A holistic approach to ecosystem health assessment using fish population characteristics

Abstract

The status of a fish population is a reflection of the overall condition of the aquatic environment in which that population resides. As such, fish population characteristics can be used as indicators of environmental health. Simple and inexpensive methods to follow fish population responses to environmental degradation are lacking. This paper outlines a protocol whereby environmental impacts on fish populations are classified by five patterns based on characteristics such as mean age, fecundity and condition factor. The patterns summarize population changes and describe responses to exploitation, recruitment failure, the presence of multiple stressors, food limitation and niche shifts. Classification is best based on the selection, and appropriate sampling, of a comparable reference population. Population characteristics can be used to examine ecosystems exposed to stressors for evidence of long-term damage, and when used with biochemical indicators, can be a powerful tool for ecosystem health assessment. The five responses are illustrated using published data on a number of species challenged by increased predation pressure, acidification, eutrophication, mine waste and reservoir impoundment. Application of this scheme will aid in directing and focusing research conditions.

Recovery of a mining-damaged stream ecosystem

“…In a survey undertaken in 1993 prior to water-quality restoration efforts, fish population counts were made by direct observation by snorkelers, but subsequent fish community surveys were conducted through electrofishing using blocknets and multiple-pass depletion. All fish were weighed and measured to enable calculation of fish condition, which is a measure of both individual and cohort (e.g., age-or size-group) wellness and is expected to decline under stress (Munkittrick and Dixon, 1989).…”

“…In stressed systems, abundance may be limited by recruitment failure or indirectly from reduced prey base (Munkittrick and Dixon, 1989;Power, 1997;Milner et al, 2003).…”

“…Natural fish populations are typically age-structured and numbers decrease with age in the total population. Selective mortality of sensitive fry may lead to recruitment failure in metal stressed populations, causing a shift to older fish (Schindler et al, 1985;Munkittrick and Dixon, 1989;Campbell et al, 2003;Milner et al, 2003).…”

“…Fish may have decreased growth or condition in metals-stressed systems from energy requirements of detoxification or food limitation/prey shifting. Condition factor and size are surrogates for energy reserves for overwinter survival and reproductive fitness (Munkittrick and Dixon, 1989;Farag et al, 1995;Cunjak et al, 1998;Campbell et al, 2003). We further explain our concepts for evaluating recovery in the context of the expected natural template for the affected streams, ecological assumptions, interpretations of chemical guidelines and project-specific goals in Text S2.…”

“…Fish populations in mining-influenced streams may be indirectly constrained by reduced macroinvertebrate prey availability (Hogsden and Harding, 2012), which could be reflected in reduced abundances or reduced condition factor (Munkittrick and Dixon, 1989 (Bailey, 1952;Allan, 1983;Esteban and Marchetti, 2004). These taxa were early colonizers in Panther Creek and remain abundant.…”