Nearshore Fish Community Comparison Using Fisheries Acoustics in Two Harbours in Lake Ontario

Assessments of the nearshore fish communities were conducted in Hamilton and Toronto Harbours using daytime fisheries acoustics in conjunction with bottom trawling. Both harbours are Great Lakes Areas of Concern and are adjacent to major population centres.  Land use around Hamilton Harbour includes heavy industry and there is direct connection to a substantial degraded wetland.  The surveys took place in September with trawling along 750 m long transects that were positioned in water depths of 6, 10 and 15 m.  Temperature and oxygen profiles were recorded at the beginning and end of each transect.  In Hamilton Harbour, 13 species were caught in the trawls and 86% of the 16,253 fishes were emerald shiners.  Alewife comprised 8% of the total catch with gizzard shad at 3% and white perch at 2%.  In Toronto Harbour, 8 species were caught; 56% were alewife, 24% round goby and 12% rainbow smelt.  Based on fisheries acoustics data, Hamilton Harbour had greater mean fish density, for both individual and schooling fish at 80.8 and 114.2 fish/ha respectively.  In Toronto Harbour, individual fish density was 35.9 and schooling fish were 107.1 fish/ha.  Smaller fishes predominated in both harbours; 64% of the total number of individual fishes in Hamilton Harbour were between 20 and 125 mm in total length, while 89% of fishes in Toronto Harbour were between 20 and 130 mm total length.  Fish densities varied spatially within each of the harbours and water temperature appeared to play a role in fish abundance and distribution.