EXECUTIVE SUMMARY

INTRODUCTION

As part of the Aquatic Effects Technology Evaluation (AETE) program, currently available methods for monitoring effects of metal mining activities on fish in Canada were reviewed. Potentially applicable monitoring tools for all levels of biological organization (chemical to community level) were initially selected by the AETE Technical Committee based on their (a) successful use in the field, and (b) cost effectiveness. In this report, these methods are described and critically evaluated for their suitability in a monitoring program for the mining industry based on a review of the literature and several recent case studies. Detailed reviews are provided for the adult fish survey and fish community survey. Metallothionein and histopathological methods are not reviewed in detail in this report because they are the subjects of separate reports prepared for the AETE Technical Committee.

Criteria for the evaluation of monitoring tools included:

• Ecological relevance.
• Ability to indicate exposure to mining-related contaminants.
• “Early warning” capacity.
• Sensitivity, specificity and response time to metals and low pH.
• Technical difficulty and costs of application.
• Availability of consultants/laboratories that provide services required for the methods.

Recommendations on the use of the reviewed assessment methods for monitoring effects of mining discharges on the contamination and health of fish populations and communities were made based on the proposed objectives and format of a mining industry Environmental Effects Monitoring (EEM) program from AQUAMIN (1996), and experience of the Canadian and Swedish Pulp and Paper Industry EEM programs. AQUAMIN is an initiative focussed on the regulatory issues of mining effluent impact. The program’s mandate is to determine whether or not the current Metal Mine Liquid Effluent Regulations (MMLER) limits have adequately protected the receiving waters of mine effluents.

EVALUATION OF METHODS

Metals-in-Tissues

Measurements of metal concentrations in fish tissues are indicative (to various degrees) of exposure of a organism to metal-contaminated effluents. Among the methods reviewed, they are the response that is most specific to high environmental metal levels. They are relatively easy and not expensive to apply, and are widely available. Tissue concentrations are related to tissue type, species, individual size (among other factors), and thus these should be standardized or controlled in assessments of metal burdens in fish.

 Biomarkers

Although biochemical-level assessment methods (biomarkers) offer the possibility of being specific responses to certain types of contaminants, and of serving as early indicators of higher-level (more ecologically important) effects, these attributes were not generally observed in studies of mining-related effects. In addition, comparatively fast response times of many biomarkers to elevated metal conditions, and non-negligible effects of natural or other confounding factors promote “background” variability that is too high for their use in a program with an annual or multi-year sampling frequency, as is common for a national EEM program.

In studies with higher sampling frequencies and effort, such as investigations of causes of observed ecological effects, certain biomarkers could provide useful information (e.g., enzymes such as delta-aminolevulinic acid dehydratase [ALAD] that are inducible by specific metals; internal ion imbalances that are associated with low pH).

 Tissue Pathology

Assessments of gross tissue pathology are not clearly distinct from methods of histopathology. Examinations of size, color, shape and incidence of lesions in relation to environmental metal concentrations were reported for muscle, liver, gonads, skeletal and dermal structures, spleen and gills. Tissue structure is affected by both general and specific stresses. Effects that were most indicative of exposure to metals and most predictive of higher-level effects were skeletal and dermal damage due to Cd and low pH, and gill lesions due to elevated metals and acidity. Like many of the biochemical-level methods though, tissue pathology appears more useful in investigative studies than in routine monitoring.

 Organism

Growth, reproduction and condition are commonly measured organism-level variables in fish surveys, and were reviewed in detail. Growth is the change in size (weight or length) with time or age. Growth is relatively inexpensive to measure, unless specialized and costly techniques are required for determining age. Growth is ecologically relevant, and is sensitive to metal contamination and low pH. Growth (i.e., size and age) can usually be measured on samples of fish collected at any time and for any purpose.

Reproduction is usually expressed as reproductive effort, or fecundity or gonad weight relative to body size. Reproduction may be the most sensitive life history variable in fish. Effects on reproduction should be evident within a year, since the reproductive tissue is generally turned over annually. Fecundity and gonad weight are relatively inexpensive to measure. Reproductive effort should be measured prior to the spawning season, when gonads will be large and well-developed.

Condition is weight relative to length (i.e., “fatness”), and can be used as a general index of well-being. Condition is not particularly sensitive, specific or ecologically relevant. However, the costs of measuring weight and length to assess condition of fish collected for other purposes are usually minimal.

 Population

Effects on fish populations can be measured directly or indirectly. Direct population surveys measure relative abundances (usually catch per unit effort [CPUE]). Large samples, in terms of numbers of fish and sample sites, are often required. CPUE and other abundance estimates often have high variances. Therefore, fisheries biologists often monitor or estimate changes in abundance indirectly, from growth, reproduction and mortality. An adult fish survey (AFS) adapts that indirect approach to environmental effects monitoring. An AFS is based on growth, reproduction, and age structure (as a surrogate for mortality), and usually includes condition and some tissue-level variables (e.g., liver size). Fewer fish and sample sites are required for an AFS than for a direct population survey based on CPUE. However, sample processing costs will be higher for an AFS because the fish must be dissected, ova counted, and ages determined.

