Developing restoration targets for nearshore fish populations in two Areas of Concern in Lake Ontario

Abstract

Restoration targets for nearshore fish populations in Hamilton Harbour and Toronto Harbour–Areas of Concern–were developed. Fish were captured in trap nets at Hamilton Harbour, Toronto Harbour, and nine unimpaired embayments of Lake Ontario. Embayments were sampled at least once and up to nine times during 2006–2013. Principal components analysis indicated the fish communities in unimpaired embayments clustered into two groups. One group had larger exposure distance (opening) to Lake Ontario and larger exposure index (surface area ÷ opening), and was termed “exposed.” The alternate group was “sheltered.” Fish communities in unimpaired embayments followed an aquatic macrophyte gradient of open-water species (e.g. White Bass, Gizzard Shad) at one end and species associated with vegetative cover (e.g. Bluegill, Pumpkinseed) at the other. A second fish community gradient was correlated with embayment opening and exposure index, and may be associated with habitat stability and exchanges with colder water from Lake Ontario. Hamilton Harbour is a sheltered embayment, but principal components analysis indicated the fish community was significantly different from all other embayments, consistent with its Area of Concern status. Northern Pike and Yellow Perch were the only target species in Hamilton Harbour close in abundance to unimpaired sheltered embayments. Common Carp, Brown Bullhead, Channel Catfish, and others were an order of magnitude higher than in unimpaired sheltered embayments. Toronto Harbour is an exposed embayment, and principal components analysis indicated the fish community was not significantly different from unimpaired embayments. Likewise, the abundance of most of the target species in Toronto Harbour was close to unimpaired embayments. Walleye, Smallmouth Bass, and Rock Bass were depressed and Gizzard Shad was elevated in Toronto Harbour, compared to unimpaired embayments.