Federal government scientists are focusing on a perplexing problem in Hamilton Harbour that is bogging down efforts to restore populations of desired fish species, a major part of the overall restoration of the bay.
They’ve found that through summer months vast sections of the harbour do not carry nearly as much dissolved oxygen as fish species require.
Researchers from Fisheries and Oceans Canada believe low oxygen is discouraging the healthy growth and reproduction of desired species such as walleye, largemouth bass and northern pike. Whereas undesired species, such as carp and goldfish, are flourishing because their needs for oxygen are much less.
Dissolved oxygen — which mostly comes from surrounding air and photosynthesis in plants — is necessary for fish to breathe, but the amount required varies depending on the species. Hamilton Harbour has chronic dissolved oxygen issues, mostly traceable to too many nutrients getting into the bay from sewage treatment plants and urban run-off.
The issue has been known about for some time. As well as impairing fish development, low oxygen is a factor with the algae blooms that have been an annual late-summer problem in the harbour.
But new research — based on work by Matthew Wells of the University of Toronto — has demonstrated an interesting side to the phenomenon.
It seems that large winds are “upwelling” oxygen-depleted water around the bay.
“When the wind blows, it pushes the warm water to one end of the harbour, and it gets replaced by cold water that doesn’t have any oxygen. So, that happens every time the wind blows strongly,” Wells said.
by Mark McNeil