Assessment of the fish populations beneficial use impairment in the Hamilton Harbour Area of Concern

Fish populations in the Hamilton Harbour Area of Concern (Hamilton Harbour AOC) were assessed as impaired under beneficial use impairment (BUI) #3 – Degradation of Fish and Wildlife Populations. We used multiple lines of evidence to evaluate the two criteria listed under BUI #3. The first criterion relates to community structure and declines in Common Carp (Cyprinus carpio) catch and biomass plus regional similarities in the density of pelagic forage fishes are positive signs. However, many native species indicated either a decline or no change, and catch rates were typically lower than regionally similar areas. Overall, the fish community continues to be more indicative of eutrophic rather than mesotrophic conditions and remains impaired. The second criterion is focused on Index of Biotic Integrity (IBI) scores, which remained below the target of 55-60. Most nearshore fish community metrics were lower than regional reference areas and trends in IBI and metric values either showed no change or were declining, indicating that fish populations remain impaired. Several factors that may limit improvements to the fish community were identified: seasonal hypoxia, aquatic invasive species, poor water quality, limited habitat supply, and impaired habitat conditions. Additional work is recommended to quantify the extent of their effects. Recommendations on monitoring actions and analysis are presented to support future assessments of fish populations.