 Community

A fish community survey (FCS) is a direct population survey extended to multiple species.  Obviously, more fish and often more sample sites will be required for an FCS than for a single species population survey. However, processing costs are often low, since the fish need only be identified and counted.

 Adult Fish Survey

AFS can be cost-effective tools for assessing population-level effects provided that:

• The target species is available and abundant enough to provide adequate sample sizes (= availability).
• Exposure to stressors of interest (e.g., metals) differs among sample sites (= exposure).
• Age, growth and reproduction can be measured precisely and accurately, at a reasonable cost (= measurement).

The availability → exposure → measurement sequence can be used to design and evaluate AFS.  Many AFS in the Canadian pulp and paper EEM program failed to meet these three criteria, all of which are necessary.

AFS have usually been conducted on intermediate-size or larger finfish such as suckers or perch. However, smaller, less mobile finfish or bivalves may be as suitable or more suitable. The major disadvantage to using small fish is that some species are multiple spawners, producing several to many clutches of mature ova per spawning season. Reproductive investment is almost impossible to estimate for multiple spawners, because the reproductive tissue may be turned over several times in one season. The limited evidence available suggests that multiple spawning may not be common at higher latitudes, in guarding species, and in other species with large ova.

Sample sites used for an AFS must differ in exposure, but should be otherwise similar. Because AFS and specific variables such as age, growth and reproduction are non-specific, responding to many different factors, study designs should eliminate as many confounding factors as possible. Sampling methods and effort will vary among species and sites, but must be adequate to provide sufficient sample sizes (usually  ≥20 fish/sex/species/site).

AFS have been used extensively in Canada and Sweden to monitor the effects of pulp and paper mill discharges. However, an AFS approach has rarely been used to assess the effects of mine discharges and other activities, even though the necessary variables have often been measured on samples collected for other purposes (e.g., to measure tissue metals).

An AFS will generally be the most suitable and cost-effective higher-level tool for monitoring the effects of mining activities, and is recommended for a national EEM program. Experience in the pulp and paper EEM program indicates that an AFS will not be suitable for every mine site. Therefore, the pool of target species should be expanded to include smaller finfish and bivalves, and alternatives such as FCS should be considered acceptable where suitable.

Fish Community Survey

FCS can range from simple qualitative surveys of the presence or absence of a few indicator taxa or guilds to more extensive quantitative surveys based on multivariate analyses or summary indices (e.g., the Index of Biotic Integrity [IBI]). In an FCS, the basic units of replication are sample sites within larger areas differing in exposure, and not individual fish. Sample sizes should be at least 5 sites per area, and 10-20 would be preferable. Consequently, communities of small fish in streams or littoral zones of lakes are usually more suitable and cost-effective than communities of larger fish.

Once fish have been captured, costs are minimal for identifying and counting them. The abundances of each species are the primary variables analyzed; weights and lengths can often be measured for little extra cost. Exposure indicators or tracers (e.g., tissue metals) are rarely measured in FCS.

Quantitative analytical approaches based on multivariate statistics or summary indices are preferred to qualitative approaches. Multivariate statistical approaches are more objective and defensible than summary indices. However, indices can be useful for reporting and management, provided that multivariate analyses indicate that the assumptions made in calculating the indices are reasonable. One common index, the IBI, is often treated as synonymous with FCS. It is not; IBI must be independently derived for each site or region, based on data from many reference sites. The IBI used in the U.S. are often based on richness of taxa with many more species than occur in Canada. Therefore, IBI will not be suitable for individual mine sites in Canada, although IBI could be developed on a regional basis.

FCS, mostly qualitative or semi-quantitative, have been used in the past in Canadian mine monitoring programs. However, FCS are more commonly used for larger-scale regional surveys, often where many stressors or point sources are present. Defensible quantitative FCS would be too costly to conduct at most individual mine sites in a national EEM program.

 RECOMMENDATIONS

An EEM program for the mining industry of the type proposed by AQUAMIN (1996) should:

1. Include standardized measurements of concentrations of metals in fish tissue as a means of determining exposure histories of fish and assessing degree of metal contamination for the protection of human health.

2. Delay the use of any of the reviewed biomarkers and tissue pathology assessments for routine monitoring until further field evaluations establish their relationships to more ecologically relevant effects, and their ease of application.

3. Consider certain tools, such as specific inhibitory or inducible enzymes and tissue pathology, as a means of establishing causal relationships in investigative studies.

4. Include some combination of organism- and higher-level tools, depending on site-specific conditions, because they are more relevant, less costly, and more widely available than lower-level variables.