years, whereas fish may not respond for up to 10 years. Consequently, the success of any rehabilitation is probably best monitored using benthic invertebrates.

Figure 1. The histogram represents the distribution of observations in unaltered reference locations. The 95th percentile denotes the numeric value for the limit of acceptable conditions. Values less than the 95th percentile would be considered acceptable. Values greater than the 95th percentile would be considered unacceptable.

Literature Cited

Environment Canada. 1997. Pulp and paper aquatic environmental effects monitoring requirements. Annex 1 to EEM/1997/1, 9/18/97.

Davis, W.S. and T.P. Simon (eds). 1995. Biological Assessment and Criteria, Tools for Water Resource Planning and Decision Making. Lewis Publishers, Boca Raton, Florida.

Fitzgerald, D.F. 1996. Evaluation of fish in anthropogenically modified streams within the Grand River watershed, Ontario. MSc thesis, University of Waterloo.

Kilgour, B.W. 1997. Fish-benthos correlations and effects on benthos that reflect significant effects on fish communities in southern Ontario streams. PhD thesis, University of Waterloo.

Previous Page | Return to Index | Next Page