Statistical Assessment of Tissue Residues in Sport Fish and Indicator Fish Species in the Detroit River to Address Fish and Wildlife Consumption

Report:

Statistical assessment of tissue residues in sport fish and indicator fish species in the Detroit River to address Fish and Wildlife Consumption.

Feb 13, 2015

Submitted by Ken G. Drouillard, Great Lakes Institute for Environmental Research, University of Windsor, Windsor, On.

To: Ted Briggs, Ontario Ministry of Environment and Climate Change, London, On.

Executive Summary

Data on priority contaminants in sport fish from the Detroit River Area of Concern (AOC) were compiled and analyzed to evaluate the delisting criteria for BUI #1 Restrictions on Fish and Wildlife Consumption. The delisting criteria specified in the Detroit River Stage 2 Remedial Action Plan (RAP) identifies walleye, brown bullhead and smallmouth bass as indicator fish species to be used for the evaluation of delisting BUI #1.  Data for the above indicator species were compiled from the Ontario Ministry of Environment’s sport fish monitoring program and supplemented, as required, with additional samples generated by the Great Lakes Institute for Environmental Research, University of Windsor.  Data were also compiled from Lake St. Clair (upstream reference region) and western Lake Erie (downstream reference area) to facilitate spatial comparisons as specified in the delisting criteria.   Contaminants of consideration focused on PCBs and mercury which are responsible for the majority of fish consumption restrictions within the AOC.  Statistical analysis was conducted to determine if priority contaminants exhibited significant differences in contamination between Detroit River fish and the upstream and downstream non-AOC reference areas designated as Lake St. Clair and western Lake Erie, respectively.  Additional factors such as fish body size and sex were taken into consideration within statistical assessments and during testing of delisting criteria for each species.

Walleye

PCBs in Detroit River walleye had significantly higher contamination than the upstream reference location.  There was no significant difference between PCB residues in walleye from Ontario waters of the Detroit River and the downstream reference region.  There was no significant effect of fish body length on PCB residues but fish sex was statistically significant.  Thus, while several samples exceeded TDI criteria used to generate fish consumption advice, highly contaminated samples were not associated with larger body sizes.  Given that body size was not a predictor of PCB residues in this species, and concentration data conform to a log normal as opposed to normal distribution, the geometric mean was considered the most appropriate measure of central tendency on which to evaluate the delisting criteria. The geometric mean PCB concentration in walleye from the upper and lower Detroit River fishing zones, while being statistically higher than the upstream reference area, was below the minimum tolerable daily intake (TDI) trigger used to establish fish consumption advice for the sensitive subpopulation. This indicates that PCBs in walleye meet the delisting criteria.

Mercury residues in Detroit River walleye were significantly lower than mercury in walleye from the upstream reference site.  There was no difference in mercury residues in Detroit River walleye compared to the downstream reference area. Mercury residues were strongly associated with fish body length as well as sex and thus fish advisories due to mercury are predicted to occur for larger fish in each of the water bodies and in male fish for some populations (Lake St. Clair only). Based on the body size/mercury relationships observed, fish consumption advisories for the sensitive sub-population would be issued for fish exceeding 41.7, 43.9 and 58.2 cm body length for the upstream reference area, Detroit River and downstream reference area fish.  Since mercury residues in walleye are higher in the upstream reference region compared to the Detroit River, and Detroit River mercury residues do not exceed the downstream reference area, the delisting criteria for Hg in walleye are met.

Brown Bullhead

Data on contaminant residues in the brown bullhead indicator species were insufficient to test the delisting criteria.  Although data on brown bullhead residues for mercury and PCBs were available in a limited number of fish from Lake St. Clair, there was no data in the OMOE CC sport fish contaminant database for either zone of the Detroit River nor were data available for western Lake Erie.  A small number of samples were available for brown bullheads from the supplemental data set to provide general spatial comparisons between Lake St. Clair and Detroit River.  However, the data were considered insufficient to adequately test the delisting criteria with statistical rigor.  Additional brown bullhead collections from the upper and lower fishing zones of the Detroit River as well as fish from western Lake Erie are required to test the delisting criteria as specified in the stage II RAP report.

Smallmouth Bass 

Data on contaminant residues in the smallmouth bass indicator fish species were insufficient to address the delisting criteria.  A small number of smallmouth bass samples were available for PCBs in the Detroit River from the supplementary dataset suggestive of intermediate PCB contamination relative to the two lake populations.  However, the number of samples available from the Detroit River were too low and restricted in their spatial extent to adequately test the delisting criteria with sufficient statistical rigor.  Data on mercury concentrations in smallmouth bass from the Detroit River were not available.  Adequate data on smallmouth bass residues were available for the upstream and downstream reference areas. Smallmouth bass collections and analysis of PCB and mercury residues from the upper and lower fishing zones of the Detroit River are required to complete the delisting criteria assessment for this indicator species.  

Conclusions

The delisting criteria for BUI #1:  Fish and Wildlife Consumption advisories could only be evaluated for one of three indicator fish species outlined in the delisting criteria.  Data for walleye meet the delisting criteria.  Additional sampling efforts and residue analysis for mercury and PCBs are required for brown bullhead and smallmouth bass in order to complete the delisting criteria assessment for the benthic in local predator indicator species.

Introduction

This report provides an evaluation of the delisting criteria for Beneficial Use Impairment #1:  Restrictions on Fish and Wildlife Consumption for the Detroit River Area of Concern.