Investigating the suitability of northern mummichog (Fundulus heteroclitus macrolepidotus) for the assessment of cumulative and non-point source pollution in Prince Edward Island estuaries

The overall objective of this study is to evaluate the use of the estuarine species, the northern mummichog (Fundulus heteroclitus macrolepidotus ) as a monitoring species for the detection of the cumulative impacts of agricultural land use in Prince Edward Island (PEI). The first study investigated the spatial and temporal variability of the somatic indices used to describe fish performance, specifically measures of energy use and storage, as indicated by liver and gonad sizes, and the overall condition of the fish. Three estuaries were sampled once in December 2006 and then on a weekly basis from May through July, with additional sampling periods in August and September 2007 to examine the temporal variability. Spatial variability was assessed by sampling populations at five spots along an estuary at a single time period. Results showed considerable variation both within and between sites over the reproductive season as well as between sites within an estuary. Repeated sampling is required to assess reproductive output in this species and densities of adults and young-of-the-year (YOY) may be the best indicator of environmental stress.

The second study was an effects-based assessment conducted in seven estuaries spanning a range of land-use, agricultural, industrial and/or municipal, and potential nutrient loadings. Over the course of the summer of 2007 somatic measures of fish performance, measures of population density and structure, and biochemical measures of exposure were monitored. The somatic and population measurements focused on the three main processes impacting population integrity: growth, reproduction, and survival; in addition to establishing a potential cause-effect relationship between stressor and response. Mummichog populations appear to be most affected in heavily eutrophic environments. The most obvious manifestation of this is an increase in recruitment and overall population number. At one site there was a significant increase in fecundity and gonad size; however survival of YOY or eggs appears to be impacted as indicated by lower YOY:adult ratios. Multivariate analysis of environmental variables clearly separates the sites on the basis of both eutrophication indicators such as nitrogen loading, chlorophyll and Ulva density in the first principal component and sediment variables in the second principle component. It is thought that the amount of fine sediment at this site may have affected YOY survival. Interestingly, fish found in these higher agriculture areas also experienced significantly lower in vitro steroid production. This decline in steroid production does not appear to have a detrimental effect on the reproductive potential of adult mummichog suggesting a possible masking effect of the nutrient enrichment.

Overall, these studies have shown that many of the performance measures typically used in environmental effects monitoring programs, fish condition and reproduction, are not efficient at determining differences among sites. This is likely due to the prolonged reproductive period followed by a short period of winter preparation. However, the abundance of mummichog found at a site combined with lower species richness may be a good indicator of environmental health.